Neuro Flashcards

Question

A 30-year-old man presents with an orbital frontal headache and visual disturbance. CT head shows a large mass arising from the region of the spheno-occiput and extending into the pontine cistern and towards the hypothalamus. The mass contains amorphous calcification and is seen to cause bone destruction. There is no reactive bone sclerosis. On MRI the mass exhibits mixed heterogeneous signal and a soap bubble appearance. The solid components show marked contrast enhancement. What is the most likely diagnosis? [B2 Q36] a. Meningioma b. Metastasis c. Chordoma d. Plasmacytoma e. Sphenoid sinus cyst

Answer 1

**Chordoma** Chordomas originate from malignant transformation of notochordal cells. They are typically located in the sacrum (50%), clivus (35%) and vertebrae (15%). They may rarely be found in the mandible, maxilla and scapula. Spheno-occipital chordomas typically affect males and females in equal incidence and the average age ranges from 20 to 40 years. Most of them demonstrate bone destruction and amorphous calcification. The solid components show variable but often marked contrast enhancement and MRI may show a ‘soap-bubble’ appearance. Bone sclerosis is rare. The description given is that of a malignant process. Meningiomas typically affect older females and only rarely (<1%) arise from the clivus. Plasmacytomas tend to occur in an older age group, are more common in the thoracic/lumbar spine and are often osteolytic and grossly expansile lesions. Metastasis is a possibility, although from the description given – particularly the calcification and amount of tumour extension – chordoma remains the most likely diagnosis.

Answer 2

**Haemangioblastoma** Haemangioblastoma is the most common primary intra-axial, infratentorial tumour in adults. They are benign autosomal dominant tumours of vascular origin. Approximately 20% occur with von Hippel–Lindau disease. Other associations include phaeochromocytomas, syringomyelia and spinal cord haemangioblastomas. About 20% of tumours cause polycythaemia. Typical CT and MRI appearances are of a largely cystic mass with an enhancing mural nodule. Oedema may be absent or extensive, but calcification is rare. Prognosis is 85% post-surgical five-year survival rate. Infratentorial pilocytic astrocytomas may have very similar appearances to haemangioblastomas but some differences exist that can help differentiate the two. Pilocytic astrocytomas predominantly occur in children and young adults, are generally larger (>5 cm) than haemangioblastomas, may contain calcifications and are not associated with polycythaemia.

Answer 3

**Cystic lesion with an enhancing mural nodule** Haemangioblastomas are the most recognized manifestation of von Hippel–Lindau syndrome. They usually occur in the cerebellum and may be multiple in up to 15% of cases. Patients also commonly develop renal cell carcinoma, and difficulty may occasionally arise in distinguishing metastases from multiple haemangioblastomas. Typical features are of a cystic mass in the hemisphere or vermis, with an enhancing mural nodule, though entirely solid lesions may also occur. Calcification is not a feature. Gyriform cortical calcifications are a feature of Sturge–Weber syndrome, and usually occur in the temporoparieto-occipital region. Calcified subependymal nodules (hamartomas) are a feature of tuberous sclerosis. A hypodense, ill-defined mass with central necrosis and marked surrounding oedema is a classic appearance of a glioblastoma multiforme.

Answer 4

**Cerebellar haemangioblastoma** These CT features are typical of this lesion. Metastases usually have ring-like enhancement or homogenous enhancement rather than having a mural nodule. Cystic astrocytomas are usually > 5 cm, show calcifications, thick walled and have no enhancing mural nodule. An arachnoid cyst is a possibility if no enhancing nodule seen. Medulloblastoma is uncommon in adults and is usually a solid tumour with homogenous enhancement.

Answer 5

**Haemangioblastoma** This is the most common posterior fossa tumour in adults after metastases. They are usually seen in the cerebellum and there is an association with von Hippel–Lindau disease. CT appearances are typically with a large hypodense cyst and an enhancing mural nodule. The cyst wall does not usually enhance. On MRI, flow voids may be seen representing draining vessels adjacent to the nodule. Juvenile pilocytic astrocytoma is seen in young age and is not associated with feeding vessels. Metastases are usually multiple in older people.

Answer 6

**Meningioma** It is rare for meningiomas to occur intraventricularly (2–5% of all meningiomas) but they are the most common trigonal intraventricular mass in adulthood. They tend to occur in 40-year-old females.

Answer 7

**Giant cell astrocytoma** The main differential for a mass at the foramen of Monro is between a colloid cyst and a subependymal giant cell astrocytoma. The latter is associated with tuberous sclerosis (TS). Renal involvement is also relatively common in TS and patients regularly have surveillance renal ultrasounds. The echocardiogram was performed to assess for cardiomyopathy/rhabdomyoma.

Answer 8

**Central neurocytoma** Central neurocytoma is an intraventricular WHO grade II neuroepithelial tumour with neuronal differentiation. This rare neoplasm tends to occur between the ages of 20–40 years. Patients typically present with symptoms and signs of hydrocephalus. Imaging typically demonstrates a globular lesion attached to the septum pellucidum. Calcification is considered characteristic; however, it may be absent in approximately half the cases. On MRI, the lesions are usually isointense to grey matter and show dense contrast enhancement. It is extremely uncommon to see peri-tumoural oedema.

Answer 9

**Choroid plexus papilloma** Other extra-axial posterior fossa masses include acoustic neuroma, meningioma, chordoma and epidermoid.

Answer 10

**A** Ependymomas followed by astrocytoma are the most common.

Answer 11

**B** Protein content/paramagnetic effect of Magnesium Mg2+/ Calcium Ca2+/ Iron Fe, in a cyst cause increased T1 and T2 SI. Colloid cysts appear iso/hyperdense on NCCT. They can occasionally widen septum pellucidum and cause asymmetrical enlargement of the lateral ventricles.

Answer 12

**Colloid Cyst** Colloid cysts arise from the inferior aspect of the septum pellucidum and protrude into the anterior aspect of the third ventricle, where they may cause positional headaches and hydrocephalus due to transient obstruction at the foramen of Monro. They usually contain mucinous fluid, desquamated cells and proteinaceous debris, making them hyperdense on CT. On MR scan, the high protein content, as well as the paramagnetic effect of magnesium, copper and iron in the cyst, results in high signal intensity on T1W and T2W sequences in 60% of cases. Meningiomas and ependymomas may also appear hyperdense, but location within the third ventricle is uncommon for both. Subependymal giant cell astrocytoma is a benign tumour occurring in the region of the foramen of Monro, which may cause obstruction, but it is usually hypodense and is nearly always seen in association with tuberous sclerosis. Choroid plexus papilloma predominantly occurs in children under 5 years of age, and location in the third ventricle is unusual.

Answer 13

**Central neurocytoma** Central neurocytomas (also known as intraventricular neurocytomas) are benign tumours of the lateral and third ventricles usually presenting in adults aged 20–40 years. They frequently calcify (69%) and contain cystic spaces. Attachment to the septum pellucidum is a characteristic feature. Lesions appear isointense to grey matter on all MR sequences and show mild-to-moderate contrast enhancement. Central neurocytomas were previously frequently mistaken for intraventricular oligodendrogliomas, which have very similar imaging features but are actually quite rare. In addition, neurocytomas undergo haemorrhage into the tumour or ventricle more frequently, helping to distinguish the two. Colloid cysts arise within the third ventricle, and rarely calcify. Subependymomas may arise in the lateral ventricles with an attachment to the septum pellucidum, and cyst formation and calcification may be seen in large tumours. However, most occur in patients over 40 years of age. Choroid plexus papillomas generally occur in children under 5 years of age.

Answer 14

**Colloid cyst** Colloid cysts are seen in the region of the interventricular foramen and cause positional and intermittent obstruction, leading to hydrocephalus and headaches. The lesion is dense on CT and high signal on T1 and T2 sequences as they commonly contain large protein molecules and the paramagnetic effect of iron and copper in the cyst. Dermoid contains fat whereas arachnoid cysts show CSF features on imaging. Meningioma is usually low signal on T1 and high signal on T2.

Answer 15

**C. Vestibular nerve schwannoma** This accounts for 75% of CPA tumors. The acute angle with the petrous bone and expansion of the internal auditory canal are characteristic features. The absence of a dural tail further supports this diagnosis. Facial nerve schwannomas are rare in this location and typically cannot be separated from the mass on imaging.

Answer 16

**D. FLAIR** On FLAIR sequences, epidermoid cysts show mixed iso- to hyperintense signal with poor demarcation, while arachnoid cysts have their signal suppressed, resembling CSF. Diffusion-weighted imaging can also help distinguish them, as epidermoid cysts show very high signal due to restricted diffusion.

Answer 17

**B. Erosion of the adjacent porus acousticus** Vestibular schwannomas typically erode the posterior edge of the porus acousticus as they grow, whereas meningiomas usually do not cause such erosion. This distinction is crucial in identifying the nature of the lesion.

Answer 18

**A. Diffusion-weighted MR imaging** Epidermoid cysts appear bright on diffusion-weighted imaging due to restricted diffusion, while arachnoid cysts appear dark. This sequence is particularly useful for distinguishing between the two cyst types when they are isodense to CSF on CT and standard MRI.

Answer 19

**B. Smooth margin** Smooth margins are characteristic of arachnoid cysts, while epidermoid cysts tend to have irregular margins and can encase vessels.

Answer 20

**A. Cerebellar pontine angle (CPA)** Epidermoid cysts are most commonly found in the CPA, accounting for 40% of cases and 5% of CPA tumors.

Answer 21

**A. Meningioma** The presence of a dural tail and broad-based attachment to the petrous bone are characteristic of meningiomas. Uniform enhancement and less bright T2 signal further support this diagnosis

Answer 22

**Presence of a dural tail** The most common causes of a cerebellopontine angle mass are vestibular schwannoma (also called acoustic neuroma) (75%), meningioma (10%) and epidermoid cyst (5%). Features suggestive of a meningioma include a dural tail (thickening of enhancing adjacent dura resembling a tail extending from the mass), adjacent hyperostosis and an obtuse angle with the petrous bone (vestibular schwannomas make an acute angle). Distinguishing features of schwannomas include extension into the internal auditory canal, causing expansion of the canal and flaring of the porus acousticus (bony opening of the internal auditory canal). Meningiomas may show a small tongue of extension into the canal but usually no expansion. Schwannomas undergo cystic degeneration and haemorrhage more commonly than meningiomas (particularly larger lesions), and may show very high signal on T2W images, which is unusual for a meningioma.

Answer 23

**Dermoid** Epidermoids and dermoids are congenital lesions resulting from inclusion of ectodermal elements during closure of the neural tube. Both have a squamous epithelial lining and produce keratin, but dermoids contain both ectodermal and mesodermal elements (hair follicles, sweat and sebaceous glands), while epidermoids contain only ectodermal elements. Epidermoids are lobulated masses, usually located off the midline, which compress adjacent structures such as cranial nerves, and tend to have appearances on CT and MR scan following that of CSF. Dermoids are usually midline in location and cause symptoms by obstruction of CSF pathways or by rupture and leakage of fat contents, causing chemical meningitis. They have appearances on CT and MR scan following that of fat and are often heterogeneous with areas of calcification and other soft-tissue components. This heterogeneity helps to distinguish a dermoid from a lipoma. Arachnoid cysts are of CSF density, but may be distinguished from epidermoid on DWI, where they do not show evidence of water restriction. Teratomas are composed of ectodermal, mesodermal and endodermal elements, and also appear heterogeneous with areas of fat, calcification and cystic components, but these lesions occur most commonly in the pineal and suprasellar regions.

Answer 24

**(c) Epidermoid cyst in the left CPA** This resembles CSF on non-enhanced CT. On MRI, the lesion is isointense, or slightly hyperintense to CSF. Incomplete attenuation on FLAIR and high signal on diffusion (suggesting restricted diffusion) concludes the diagnosis. Non enhancement is the rule.

Answer 25

**(a) Schwannoma** Vestibular schwannomas are the most common cerebellopontine angle tumours with typical imaging features as given above. These are typically benign, slow growing tumours from Schwann cells which envelop and myelinate cranial, spinal and peripheral nerves. In the skull, they most commonly arise in the cerebellopontine angle, from the vestibular portion of the 8th cranial nerve. The main differential diagnosis is meningioma, which can also grow from the 8th cranial nerve. A schwannoma is hyperintense on T2 while a meningioma is isohypointense. Also, a meningioma forms an obtuse angle with the petrous bone while a schwannoma forms an acute angle. Finally, a meningioma may have a dural tail, which is absent in a schwannoma.

Answer 26

**(a) Arachnoid cyst** An arachnoid cyst returns signal characteristics of cerebrospinal fluid. High on T2, intermediate on T1 and no restriction on diffusion-weighted images.

Answer 27

**Cerebellopontine angle lipoma** The lesion has characteristics of fat on all sequences (high signal on T1 and T2 with loss of signal on fat-suppression imaging).

Answer 28

**No change in size, shape, or signal intensity on follow-up MR**I. Hypothalamic hamartomas are developmental malformations located in the tuber cinereum of the hypothalamus. The typical patient is male, in the first or second decade of life, presenting with precocious puberty or gelastic seizures. On MRI, they appear as well-defined pedunculated or sessile lesions that are iso/mildly hypointense on T1WI and iso/hyperintense on T2WI, with no contrast enhancement or calcification. Lack of interval change strongly supports the diagnosis.

Answer 29

**Rathke cleft cyst**. These are benign cystic lesions of the pituitary fossa derived from the Rathke pouch. They are usually asymptomatic. Rathke cleft cysts are in the midline between the anterior and posterior pituitary lobes and have a characteristic kidney shape on axial images. They are homogenously hyperintense on T1WI, due to high protein concentration, and hypointense on T2WI, due to low intracystic water content. They do not enhance following contrast administration. Absence of a fluid–fluid level is helpful in differentiating Rathke cleft cyst from hemorrhagic adenoma. Acute haemorrhage has heterogenous signal on T2WI and may demonstrate thin peripheral enhancement on T1WI. Craniopharyngiomas have variable solid, cystic, and calcified components. They demonstrate heterogenous enhancement following contrast. They may be intrasellar or suprasellar. A pseudo-fluid–fluid level may occasionally be seen in craniopharyngioma. Lipoma and cholesterol granuloma are hyperintense on both T1WI and T2WI.

Answer 30

**Loss of the posterior pituitary bright spot**. Autoimmune hypophysitis (AH) and non-secreting pituitary adenomas can only be differentiated with certainty on histology. As a result, approximately 40% of patients with AH are misdiagnosed as having pituitary macroadenoma and undergo unnecessary surgery. Hormone production is compromised in both conditions, although a history of infertility is common with adenomas, whereas patients with AH typically achieve spontaneous pregnancy. To develop a scoring system to differentiate the two conditions, a recent study found that features significantly associated with AH over adenoma were age <30, relation to pregnancy, homogenous gadolinium enhancement, loss of the posterior pituitary bright spot, and enlarged stalk. Features consistent with adenoma were asymmetrically enlarged pituitary, size >6 cm³, and associated sinus mucosal thickening. The normal posterior pituitary gland is bright on T1WI due to the rich content of vasopressin neurosecretory granules. This is frequently lost in AH due to direct autoimmune involvement of the neurohypophysis, whereas it is conserved in most adenomas, even when displaced by large tumour size.

Answer 31

**Pituitary adenoma** Pituitary adenomas are divided into microadenomas (<1 cm) and macroadenomas (>1 cm). Macroadenomas may present with endocrine dysfunction but are generally less active than microadenomas. Thus, macroadenomas often present with symptoms of mass effect on the optic chiasm, or if there is lateral extension into the cavernous sinuses, patients may present with other local cranial nerve palsies (III, IV, VI). The differential diagnosis of a suprasellar mass includes (‘SATCHMO’): Suprasellar extension of pituitary adenoma/sarcoid; Aneurysm/arachnoid cyst; TB/teratoma (other germ-cell tumours); Craniopharyngioma; Hypothalamic glioma or hamartoma; Meningioma/metastases (especially breast); and Optic/chiasmatic glioma. In this case, the sellar is widened and the floor is eroded suggesting the mass arises from the pituitary itself. Low-density/low-intensity regions on CT/T1 MRI correspond to necrotic areas and high-signal foci on T1 MRI (found relatively frequently) represent areas of recent haemorrhage.

Answer 32

**Absence of calcification** Rathkes cleft cysts do not calcify. They affect women to men in a 2:1 ratio and adults from 40-60 years of age. They cause variable MR appearances depending on protein content of cyst. They can rarely show enhancement.

Answer 33

**Focus of hypo-intensity within normal enhancing gland** Pituitary microadenomas are typically hypointense compared with the normal gland on unenhanced T1W images, and the diagnosis can usually be made without contrast. Following contrast, the microadenoma does not initially enhance, and maximal contrast between enhancing normal gland and pituitary tumour is seen on dynamic images obtained within the first minute. Contrast enhancement may therefore be useful in identifying lesions that are not obviously hypointense on the unenhanced images. However, contrast enhancement of the tumour relative to the normal gland may be seen on delayed (>20 min) images.

Answer 34

**Craniopharyngioma** Craniopharyngiomas are the most common suprasellar mass, predominantly occurring in the ﬁrst and second decades, but with a second peak in the ﬁfth decade. Presenting symptoms include headache secondary to hydrocephalus, bitemporal hemianopia (compression of the optic chiasm) and diabetes insipidus (compression of the pituitary gland). Typical imaging features are calciﬁication, cyst formation and enhancement that may be solid or nodular. Meningiomas may arise in the suprasellar region and commonly demonstrate calciﬁication but are generally not cystic. Epidermoids may occasionally demonstrate rim calciﬁication but rarely enhance following intravenous contrast. Pituitary macroadenomas may undergo haemorrhage, resulting in heterogeneity that can cause confusion with craniopharyngioma, but this typically occurs in adolescence. Calciﬁication in macroadenomas is infrequent. Rathke’s cleft cysts are thin-walled, benign cysts arising in the anterior sellar or suprasellar region. They show no contrast enhancement and rarely calcify.

Answer 35

**Hypothalamic hamartoma** Also called hamartoma of the tuber cinereum, this is seen in children less than 2 years of age. Precocious puberty is due to luteinising releasing hormone secretion. Craniopharyngioma presents with growth failure and visual field defects. Kallmann syndrome presents with hypogonadism in later age. Pituitary adenomas are seen in girls (9–13 years of age) and are usually prolactin or adrenocorticotropic hormone secreting lesions.

Answer 36

**Chiasmal glioma** Chiasmal glioma is associated with NF1 in 15-25% cases. Craniopharyngioma tends to displace the chiasm rather than enlarge it. It is often cystic and may show calcification. Lymphoma is more likely to involve peripheral nerves. Tuberculosis may involve the chiasm but in the setting of basal meningitis, leptomeningeal enhancement and multiple cranial neuropathies.

Answer 37

**Germinoma**. The lesion is described in the pineal region, so the differential of pineal tumours should be considered. These are differentiated between germ cell tumours and pineal cell tumours. Germinomas account for 40% of all pineal region masses and are much more frequent in males than females. They are also the most common germ cell tumour, with teratomas and choriocarcinoma having different imaging characteristics. The main differential in this case is between pineoblastoma and germinoma, as both occur in patients of this age group and both are hyperdense on CT. Imaging features described to help differentiate are the avid enhancement, which is more characteristic of germinomas, but can occur in either. Central calcification is seen commonly in germinomas, but is uncommon in pineoblastomas, and when it occurs is often peripheral, giving the impression of an ‘exploded’ pineal gland. Subarachnoid seeding is seen in both tumours and if present CSF sampling can yield a tissue diagnosis. Pineocytomas occur in an older age group and infrequently cause subarachnoid seeding.

