SKULL & BRAIN Flashcards

Question

MULTIPLE RING-ENHANCING LESIONS | Neoplastic

Answer 1

1. Metastases—at GWMJ, rarely involve corpus callosum (cf. glioma, lymphoma); see Section 13.8. 2. Multifocal glioma—often lesions are connected by abnormal T2 signal (nonenhancing tumour) and conform to path of WM tracts (e.g. along genu of corpus callosum); see Section 13.8. 3. Lymphoma†*—typically solid enhancement but in the immunocompromised (or after steroid treatment) may show atypical ring enhancement. Important to differentiate from toxoplasmosis (see following); lymphoma tends to be fewer in number with a subependymal distribution.

Answer 2

1. Abscesses†—may be localized due to direct spread from adjacent structures, e.g. sinusitis/mastoiditis; if haematogenous in origin S then can be scattered across all vascular territories; 2. Septic emboli†—multiple microabscesses and associated infarcts; check for arteritis (arterial irregularity and stenoses) and mycotic aneurysms. Risk factors: infective endocarditis, IV drug abuse, arteriovenous shunts and indwelling vascular lines. 3. Tuberculoma† 4. Toxoplasmosis†—basal ganglia and GWMJ, concentric alternating low and high T2 signal, eccentric ‘target sign’ enhancement. 5. Neurocysticercosis—endemic in South America, Asia and Africa. Cysts in subarachnoid space or parenchyma; appearance depends on stage

Answer 3

1. Demyelination—acute demyelinating plaques may enhance, usually with an ‘open ring’ pattern incomplete to the gyral surface. Characteristic locations: periventricular, juxtacortical, infratentorial and spinal cord; 2. Radiation necrosis 3. PML-IRIS†( Progressive multifocal leukoencephalopathy immune reconstitution inflammatory syndrome)

Answer 4

Contusion/haematoma—orbitofrontal and anterior temporal | regions;

Answer 5

1. Haemangioblastoma—nonenhancing cyst wall, posterior fossa; 2. Pilocytic astrocytoma—enhancing cyst wall, posterior fossa; see 3. Cystic metastasis—adenocarcinoma, SCC. Thick irregular wall ± haemorrhage. 4. Pleomorphic xanthoastrocytoma—young adults, temporal lobe; 5. Craniopharyngioma—multilocular cystic lesion, often in suprasellar region with variable calcification and high T1 signal; see 6. Ganglioglioma 7. Rosette-forming glioneuronal tumour 8. Pineocytoma

Answer 6

1. Neurocysticercosis—vesicular and colloidal vesicular stages, central dot from scolex

Answer 7

1. Chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS)—characteristic punctate and linear enhancement in pons with minimal oedema/ mass effect; normal intracranial arteries. 2. Neurosarcoid—associated with abnormal thickening and enhancement of dura, cranial nerves and pituitary stalk. 3. Vasculitis—evidence of arteritis with stenoses, beading and infarcts. 4. Lymphoma*—elderly, fluctuating areas of T2 and diffusion abnormality, surrounding mass-like enhancement. 5. Lymphomatoid granulomatosis—in the immunocompromised. Multifocal periventricular linear T2 hyperintensities + enhancement. 6. Behçet’s*—young adults, orogenital ulcers. Brainstem and deep ganglionic structures, oedema and mass effect (cf. CLIPPERS). 7. Langerhans cell histiocytosis*—children and young adults, commonly presents with diabetes insipidus;

Answer 8

1. Postoperative—greatest at site of craniotomy, usually unilateral, smooth and thin dural enhancement. 2. Intracranial hypotension—due to a drop in CSF volume. Orthostatic headaches, brainstem ‘slumping’, subdural effusions and convex dural venous sinuses and bulky pituitary from pull of negative pressure. Bilateral smooth and thin dural enhancement. (subdural effusions, smooth diff pachymenin CE, eff suprasellar cist, reduced pontomesencephalic angle, reduced pontomamillary distance, cereb tonsillar descent, flattening of pons, convex of pituitary, rounding of transverse sinuses) (a) Following lumbar puncture—mild and transient. (b) Overshunting—slit-like ventricles. (c) Skull base leak—following surgery/trauma, presents with CSF rhinorrhoea or otorrhoea. Diagnosed with skull base CT looking for a fracture or defect. (d) Spinal leak—e.g. meningocoele, posttraumatic. Often subtle, may need a myelogram to localize. 3. Infection—localized to adjacent osteomyelitis or sinusitis. Irregular, thick enhancement. 4. Neoplastic. (a) Meningioma—reactive tapered dural thickening around lesion (‘dural tail’). (b) Metastasis—e.g. breast, prostate; smooth or nodular enhancement. (c) Secondary CNS lymphoma*—meningeal > parenchymal involvement. (d) Solitary fibrous tumour of the dura—similar appearance to meningioma, but tends to be of lower T2 signal, with internal flow voids and a higher propensity for skull invasion. No calcification or associated hyperostosis. 5. Granulomatous disease—TB, sarcoid, Wegener’s, rheumatoid, Sjögren’s, Behçet’s, Erdheim-Chester, syphilis, fungal disease. Multifocal nodular and thick enhancement. Basal distribution in TB meningitis. 6. Extramedullary haematopoiesis—dural involvement rare, seen in thalassemia and myelofibrosis. Widened diploic space in skull. 7. Idiopathic hypertrophic cranial pachymeningitis—mass-like thickening of the dura, often with cranial nerve involvement. Some cases are due to IgG4-related disease