Answer 38

**Germinoma**. Germinomas are germ-cell tumours arising from primordial germ cells. They frequently occur in the midline, mostly in the pineal region but also in the suprasellar region. In men, 80% of pineal masses are germ-cell tumours, in contrast to 50% in women. They tend to occur in children or young adults (10–25 years old). Symptoms depend on the location, but the case describes Parinaud syndrome – paralysis of upward gaze due to compression of the mesencephalic tectum. Germinomas may also cause hydrocephalus by compression of the aqueduct of Sylvius, thus patients may present with signs and symptoms of raised intracranial pressure. Germinomas are a known cause of precocious puberty in children under the age of ten years. They are malignant tumours and may show CSF seeding, making cytological diagnosis possible with lumbar puncture. They are, however, very radiosensitive and show excellent survival rates. Pineal teratomas tend to be heterogeneous masses containing fat and calcifications. Pineoblastoma is a highly malignant tumour which is more common in children and usually has poor tumour margins.

Answer 39

**Pineal germinoma (also called pinealoma)**. This is the most common pineal tumour and is associated with precocious puberty in children less than 10 years old. The finding of pineal calcification before 10 years with a pineal mass enhancing with contrast is usually diagnostic. Hydrocephalus is secondary to compression of the cerebral aqueduct. Medulloblastoma is a tumour usually in the posterior fossa and presenting in childhood. Suprasellar meningioma does not arise from the pituitary fossa.

Answer 40

**Primary CNS lymphoma (PCNSL)**. PCNSL is the second most common cause of a CNS mass in patients with AIDS (behind toxoplasmosis). Typical features include periventricular location with subependymal spread and crossing of the corpus callosum. Non-contrast CT may show a hyperdense lesion due to dense cellularity (for this reason it may also be hypointense on T2/FLAIR). There is often a paucity of oedema and frequent ring enhancement due to central necrosis (note this is in contrast with the solid homogeneous enhancement seen with lymphoma in the immunocompetent patient). Cryptococcosis is the most common cause of fungal infection in AIDS patients. CT is frequently normal, and MRI shows low T1 and high T2 signal intensities without enhancement in the lenticulostriate region. Progressive multifocal leukoencephalopathy typically shows bilateral white matter lesions in the periventricular region, centrum semi-ovale or subcortical white matter, which are hypointense on T1 and hyperintense on T2/FLAIR. There is typically no oedema nor mass effect and no contrast enhancement.

Answer 41

**Lymphoma** This is seen not only in immunocompromised but also immunocompetent patients. On CT, the lesion is usually hyperdense showing homogenous enhancement. Resolution with steroids and/or radiotherapy is a characteristic finding of cerebral lymphoma.

Answer 42

**Haemangiopericytoma**. The imaging findings clearly describe an extra-axial tumour. These are classed as either lesions of meningeal origin or tumours of neurogenic origin. The broad dural base and dural tail indicates that this is a tumour of meningeal origin. Meningioma is the most common of these tumours, but the imaging characteristics are not typical. World Health Organization (WHO) 1 and 2 meningiomas demonstrate uniform enhancement, although haemorrhage into meningiomas is recognized. WHO 3 meningiomas (malignant meningiomas) are indicated on imaging when there is invasion of the adjacent parenchyma, which is not described. Otherwise, the diagnosis of malignant meningioma is made by an aggressive pattern of growth on serial imaging and biopsy. The dual arterial supply is also atypical. While meningiomas can have dual supply, they more typically derive their arterial supply from the external carotid (via the meningeal artery). Melanocytomas are suggested on imaging by increased signal on T1WI and are more commonly infratentorial. Without this, the diagnosis is again reached most following biopsy. All the features described are typical of haemangiopericytoma.

Answer 43

**Meningioma** It is rare for meningiomas to occur intraventricularly (2–5% of all meningiomas) but they are the most common trigonal intraventricular mass in adulthood. They tend to occur in 40-year-old females.

Answer 44

**E** Dural meningeal carcinomatosis is rarely associated with positive cytology and involves localised or diffuse curvilinear enhancement underneath inner table in expected position of dura.

Answer 45

**Meningioma** Meningioma is the most common radiation-induced CNS tumour and has been particularly associated with low-dose radiation treatment for tinea capitis. For the diagnosis of radiation-induced meningioma to be made, the meningioma must arise in the radiation field, appear after a latency period of years and should not have been the primary tumour irradiated. Radiation-induced meningiomas are more frequently multiple and have higher recurrence rates than non-radiation-induced tumours.

Answer 46

**Meningioma** These are all typical features of a meningioma. Medulloblastoma is a childhood infratentorial tumour which is usually hyperdense and enhances with contrast. Lymphoma can be isodense with homogenous enhancement but usually is associated with significant peritumoral oedema and no calcifications. Glioblastoma multiforme is seen as an irregular lesion with mass effect, oedema and a heterogenous enhancement pattern. Sarcoma metastases are rare and would induce peritumoral oedema.

Answer 47

**Meningioma** These tumours arise from the arachnoid ‘cap’ cells of the arachnoid villi.

Answer 48

**Ependymoma**. Ependymoma is the most common intramedullary neoplasm in adults. It tends to be centrally located within the cord, unlike astrocytoma, which can be eccentric. Astrocytoma can have a longer segment of cord involvement than ependymoma and may have a more infiltrative margin. The peripheral low signal areas seen on T2WI in ependymoma are related to haemosiderin deposition from prior haemorrhage.

Answer 49

**D** Eccentrically placed lesion in the cord. Table 6.2 illustrates the diagnostic features of astrocytoma and ependymoma.

Answer 50

**Meningioma**. Spinal meningiomas are typically iso- to hypointense on T1WI and slightly hyperintense on T2WI. There is usually strong and homogeneous enhancement with gadolinium. However, some meningiomas may contain calcification and are typically the only intradural extramedullary tumours to do so. Some meningiomas can be heavily calcified and such a meningioma is being described in the question. These will remain dark on all MRI sequences and demonstrate only little contrast uptake (in the non-calcified areas). Schwannomas, neurofibromas, and metastases would not typically be hypointense on T2WI. Meningeal lymphomas are very rare and usually manifest as diffuse thickening of nerve roots and/or multiple enhancing nodules.

Answer 51

**Myxopapillary ependymoma** This is a variant of ependymoma and is the most common neoplasm of the conus medullaris. It originates from ependymal glia of the filum terminale. Average age at presentation is 35 years and it is more common in men. T1-weighted imaging shows an isointense or occasionally hyperintense (due to the mucin content) mass. It is hyperintense on T2 and almost always shows enhancement postcontrast. Intradural lipomas are hyperintense on T1-weighted imaging, but they should not enhance. They also tend to occur in younger individuals and usually have an associated, clinically apparent lumbosacral mass. Haemangioblastoma can also demonstrate high signal on T1 but is also highly vascular, can show signal voids and approximately half of them will have an intra-tumoural cystic component. Gangliogliomas are much more common at the cervical and thoracic levels.

Answer 52

**E** Drop metastases are usually dorsal in location in the spinal canal. Medulloblastomas are the most common cause of drop metastases. A higher percentage of CSF cytology is positive.

Answer 53

**Ependymoma** Other intramedullary masses include astrocytoma are dermoids (lipoma/teratomas), acutely expanding infarcts and haematoma.

Answer 54

**Meningioma** Meningiomas in the spine are seen mainly in females (80%) and in those over 40 years of age. They have similar signal characteristics to the cord on MRI and enhance avidly. They can cause symptoms related to cord compression. Bone erosion is seen in ,10%. Nerve sheath tumours produce fusiform masses arising from the nerve roots, often extending through the intervertebral foramen, causing them to be dumbbell shaped. They are isointense to muscle on T1W and hyperintense to fat on T2W images. Ependymomas are usually located in the filum terminale and show low/intermediate signal on T1W images, with foci of high signal on T2W images, and they often enhance. Dermoids usually occur in the conus or cauda equina and are associated with spinal dysraphism in one-third of cases. They are variable in signal on T1W but are high signal on T2W images.

Answer 55

**Glomus jugulare tumour** All the tumours listed in the differential (apart from cholesteatoma) are paragangliomas. They grow slowly and rarely metastasise. Glomus jugulare tumours originate from the adventitia of the jugular vein. CT demonstrates a soft-tissue mass in the region of the jugular bulb/hypotympanum/middle ear space. Local bone destruction is common, particularly of the jugular plate or the lateral portion of the carotico-jugular spine. A unique ‘salt-and-pepper’ pattern of hyper- and hypo-intensity on T1- and T2-weighted images is also seen. This represents multiple small tumour vessels. They are highly vascular lesions, usually deriving a blood supply from branches of the external carotid artery.

Answer 56

**Paraganglioma**. Paragangliomas are rare intradural extramedullary tumours that are usually benign and have imaging characteristics as those described. Schwannomas, neurofibromas, and meningiomas are much more common, but do not typically contain vascular flow voids or areas of hemorrhage. Meningiomas may have a dural tail or foci of calcification. Schwannomas and neurofibromas can be difficult to distinguish on imaging. They are typically isointense on T1WI and markedly hyperintense on T2WI. Enhancement may be intense and homogenous or peripheral. Neurofibromas tend to encase, rather than displace, nerve roots. Leptomeningeal metastases present with three different imaging patterns: 1) Diffuse, thin enhancing coating of the surface of the spinal cord and nerve roots. 2) Multiple small enhancing nodules on the surface of the cord and nerve roots. 3) A single mass in the lowest part of the thecal sac.

Answer 57

**D. Splaying of the internal and external carotid arteries**. Carotid body tumour or paraganglioma is the most common paraganglioma of the head and neck. It arises from the paraganglionic cells located on the medial aspect of the carotid bifurcation. On MRI, they are of low to intermediate signal intensity on T1WI and hyperintense on T2WI. They are hypervascular and demonstrate intense enhancement after contrast administration. Splaying of the internal and external carotid arteries and multiple flow voids producing a ‘salt and pepper’ appearance are distinctive features on imaging.

Answer 58

**Both FNA and core biopsy contraindicated** The imaging appearances are highly suggestive of a carotid body tumour (paraganglioma), and biopsy should not be performed, as hemorrhage would be certain due to the high vascularity of the lesion (in addition to the proximity of the carotid system). They present as painless, pulsatile masses in the neck of adults, below the angle of the jaw, and are laterally mobile but vertically fixed. There is splaying of the carotid bifurcation but preservation of calibre of the two arteries. Contrast imaging shows avid enhancement.

Answer 59

**Carotid body paraganglioma** Carotid body tumours are the most common extracranial head and neck paragangliomas. These typically splay the internal and external carotid arteries because they arise from the tissue located at the carotid artery bifurcation. They demonstrate an intense and persistent vascular blush on imaging. The combination of intense blush with flow voids on MRI has been described as a ‘salt and pepper’ appearance. These tumours may be familial and multicentric and are malignant in 10% cases.

Answer 60

**Metastasis**. The answer options give some of the classical radiological differentials for a ring-enhancing lesion in the brain: MAGIC DR (metastasis, abscess, glioblastoma multiforme, infarct, contusion, demyelinating conditions, and post-radiotherapy change). The clinical history should steer the reader toward the first two. DWI is reasonably useful at differentiating between these two (exceptions being in some fungal infections and toxoplasmosis), with necrotic metastasis having unrestricted diffusion and abscess having restricted diffusion. The appearances in this case are slightly confused by the DWI b1000 imaging showing increased signal. However, the presence of increased signal on the ADC map correctly identifies this as being T2 shine through, showing the importance of checking both sequences.

Answer 61

**Renal cell metastasis with subsequent CT staging** Brain metastases account for approximately a third of all intracranial tumours and are the most common intracranial neoplasm. They characteristically occur at the corticomedullary junction of the brain and have surrounding oedema that typically exceeds the tumour volume. Multiple lesions are present in approximately two-thirds of cases and should be searched for with administration of intravenous contrast. Most are hypodense on CT unless haemorrhagic or hypercellular, hence the lesion in this case is haemorrhagic. This lends itself to a differential of primary neoplasms which includes melanoma, renal cell carcinoma, thyroid carcinoma, bronchogenic carcinoma, and breast carcinoma. The history of back pain also suggests bone metastases. Glioblastoma multiforme usually appears as an irregular, heterogeneous, low-density mass. Abscesses typically demonstrate ring enhancement post-contrast and may show loculation and specules of gas. The patient’s history describes collapse rather than headache or confusion following a fall, which moves the differential away from traumatic contusion. Although prostate cancer typically metastasises to the vertebrae, it is an uncommon primary site for brain metastases, especially as the lesion described is haemorrhagic.

Answer 62

**Breast** Most retrobulbar metastases are extraconal (outside the muscle cone). Neuroblastoma and Ewing’s sarcoma are the most common in children and produce smooth extraconal masses related to the posterior lateral wall of the orbit. In adults, an infiltrative retrobulbar mass and enophthalmos is characteristic of scirrhous carcinoma of the breast (invasive ductal carcinoma). Enophthalmia is also considered to be one of the earliest signs of metastatic breast cancer.

Answer 63

**Short discontinuous thin sections of enhancement** Dural meningeal carcinomatosis is rarely associated with positive cytology and involves localised or diffuse curvilinear enhancement underneath inner table in expected position of dura.

Answer 64

**Adenocarcinoma of the lung** Squamous cell lung cancer and adenocarcinoma of the lung cause cystic metastasis to the brain. Answers B-E are causes of haemorrhagic metastases.

Answer 65

**Chest Radiograph** Brain metastases are the most common intracranial tumours. Six primary tumours account for 95% of all brain metastases. Primary bronchial carcinoma is the most common (47% of cases), though squamous cell carcinoma rarely metastasizes to the brain. Other common primary tumours are breast carcinoma (17%), gastrointestinal malignancy (15%), renal cell carcinoma, melanoma and choriocarcinoma. Metastases characteristically occur at the grey–white matter junction, are multiple in 66% of cases, and typically appear as hypodense masses that demonstrate solid or ring enhancement.

Answer 66

**Melanoma metastases** The T2 shortening effect is attributed to the paramagnetic effects of iron and copper bound to melanin.

Answer 67

**Two episodes of vomiting**. Almost anything will buy you a CT brain these days, but surprisingly, the GCS must be less than 13 in the A&E department within 2 hours of the injury under NICE guidelines to warrant one. After 2 hours have passed, a GCS of anything less than normal is an indication for scanning. Other factors which require a CT within 1 hour are suspected open or depressed skull fracture, sign of fracture at skull base, post-traumatic seizure, focal neurological deficit and amnesia, or loss of consciousness and coagulopathy. Additional factors which necessitate a CT brain within 8 hours are amnesia of events for greater than 30 minutes before impact, and if there is any amnesia or loss of consciousness and the patient is older than 65/dangerous mechanism of injury. Note that, perversely, even if the scan can be delayed but be performed within 8 hours, the guidelines state it should be requested immediately. Prepare to be awoken from your sleep!

Answer 68

**Diffuse axonal injury (DAI)**. CT is initially often normal (up to 80% of cases) in DAI. If positive, it may reveal small low attenuation foci (oedema) or high attenuation foci of petechial haemorrhage. The gray/white matter interface of the frontotemporal lobes, corpus callosum (especially the splenium), and brainstem are the most involved sites in DAI. MRI is much more sensitive and is the investigation of choice. The signal on MRI depends on the age of the lesion and whether haemorrhage is present, but classically hyperintense foci on T2WI sequences are seen acutely. In the more chronic phase, the lesions may only be detected as hypointense foci at characteristic locations on GE sequences: this appearance may remain for years. DWI reveals hyperintense foci of restricted diffusion on B1000 images, with corresponding low signal on the ADC map. The findings on DWI are easily distinguishable from extradural haematoma/subarachnoid haemorrhage/subdural haematoma/generalized oedema, which are discussed in other questions in this chapter.

Answer 69

**Le Fort fractures by definition refer to fractures involving the maxilla bilaterally**. Separation of all or a portion of the maxilla from the skull base is described as a Le Fort fracture. This can be unilateral when it is associated with sagittal or parasagittal fractures of the palate. Le Fort fractures by definition involve the posterior maxillary buttress at the junction of the posterior maxillary sinus and the pterygoid plates of the sphenoid. This may be either through the pterygoid plates or through the posterior walls of the maxillary sinus. Once a pterygomaxillary disruption has been identified, the remaining facial buttresses are inspected to identify the type of Le Fort fracture. In Le Fort I fracture, the maxillary arch will move in relation to the rest of the face and skull. In Le Fort II fracture, the entire maxilla will move in relation to the skull base. In Le Fort III, there is complete craniofacial separation. Any combination of Le Fort I, II, and III can occur. Posterior extension of Le Fort fracture into the hard palate results in widening of the maxillary arch and dental malocclusion.

Answer 70

**Amnesia of events <30 minutes after impact** NICE defines head injury as ‘any trauma to the head, other than superficial injuries to the face’. All of the other criteria listed are requisites for an acute head CT scan. Haemotympanum implies a basal skull fracture which should be investigated by CT. Amnesia of events >30 minutes before impact would require an acute head CT. Any amnesia or loss of consciousness since the injury requires a CT scan if the patient is equal to or older than 65 years, has a coagulopathy (including warfarin treatment) or if there is a history of dangerous mechanism of injury, which is listed as: * Pedestrian or cyclist struck by a motor vehicle. * Occupant ejected from a motor vehicle. * Fall from over one metre or five stairs.

Answer 71

**b. diffuse axonal injury** Diffuse axonal injury is characterized by widespread axonal disruption occurring in response to acceleration or deceleration forces – direct impact is not necessary. Typically, patients are immediately unconscious after the injury. CT is commonly negative, though 20% of lesions contain sufficient haemorrhage to be visible. On MR scan, typical findings are of multiple small foci of decreased signal intensity on T1W images and increased signal intensity on T2W images. Characteristic locations are the frontal and temporal white matter near the grey–white matter junction. More severe injuries may involve the lobar white matter and corpus callosum, with the brain stem involved in the most severe cases. Cortical contusions usually involve the superficial grey matter, and patients are less likely to present with immediate loss of consciousness. They characteristically occur near bony protuberances and are more commonly haemorrhagic. Subcortical grey matter injury is an uncommon type of injury seen after severe head trauma, with petechial haemorrhages in the basal ganglia and thalamus.

Answer 72

**A. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)**. This is a hereditary small vessel disease, which causes stroke in young adults. The genetic mutation is found on chromosome 19. Presentation can include migraine, cognitive decline, psychiatric disturbance, TIAs, and stroke, the latter usually with substantial/complete recovery after individual strokes, particularly early in the disease process. Imaging reveals subcortical lacunar infarcts and leukoencephalopathy in young adults. The frontal lobe has the highest lesion load, followed by the temporal lobe and insula. Anterior temporal pole and external capsule lesions have higher sensitivity and specificity for CADASIL. The cerebral cortex is usually spared. MRI is the investigation of choice: CT will reveal only areas of hypodensity, and angiography is normal. sSAE is associated with hypertension and results in multiple lacunar infarcts in the lenticular nuclei, pons, internal capsule, and caudate nuclei. MELAS and MERRF are mitochondrial disorders. MELAS results in bilateral multiple cortical and subcortical hyperintense lesions on FLAIR images; MERRF has a propensity for the basal ganglia and caudate nuclei, and watershed ischaemia/infarcts are common. Hypercoagulable states such as protein S deficiency result in cortical and lacunar infarcts of various sizes, but the cerebral angiogram is abnormal.

Answer 73

**A. Decreased CBF/decreased CBV/increased MTT**. In identifying the ischaemic penumbra, CT perfusion offers promise in improved patient selection for thrombolysis beyond a rigid time window. In the infarct core (tissue which is not salvageable) both CBF and CBV are decreased with a corresponding increase in MTT. Penumbral tissue (which is potentially recoverable by thrombolysis) exhibits a CBF/CBV mismatch with an increased CBV, but decreased CBF (and increased MTT). An increase in CBF and CBV with decreased MTT is a feature noticed in tumours secondary to angiogenesis and microvascular permeability.

Answer 74

**C. DWI.** The sensitivity and specificity of DWI in detecting acute ischaemia are 88–100% and 86–100%, respectively, and DWI is established as better than other conventional MRI techniques. In addition, acute from chronic ischaemia can be differentiated. DWI is a measure of the Brownian motion of water molecules within a tissue. Two sets of images are acquired: the DWI and the quantitative ADC map. Chronic lesions may appear bright on the DWI (T2 shine through), but only acute lesions with restricted diffusion will be dark on the ADC map. It should be noted, however, that high signal intensity on DWI with low ADC has been reported in a variety of conditions such as abscess, lymphoma, and gliomas. GE is useful for identifying microbleeds that may influence antithrombotic treatment.

Answer 75

**c. Middle cerebral artery infarction** Vascular occlusive disease is rare in the neonatal period. When present, it is more common in the term infant and usually results from thrombosis rather than embolism. The MCA is most involved. Aetiology includes traumatic delivery, vasospasm due to meningitis and emboli secondary to congenital heart disease. Ultrasound demonstrates echogenic parenchyma in the distribution of the arterial territory.

Answer 76

**b. Hyperintense on DW MRI and low ADC values** Diffusion-weighted imaging is dependent on the motion of water molecules and provides information on tissue integrity. It is thought that interruption of cerebral blood flow results in rapid breakdown of energy metabolism and ion exchange pumps. This causes a shift of water from the extracellular compartment into the intracellular compartment, giving cytotoxic odema. This produces the hyperintensity on DW MR images. ADC values tend to be low within hours of stroke and continue to decline for the next few days. They remain reduced through the first four days and then show pseudonormalisation between four and ten days. After ten days the ADC tends to rise. Hyperintensity on diffusion weighted (DW) MRI and low ADC values are not pathognomonic of acute infar

Answer 77

**B** Multiple flow voids are due to hypertrophied lenticulostriate arteries. Children more often present with ischemia and infarct in cortical/subcortical areas. Adults more often present with haemorrhage than children, but when infarcts do occur, they are most often in the deep white matter. The disease can involve the posterior circulation. The supra-clinoid MCA is the first to be involved.

Answer 78

**250 cm/s** Carotid ultrasound scan can be used to assess the common, external, and internal carotid arteries and the carotid bulb, including the vessel walls and the presence of plaques and stenoses. Doppler scan can display velocity profiles and allow waveform analysis and peak velocity measurement. Flow velocity increases proportionally with the degree of stenosis, except when the affected vessel is almost completely or totally occluded. Here flow velocity drops off. Stenosis above 70% is considered for surgery. This corresponds to a flow rate of greater than 250 cm/s.

Answer 79

**Anterior temporal pole** A young patient with migraines, auras, TIAs or subcortical strokes should raise suspicion of CADASIL. Subcortical infarcts are characteristically in the anterior temporal pole and external capsule but may involve C, D and E.

Answer 80

**Decreased, Increased, Decreased** Cerebral perfusion CT can distinguish viable but ischaemic tissue (the penumbra) from tissue that is beyond recovery. Other uses include evaluation of vasospasm after subarachnoid haemorrhage, assessment of cerebrovascular reserve with acetazolamide (cerebral arteriole vasodilator) in cases of vascular stenosis, evaluation of collateral flow and cerebrovascular reserve in patients having temporary balloon occlusion and assessment of microvascular permeability of intracranial neoplasms. Cerebral perfusion CT utilizes the central volume principle. This states that CBF=CBV/MTT, where CBF is cerebral blood flow, CBV is cerebral blood volume and MTT is mean transit time. In practice, two CT perfusion techniques can be used. One is perfused-blood volume mapping, in which a quantity is assigned to cerebral blood volume by subtracting unenhanced CT data from CT angiographic data. It has the advantage of imaging the whole brain. The second technique is a dynamic, contrast-enhanced technique that acquires data from a limited number of axial slices and monitors the first pass of an iodinated contrast agent bolus through the cerebral circulation. This requires an unenhanced CT brain, followed by a dynamic CT performed during injection of 50 ml of iodinated contrast (300 mg I/ml) at 4 ml/s. The first pass of contrast is observed in the brain. Cerebral perfusion is related to the concentration of iodinated contrast, which is directly related to the attenuation measured. Several maps are produced, including the CBV, CBF and MTT. MTT is derived from arterial and venous enhancement curves, measured by using regions of interest placed on an artery (one that is not occluded as part of an acute event) and a venous sinus. CBV is the area under the enhancement curves, and CBF is obtained from the central volume equation. Differentiation of infarcted brain from penumbra is important because, while penumbra can be saved by timely thrombolysis, infarcted tissue has an increased risk of bleeding from thrombolysis with no chance of recovery. CBF is decreased in both ischaemia and infarction, MTT is longer (.6 s) in both, while CBV is decreased in infarct but increased (or normal) in the penumbra due to cerebral autoregulatory mechanisms. MTT is the most sensitive for stroke. So, this or CBF can be used to detect stroke while CBV is used to determine whether there is infarct or reversible ischaemia.

Answer 81

**Right Middle Cerebral Artery Fat Embolism** The hypodense artery sign is described, representing a single, large, macroscopic fat embolus within the middle cerebral artery, giving rise to a stroke syndrome. It may occur during cardiac surgery, resulting in dislodgement of fat from the surrounding tissue. This is distinct from the shower of microscopic fat emboli that occurs in the fat embolism syndrome.

Answer 82

**Contrast-Enhanced CT of the brain** In this scenario, the low attenuation and surrounding changes most likely represent brain oedema. This may be due to an evolving infarction or oedema around a metastatic deposit from the previous lung cancer. Differentiation between the two will immediately affect patient treatment, as anti-platelet therapy for ischaemic stroke will increase the risk of haemorrhage from a metastasis and therefore should be withheld if a metastatic deposit is suspected or diagnosed. The primary factor in determining whether a lesion will enhance on CT after administration of intravenous iodinated contrast is the integrity of the blood–brain barrier in that region of the brain substance. A large molecule such as iodinated contrast would not be able to enter the brain unless the integrity of the barrier were compromised. Many aggressive tumours, including metastases, will disrupt this barrier, and so contrast enhancement will be seen in the solid component of these lesions. Acute infarction will typically not show areas of enhancement.

Answer 83

**B** Multiple flow voids are due to hypertrophied lenticulostriate arteries. Children more often present with ischemia and infarct in cortical/subcortical areas. Adults more often present with haemorrhage than children, but when infarcts do occur, they are most often in the deep white matter. The disease can involve the posterior circulation. The supra-clinoid MCA is the first to be involved.

Answer 84

**e. 250 cm/s** Carotid ultrasound scan can be used to assess the common, external, and internal carotid arteries and the carotid bulb, including the vessel walls and the presence of plaques and stenoses. Doppler scan can display velocity profiles and allow waveform analysis and peak velocity measurement. Flow velocity increases proportionally with the degree of stenosis, except when the affected vessel is almost completely or totally occluded. Here flow velocity drops off. Stenosis above 70% is considered for surgery. This corresponds to a flow rate of greater than 250 cm/s.

Answer 85

**A. Anterior temporal pole** A young patient with migraines, auras, TIAs or subcortical strokes should raise suspicion of CADASIL. Subcortical infarcts are characteristically in the anterior temporal pole and external capsule but may involve C, D and E.

Answer 86

**d. decreased, decreased, decreased** Cerebral perfusion CT can distinguish viable but ischaemic tissue (the penumbra) from tissue that is beyond recovery. Other uses include evaluation of vasospasm after subarachnoid haemorrhage, assessment of cerebrovascular reserve with acetazolamide (cerebral arteriole vasodilator) in cases of vascular stenosis, evaluation of collateral flow and cerebrovascular reserve in patients having temporary balloon occlusion and assessment of microvascular permeability of intracranial neoplasms. Cerebral perfusion CT utilizes the central volume principle. This states that CBF=CBV/MTT, where CBF is cerebral blood flow, CBV is cerebral blood volume and MTT is mean transit time. In practice, two CT perfusion techniques can be used. One is perfused-blood volume mapping, in which a quantity is assigned to cerebral blood volume by subtracting unenhanced CT data from CT angiographic data. It has the advantage of imaging the whole brain. The second technique is a dynamic, contrast-enhanced technique that acquires data from a limited number of axial slices and monitors the first pass of an iodinated contrast agent bolus through the cerebral circulation. This requires an unenhanced CT brain, followed by a dynamic CT performed during injection of 50 ml of iodinated contrast (300 mg I/ml) at 4 ml/s. The first pass of contrast is observed in the brain. Cerebral perfusion is related to the concentration of iodinated contrast, which is directly related to the attenuation measured. Several maps are produced, including the CBV, CBF and MTT. MTT is derived from arterial and venous enhancement curves, measured by using regions of interest placed on an artery (one that is not occluded as part of an acute event) and a venous sinus. CBV is the area under the enhancement curves, and CBF is obtained from the central volume equation. Differentiation of infarcted brain from penumbra is important because, while penumbra can be saved by timely thrombolysis, infarcted tissue has an increased risk of bleeding from thrombolysis with no chance of recovery. CBF is decreased in both ischaemia and infarction, MTT is longer (.6 s) in both, while CBV is decreased in infarct but increased (or normal) in the penumbra due to cerebral autoregulatory mechanisms. MTT is the most sensitive for stroke. So, this or CBF can be used to detect stroke while CBV is used to determine whether there is infarct or reversible ischaemia.

Answer 87

**c. right middle cerebral artery fat embolism** The hypodense artery sign is described, representing a single, large, macroscopic fat embolus within the middle cerebral artery, giving rise to a stroke syndrome. It may occur during cardiac surgery, resulting in dislodgement of fat from the surrounding tissue. This is distinct from the shower of microscopic fat emboli that occurs in the fat embolism syndrome.

Answer 88

**e. Contrast-Enhanced CT of the brain** In this scenario, the low attenuation and surrounding changes most likely represent brain oedema. This may be due to an evolving infarction or oedema around a metastatic deposit from the previous lung cancer. Differentiation between the two will immediately affect patient treatment, as anti-platelet therapy for ischaemic stroke will increase the risk of haemorrhage from a metastasis and therefore should be withheld if a metastatic deposit is suspected or diagnosed. The primary factor in determining whether a lesion will enhance on CT after administration of intravenous iodinated contrast is the integrity of the blood–brain barrier in that region of the brain substance. A large molecule such as iodinated contrast would not be able to enter the brain unless the integrity of the barrier were compromised. Many aggressive tumours, including metastases, will disrupt this barrier, and so contrast enhancement will be seen in the solid component of these lesions. Acute infarction will typically not show areas of enhancement.

Answer 89

**c.** Width 8 HU, centre 32 U

Answer 90

**Acute occipital lobe infarct in posterior cerebral artery territory** Homonymous visual field defects result from retrochiasmal lesions, which include the optic tracts, lateral geniculate body, optic radiations, and visual cortex. Unilateral posterior cerebral artery infarction results in isolated hemianopia. The superior portion of the visual field projects to the inferior occipital cortex. Thus, a partial or branch occlusion of the posterior cerebral artery may lead to an isolated superior or inferior visual field defect.

Answer 91

**Haematoma hyperintense to grey matter on both T1WI and T2WI**. The MRI appearances of intracranial haemorrhage are determined primarily by the state of the haemoglobin (Hb), which evolves with age. This can be staged as hyperacute (ﬁrst few hours), acute (1–3 days), early subacute (3–7 days), late subacute (4–7 days to 1 month), or chronic (1 month to years).

Answer 92

Intracellular methaemoglobin

Answer 93

**Multiple, peripheral haemorrhagic foci in a normotensive elderly patient** Multiple peripheral haemorrhages (corticomedullary junction) in normotensive elderly patients are suggestive of amyloid angiopathy. Hypertensive haemorrhage tends to occur centrally around the basal ganglia (putamen, external capsule), thalamus and pons.

Answer 94

**A** B represents early subacute haemorrhage, C represents acute (12-72 hours), D represents hyperacute (less than 12 hours) and E represents chronic haemorrhage (> 1 month).

Answer 95

**1 week to several months** In the ﬁrst 3–6 hours (hyperacute stage) following haemorrhage, the intact red cells contain mostly oxyhaemoglobin, which appears hyperintense on T2W images. Desaturation occurs peripherally, forming deoxyhaemoglobin, which is seen as hypointensity on T2W images. In the acute stage (8–72 hours), there is rapid deoxygenation of the oxyhaemoglobin to deoxyhaemoglobin, which, together with the high protein content of the clot and susceptibility effects, results in iso- to hypointensity on T1W images and hypointensity on T2W images. In the early subacute stage (3–7 days), oxidation of deoxyhaemoglobin to methaemoglobin occurs inside the red cell, resulting in characteristic hyperintensity on T1W images due to paramagnetic effects, and marked hypointensity on T2W images. In the late subacute stage (1 week to months), extracellular methaemoglobin results in persistent hyperintensity on T1W images, but increasing signal intensity on T2W images, with peripheral susceptibility effects causing a low intensity rim. In the chronic stage (months to years), iron atoms are deposited as haemosiderin and ferritin, which cause susceptibility effects resulting in low signal intensity on both T1W and T2W images.

Answer 96

**Post-contrast enhancement of non-haemorrhagic areas** Haemorrhage occurs in 5–10% of tumours. Features suggesting tumour rather than benign haemorrhage include complex CT pattern, incomplete haemosiderin ring, persisting oedema or mass on follow-up studies, and multiple lesions.

Answer 97

**Hyperintense on T1W images and hyperintense on T2W images** The MRI signal of blood depends first on whether it is moving or static, since on most sequences movement produces a signal void. When it is static, the signal returned by blood reflects the magnetic properties of the blood products and their location. Hyperacute haemorrhage is intracellular oxyhaemoglobin that is diamagnetic, returning an isointense T1 and bright T2 signal. At 1–2 days, deoxygenation has occurred, making the iron paramagnetic. It remains intracellular and returns an isointense T1 signal and is dark on T2W images. At 2–7 days, haemorrhage contains paramagnetic intracellular methaemoglobin. This is bright on T1W images and dark on T2W images. The methaemoglobin becomes extracellular from 1 week to 4 weeks, and the MRI signal is bright on both T1W and T2W sequences. Chronic haemorrhage contains haemosiderin/ferritin, which is ferromagnetic, is dark on T1W images and has a dark rim on T2W sequences.

Answer 98

**FLAIR**. Although CT is generally used for investigating acute subarachnoid haemorrhage (SAH), FLAIR sequence on MRI has been suggested as being as sensitive as or more sensitive than CT. It is particularly useful in regions where CT may be limited due to beam hardening artefacts or if there is a very small amount of blood. Acute SAH appears as high intensity on FLAIR within the cisterns and sulci. Subacute SAH may be better appreciated on MRI because of its high signal intensity when the blood is isointense to CSF on CT. SAH differs from intra-parenchymal haemorrhage in that the mix of blood with high-oxygen tension CSF delays generation of paramagnetic deoxyhaemoglobin, and oxyhaemoglobin remains present longer than in intra-parenchymal haemorrhage. This contributes to continued T2 prolongation. Beware that there are other pathological (meningitis, leptomeningeal metastases, acute stroke, fat-containing tumour/dermoid rupture) and benign (artefact, supplemental oxygenation) causes of FLAIR hyperintensity in the subarachnoid space. Chronic haemorrhage from SAH is best detected on GE sequences, resulting in marked subarachnoid low signal (the blooming of superficial siderosis).

Answer 99

**Subdural hygroma** This is a traumatic subdural effusion which shows up as a localised CSF-fluid collection within the subdural space. They present in the elderly or in young children usually 6–30 days following trauma. The majority are asymptomatic, but patients may present with increasing confusion or headaches. They are devoid of blood products on imaging, unlike chronic subdural haematomas. Subdural haematomas are also more likely to cause effacement of the ventricular system and loss of the normal sulci-gyral pattern. Normal inflammatory markers and lack of pyrexia lessen the probability of an empyema.

Answer 100

**The haematoma crosses sutures**. An SDH will cross suture lines and may extend over the whole cerebral hemisphere; an EDH will not. Only an EDH can cross the midline, and this usually occurs at the vertex in the setting of a venous EDH. EDHs are more usually arterial bleeds and associated with temporal skull fractures, which disrupt the adjacent middle meningeal artery. The latter are typically biconvex; SDHs are typically lentiform in shape. Both measure 50–60 HU if acute. Chronic SDHs may be iso- or hypodense to brain, although anaemia or clotting disorders can produce a similar appearance. EDH is a neurosurgical emergency more so than SDH because of the potential lucent period followed by sudden deterioration as arterial bleeding continues after having stripped the dura from the inner table of the skull.

Answer 101

**Association with vomiting**. Headache accounts for approximately 2% of all A&E department visits, yet subarachnoid haemorrhage accounts for less than 3% of these headaches. Up to half of all patients with subarachnoid haemorrhage, however, will be alert and neurologically intact. A recent study prospectively assessed neurologically intact patients presenting with headache peaking within 1 hour to determine which variables are predictive of subarachnoid haemorrhage. High-risk variables include age >40, neck pain, witnessed loss of consciousness, onset with exertion (but not sexual activity), arrival by ambulance, vomiting, and blood pressure >160/100 mmHg. The presence of one or more of these findings in a patient with an acute non-traumatic headache reaching maximum intensity within 1 hour should prompt further investigation.

Answer 102

**Catheter angiography.** Peri-mesencephalic haemorrhage is confined to the cisterns around the midbrain. In some cases, the only blood is found anterior to the pons. Some sedimentation into the lateral ventricles may occur, but frank haemorrhage into the ventricles and/or extension into the sylvian fissure or anterior interhemispheric fissure (as in this case) indicates arterial haemorrhage. Catheter angiography following a negative CTA in the setting of a peri-mesencephalic bleed arguably does not have any extra diagnostic yield. However, catheter angiography remains the gold standard for detecting aneurysms, and in this case an anterior communicating artery aneurysm requires exclusion.

Answer 103

**Anterior communicating artery**. A clot in the septum pellucidum is virtually diagnostic of an aneurysm of the anterior communicating artery. Aneurysms of the distal anterior cerebral artery are less common.

Answer 104

**d.** 98% positive at 12 hours to 75% positive at 3 days

Answer 105

**D** Both are extra-axial and can be of mixed attenuation. Although skull fractures are more common in EDH, this cannot be the single best answer as EDH cross dural attachments are limited by cranial sutures.

Answer 106

**c. junction of anterior cerebral and anterior communicating arteries** It is at this location that 35% of berry aneurysms are found. This is the same proportion that occurs at the junction of the internal carotid and posterior communicating arteries. Five per cent occur at the basilar tip and 20% at the middle cerebral artery bifurcation. Two per cent of the population have cerebral aneurysms. They are multiple in 20% of cases and giant in 25% (over 25 mm in diameter). They are caused by degenerative vascular changes, trauma, infection, tumour and vasculopathy. The incidence is increased in adult polycystic renal disease, aortic coarctation, fibromuscular dysplasia, and Marfan’s and Ehlers–Danlos syndromes.

Answer 107

**a. CT angiography** Some 80–90% of subarachnoid haemorrhage is due to aneurysmal rupture. Therefore, when the diagnosis is proven or strongly suspected, the cerebral arterial circulation requires assessment. Sixteen-slice CT angiography (CTA) is as accurate for aneurysm detection as 2D catheter digital subtraction angiography (DSA). CTA can be used as primary imaging and DSA reserved for difficult cases. It has the advantages of being safe, immediate, swift and less likely to need sedation or general anaesthetic. CTA also offers anatomical information beyond just the cerebral vasculature, in contrast to DSA. With 16-slice CTA, the spatial resolution is similar to DSA: 0.40 mm for CTA and 0.32 mm in DSA (2D DSA 33 cm FOV, 1024×1024 matrix, resolution 0.32×0.32 mm). When DSA is performed with AP and lateral projections, aneurysms may be masked, but 3D rotational DSA avoids this problem. The CTA parameters are as follows: 0.5 rotation/s with a 10 mm table advance per rotation and a 5-scan, 16 rows of 0.75 mm reconstructed to 0.4 mm, kVp 120, mA 130.

Answer 108

**c. vasospasm and infarction** Infarction in this case is cerebellar. Vasospasm is the leading cause of death and morbidity following subarachnoid haemorrhage. It occurs after 72 hours with a peak at 5–17 days. Acute obstructive hydrocephalus results from intraventricular blood or the resultant ependymitis obstructing the aqueduct of Sylvius or the outlet of the fourth ventricle. Communicating hydrocephalus usually occurs after 1 week when the haemorrhage causes impaired CSF absorption.

Answer 109

**b. acute extradural haematoma** Acute extradural haematomas are traumatic in origin and tend to be commoner in younger patients. Two-thirds of cases involve the temporoparietal region, and 75–95% of patients have an associated skull fracture. Bleeding is usually from the underlying middle meningeal artery, though it may also be due to disruption of the middle meningeal vein, dural venous sinuses or diploic veins. Typical appearances are of a high-density lentiform or biconvex collection, which forms between the inner table of the skull and the dura mater. The dura is firmly bound to the skull at sutural margins, so extradural haematomas tend not to cross suture lines. Acute subdural haematomas usually follow severe trauma and have a poorer prognosis than acute extradural haematomas due to a high incidence of associated contusions and other brain injuries. They tend to be crescentic in shape and may freely extend across suture lines, being limited only by the interhemispheric fissure and tentorium. They are commonly bilateral, particularly in infants, and have no association with skull fractures.

Answer 110

**(c) Left middle cerebral artery (MCA)** Rupture of a left MCA aneurysm is likely to be seen as haemorrhage in the ipsilateral sylvian fissure.

Answer 111

**(b) Extradural haematoma** Classically an extradural haematoma is seen as a lentiform/biconvex hyperdense collection bounded by cranial sutures and associated with skull fracture. The collection may be heterogeneous if active bleeding is occurring.

Answer 112

**(a) Central nervous system siderosis** Recurrent subarachnoid bleeds cause haemosiderin deposition on the surface of the brain, brainstem and leptomeninges. This is seen as hypointense signal on T2 and T2* GRE images.

Answer 113

**Straight sinus**. Pregnancy is a risk factor for both venous sinus thrombosis and hypertensive haemorrhage secondary to eclampsia. Hyperattenuating thrombus within the occluded sinus is classical on the unenhanced CT but is seen in only 25% of cases. On the contrast-enhanced study, a central filling defect surrounded by enhancing dura (empty delta sign) is present in over 30%. Most of the superior cerebrum is drained by the superior sagittal sinus. The transverse sinuses receive blood from the temporal, parietal, and occipital lobes. The transverse sinuses drain into the sigmoid sinuses and on into the internal jugular veins. The straight sinus forms from the confluence of the inferior sagittal sinus and vein of Galen. The vein of Galen is part of the deep venous system, which drains the corpus callosum, basal ganglia, thalami, and upper brainstem. Cavernous sinus thrombosis presents with proptosis and cranial nerve palsies (usually cranial nerve VI first). The cavernous sinus receives the petrosal sinuses and middle cerebral veins.

Answer 114

**Dilated superior ophthalmic vein** Carotid–cavernous sinus fistula can be caused by penetrating injury, base of skull fracture or rupture of an intracavernous internal carotid artery aneurysm. Drainage from the affected cavernous sinus is via the superior ophthalmic vein, contralateral cavernous sinus, petrosal sinus and, rarely, cortical veins. Pulsatile exophthalmos and orbital bruit are evident, as are chemosis, conjunctival oedema and increased intraocular pressure. On imaging, the cavernous sinus may be enlarged, and can cause erosion of the sella and enlargement of the superior orbital fissure. Regarding the differentials for extraocular muscle swelling, Graves’ disease typically spares the muscle attachments whereas inflammatory orbital pseudotumour affects the tendons while also causing orbital fat stranding.

Answer 115

**Basal vein of Rosenthal** These veins are all part of the supratentorial venous system. The superficial middle cerebral vein forms an arc along the surface of the sylvian fissure and is continuous with the sphenoparietal sinus. The veins of Trolard and Labbe are anastomotic veins that connect the superficial middle cerebral vein to the superior sagittal and transverse sinuses respectively. The thalamostriate vein is a subependymal vein that passes across the floor of the lateral ventricle, over the thalamus and into the internal cerebral vein behind the foramen of Monro. The paired internal cerebral veins run along the roof of the third ventricle and enter the vein of Galen with the paired basal veins of Rosenthal. The vein of Galen joins the inferior sagittal sinus and the straight sinus at the ‘venous confluence’ within the quadrigeminal plate cistern. The straight sinus lies along the junction of the falx and tentorium. The straight sinus, transverse sinus and superior sagittal sinus meet as the torcular herophili.

Answer 116

**Carotid-cavernous fistula** Carotid–cavernous sinus fistula may occur spontaneously (secondary to aneurysm rupture, dural sinus thrombosis or atherosclerosis) or after trauma/surgery. It presents with a classic triad of pulsatile exophthalmos, conjunctival chemosis and auscultatory bruit. However, reduction in visual acuity may be the only sign. Secondary findings such as proptosis, congestive extraocular muscle enlargement, and distension with enhancement of the superior ophthalmic vein and cavernous sinus are usually identified on routine CT or MRI. However, catheter angiography is usually required for lesion classification and treatment planning prior to embolization. Drainage may also occur into the contralateral cavernous sinus, resulting in dilatation and enhancement. Ophthalmic varices present with intermittent exophthalmos related to straining, with dilatation of superior and/or inferior ophthalmic veins, which may thrombose. Orbital pseudotumour is an idiopathic inflammatory condition affecting all orbital contents, but vascular dilatation is not a feature.

Answer 117

**Empty delta sign** The patient has a venous sinus thrombosis causing congestion and venous infarction. Veno-occlusive disease is commoner in the first 3 weeks postpartum, especially if there is underlying hypercoagulability, including factor V Leiden abnormality, antiphospholipid antibody syndrome, and protein C, protein S or antithrombin III deficiency. On unenhanced CT, there may be hyperdense veins, grey–white matter junction haemorrhage and brain oedema. On CT venography, an ‘empty delta’ can be seen because thrombus rather than iodinated contrast occupies the affected dural venous sinus.

Answer 118

**Early venous drainage**. Brain AVMs are abnormal connections between arteries that would normally supply the brain tissue and veins that normally drain the brain, resulting in shunting with an intervening network of vessels within the brain parenchyma. The finding of early venous drainage is important in differentiating brain AVMs from other vascular lesions. Cortical venous drainage may be seen in superﬁcial lesions. Recruitment of transdural supply is observed in large lesions, although this is a more typical feature of proliferative angiopathy, which is a diffuse type of AVM. Classically, in this condition, normal brain parenchyma is interspersed between the abnormal vessels. Stenoses of feeder vessels are also often identified in proliferative angiopathy. The caput medusa of dilated medullary veins is a feature of DVAs, a normal variant. Dilated cortical veins are seen in dural arteriovenous fistulas (DAVFs), which are abnormal connections between arteries that normally supply the meninges (but not the brain) and small venules within the dura.

Answer 119

**Cavernous malformation (cavernoma)**. This is a benign vascular hamartoma, which can occur anywhere throughout the CNS, although spinal cord involvement is rare. It is typically a discrete, lobulated mass <4 cm containing blood products at different stages of evolution. On MRI they are described as having a ‘popcorn’ appearance of mixed signal intensity with a hypointense haemosiderin rim. They display little to no enhancement. Prominent susceptibility effect on T2* GE is typical. AVMs will demonstrate multiple flow voids. Haemorrhagic neoplasms will exhibit strong enhancement and an incomplete haemosiderin rim. Multiple ‘black dots’ are a feature of amyloid angiopathy. Capillary telangiectasias are poorly demarcated lesions, usually <1 cm, demonstrating ‘brush-like’ enhancement on T1WI post contrast. They are not usually identified on CT.

Answer 120

**d. Normally the risk of haemorrhage is 2–3% per year but there is no significant increase in risk during pregnancy. Recommend review after delivery to discuss treatment options**. Arteriovenous malformations (AVMs) are congenital lesions consisting of multiple arteries and veins, connecting as a fistula without an intervening normal capillary bed. The majority are solitary lesions except when associated with hereditary haemorrhagic telangiectasia. Approximately 90% occur in the supratentorial region (parietal > frontal > temporal). About half of AVMs present with haemorrhage (intracerebral > subarachnoid > intraventricular), approximately 25% present with focal or generalised seizures and 15% present with headache. The overall risk of haemorrhage for an unruptured AVM is about 2–3% per year. This increases to 6–17% in the first year following first haemorrhage and then decreases to a baseline level by the third year. Following a second haemorrhage, the annual risk of re-bleed rises to 25% in the following year. An approximate lifetime risk for patients with previously unruptured AVMs can be calculated as 105 minus the patient’s age in years. Current data suggests that pregnancy does not increase the risk of an AVM haemorrhage, however, when possible, AVMs should be treated before pregnancy. If the lesion is noted during pregnancy and there is no haemorrhage, treatment risks should be considered higher than the risk of haemorrhage, and treatment may be deferred until after pregnancy.

Answer 121

**A**. Cavernomas are most located in subcortical regions and are hypodense areas which can calcify. They are associated with minimal mass effect/oedema. Cavernomas can undergo haemorrhagic change and are associated with seizures.

Answer 122

**A. Carotid-cavernous fistula**. MR angiography shows reversal of flow through the Superior Ophthalmic Vein (SOV), rapid progress of proptosis, visual loss or raised intracranial pressure requiring emergency treatment.

Answer 123

**b. multiple aneurysms with stenoses and occlusions**. Nasal and paranasal involvement and migratory lung nodules, which can be cavitary, are typical features of Wegener’s granulomatosis. Cerebral vasculitis can also be a feature. MRI findings are non-specific and include hyperintensities on T2W images, infarcts and haemorrhage. Angiography may demonstrate occlusion, stenoses and aneurysms.

Answer 124

**d. Moyamoya syndrome**. Moyamoya disease is progressive arteritis typically affecting both supraclinoid internal carotid arteries and the anterior two vessels of the circle of Willis – the anterior and middle cerebral arteries. It is termed ‘Moyamoya syndrome’ when associated with neurofibromatosis, bacterial meningitis, head trauma, tuberculosis, oral contraceptives, atherosclerosis or sickle cell anaemia. Sickle cell anaemia and atherosclerosis are not associated with axillary freckling, unlike neurofibromatosis type 1. Amyloid angiopathy should be suspected in elderly normotensive patients with multiple areas of intra-axial haemorrhage sparing the basal ganglia.

Answer 125

**D. Normal pressure hydrocephalus**. Fifty per cent of cases of normal pressure hydrocephalus (NPH) are idiopathic, while 50% have a cause, e.g. meningitis, neurosurgery, head trauma, or, as in the current vignette, previous subarachnoid haemorrhage. The imaging reveals dilated ventricles with rounded frontal horns, which are enlarged out of proportion to the degree of sulcal enlargement (as one would see in cerebral atrophy). On CT there may be periventricular low attenuation in the frontal and occipital regions, representing transependymal CSF flow. The MRI equivalent is periventricular high signal and there are other MRI findings, including upward bowing of the corpus callosum and the aqueductal flow void sign (reflecting increased CSF velocity through the cerebral aqueduct). The bradykinesia and gait apraxia of NPH may mimic Parkinson’s disease, although there is typically no associated tremor. Binswanger’s disease (also known as subcortical arteriosclerotic encephalopathy) is a continuous, irreversible ischaemic degeneration of periventricular and deep white matter. MRI reveals extensive periventricular and deep white matter hyperintensities, which reflect microinfarctions and demyelination, and enlarged ventricles.

Answer 126

**D. Funnel-shaped aqueduct**. Aqueductal stenosis is a focal reduction in aqueduct size, which can be congenital or acquired. Stenosis occurs at the level of the superior colliculi or at the inter-collicular sulcus. The best diagnostic clue is a funnel-shaped aqueduct. There is resultant ballooning of the lateral and third ventricles. The fourth ventricle is normal distal to the obstruction. The most specific finding is lack of CSF flow through the aqueduct on phase contrast MRI. Other findings include thinning of the corpus callosum and downward displacement of the internal cerebral veins and third ventricular floor. In older patients it can present similarly to NPH. Imaging findings in NPH include ventriculomegaly (with relative sparing of the fourth ventricle) out of proportion to sulcal enlargement, with normal hippocampi. The aqueductal ‘flow-void’ sign reflects increased CSF velocity through the aqueduct, although this can be observed in normal individuals.

Answer 127

**C. Does not extend anterior to foramen of Monro.** Cavum septum pellucidum (CSP), cavum vergae (CV), and cavum vellum interpositum (CVI) are all considered normal variants, although CSP is possibly more prevalent in boxers due to repeated head trauma, most famously referred to in Rocky V. CSP is universal in foetuses, but decreases with age. CSP is an elongated finger-shaped CSF collection between the frontal horns of the lateral ventricles. Posterior extension between the fornices is referred to as CV. CV almost never occurs in the absence of CSP. CVI, however, is a triangular-shaped CSF space between the lateral ventricles that does not extend anterior to the foramen of Monro. Absent septum pellucidum can look like CSP/CV on sagittal imaging. It is commonly associated with other congenital anomalies.

Answer 128

**a. Dandy–Walker malformation** Dandy–Walker malformation is characterised by an enlarged posterior fossa (not seen in Dandy–Walker variant) with high-rising tentorium cerebelli, dys/agenesis of the cerebellar vermis (intact in megacisterna magna) and cystic dilatation of the fourth ventricle (normal in arachnoid cyst). Ventriculomegaly is also common.

Answer 129

**A. Cavum septi pellucidi** Occurs in 80% of term infants and 15% of adults. Rarely may dilate and cause obstructive hydrocephalus.

Answer 130

**e. enlarged temporal horns of the lateral ventricles** In many cases of hydrocephalus due to subarachnoid haemorrhage, the temporal horns of the lateral ventricles become dilated sooner than the frontal horns. Dilatation of the temporal horn is often particularly conspicuous, as it is frequently not visualized at all on CT of normal brains. Uncal herniation is herniation of the medial temporal lobe into a subtentorial location, where it may exert pressure on the brain stem and is a late sign of raised intracranial pressure, often presenting with oculomotor nerve palsy resulting in a fixed dilated pupil.

Answer 131

**a. intracranial hypotension** Spontaneous intracranial hypotension is a syndrome of low CSF pressure characterized by postural headaches in patients without any history of dural puncture or penetrating trauma. It is thought to arise from an occult CSF leak due to dural defects reducing CSF volume and subsequently pressure. Intracranial findings include downward displacement of the brain, subdural effusions, engorgement of other venous structures (including the hyperaemic pituitary) and low-lying cerebellar tonsils. There may be flattening of the pons as the brain sags against the skull base. Diffuse pachymeningeal enhancement is due to increased venous supply to maintain intracranial volume and therefore pressure, according to the Monro–Kellie doctrine. In the spine, extradural fluid collection is indicative of an occult leak. Treatment is with an epidural blood patch where autologous blood is introduced into the extradural (epidural) space in an attempt to seal the microscopic dural defects.

Answer 132

**(a) Aqueduct stenosis** There are various causes for aqueductal stenosis, however the imaging features of this condition are dilated lateral and third ventricles with a normal 4th ventricle. This is the most frequent cause of congenital hydrocephalus. Its aetiology may be classified as post-inflammatory (commonest), congenital or neoplastic (rare).

Answer 133

**Porencephalic cyst**. * Porencephaly is a congenital/acquired cystic cavity within the brain parenchyma with adjacent enlargement of the lateral ventricle. They develop in utero or early infancy. * Arachnoid cysts are also CSF isointense, but are extra-axial, displacing the brain away from the adjacent skull. * Ependymal cysts are intra-ventricular and the surrounding brain is usually normal. * Schizencephaly is characterized by an intraparenchymal cleft extending from the ventricular surface to the brain surface lined by gray matter. * Hydranencephaly results from an early destructive process of the developing brain. The cranial vault is CSF filled with absence of the cortical mantle and ventricles (water-bag brain). Death in infancy is typical.

Answer 134

**Dandy–Walker malformation** Dandy–Walker malformation is characterised by an enlarged posterior fossa (not seen in Dandy–Walker variant) with high-rising tentorium cerebelli, dys/agenesis of the cerebellar vermis (intact in megacisterna magna) and cystic dilatation of the fourth ventricle (normal in arachnoid cyst). Ventriculomegaly is also common.

Answer 135

**Schizencephaly** The combination of absent septum pellucidum and optic nerve hypoplasia is indicative of septo-optic dysplasia (SOD). Most patients present in infancy with visual disturbance, seizures, or endocrine abnormalities (pituitary dysfunction is seen in approximately 50% of cases). Additional abnormalities are often present with schizencephaly being the most common (50%).

Answer 136

**D. Wilson’s disease** Due to excess iron accumulation, a central gliosis is associated with Haltervorden-Spatz disease, dementia, retinitis pigmentosa, X-linked disorders with mental retardation, atrophy and Parkinsonian disorders.

Answer 137

**A. Klippel-Feil anomaly** Syringohydromyelia, hydrocephalus, malformation of small bones and spine are also associations of Type I Chiari malformation.

Answer 138

**e. septum pellucidum** Holoprosencephaly is failure of the primitive brain to cleave into two hemispheres and is commonly associated with midline facial abnormalities (ranging from cyclopia to hypertelorism) and absence of many intracranial midline structures. There are three types, the most severe being the alobar form, which shows no cleavage at all, with absence of the falx cerebri and third ventricle, fusion of the cerebral hemispheres and thalami, and a single large lateral ventricle. The semilobar form has variable cleavage with a partially formed falx, rudimentary third ventricle, and variable cleavage of the thalami, lateral ventricles and cerebral hemispheres. In the lobar type of holoprosencephaly, brain formation may be nearly normal, but the septum pellucidum is always absent, as in all forms. The falx, corpus callosum and ventricular system may be normal in the lobar type.

Answer 139

b.**schizencephaly** The development of the cerebral cortex takes place in three stages: cell proliferation, cell migration and cortical organization. Schizencephaly is a disorder of the final stage where there is a CSF-containing cleft lined with grey matter (which is often polymicrogyric) connecting the subarachnoid CSF space with the ventricular system. Differentiation can be made from the cyst or cavity of porencephaly, by the presence in schizencephaly of a lining of heterotopic grey matter, whereas a porencephalic cyst is lined by white matter. To result in schizencephaly, the insult must involve the entire thickness of the cerebral hemisphere during cortical organization, as in injuries due to prenatal infection, ischaemia or chromosomal abnormalities. Clinical presentation varies but often includes developmental delay, motor impairment and seizures.

Answer 140

**b. Dandy-Walker malformation** Classically, the Dandy–Walker malformation consists of partial or total absence of the cerebellar vermis, dilatation of the fourth ventricle into a large cystic mass, an enlarged posterior fossa, hydrocephalus (in 75% of cases) and torcular–lambdoid inversion (elevation of the torcular herophili above the lambdoid suture). The proposed aetiology is obstruction of CSF outflow at the foramina of Magendie and Luschka. The vermis abnormality is the key component in all forms of the Dandy–Walker complex. The variant is less severe with a better prognosis. Chiari malformations have the fundamental abnormality of an underdeveloped, small posterior fossa, in contrast to the Dandy Walker complex where it is normal or enlarged.

Answer 141

**Lipoma** Intracranial lipomas appear as well-circumscribed masses of fat density on CT with occasional rim calcification. On MR scan, characteristic appearances are of hyperintensity on T1W images, with chemical shift artefact or signal suppression on fat-saturated sequences. Approximately 30% of intracranial lipomas occur in the pericallosal region, and there is a high incidence of associated congenital anomalies, most commonly agenesis of the corpus callosum, but also encephalocele and cutaneous frontal lipomas. Interhemispheric arachnoid cysts may occur in association with agenesis of the corpus callosum, but they are of CSF density and, like epidermoid, appear hypointense on T1W images. Dermoids have signal characteristics following those of fat but are usually more heterogeneous and not associated with callosal anomalies. Lymphoma may involve the corpus callosum but appears iso or hypointense on T1W images.

Answer 142

**Agenesis of corpus callosum** This is associated with parallel, widely spaced lateral ventricles that may appear crescent shaped. There is dilatation of trigones and the occipital horn of lateral ventricles, along with a high riding 3rd ventricle. Callosal agenesis is associated with Dandy–Walker syndrome, Chiari malformations and fetal alcohol syndrome.

Answer 143

**Chiari I malformation** Chiari I malformation is characterised by cerebellar ectopia and is frequently an isolated hindbrain abnormality without supratentorial abnormalities. 20–30% of cases are associated with syringomyelia.

Answer 144

**Symmetrical involvement of cerebral white matter**. Symmetrical involvement of the cerebral hemispheres or cerebellar peduncles is unusual in MS and is occasionally seen in acute disseminated encephalomyelitis (ADEM). ADEM can mimic an acute presentation of MS both clinically and in terms of imaging findings. The monophasic nature of ADEM can be deduced both from the uniformity of lesional oedema and contrast enhancement in the acute phase. Lesions in ADEM resolve on follow-up, and although enhancing and non-enhancing lesions can coexist for a period, new lesions should not appear. MS plaques are classically seen in the periventricular and juxtacortical white matter. The other options in the question are all common plaque locations. Involvement of the corpus callosum is characteristic. Other common supratentorial sites include the white matter abutting the temporal horns and trigones of the lateral ventricles. Cortical lesions are less conspicuous on MRI than white matter lesions, but their detection is improved by the inclusion of a FLAIR sequence. Juxtacortical white matter lesions are highly suggestive of MS, as lesions are not commonly seen in this region in normal ageing. Twelve per cent of patients have lesions on MRI limited to the spine without brain involvement.

Answer 145

**Pre- and post-contrast T1WI**. MS plaques are generally most conspicuous on FLAIR sequences. However, if there are enhancing and non-enhancing plaques on T1WI post-contrast, this indicates plaques of differing ages, i.e. dissemination in time. While this is not diagnostic of MS (imaging alone never is), it is very suggestive. Proton density sequences are useful, but not quite as useful as FLAIR sequences, in showing periventricular lesions. T2WI sequences are superior to FLAIR sequences when it comes to detection of lesions in the posterior fossa and spinal cord. T2W STIR is probably superior to standard T2WI sequences in detecting spinal cord lesions but is not routinely used. STIR sequences or fat suppression are useful when imaging the optic nerves, as contrast between lesions and the surrounding orbital fat is increased.

Answer 146

**MS**. The key feature in this clinical vignette is the identification of the mass lesion crossing the midline. Only a few lesions demonstrate this ability, and they are GBM, lymphoma, metastases, MS and other white matter disorders, lipoma, stroke, and shearing injuries. Abscess is thus excluded and would be unlikely given the clinical features. GBM is unlikely given the absence of necrosis and would be rare in a patient of this age group. High-grade astrocytomas do not involve the corpus callosum and cross the midline. Lymphoma exhibiting these features would be uncommon in immunocompetent patients, being more typically associated with HIV-related lymphoma. Tumefactive MS typically presents with an acute clinical history and frequently displays the imaging features described. The presence of vascular structures crossing the lesion also indicates this diagnosis, as these would be displaced by neoplastic lesions.

Answer 147

**T2-weighted spin-echo** Multiple sclerotic plaques can be located anywhere in the central nervous system but typically they form at the junction of the cortex and white matter and periventricularly. FLAIR sequences are excellent at identifying lesions located in the cerebral hemispheres, but T2-weighted spin-echo sequences tend to be superior in detecting lesions located in the posterior fossa. With the extensive degree of variation seen in the posterior fossa structures, a combination of T1-weighted and T2-weighted sequences can be useful.

Answer 148

**Axial FLAIR** The FLAIR MR sequence is a heavily T2-weighted inversion recovery sequence designed to nullify the signal from CSF. This highlights any T2 high-signal lesions that may be masked on standard T2W images by adjacent high signal of CSF. This is particularly beneficial in the periventricular region and corpus callosum, and studies have shown that FLAIR has higher accuracy than intermediate and T2W sequences in detecting supratentorial cortical, subcortical, and periventricular multiple sclerosis lesions. Some lesions can be best seen on standard T2W images, particularly in the posterior fossa, brain stem, and spinal cord.

Answer 149

**Multiple sclerosis** MRI is a crucial tool for supporting the clinical diagnosis of multiple sclerosis, an inflammatory autoimmune disease characterized by demyelination. The lesions appear high signal on T2W sequences (including FLAIR) and are commonly found in the periventricular white matter, often resembling Dawson’s fingers. The presence of these high-signal lesions in the corpus callosum and periventricular white matter, alongside the clinical symptoms, strongly indicates multiple sclerosis.

Answer 150

**Multiple sclerosis** MS typically presents with multiple white matter lesions that are hyperintense on T2 and FLAIR. These lesions align perpendicularly to the ventricles, and contrast enhancement may indicate active lesions.

Answer 151

**SLE**. The presence of white matter hyperintensities and focal infarcts, combined with established neurological symptoms in a young woman, strongly suggests cerebral lupus. Imaging findings include small multifocal T2WI or FLAIR hyperintense white matter lesions and potentially enhancing lesions. SLE can cause a variety of neuropsychiatric symptoms due to vasculitis and thrombosis.

Answer 152

**Progressive multifocal leukoencephalopathy** PML is characterized by single or multiple hypoattenuating white matter lesions **without oedema or mass effect** in AIDS patients. Other conditions listed would present with enhancement and surrounding oedema. Toxoplasmosis is the most common CNS mass lesion in AIDS, but PML lesions do not exhibit enhancement and are typically non-edematous.

Answer 153

**D. Parieto-occipital region** PML has a predilection for the parieto-occipital region, often presenting with characteristic imaging findings in this area.

Answer 154

**Involvement of subcortical U fibres** This is characterised by a symmetrical, non-inflammatory demyelination of the basis pontis. The underlying cause is rapidly corrected hyponatraemia. MRI appearances are characteristic with a sparing of peripheral rim of tissue. The corticospinal tracts are generally spared as well.

Answer 155

**Adrenoleukodystrophy (ALD)** ALD is an inherited metabolic disorder characterised by progressive demyelination of cerebral white matter. It is commonly X-linked recessive and boys present between the ages of 3 and 12 years with ataxia, deteriorating vision, hearing loss, altered behaviour and mental deterioration. It is associated with adrenal insufficiency (Addison’s disease). Predominantly, there is posterior white matter involvement with the disease advancing toward the frontal lobes and cerebellum. Imaging shows CT hypodensity, MR T1 hypointensity and T2 hyperintensity. Administration of contrast shows enhancement of the lateral margins of the lesions, indicating areas of active demyelination.

Answer 156

**Metachromatic leukodystrophy** HIV encephalopathy is a progressive subcortical dementia caused by direct infection of the central nervous system by HIV. It is therefore not an opportunistic infection and is seen in up to 60% of AIDS cases. The most striking feature is cerebral atrophy and diffuse myelin pallor, manifested as ill-defined, confluent areas of high signal in the white matter on T2W sequences or low attenuation on CT. Changes are usually bilateral but asymmetrical, with characteristic sparing of the grey matter. Progressive multifocal leukoencephalopathy occurs in only 2–4% of AIDS cases and is a reactivation of the JC (John Cunningham) virus, resulting in destruction of oligodendrocytes. The most common location is posterior whereas HIV encephalopathy is more commonly frontal; however, this is an unreliable discriminator. Progressive multifocal leukoencephalopathy characteristically involves the subcortical U fibres and also affects grey matter. It has a very poor prognosis, death occurring within 2–5 months.

Answer 157

**Pontine myelinolysis** Also known as osmotic myelinolysis. This condition is seen in people with rapidly corrected hyponatraemia with intravenous fluids. The rapid correction of sodium releases myelinotoxic compounds resulting in destruction of myelin sheaths. This is particularly common in alcoholics.

Answer 158

**Central pontine myelinosis** Dysmyelinating diseases (leukodystrophies) are a wide spectrum of inherited neurodegenerative disorders affecting myelin in the brain and peripheral nerves. Most fall into one of three categories: lysosomal storage diseases, peroxisomal disorders and diseases caused by mitochondrial dysfunction. The most common, metachromatic leukodystrophy, is an autosomal recessive disorder caused by a deficiency of the lysosomal enzyme arylsulphatase A, which leads to accumulation of sulphatides in tissues. It usually manifests as a late infantile subtype in children at 12–18 months of age and is characterized by motor signs of peripheral neuropathy followed by deterioration in intellect, speech and coordination, leading to death within a few years. On T2W MRI, symmetrical confluences of high signal intensity are seen in the periventricular white matter with sparing of the subcortical U fibres. Sparing of the perivascular white matter gives a striped or tigroid appearance to the periventricular area of abnormality, particularly well seen in the centrum semiovale. Other sites often affected are the corpus callosum, internal capsule and corticospinal tracts.

Answer 159

**Friedreich’s Ataxia** Loss of myelinated fibres and gliosis in the posterior and lateral columns of the spinal cord are the histopathological hallmarks of Friedreich’s ataxia. On MRI, the predominant radiological finding is thinning of the cervical spinal cord and medulla, and there may be associated mild cerebellar atrophy. Conversely, in most other forms of ataxia such as early onset cerebellar ataxia and olivopontocerebellar atrophy, atrophy of the cerebellum and pons predominates with relative sparing of the cord. Although cerebellar atrophy may be seen in Friedreich’s ataxia, it is less pronounced than in these other diseases.

Answer 160

**Wilson’s disease**. Hyperintensity in the tegmentum (except for the red nucleus) and hypointensity of the superior colliculus are described as the ‘face of the giant panda sign’ and are seen in axial T2WI sections of the midbrain in Wilson’s disease. A ‘double panda sign’ has also been described, with a second ‘panda cub face’ in the pons. Abnormal signal can also be seen in the basal ganglia and thalamus in Wilson’s disease (putamen most commonly). The signal abnormalities are due to copper deposition. Signal is generally reduced on T1WI sequences, although it may be increased due to the paramagnetic effects of copper and due to the hepatic component of Wilson’s disease (a portocaval shunt can produce this latter finding). Signal is generally increased on T2WI sequences, but it can be of mixed or reduced intensity. Similarly, carbon monoxide poisoning and methanol poisoning can cause increased or reduced signal on T1WI. Methanol poisoning typically causes abnormal signal in the putamen, with haemorrhagic necrosis being more typical, whereas carbon monoxide poisoning typically affects the globus pallidus. The latter would be expected to cause low attenuation in the basal ganglia on CT.

Answer 161

**Marchifava–Bignami disease**. This is a rare complication of chronic alcohol consumption characterized by demyelination and necrosis of the corpus callosum, although other white matter tracts (such as the external capsule) may be involved. Bilateral and symmetrical T2WI hyperintensities within the thalami, periaqueductal grey, and mammillary bodies are seen in Wernicke’s encephalopathy. Osmotic myelinolysis is usually secondary to rapid changes in serum sodium and results in increased T2WI signal within the central pons. Extrapontine myelinolysis is rare. In alcohol withdrawal syndrome, patients present with seizures and delirium tremens. MRI may show volume loss in the temporal cortex and anterior hippocampus. Hepatic encephalopathy secondary to hepatocellular failure may produce T1WI hyperintensity within the caudate nucleus, globus pallidus, putamen, and anterior midbrain due to increased concentration of manganese.

Answer 162

**Normal calcium-phosphorus metabolism.** Fahr disease is a rare degenerative neurological disorder characterized by extensive bilateral basal ganglia calcifications that can lead to progressive dystonia, parkinsonism, and neuropsychiatric manifestations. CT has higher diagnostic specificity for basal ganglia calcification over MRI. The distribution of calcifications is similar in endocrinological disorders such as hyperparathyroidism, hypoparathyroidism, and pseudohypoparathyroidism. The calcium-phosphorus metabolism is usually normal in Fahr disease. In pseudohypoparathyroidism the serum calcium is low with an appropriately high parathyroid hormone (PTH), due to PTH resistance.

Answer 163

**Hallervorden–Spatz (HS) syndrome** The finding described on MRI is the ‘eye-of-the-tiger’ sign. This is closely associated with HS. HS is a progressive neurodegenerative metabolic disorder characterised by extrapyramidal and pyramidal signs. The condition (for which the pathophysiology is unclear) results in the accumulation of iron within the globus pallidi and brainstem nuclei. Two clinical entities exist: familial and sporadic. The familial (classic) form shows earlier onset and rapid progression. The sporadic (atypical) form is characterised by a later onset, often in teenage years, with slower progression. Although the ‘eye-of-the-tiger’ sign is closely associated with HS, it has been demonstrated in other rare extrapyramidal parkinsonian disorders including cortical-basal ganglionic degeneration, early-onset levodopa-unresponsive parkinsonism and progressive supranuclear palsy.

Answer 164

**Wilson disease** Causes of basal ganglia calcification include: * Physiological aging. * Infections/inflammatory: TORCH infection, TB, cysticercosis, measles, chickenpox, pertussis, Coxsackie B virus, AIDS, SLE. * Toxins: lead, carbon monoxide, birth anoxia/hypoxia, chemotherapy/radiotherapy, nephrotic syndrome. * Congenital: Cockayne’s, Fahr’s and Down’s syndromes, neurofibromatosis, tuberous sclerosis, methaemaglobinopathy. * Endocrine: hypothyroidism, hypoparathyroidism, pseudo-hypoparathyroidism, pseudo-pseudo-hypoparathyroidism, hyperparathyroidism. * Metabolic: Leigh disease, mitochondrial cytopathies. * Trauma: infarction

Answer 165

**e. Osmotic myelinolysis** Osmotic myelinolysis is also referred to as central pontine myelinolysis or osmotic demyelination syndrome. It is classically seen in an alcoholic, hyponatraemic patient in which rapid correction of sodium releases myelinotoxic compounds leading to destruction of myelin sheaths. The pons is the commonest site, although extra-pontine areas such as basal ganglia, cerebellar white matter and thalami may also be involved. Some patients completely recover but the six-month survival rate is only 5–10%.

Answer 166

**d. Wernicke’s encephalopathy** WE refers to an acute or subacute syndrome characterised by disorientation, gaze paralysis, ataxia and nystagmus. It invariably occurs in chronic alcoholics but it is caused by thiamine deficiency. Involvement of the medial thalami is characteristic and typically the mamillary bodies, peri-aqueductal grey matter and hypothalamus are also involved. In the acute stages of the disease, haemorrhage, necrosis and oedema are encountered, whereas in the latter stages these regions tend to atrophy, particularly the mamillary bodies.

Answer 167

**A. Wilson’s disease** Other causes increase carbon monoxide poisoning, barbituate intoxication, hypoxia, hypoglycaemia and lacunar infarcts.

Answer 168

**c. carbon monoxide** Carbon monoxide poisoning results in irreversible formation of carboxyhaemoglobin in the blood, causing anoxic ischaemic encephalopathy. These changes are usually bilateral and affect the basal ganglia, most commonly the globus pallidus. Injury is demonstrated as high signal on T2W and FLAIR images and shows restricted diffusion on DWI. Areas less commonly affected acutely are the putamen (which is characteristically involved in methanol poisoning) and caudate nucleus. Involvement elsewhere can occur but is less common than basal ganglia changes. Delayed post-anoxic encephalopathy may develop several weeks after carbon monoxide poisoning, and MRI then shows further high T2 signal changes in the corpus callosum, subcortical U fibres, and internal and external capsules, with low T2 signal changes in the thalamus and putamen.

Answer 169

**B. Reduced activity in the precuneus and posterior cingulate gyrus**. FDG-PET-CT has been shown to have a sensitivity and specificity of 93% for mild to moderate Alzheimer’s disease. The technique has been shown to provide important prognostic information so that a negative PET-CT scan is indicative of unlikely progression of cognitive impairment for a mean follow-up of 3 years in those patients who initially present with cognitive symptoms of dementia. The more specific findings on PET-CT in Alzheimer’s disease are early reduced activity in the precuneus/posterior cingulate gyrus and the superior, middle, and inferior temporal lobe gyrus, with relative sparing of the primary sensorimotor and visual cortex, and sparing of the striatum, thalamus, and cerebellum.

Answer 170

**B. Multisystem atrophy (MSA).** T2WI cruciform hyperintensity or the ‘hot cross bun’ sign within the pons, is suggestive of MSA, although it is not specific, as it also occurs in spinocerebellar ataxia. Other MRI features include hyperintensity within the putamen. Patients with MSA typically have parkinsonian features poorly responsive to levodopa therapy and autonomic disturbance.

Answer 171

**Alzheimer’s disease** Alzheimer’s disease typically presents with atrophy and reduced perfusion to the mesotemporal regions bilaterally, but, in younger patients, it often presents with posterior parietal perfusion abnormalities. Vascular dementia shows patchy cortical and subcortical perfusion defects, with involvement of the cerebellum. Lewy body dementia is like Alzheimer’s disease but with less occipital sparing; Parkinson’s dementia is also similar but with less mesiotemporal change and more involvement of the visual cortex.

Answer 172

**Variant Creutzfeldt-Jakob Disease** Variant Creutzfeldt–Jakob disease is a rare but important, transmissible, rapidly progressive spongiform encephalopathy and a cause of dementia and death in young patients. The transmissible agent is thought to be a prion protein (proteins devoid of nucleic acid), and the condition is causally linked to bovine spongiform encephalopathy. CT is typically normal, but symmetrical hyperintensity in the pulvinar nuclei of the posterior thalami (pulvinar sign) on T2W or FLAIR MR images has been described as a specific sign for the variant form. The classic form affects an older age group and is often genetically linked, whereas the variant form is sporadic. The pulvinar sign is seen only in the variant form, with the classic type typically showing similar hyperintense abnormalities located in the caudate nucleus and putamen.

Answer 173

**Putamen** Non-haem brain iron is normally found within oligodendroglia and astrocytes, with smaller amounts in neurons and myelinated axons. Half is found within the mitochondria and 10% in the nuclei, and 40% represents a soluble fraction. The areas of maximum iron concentration in normal adults are found in the globus pallidus, red nucleus, pars reticulata of the substantia nigra and dentate nucleus of the cerebellum. The brain concentration is independent of general body stores, and the mechanism by which it crosses the blood–brain barrier is not fully understood. By the eighth decade, the concentration of iron may increase in the caudate nucleus and putamen to levels similar to those seen in the globus pallidus. Excessive or premature accumulation in these areas has been seen in various forms of senile dementia including Alzheimer’s disease. Iron deposition is identified on T1W and T2W sequences as signal hypointensity due to magnetic susceptibility.

Answer 174

**Alzheimer’s disease** Alzheimer’s disease is a progressive neurodegenerative disorder and the most common cause of dementia in elderly people. Current thinking is that imaging can help in the early diagnosis by documenting or quantifying atrophy in certain regions of the brain such as the hippocampus and entorhinal cortex. However, conventional structural imaging has a relatively low sensitivity in Alzheimer’s disease and may be normal. Therefore, use is limited to identification of patterns of atrophy and the exclusion of other potential causes of dementia such as normal pressure hydrocephalus, vascular dementia or space-occupying lesion. Patterns of atrophy, when seen, may be relatively specific for different causes of dementia, with hippocampal atrophy a cardinal radiological sign of Alzheimer’s disease. Pick’s disease has a frontal and temporal preponderance and is part of the rarer group of diseases under the umbrella term ‘frontotemporal lobar degeneration’. Lewy body dementia typically affects the parietal and occipital lobes and the cerebellum, which are usually spared in Alzheimer’s disease. Multiinfarct dementia is vascular in origin and will show a patchy distribution of change. The different patterns of atrophy have also been recently demonstrated with 18 FDG PET.

Answer 175

**Measure blood pressure** The CT findings are consistent with PRES. This is a usually reversible neurological syndrome with a variety of presenting symptoms ranging from altered mental status to seizures, headache, and loss of vision. Common causes include hypertension, eclampsia and preeclampsia, immunosuppressive medications such as cyclosporine, various antineoplastic agents (including interferon), SLE, and various causes of renal failure. Hypertension is common in PRES, but may be mild and is not universally present, especially in the setting of immunosuppression. However, in the vignette given, hypertension is a possible cause and should be sought. Cyclosporin or tacrolimus might be causes; the former is thought to result in PRES both via a direct neurotoxic effect and by causing hypertension. The condition is not always reversible and may result in haemorrhagic infarcts. The classic MRI finding is of hyperintensity on FLAIR in the parieto-occipital and posterior frontal cortical and subcortical white matter. Less commonly the brainstem, basal ganglia, and cerebellum are involved. Atypical imaging appearances include contrast enhancement, haemorrhage, and restricted diffusion on MRI. Abnormalities can often be seen on CT, as described in the vignette.

Answer 176

**Posterior reversible encephalopathy syndrome (PRES)** This is a disorder of cerebrovascular autoregulation and is associated with eclampsia, which is defined clinically as seizure or coma with pregnancy-induced hypertension. There is a predilection for the posterior circulation and watershed zones, possibly due to its sparse vasomotor sympathetic innervation. T2WI hyperintense lesions within the posterior cortex and subcortical white matter, without diffusion restriction, are typical. Diffusion restriction/low ADC will be found in infarction. The diagnosis of postpartum cerebral angiopathy should be considered in normotensive postpartum women presenting with intracerebral haemorrhage. Reversible high T2WI signal abnormalities may also be seen in the cortex and subcortical white matter. Multifocal stenoses and beading of the intracranial vasculature are also a feature. PML presents with asymmetrical T2WI hyperintensity in the periventricular and subcortical white matter, with cortical sparing. It is seen in the immunocompromised. Gliomatosis cerebri is a diffusely infiltrating tumour involving two or more lobes and is frequently bilateral. Enlargement of the involved structures is seen. It can mimic brainstem PRES.

Answer 177

**A** These are typical imaging findings but the abnormalities are not always reversible or posterior.

Answer 178

**Toxoplasmosis**. This is the most common intracranial opportunistic infection in AIDS patients and the most common cause of intracranial mass lesions in this population, with lymphoma second and cryptococcus third. Differentiating toxoplasmosis from lymphoma has been the subject of much debate in the literature and ultimately there is no definitive means of differentiating them on imaging alone. As described toxoplasmosis causes multiple ring-enhancing lesions and often affects the basal ganglia. Lymphoma tends to involve the subependymal regions and can cause leptomeningeal enhancement. Lymphoma can cause encasement of the ventricle, which is not seen with toxoplasmosis. Toxoplasmosis tends to be higher intensity on T2WI/FLAIR than lymphoma. PET and thallium SPECT have also been reported to show abnormal uptake in lymphoma, but not toxoplasmosis, although exceptions exist. Response to anti-toxoplasma treatment is often used as a clinical differentiator. Cryptococcus classically causes dilatation of Virchow–Robin spaces. PML is a demyelinating condition secondary to JC virus of oligodendrocytes and is differentiated from other HIV-related demyelinating conditions by affecting the subcortical U fibres.

Answer 179

**Japanese encephalitis.** Japanese encephalitis and herpes simplex virus (HSV) encephalitis both present with similar acute and rapidly progressive neurological symptoms. The key differentiator is involvement of the basal ganglia, which is typical in Japanese encephalitis but rare in HSV. Both commonly involve the hippocampi, this being the classical appearance of HSV encephalitis. HSV type 1 is the subtype that affects adult and older children. HSV type 2 causes neonatal and in utero infection. Herpes varicella zoster virus (VZV) infection can be seen in immunocompromised children, but in the immunocompetent population is more typically seen in elderly patients, often, but not exclusively, in the presence of cutaneous shingles. It causes a vasculitis, which can be seen angiographically and causes bilateral increased T2WI/FLAIR foci and gyriform enhancement in the distribution of the vasculitis. SSPE presents with a more protracted history of neurological decline.

Answer 180

**Herpes simplex encephalitis (HSE)** There are two main types of herpes simplex virus (HSV) – HSV type I and HSV type II. Type I (oral herpes) tends to affect older infants, children, and adults whereas type II (genital herpes) is the usual cause of HSE in neonates. HSE is a necrotising meningoencephalitis which has a predilection for the limbic system (temporal lobes, insula, cingulated gyri). Characteristically, there are poorly defined areas of low attenuation in one or both temporal lobes/limbic system on unenhanced CT, low signal on T1 (gyral oedema) and high signal on T2. The T2 high signal typically spares the putamen and forms a sharply defined border. Changes may initially appear unilateral but contralateral disease invariably follows. This sequential bilaterality is characteristic of HSE. Haemorrhage is typically a late finding. Mortality ranges from 30% to 70% but is reduced with early antiviral therapy.

Answer 181

**Pyogenic abscess** The differential diagnosis for a solitary ring-enhancing lesion of the brain includes (‘MAGICAL DR’): Metastasis; Abscess; Glioma/Glioblastoma multiforme; Infarction; Contusion; AIDS (toxoplasmosis); Lymphoma (often AIDS-related); Demyelinating disease; Resolving haematoma/Radiation necrosis. Classically, abscesses are located at the corticomedullary junction in the frontal and temporal lobes. The most common causative organism is Streptococcus. The wall is generally smooth and regular with relative thinning of the medial wall secondary to a poorer blood supply from white matter (neoplastic lesions usually have a thick, nodular, irregular rim). In this scenario, the enhancing, T2-hypointense rim suggests abscess. Restricted diffusion is also highly suggestive of an abscess. Lymphoma may be hyperdense on CT due to a high nuclear-to-cytoplasmic ratio and typically shows solid homogeneous enhancement in immunocompetent patients.

Answer 182

**Cytomegalovirus infection** This is the most common intrauterine infection and the leading cause of brain disease and hearing loss in children. Typical imaging findings include periventricular subependymal cysts representing focal areas of necrosis and glial reaction, periventricular post inflammatory calcifications, scattered calcifications in basal ganglia and brain parenchyma, microcephaly due to disturbance of cell proliferation and hypoplasia of the cerebellum. There may also be lissencephaly, cortical dysplasia, polymicrogyria and schizencephaly due to disturbed neuronal migration.

Answer 183

**D** Early CT findings may show medial temporal hypodensity. Areas poorly enhance on CT and MR. Signal abnormalities often decrease in response to treatment.

Answer 184

**A** 75% of cases are in the basal ganglia.

Answer 185

**d** Hypo-vascularity on MR perfusion study Toxoplasmosis is the most common cause of a cerebral mass lesion in patients with AIDS. Typical appearances are of multiple, hypoattenuating, 2 cm lesions with a predilection for the basal ganglia. Lymphoma is the second commonest mass lesion, with characteristic features including hyperdense lesions (though less frequently than in non-AIDS lymphoma) in a periventricular location with subependymal spread. Lesions in both conditions may show solid or ring enhancement. Haemorrhage is unusual in lymphoma but may be seen in toxoplasmosis.

Answer 186

**d** Herpes simplex encephalitis Herpes simplex virus is the most common cause of fatal endemic encephalitis, often leaving survivors with severe memory and personality problems. Both oral (type 1) and genital (type 2) strains may produce encephalitis with a multimodal distribution, affecting neonates (due to cross-infection with type 2 from the mother during birth), children and adults. Childhood and adult infection is caused by the type 1 virus and results in fulminant necrotizing encephalitis presenting with acute confusion and deteriorating rapidly to coma. Focal neurological deficits are seen in only 30% of cases. The virus asymmetrically affects the temporal lobes, insula, orbitofrontal region and cingulate gyrus, causing oedema. This is seen as high signal on T2W/FLAIR images, with DWI appearances variable depending on the presence of infarction. The putamen is characteristically spared, and the areas of encephalitis typically do not show enhancement on CT or MRI.

Answer 187

**(b)** Neurocysticercosis This is the most common parasitic infection of the brain and is particularly prevalent in South America, Asia and Africa. In the vesicular stage, CT and MRI show multiple, thin-walled cysts containing scolex with minimal surrounding oedema.

Answer 188

**D** MRI due to deterioration in clinical course. In the absence of clinical features of raised intracranial pressure a CT is not necessarily indicated prior to lumbar puncture to exclude raised intracranial pressure. CT is also insensitive at diagnosing meningitis, being normal in most uncomplicated cases. MRI is also negative in 50% of cases of uncomplicated meningitis. The value of imaging is in the detection of complications of meningitis, including hydrocephalus, abscess, cerebritis, venous thrombosis, and infarction.

Answer 189

**Arachnoiditis** Arachnoiditis is an intrathecal inflammatory reaction which usually results from iatrogenic injury. Previously, it was associated with the injection of contrast agents during myelography. Now, it is most seen following lumbar surgery. Intradural infections (TB, fungal, parasitic) are rare causes. Radiologically, arachnoiditis appears as nerve root adhesion. Commonly the nerves are clumped together simulating a solid mass, although the nerves may also adhere to the dura, giving the appearance of an ‘empty thecal sac’. In severe cases, the thecal sac may become loculated and compartmentalised. Clumped nerve roots suggest arachnoiditis and the lack of enhancement makes tumours unlikely.

Answer 190

**d** Tuberculosis The vertebral column is the most common site of osseous involvement of tuberculosis (TB), usually as the result of haematogenous spread from pulmonary involvement. The lower thoracic and upper lumbar vertebrae are the most frequently affected. It can be difficult to differentiate between pyogenic and TB spondylodiscitis on imaging but several features favour a diagnosis of TB: multilevel involvement/skip lesions, relative sparing of the disc spaces, large pre/paravertebral collections which are more likely to calcify, subligamentous spread and meningeal involvement.

Answer 191

**A** More commonly cryptococcus meningitis but cryptococcus or gelatinous pseudocysts reside in dilated perivascular spaces.

Answer 192

**Encephalomalacia** Diagnosis of meningitis is made by clinical examination and examination of CSF. Imaging is reserved for complications and to identify contraindications to lumbar puncture. The mechanism of spread is usually haematogenous, common organisms being Neisseria meningitidis (meningococcus) in young adults, Escherichia coli and Haemophilus inﬂuenzae. Complications that can be identiﬁed on CT include subdural empyema (sterile effusion can be seen with H. inﬂuenzae), venous sinus thrombosis, infarction, cerebritis and abscess formation. Leptomeningeal thickening and enhancement may be seen, but its absence does not exclude a diagnosis of uncomplicated meningitis. CT may also identify a potential source of infection such as otitis media, mastoiditis, sinusitis or orbital cellulitis.

Answer 193

**Restricted diffusion on MR DWI** Abscess cavities and empyemas are homogeneously hyperintense on MR DWI and low on ADC map due to the increased viscosity of the purulent material that they contain, resulting in restricted diffusion of water. Sterile effusions are hypointense on DWI and have an ADC appearance similar to that of CSF due to their lower viscosity and free macro-diffusion of water. Diffusion images can therefore be important when deciding whether to intervene surgically or conservatively manage subdural collections, as empyema requires timely surgical drainage. Contrast enhancement of the wall of the collection may be seen on CT and MRI, but its absence does not exclude the diagnosis of a purulent collection. Likewise, one may expect to see additional mass effect with an infected collection, but this too is not sensitive enough to exclude infection by its absence.

Answer 194

**Von Hippel–Lindau syndrome**. This syndrome is characterized by retinal lesions variously described as being retinal angiomas, retinal haemangiomas, or retinal hamartomas. These lesions (Lindau tumours) cause retinal calciﬁcation, although this is also seen in NF-1 and tuberous sclerosis (TS) from other causes. The findings describe the classical appearance of a cerebellar haemangioblastoma. These lesions can also be entirely cystic or solid in a minority of cases. A signal void and lack of dural enhancement help differentiate this from other infratentorial masses in adults. Twenty per cent of haemangioblastomas are associated with Von Hippel–Lindau syndrome and 80% of Von Hippel–Lindau syndrome patients have this tumour. The spinal finding also indicates a further haemangioblastoma in the cord. Unlike in the posterior fossa, these seldom have flow voids, but are associated with the development of a syrinx.

Answer 195

**Neurosarcoid**. Whilst primary neurosarcoid is rare, it is not uncommon for the systemic disease to present via its neurological manifestations. The findings of neurosarcoid are non-specific, with the common manifestations mirroring those described in this patient. Leptomeningeal thickening and enhancement are classical. Involvement of the perivascular spaces adjacent to this can cause increased signal in the adjacent cortex. This appearance can mimic meningioma. Multifocal meningiomas and nerve sheath schwannomas are features of NF-2, but this would not be expected to resolve with steroid therapy. The features described are not typical of TS. The meningeal disease would make MS unlikely, even given the periventricular high-signal lesions, which are the most common intraparenchymal finding in neuro-sarcoid. Sarcoid involving the skull table is not directly related to the neurosarcoid and is more commonly seen with other manifestations of musculoskeletal sarcoid. Toxoplasmosis, in the absence of immunocompromise, is unlikely. Overall, the response to steroid, along with the wide variation of CNS disease described, are the strongest indicators for sarcoid. Whilst neurosarcoid does typically respond well to steroid therapy, it has a high recurrence rate.

Answer 196

**Optic nerve glioma.** NF-1 is an autosomal dominant neurocutaneous disorder. The gene locus is located on 17q11.2. Diagnosis of NF-1 requires two or more of the following: six or more cafe-au-lait spots, two or more neuroﬁbromas (or one plexiform neuroﬁbroma), axillary/inguinal freckling, optic nerve glioma, sphenoid wing dysplasia or a first-degree relative with NF-1. The classic imaging appearance is multiple focal areas of white matter and deep gray matter signal abnormality. Other potential findings include intracranial stenoses and moyamoya type proliferation. NF-2 characteristically presents with multiple intracranial schwannomas, meningiomas and ependymomas (MISME). Bilateral vestibular schwannomas are diagnostic of NF-2.

Answer 197

**Enhancing heterotopic grey matter** All of the other features may be found in either condition. Giant cell astrocytomas located in the region of the foramen of Monro in tuberous sclerosis may degenerate into high-grade astrocytomas. Cortical tubers show as multiple nodules which are hyperintense on T2/FLAIR imaging. CNS hamartomas (occurring in up to 75–90% of NF1) also display these characteristics they are often termed ‘unidentified bright objects.’

Answer 198

**Sturge–Weber syndrome** Sturge–Weber syndrome is a congenital disease characterised by capillary venous angiomas involving the face (port-wine stain, usually ophthalmic division of trigeminal nerve), choroid of the eye and leptomeninges. Clinical manifestations include focal seizures (80% in the first year of life), developmental delay, hemiparesis and homonymous hemianopia. Seizures typically become refractory to medication. Leptomeningeal angiomas are confined to the pia mater and occur primarily within the parieto-occipital region. There is cortical hemiatrophy beneath the angioma due to local anoxia and usually after the age of two years there is cortical calcification manifesting as low signal intensity on T1 post-contrast images. Other findings include enlargement of the ipsilateral choroid plexus, dilatation of the transparenchymal veins that communicate between the superficial and deep cerebral venous systems, and orbital choroidal haemangiomas.

Answer 199

**Sarcoidosis** Neurologic manifestations of sarcoidosis occur in 5% of patients. In over 80% of established cases, the chest radiograph is abnormal. Sarcoidosis commonly involves the leptomeninges, especially the basal meninges and midline structures, including the hypothalamus and optic chiasm. The facial nerve is the most commonly involved cranial nerve clinically, while the optic nerves are often affected radiologically. Dural thickening may also be present, along with enhancing granulomas in the superficial parenchyma.

Answer 200

**A. Tuberous sclerosis** These findings are characteristic of tuberous sclerosis.

Answer 201

**A. Leptomeningeal contrast enhancement** This is a common finding; however, other features can also be present in neurosarcoidosis.

Answer 202

**A. VHL** Approximately one-third of hemangioblastomas are associated with cystic lesions and mural nodules.

Answer 203

**E. Sturge-Weber** This condition is associated with tram track calcifications, cortical atrophy, and choroid plexus enlargement.

Answer 204

**Neurofibromatosis type 1** This condition is characterized by plexiform neurofibromas and vertebral abnormalities such as posterior scalloping and dural ectasia.

Answer 205

**Tuberous sclerosis** The classical triad includes adenoma sebaceum, mental retardation, and seizures, along with bilateral renal angiomyolipomas.

Answer 206

**Sturge–Weber syndrome** Characterized by meningeal angiomatosis and associated findings such as cortical atrophy and calcifications.

Answer 207

**Neurofibromatosis type 1** This condition includes optic nerve gliomas and other characteristic lesions like café au lait spots and freckling.

Answer 208

**Chiasmal glioma** This condition is associated with NF1 and typically presents with optic chiasm enlargement.

Answer 209

**Neuroamyloidosis** Cerebral amyloid angiopathy is characterized by deposition of b-amyloid protein in cortical, subcortical and leptomeningeal vessels. It usually occurs in sporadic form and increases in frequency and severity with increasing age. The condition produces a wide variety of clinical symptoms and varied imaging appearances. Many cases are asymptomatic but progressive neurological symptomatology and cognitive decline may be a feature. Chronic haemorrhage in a distinctive distribution, or catastrophic acute intracerebral/subarachnoid haemorrhage, may also occur. Amyloid angiopathy should be strongly considered in elderly normotensive patients with spontaneous intracranial haemorrhage, particularly when associated with leukoencephalopathy and atrophy related to small-vessel cerebrovascular disease. Definitive diagnosis is usually only made postmortem, with a presumptive diagnosis made on clinical presentation and imaging findings.

Answer 210

**Neurosarcoidosis** Neurosarcoidosis is seen in up to 8% of cases of sarcoidosis and has a tendency to involve the base of the brain. Cranial nerve involvement occurs frequently and nerve palsies are a common presenting feature. Bilateral facial nerve palsies, particularly in young adults, are most commonly due to neurosarcoidosis. The most common imaging manifestation is diffuse basomeningeal thickening, which typically shows enhancement with intravenous gadolinium. Also frequently seen are meningeal nodules and deep white matter lesions with high T2 signal. Multiple or solitary parenchymal masses may also occur, which can have a ring-like appearance and may therefore mimic primary or metastatic neoplasia.

Answer 211

**Sheehan’s Syndrome** Many of the acute neurological conditions of pregnancy occur with rising blood pressure. Sheehan’s syndrome results from haemorrhage-induced hypotension causing pituitary infarction. Early on, this appears as an enlarged homogeneous pituitary with low T1 signal, high T2 signal and post-contrast ring enhancement. Later, there is an empty sella. Clinical manifestations include visual field loss, headache, ophthalmoplegia and pituitary dysfunction (diabetes insipidus). Reversible posterior leukoencephalopathy produces cortical blindness, headaches, confusion and seizures. Those affected are often taking immunosuppressant treatment. Imaging features can be identical to eclampsia, peripartum cerebral angiopathy and hypertensive encephalopathy, but with a posterior predominance. On CT, there is low attenuation change. On MRI, there is high signal on T2W/FLAIR images. ADC maps can differentiate between likely reversible vasogenic oedema (high signal on ADC map showing unrestricted diffusion) and cytotoxic oedema (low signal due to restricted diffusion), which is more likely to progress to infarct. Microangiopathic haemolytic anaemias, such as thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome, give widespread ischaemia/infarction and haemorrhagic transformation. There is no increased risk in pregnancy of vasculitis such as systemic lupus erythematosus, Takayasu’s syndrome or Moyamoya syndrome. Arteriovenous malformation is no more likely to bleed in pregnancy, but there is an increased risk with arterial aneurysms. Haemorrhage, sepsis and pulmonary embolism cause hypotension that can cause watershed infarction as well as Sheehan’s syndrome.

Answer 212

**99m Tc-labelled ECD** Conventional radionuclide brain scans are not indicated when CT or MRI can be used. Brain accumulation of radiotracer occurs at sites of blood–brain barrier disruption and increased vascularity such as cerebral metastases, meningioma and high-grade glioma. Reagents used are 99m Tc-labelled pertechnetate, 99m Tc-labelled DTPA, and, when it was available, 99m Tc-labelled glucoheptonate. Radionuclide imaging is also able to provide regional blood flow mapping, which is used to localize epileptic foci, map cerebrovascular disease, investigate dementia, assess treatments and confirm brain death. 99m Tc-labelled HMPAO is the most used radiopharmaceutical overall. It is lipophilic and therefore crosses the blood–brain barrier, and in doing so is distributed in proportion to cerebral blood flow. 99m Tc-labelled ECD is another regional blood flow imaging tracer and can therefore also be used in the localization of epileptic foci. 18 FDG PET tracers are distributed through the brain according to metabolic activity.

Answer 213

**Localization of speech and memory centres** SPECT of the central nervous system allows assessment of the collateral circulation during balloon occlusion, mapping the extent and distribution of vasospasm associated with subarachnoid haemorrhage, evaluation of cerebrovascular reserve prior to carotid endarterectomy, identification of seizure foci and guiding of stereotactic brain biopsy in tumour recurrence. The Wada test is used to predict the probability of memory and speech complications in patients before they undergo anterior temporal lobectomy with amygdalohippocampectomy, a surgical treatment for medically refractory epilepsy. The test involves injection of radiopharmaceutical and short-acting barbiturate (usually sodium amobarbital) into each of the carotid arteries in turn. Loss of memory or speech following one of the injections indicates that these centres lie in the ipsilateral temporal lobe. The results of the Wada test can be negated by vessels crossing the midline, and the presence of such collateral circulation may not be readily apparent without SPECT.

Answer 214

**Normal appearances** Opsoclonus–myoclonus syndrome is characterized by opsoclonus in combination with myoclonus of the trunk, limbs or head. It may be idiopathic or occur as a paraneoplastic syndrome, when it may follow a relapsing–remitting course. In adults, it is most commonly associated with breast and squamous cell lung carcinoma, while in children it is associated with neuroblastoma. The syndrome usually precedes diagnosis of the underlying malignancy, and in children should prompt investigation to identify an underlying neuroblastoma. MIBG whole-body scintigraphy may be helpful in identifying occult disease if conventional imaging is negative. MR scan of the brain is usually normal.

Answer 215

**Cavernous haemangioma**. The orbital compartments are split up into extraconal, conal, intraconal, and globe. The extraconal compartment consists of fat, lacrimal gland, and bony orbit. Pathology in this region includes infection, neurofibroma, adenocarcinoma, mucoepidermoid and adenoid cystic carcinoma, neoplasia of bone, and lymphoma. Conal pathology (muscle) includes rhabdomyosarcoma, thyroid eye disease, and idiopathic orbital inflammation (pseudotumour). The intraconal compartment consists of fat, lymph nodes, vessels, nerves, and the optic nerve sheath complex. Pathology in this region includes venolymphatic malformation, haemangioma, arteriovenous malformation, optic nerve meningioma/glioma, and lymphoma. Pathology in the globe includes retinoblastoma, metastasis, and melanoma.

Answer 216

**Cavernous haemangioma** This is the most common orbital mass in adults and is the most common vascular malformation of the orbit. CT demonstrates the location of the lesion and microcalcifications. Remodelling of the bone may be seen. MRI features are typical as given.

Answer 217

**Inferior and medial**. The question refers to Graves ophthalmopathy, where enlargement of the extraocular muscles is observed, with sparing of the tendinous insertions. This is in distinction to idiopathic orbital inflammatory syndrome, where the muscle swelling typically involves the tendinous insertions. In Graves ophthalmopathy, the extra-orbital muscles are involved with decreasing frequency as follows: inferior, medial, superior, and lateral recti.

Answer 218

**Rhabdomyosarcoma**. The clinical and radiological features described are typical of rhabdomyosarcoma. It usually presents in the first decade of life with a rapidly growing mass causing proptosis. The globe is often distorted and displaced, but rarely invaded. The lesion is aggressive and there may be extension into the sinuses or intracranial compartment, and bony destruction can occur. NHL is usually found in older adults, but it can occur in older children or adolescents. Unlike rhabdomyosarcoma, NHL commonly causes lacrimal gland involvement, may be hypointense on T2WI, and encases rather than distorts the globe. Capillary haemangioma typically presents in the first few months of life. They have a proliferative phase for approximately 12 months following diagnosis and then are stable, before gradually involuting over a period of years. These lesions show rapid and persistent enhancement on CT and MRI. On unenhanced MRI, it is typically iso- to hyperintense relative to muscle on T1WI and moderately hyperintense on T2WI, with flow voids at the periphery of or within the tumour. A ruptured dermoid cyst can mimic a rhabdomyosarcoma both clinically and radiologically, but one might expect to see calcification or fatty or cystic components in the native lesion. Retinoblastoma is an intraorbital lesion.

Answer 219

**Venous-lymphatic malformation**. Venous-lymphatic malformation (previously known as a lymphangioma) typically has a presentation in childhood. MRI is the modality of choice for diagnosis, as fluid–fluid levels are almost pathognomic of this condition and these represent areas of haemorrhage of varying ages. The MRI findings are as those described and there are typically no large feeding vessels or flow voids. The lesion is predominantly extraconal but can insinuate into the intraconal compartment. Capillary haemangioma also presents in childhood but may be apparent clinically and on MRI there are not typically fluid–fluid levels, but there may be flow voids within the lesion from prominent vessels. Also, enhancement is usually more rapid and persistent in capillary haemangioma than in venous-lymphatic malformation. Orbital varices usually present in young adults and on imaging have the appearance of dilated, tortuous vessels. Cavernous haemangioma typically presents in adulthood. They are usually well-circumscribed and most often occur in the lateral aspect of the retrobulbar intraconal space. On CT, they are slightly hyperattenuating prior to contrast and may contain phleboliths. On MRI, they are isointense to muscle on T1WI and hyperintense on T2WI. They show progressive enhancement on multiphase dynamic imaging. Haemangiopericytomas are rare vascular tumours that are more often seen in adults than children. Large lesions may show bony erosion and they do not typically have fluid–fluid levels on CT or MRI.

Answer 220

**Presence of optic canal widening**. The presence of a widened optic nerve canal occurs in up to 90% of cases of optic nerve glioma. While it can also occur in meningioma, it is more common in glioma and some cases of meningioma may even have a narrowed canal secondary to bony hyperostosis. The ‘tram-track’ sign is typically associated with meningioma and refers to the more avidly enhancing meningioma surrounding the non-enhancing optic nerve on axial CT and MR imaging of the orbit. Although both meningioma and glioma enhance following intravenous contrast, it is meningioma that is more typically associated with marked intense enhancement. Calcification and bony hyperostosis are features associated with meningioma. Calcification is rare in gliomas, unless they have previously undergone radiotherapy.

Answer 221

**Optic nerve glioma**. NF-1 is an autosomal dominant neurocutaneous disorder. The gene locus is located on 17q11.2. Diagnosis of NF-1 requires two or more of the following: six or more cafe-au-lait spots, two or more neurofibromas (or one plexiform neurofibroma), axillary/inguinal freckling, optic nerve glioma, sphenoid wing dysplasia or a first-degree relative with NF-1. The classic imaging appearance is multiple focal areas of white matter and deep gray matter signal abnormality. Other potential findings include intracranial stenoses and moyamoya type proliferation. NF-2 characteristically presents with multiple intracranial schwannomas, meningiomas and ependymomas (MISME). Bilateral vestibular schwannomas is diagnostic of NF-2.

Answer 222

**Malignant melanoma** This is the most common primary intraocular neoplasm in adult Caucasians. The typical age range is 50–70 years old. They are almost always unilateral and located in the choroid, although ciliary body and iris melanomas are not uncommon. Presentation can be with retinal detachment, vitreous haemorrhage, astigmatism or glaucoma. MRI shows a sharply circumscribed hyperintense lesion on T1, due to the paramagnetic properties of melanin, and hypointense relative to the vitreous body on T2.

Answer 223

**Perioptic meningioma**

Answer 224

**Pseudotumour** Pseudotumour is the commonest cause of an intra-orbital mass lesion in adults. It is an idiopathic inflammatory condition and about 10% of cases occur in association with autoimmune conditions such as retroperitoneal fibrosis. It usually presents with unilateral painful opthalmoplegia. It can be acute (more common) or chronic. The former has a more favourable prognosis as it is responsive to steroids. In contrast, the chronic type frequently requires chemotherapy and radiotherapy. On MRI, pseudotumour is hypointense to fat on T2, whereas true tumours are hyperintense. Grave’s disease is the most common cause of uni/bilateral proptosis in adults (85% bilateral, 15% unilateral). However, involvement of extra-ocular muscles tends to maximally affect the midportion with relative sparing of the tendinous insertions. This gives rise to the so-called ‘Coke-bottle’ sign.

Answer 225

**Breast** Most retrobulbar metastases are extraconal (outside the muscle cone). Neuroblastoma and Ewing’s sarcoma are the most common in children and produce smooth extraconal masses related to the posterior lateral wall of the orbit. In adults, an infiltrative retrobulbar mass and enophthalmos is characteristic of scirrhous carcinoma of the breast (invasive ductal carcinoma). Enophthalmia is also considered to be one of the earliest signs of metastatic breast cancer.

Answer 226

**Capillary haemangioma** Capillary haemangiomas are the most common vascular orbital masses in children. They typically present at birth or shortly after. CT shows a diffuse, usually poorly marginated mass which shows diffuse contrast enhancement. On MRI the mass is hypointense to fat on T1, and on T2 it is hyperintense to muscle and fat but hypointense compared to fluid. Curvilinear flow voids representing blood vessels are typical within the mass. They tend to grow rapidly over the first six months of life, stop growing during the second year and then slowly involute over subsequent years.

Answer 227

**D** Sparing of muscle tendons is typical. Most cases are bilateral.

Answer 228

**A** Other causes are lymphoma, adenocarcinoma, adenoid cystic carcinoma, mucoceles and paranasal sinusitis.

Answer 229

**Carotid-cavernous fistula** Important imaging findings include: extraocular muscle enlargement, proptosis, chemosis and dilatation of ipsilateral cavernous sinus and superior ophthalmic vein. Graves’ disease affects older ages and bilateral involvement is typical. An orbital pseudotumour is a non-specific inflammation involving any area of orbit. Orbital bruit and a dilated superior ophthalmic vein are not usually seen.

Answer 230

**Graves’ disease** Graves’ ophthalmopathy (thyroid eye disease) features bilateral exophthalmos with bilateral enlargement of the extraocular muscles. The condition particularly affects the inferior, medial and superior rectus muscles.

Answer 231

**Cholesterol granuloma**. The findings described are typical of cholesterol granuloma. A critical distinction is between this and a petrous carotid artery aneurysm, which may show similar features of increased T1WI signal. However, the presence of flow void, lesion centred on the carotid canal, and additional complex areas of signal due to blood products of varying ages might be expected in an aneurysm. A petrous apex cephalocele is an area of fluid signal (hypointense T1WI, hyperintense T2WI) adjacent to the petrous apex that is in communication with Meckel’s cave. A mucocele of the petrous apex may cause benign bony expansion and is typically of decreased signal on T1WI and increased signal on T2WI and is non-enhancing. A cholesteatoma may have similar T1WI and T2WI signal characteristics, but these entities may be differentiated by DWI. On DWI, cholesteatoma is typically of increased signal, whereas a mucocele is of decreased signal. Petrous apicitis is an aggressive process that typically enhances with gadolinium and is secondary to infection. There may be an accompanying history of infection, middle ear disease, diabetes, or immunocompromise.

Answer 232

**Transverse/labyrinthine**. Transverse temporal bone fractures are more commonly associated with facial nerve paralysis (approximately up to 50%) than longitudinal temporal bone fractures (approximately up to 20%). The labyrinthine segment is the most likely segment of the facial nerve to be associated with facial paralysis.

Answer 233

**Erosion of the adjacent porus acousticus**. A large meningioma at the cerebellopontine angle can easily grow into the adjacent internal auditory meatus (IAM), but typically does so without causing any enlargement or erosion of this structure. Most vestibular schwannomas arise from the inferior vestibular nerve within the IAM and as they grow they smoothly erode the posterior edge of the porus acousticus. Although dural enhancement has been described adjacent to vestibular schwannomas, an enhancing ‘dural tail’ would be a finding more commonly associated with a lesion arising from the dura, typically a meningioma. Bony hyperostosis is a finding that is associated with meningioma. Both meningiomas and vestibular schwannomas typically show avid enhancement with intravenous gadolinium.

Answer 234

**Cholesteatoma** A cholesteatoma consists of a sac lined with stratified squamous epithelium and filled with keratin – essentially ‘skin growing in the wrong place’. They can be acquired (98%) or congenital (2%). Most acquired cholesteatomas arise in the superior portion of the tympanic membrane (pars flaccida) and extend into Prussak’s space where they can cause medial displacement of the head of the malleus and erosion of the bony scutum. The characteristic imaging feature of a cholesteatoma is bone erosion associated with a non-enhancing soft-tissue mass. Complications can be intratemporal and intracranial: Intratemporal: ossicular destruction, facial nerve paralysis, labyrinthine fistula, complete hearing loss, automastoidectomy. Intracranial: meningitis, sinus thrombosis, abscess, CSF rhinorrhea.

Answer 235

**A** Glomus tumour is the most common cause of pulsatile tinnitus.

Answer 236

**Conductive hearing loss** Longitudinal fractures of the temporal bone represent 75% of temporal bone fractures and run parallel to the axis of the petrous pyramid. They may cause dislocation of the auditory ossicles, usually the incus, causing a conductive deafness. Sensorineural hearing loss is associated with transverse fractures of the temporal bone, as is vertigo. Facial nerve palsy is seen in both fracture types, but is less common in longitudinal fractures, where it frequently recovers spontaneously. Carotid artery and major sinus injuries are not directly associated with petrous temporal fractures.

Answer 237

**Cholesteatoma** Cholesteatoma is an abnormal collection of keratinized debris arising from an ingrowth of stratified squamous epithelium and occurs in primary (2%) or acquired (98%) types. The acquired type can be further subdivided, with the most common being a primary, acquired, epidermoid-type lesion of the pars flaccida, located in the attic of the middle ear. Cholesteatomas are benign lesions but cause bone erosion, including the auditory ossicles, resulting in conductive hearing loss. Local extension may compress the geniculate ganglion in the facial canal.

Answer 238

**Secondary cholesteatoma** Definitive diagnosis of cholesteatoma requires CT evidence of bone erosion, either of the ossicular chain or the walls of tympanic cavity. Pars tensa cholesteatoma typically spares the scutum and results in lateral displacement of the head of the malleus and the incus. Granulation tissue shows high signal on T2 and enhances with gadolinium. Squamous cell carcinoma also shows contrast enhancement.

Answer 239

**Pars flaccida cholesteatoma** This typically causes erosion of the scutum, ossicles or the lateral epitympanic wall. Pars flaccida is a small superior portion of the tympanic membrane. Scutum erosion is common and three-quarters of cases may have erosion of the ear ossicles.

Answer 240

**Cholesterol granuloma** This is caused by recurrent haemorrhage into the middle ear cavity forming an inflammatory mass of granulation tissue. Diagnosis is made by demonstration of bony expansion on CT and high signal on T1 and T2.

Answer 241

**Fibrous dysplasia** CT appearances are typical showing increased volume of bone with ‘ground-glass’ appearance.

Answer 242

**Inverted papilloma** Inverted papillomas are uncommon benign epithelial neoplasms with significant malignant potential. They arise from the lateral nasal wall or maxillary sinus. They are most seen in 40–70-year-olds with a male to female ratio of 2–4:1. CT demonstrates a soft-tissue mass centred in the middle meatus associated with bone remodelling. Stippled calcification is seen in 20% of cases. On MRI, it is isointense on T1WI and iso/hypointense on T2WI. Heterogeneous enhancement is seen in 50% of cases. A convoluted cerebriform pattern on T2WI or enhanced T1WI is typical of inverted papillomas. Juvenile angiofibromas are seen in younger patients and are in the posterior nasal cavity. They demonstrate intense enhancement and flow voids on MRI. Antrochoanal polyps are homogenously hyperintense on T2WI. Invasive fungal sinusitis is primarily seen in immunosuppressed patients. They are frequently bilateral. CT findings include complete opacification of sinuses by hyperdense mass, erosion or remodelling of sinuses, and intra-sinus calcification. They are hypointense on T2WI. Nasal carcinomas cause bone erosion/destruction rather than remodelling.

Answer 243

**Medialization of middle turbinate**. FESS is the treatment of choice for patients with medically refractory sinusitis. Obstruction of the frontal recess is the main cause for medically refractory frontal sinusitis. The frontal recess is considered a difficult area to treat with FESS and it is also prone to re-stenosis. All of the above options are commonly associated with postoperative frontal recess stenosis except medialization of middle turbinate. Medialization (‘Bolgerization’) is performed to treat a lateralized middle turbinate, which is a well-recognized cause of frontal recess stenosis.

Answer 244

**Granulocytic sarcoma** Granulocytic sarcoma is a rare complication of acute and chronic myeloid leukaemia (AML & CML), occurring in approximately 3% of patients. It is a soft-tissue infiltrate of immature myeloid elements. The mean age at presentation is 48 years and most patients present with a solitary lesion. In the head and neck, they have been reported in the skull, face, orbit and paranasal sinuses. Extramedullary lesions have been reported in the tonsils, the oral and nasal cavities and within the lacrimal, thyroid and salivary glands. They are also referred to as chloromas, a term used to describe their green colour seen on sectioning. The prognosis of patients with AML does not change in the presence of a chloroma, however, in patients with CML it may represent worsening of the disease as their presence is associated with the acute or blastic phase. Approximately 30% of patients with chloromas have no haematological disease at the time of presentation.

Answer 245

**Referral to an appropriate clinician – you have made a confident diagnosis of a benign aetiology** This is almost certainly a mucocoele. Mucocoeles represent the end stage of a chronically obstructed sinus. They most commonly affect the frontal sinus (60%), with ethmoid (30%), maxillary (10%) and sphenoid (rare) following respectively. Patients present with symptoms as described in the question. Increased intrasinus pressure results in expansion and erosion of the sinus walls. There may be a surrounding zone of bone sclerosis. Contrast injection typically reveals rim enhancement, which helps to differentiate from the more solid enhancement pattern of neoplasms.

Answer 246

**Nasolacrimal duct** The lateral nasal wall is separated into superior, middle, and inferior meatuses by three curled bony shelves called turbinates (or conchae). The nasolacrimal duct opens into the anterior aspect of the inferior meatus and is usually the only opening seen there. The other ostia all open into the middle meatus, with the exceptions of the posterior ethmoidal ostia (superior meatus) and sphenoidal ostia (posterior to the superior turbinate in the sphenoethmoidal recess). The sphenopalatine foramen lies inferior to the sphenoethmoidal recess posterior to the middle turbinate.

Answer 247

**Fungal sinusitis** CT findings are typical, showing a hyperdense lesion with calcifications and bony erosion. The ethmoid sinus is most involved and bony expansion with erosion is characteristic. On MRI, the lesion is low signal on T1 and T2 due to high fungal mycelial iron, magnesium and manganese from amino acid metabolism.

Answer 248

**Antrochoanal polyp** These are seen as low attenuating masses from the maxillary antrum extending through a sinus ostium to the choana. They show non-aggressive features with peripheral enhancement. MRI shows a hypo to variable signal on T1 with hyperintense on T2 with peripheral enhancement. Juvenile angiofibroma is seen in adolescent males with an intensely enhancing mass extending to the posterior nasopharynx. Inverted papilloma are seen in older males as a locally aggressive mass of the middle meatus extending into the maxillary sinus. Intranasal glioma usually presents at birth as a very soft mass centred at the nasal dorsum.

Answer 249

**Rhabdomyosarcoma** Bone destruction suggests an aggressive lesion at this site and rhabdomyosarcoma would be the most likely diagnosis in a young person.

Answer 250

**Nasopharyngeal carcinoma** The lesion is aggressive with bony destruction and is likely to be malignant. Nasopharyngeal carcinomas have a high incidence in the Chinese population. It can feature bony destruction of the basisphenoid, basiocciput or the petrous tip. There may also be cranial nerve involvement, either at their exit through the foramina or secondary to intracranial extension.

Answer 251

**Juvenile angiofibromas** Juvenile angiofibromas are benign but locally aggressive tumours with high vascularity. They typically occur in adolescent boys and present with recurrent epistaxis and nasal obstruction. They are centred within the sphenopalatine foramen and involve the pterygopalatine fossa, producing a bowed appearance of the posterior wall of maxillary sinus and widening of pterygopalatine fossa, inferior orbital, and pteryogomaxillary fissures. Osseous erosion is commonly seen. The specific differentiating feature on MRI is the presence of multiple flow voids on T2WI and enhanced T1WI.

Answer 252

**Parotid space.** Loss of symmetry and displacement of the parapharyngeal space are useful for lesion identification and localization in the parapharyngeal soft tissues. A thorough knowledge of the anatomical relationship between the spaces is essential. The parapharyngeal space is shaped like an inverted pyramid with the apex pointing inferiorly toward the greater cornu of the hyoid bone and the skull base demarcates the base superiorly. A lesion arising from the parotid space displaces the fat in the parapharyngeal space anteromedially. A lesion in the masticator space displaces the parapharyngeal fat postero-medially. Carotid space lesions displace it anteriorly, mucosal space lesions displace it postero-laterally, and retropharyngeal space lesions displace it anterolaterally. Posterior displacement of the carotid space or parapharyngeal fat completely surrounding a lesion localizes it to the parapharyngeal space.

Answer 253

**Filling of retropharyngeal space from side to side.** Understanding the retropharyngeal space anatomy is crucial in differentiating retropharyngeal space abscess and retropharyngeal suppurative lymph node. The retropharyngeal space is bounded by visceral fascia covering the pharynx and oesophagus anteriorly, the prevertebral fascia covering the prevertebral muscles posteriorly, and the carotid sheaths laterally. A retropharyngeal suppurative lymph node is unilateral, whereas a retropharyngeal abscess fills the entire retropharyngeal space from side to side. The differentiation is important because many cases of suppurative lymph nodes do not have purulent material at surgery. The treatment for suppurative lymph nodes is a trial of antibiotics if the patient is stable. Surgical drainage is considered if there is progression or if the suppurative lymph node is large at presentation. The volume of central low density is a better predictor of purulence than the mere presence of rim enhancement and low-density centre.

Answer 254

**Tornwaldt’s cyst** Tornwaldt’s cyst is a benign mass typically located in the midline, between the longis colli muscles, in the posterior nasopharynx. They arise as a result of a focal adhesion between the ectoderm and regressing notochord. This causes the creation of a pouch but when the communication with the pouch is lost, a cyst develops. Tornwaldt’s cysts are usually asymptomatic and are picked up as incidental findings. Periodically, the pressure within the cyst increases causing the release of its contents into the nasopharynx. This leads to presentations including halitosis, foul taste in the mouth and persistent nasopharyngeal drainage. Peak age at presentation is 15–30 years. Imaging features can vary depending on the protein content within the cyst but typical features are of a well-delineated, thin-walled, midline cystic lesion measuring 2–10 mm in diameter. They are hypodense on CT, rarely calcify and do not enhance. They can be high or low on T1 (depending on protein content) but are high on T2-weighted imaging. Rathke’s pouch cysts are located anterior and cephalad to Tornwaldt’s cysts.

Answer 255

**Venous Vascular Malformation** Phleboliths if present are unique to vascular malformations. Arterial malformations are high flow, while venous, capillary or combined malformations are low flow. MRI is required to assess the full extent, particularly intraosseous and intracranial, of head and neck vascular malformations. Benign lymph nodes are smooth, elliptical and hypoechoic with hilar architecture and vascularity. Malignant lymph nodes are typically round, are hypoechoic, have no hilum and show peripheral vascularity. Malignant lymph nodes with necrosis are seen with squamous cell and papillary cell carcinoma of the thyroid. Internal punctate calcification is seen in metastases from papillary or medullary carcinoma of the thyroid.

Answer 256

**Maxillary artery** The parapharyngeal space is triangular shaped and extends from the skull base to the hyoid. It contains fat, branches of the mandibular division of the trigeminal nerve, maxillary artery, ascending pharyngeal artery and pharyngeal venous plexus. The internal carotid artery, vagus nerve and hypoglossal nerve lie in the carotid space. The lingual tonsils lie in the pharyngeal mucosal space.

Answer 257

**Warthin tumours**. Warthin tumour or adenolymphoma is the second most common benign tumour of the parotid gland. It is usually solitary. Multiple or bilateral parotid masses and increased uptake on 99m Tc are strongly suggestive of Warthin tumour. Warthin tumours do not enhance following gadolinium administration. Pleomorphic adenomas are usually solitary and unilateral. They appear as hypoechoic, lobulated, well-defined lesions with posterior acoustic enhancement on ultrasound scan (USS). On MRI, they are of intermediate signal on T1WI and hyperintense on T2WI. They demonstrate homogenous enhancement following gadolinium administration. Mucoepidermoid carcinomas vary in appearances. Low-grade tumours are similar to pleomorphic adenomas. High-grade tumours are heterogenous with low to intermediate signal intensity on T1WI and T2WI. They demonstrate infiltrating margins and heterogenous enhancement following gadolinium administration.

Answer 258

**A.** Warthin’s tumours are benign salivary gland tumours, accounting for 6-10% of all parotid tumours. Warthin’s tumours are bilateral in 15% of cases.

Answer 259

**Lymph node** Typical appearances of intraglandular lymph nodes are of a hypoechoic periphery with a fatty hyperechoic centre.

Answer 260

**Sjögren syndrome** An autoimmune condition causing salivary and lacrimal gland destruction. The secondary type is commonly related to rheumatoid arthritis, presenting with recurrent dry eyes, mouth and skin and parotid swellings. CT and MRI appearances are typical as described. Non-Hodgkin’s lymphoma has bilateral solid masses in the parotids and usually has chronic systemic manifestations. Warthin’s tumours are characteristically inhomogeneous and, if cystic, show mural nodules. Metastatic tumours are solid enhancing lesions and a primary would usually be apparent on further investigation. Pleomorphic adenoma is usually a unilateral, well demarcated, solid, intra-parotid lesion with contrast enhancement.

Answer 261

**Keratocystic odontogenic tumour**. These are benign but locally aggressive developmental tumours affecting adults in the second to fourth decades. They are most commonly located in the mandibular ramus and body, and are associated with an impacted tooth. They may be unilocular or multilocular and often contain daughter cysts extending into the surrounding bone. They can be associated with cortical expansion and erosion. They demonstrate minimal peripheral enhancement with contrast. The presence of **multiple keratocystic odontogenic tumours** raises the possibility of **Gorlin basal cell nevus syndrome**, which is an autosomal dominant disorder. Associated features include multiple **basal cell carcinomas of the skin, mental retardation, midface hypoplasia, frontal bossing and prognathism, calcification of the falx and dura, and bifid ribs.**

Answer 262

**E** Matting is associated with tubercular lymph nodes. Increased peripheral vessels is a feature of malignant nodes.

Answer 263

**Ameloblastoma** Ameloblastoma (adamantinoma of the jaw) is a benign, locally aggressive lesion that occurs mainly in patients between 30 and 50 years of age. They are found in the mandible (75%) and the maxilla (25%) and are often associated with an impacted/unerupted tooth. When in the mandible, they typically occur in the region of the molars/angle of the mandible. Typically, ameloblastomas are radiolucent lesions that contain septa or locules of variable size, which produce a honeycombed appearance. The margin is usually well defined but when large it can produce jaw expansion with perforation of the cortex. They may infiltrate adjacent soft tissues and show local recurrence following excision. Ameloblastomas may be unicystic but these tend to occur around the age of 20 years and there is also a very rare malignant variety which can cause lung metastases. Odontogenic keratocysts, dentigerous cysts, odontogenic myxomas and periapical cysts are invariably unilocular.

Answer 264

**A** Ameloblastomas grow in the buccolingual direction and are expansile.

Answer 265

**d** Soap-Bubble Appearance Both ameloblastoma and radicular cysts most commonly present in the third to ﬁfth decades of life as a painless lump, often as an incidental finding. Neither typically shows matrix mineralization. Ameloblastoma represents 10% of all odontogenic (developing during or after the formation of teeth) tumours, with the majority located in the posterior body or ramus. They are frequently associated with the crown of an impacted or unerupted tooth. They can vary in radiographic appearance, an expansile, multiloculated lesion being typical. They are often resected due to locally aggressive infiltration. Radicular cysts are unilocular with a rim of cortical bone and usually develop at the root apex of a carious tooth as the end stage of the inflammatory process.

Answer 266

d **Radicular cyst** A radicular cyst is the commonest type of cyst in the jaw and is associated with the apex of a tooth. It may displace teeth and cause mild root resorption. Ameloblastoma (adamantinoma of the jaw), odontogenic keratocyst and dentigerous cyst are all associated with the crown of a tooth, usually unerupted, and can be difficult to distinguish from each other on imaging alone. They are all odontogenic with no mineralization and may be large and expand the mandible. Odontomas are the commonest odontogenic mass (67%) and show mineralization. They are seen in 10–20-year-olds presenting with single or multiple, tooth-like masses.

Answer 267

**B** II Lymph nodes in the neck have been divided into seven levels, generally for the purpose of squamous cell carcinoma staging. This is, however, not all inclusive, as the parotid nodes and retropharyngeal space nodes are not included in this system. Level I: Below mylohyoid to hyoid bone anteriorly Level Ia: Submental Level Ib: Submandibular Level II: Jugulodigastric (base of skull to hyoid) Level III: Deep cervical (hyoid to cricoid) Level IV: Virchow (cricoid to clavicle) Level V: Posterior triangle groups Level V: Accessory spinal (posterior triangle), Level Va: superior half, Level Vb: inferior half Level VI: Prelaryngeal/pretracheal/Delphian node Level VII: Superior mediastinal (between common carotid arteries (CCAs), below top of manubrium) Lymph node levels of the neck. Radiopaedia.org.

Answer 268

**E** Second branchial cleft cyst. The majority of branchial cleft anomalies arise from the second branchial cleft. The described findings are typical of a second branchial cleft cyst. Similar ultrasound appearances may be seen in a first branchial cleft cyst or a dermoid cyst. The anatomical location is the key to the diagnosis. Dermoid cysts are typically midline in location in the neck and first branchial cleft cysts are located in the region of parotid gland, external auditory canal, and angle of mandible. Lymphangiomas are typically located in the posterior triangle. On ultrasound, they appear multiloculated with intervening thin septa. Abscesses appear as ill-defined, irregular collections with thick walls and internal debris. Surrounding soft-tissue oedema, hyperaemia, and enlarged adjacent lymph nodes are also noted.

Answer 269

**e** Second branchial cleft cyst Failure of involution of branchial clefts can lead to branchial cleft cysts, fistulae and/or sinuses. Second branchial cleft cysts account for 95% of all branchial cleft anomalies. Male and female incidence is equal and the typical age of presentation is 10–40 years. Second branchial cleft cysts are classified into four types depending on their location. The most common is type II, which occurs along the anterior surface of the sternocleidomastoid muscle, lateral to the carotid space and posterior to the submandibular gland adhering to the great vessels. On CT/MR the ‘beak sign’ is pathognomonic. This is a curved rim of tissue pointing medially between the internal and external carotid arteries.

Answer 270

**a** Subdural hygroma This is a traumatic subdural effusion which shows up as a localised CSF-fluid collection within the subdural space. They present in the elderly or in young children usually 6–30 days following trauma. The majority are asymptomatic but patients may present with increasing confusion or headaches. They are devoid of blood products on imaging, unlike chronic subdural haematomas. Subdural haematomas are also more likely to cause effacement of the ventricular system and loss of the normal sulci-gyral pattern. Normal inflammatory markers and lack of pyrexia lessen the probability of an empyema.

Answer 271

**a** Infected thyroglossal duct cyst Thyroglossal duct cysts arise from the remnants of the embryonic thyroglossal duct and account for up to 70% of congenital neck masses in children. Typically, children present with a non-tender mass that elevates on swallowing. If infected there may be pain, local tenderness and recent increased growth. Most are midline, although they become more paramedian below the level of the hyoid. Approximately 20% are suprahyoid, 15% occur at the level of the hyoid and 65% are infrahyoid. Generally they are thin-walled cysts and show typical cystic imaging characteristics. If infected or if the cyst has haemorrhaged, high signal may be seen on T1 and low signal may be present on T2-weighted MR images. Haemorrhage and infection may also cause thickening and marked enhancement of the wall.

Answer 272

**e** Larynx The lymph node chains in the neck are complex and consist of a superficial circular nodal group and a deep cervical chain. Supraglottic laryngeal squamous cell carcinoma tends to spread to the high internal jugular vein chain of nodes, which are in level II, with tumours of the epiglottis, aryepiglottic folds and pyriform sinuses most likely to present with adenopathy. This can be ipsilateral (most common), contralateral or bilateral. Subglottic tumours tend to spread to bilateral middle- or lower-level nodes of the internal jugular vein chain in level III or IV. The level IV lymph nodes also drain the hypopharynx, thyroid and upper oesophagus. The oral cavity, including the tongue and nasopharynx, drains to the level II nodes. The salivary glands drain to level I or II nodes. Tumours confined to the vocal cords do not normally metastasize to lymph nodes.

Answer 273

**a** Tuberculosis Tuberculous lymphadenitis is the most common form of head and neck tuberculosis, representing 15% of all extrapulmonary tuberculous infections. It is frequently bilateral and, the more inferior the involved nodes, the higher the prevalence of associated pulmonary disease. Peripherally enhancing lymph nodes are seen with tuberculosis, metastatic disease (usually squamous cell tumours), lymphoma or infection. The presence of calcification suggests tuberculosis, but it may also be seen with papillary or medullary thyroid carcinoma. The other diagnoses listed may cause cervical lymphadenopathy, but the lung lesion would be unusual in all except a cavitating squamous cell carcinoma of the lung.

Answer 274

**c** Level III Levels II, III and IV lie anterior to the sternocleidomastoid. Level II is from base of skull to hyoid, level III from hyoid to cricoid, and level IV from cricoid to clavicle. Level I is the submandibular space. Level V is posterior to sternocleidomastoid.

Answer 275

**No radioiodine or pertechnetate uptake but frequently concentrates thallium201 – medullary carcinom**a Types of thyroid carcinoma in order of worsening prognosis are papillary, follicular, medullary and anaplastic. Papillary tumours usually concentrate radioiodine, follicular tumours concentrate pertechnetate but fail to accumulate radioiodine, and anaplastic tumours show no radioiodine uptake.

Answer 276

**T2 fat-suppressed in the axial plane**

Answer 277

**Calcified lymph nodes – medullary carcinoma** Lymph node calcification accompanied by a thyroid tumour is highly suggestive of medullary carcinoma. This tumour arises from parafollicular C-cells and can cause elevated calcitonin levels. The familial form of medullary carcinoma is associated with MEN II (parathyroid hyperplasia, phaeochromocytoma).

Answer 278

**Hypothyroidism** Many of the features listed may be seen in any of the differential conditions provided. However, large sella and hypertelorism favour a diagnosis of hypothyroidism.

Answer 279

**D** Parathyroid adenomas are typically well circumscribed, round or oval hypoechoic nodules. They are usually low signal on T1 and high on T2. However, they may appear as high signal on both in the presence of haemorrhagic change. Parathyroid adenomas are usually hyperdense on CT.

Answer 280

**B** Other causes include early thyroiditis, hyperthyroidism, and rebound after withdrawal of anti-thyroid medications.

Answer 281

**C** Other causes include autonomous adenoma and, very rarely, thyroid cancer. Any hot nodule on Tc-99m should be imaged with I-123 to differentiate between autonomous and cancerous lesions.

Answer 282

**No uptake on pertechnetate, increased uptake on sestamibi with delayed washout** Parathyroid adenomas do not take up pertechnetate, which is accumulated by thyroid tissue, whereas sestamibi is taken up by both thyroid and parathyroid tissue. Subtraction of these two images can then be used to show any difference that can be attributed to a parathyroid adenoma. The delayed image typically shows retention of sestamibi in parathyroid adenomas (delayed washout) compared with normal parathyroid and thyroid. Small parathyroid adenomas are often missed by scintigraphy.

Answer 283

**Do not perform FNA** The appearances are characteristic of a multinodular goitre, and FNA can be misleading in these cases. Imaging diagnosis alone is usually sufficient. If there is a dominant nodule that is clearly larger than the others or a solitary enlarging nodule found on follow-up, then FNA should be performed to exclude malignancy.

Answer 284

**4 months** The imaging ﬁndings are in keeping with a chronic infarct, in which the unrestricted extra water within gliosis gives a high T2 signal, dark DWI and bright ADC. Cytotoxic oedema occurs because of early ischaemic damage to the cell membrane Na+ /K + ATPase pump. This can be seen as early as 30 minutes after symptom onset as a bright DWI region. T2W images will be normal this early and the corresponding ADC map dark. DWI signal increases during the ﬁrst week due to restricted diffusion but may remain bright for a prolonged period due to T2 ‘shine-through’. ADC will return to normal at 1–4 weeks (pseudonormalization) when restricted diffusion is matched by increasing amounts of vasogenic oedema that is not restricted. Long-term gliosis has extra water that is not restricted. DWI can be usefully thought of as a T2 signal diminished by net water movement. Since the DWI can be bright

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