Answer 9

1. Carcinomatosis—typically nodular. Metastatic (breast, lung), lymphoma, ependymoma, germinoma, medulloblastoma, glioblastoma, pineoblastoma. Image whole neuraxis to assess extent of disease. 2. Meningoencephalitis—bacterial, viral, fungal, Lyme disease. Cerebral swelling. 3. Granulomatous disease—TB, sarcoid, Wegener’s, rheumatoid nodules, fungal disease. 4. Vascular—collateral flow (ischaemia) or increased flow, e.g. dural fistula, pial angioma of Sturge-Weber

Answer 10

1. Infection—ventriculitis. (a) Bacterial—intraventricular pus restricts diffusion, and may be related to an adjacent cerebral abscess. Ependymal enhancement is an early sign of ventriculitis and warrants escalation of therapy and consideration of shunting for hydrocephalus. (b) Viral—CMV, VZV; immunocompromised patients. 2. Neoplastic—abutting ventricular surface or intraventricular. (a) Nodular/linear—lymphoma, glioblastoma, ependymoma, germ cell tumour, metastases. (b) Mass-like—ependymoma, giant cell astrocytoma. 3. Granulomatous—TB (basal meningitis), sarcoidosis (cranial nerves and dura). 4. Intraventricular haemorrhage—hyperdense blood within the ventricles. 5. Subependymal venous congestion—can mimic ependymal enhancement. (a) Deep cerebral vein thrombosis—hyperdense vein, oedema. (b) AVM or AVF—dilated abnormal vessels. (c) Sturge-Weber*—cortical calcification, cerebral atrophy and enlarged ipsilateral choroid plexus.

Answer 11

1. Primary. (a) Schwannoma—CN VIII; sporadic or NF2 (diagnostic if bilateral). (b) Meningioma—‘tram-track’ enhancement, CN II. (c) Neurofibroma—rarer to involve CN, T2 hyperintense rim with central low signal (target sign). NF1: plexiform neurofibromas of CN III and CN V. (d) Optic nerve glioma—pilocytic astrocytomas, associated with NF1 2. Secondary. (a) Leptomeningeal dissemination—nodular involvement, seeding from primary CNS (ependymoma, medulloblastoma, germinoma, lymphoma) or secondary metastatic (breast, lung, melanoma). (b) Perineural spread—from head and neck tumours, e.g. mucosal SCC and salivary gland adenoid cystic carcinoma (CN VII), lymphoma, melanoma.

Answer 12

1. Meningitis. (a) Viral infections—HSV type 1, CMV, and VZV (Ramsay Hunt Syndrome—vesicular eruptions). CN VII. (b) TB*—cisternal segments of CN, surrounding exudate. (c) Cryptococcus neoformans—infiltration of meninges around optic tracts, nerves and chiasm. 2. Lyme disease—may involve CN III to VII. 3. Fungal—aspergillosis, mucormycosis, actinomycosis. Perineural spread from sinus disease. Elderly diabetic patients are most at risk

Answer 13

1. Bell’s palsy—uniform linear enhancement of CN VII. 2. Miller-Fisher syndrome—variant of Guillain-Barré, multiple CN, linear enhancement. 3. Chronic inflammatory demyelinating polyneuropathy—‘onion bulb’ thickening of multiple peripheral and cranial nerves, with diffuse enhancement. 4. Demyelinating—multiple sclerosis (MS) and NMO. CN II (optic neuritis

Answer 14

1. Sarcoidosis*—any CN with thickening, most commonly CN II centred around chiasm and pituitary stalk. 2. Wegener’s granulomatosis*—spread from sinuses, associated with dural thickening, vasculitis with infarcts. 3. Tolosa-Hunt—idiopathic inflammation of cavernous sinus and orbital apex. Painful ophthalmoplegia, enlarged cavernous sinus with internal carotid artery (ICA) narrowing and enhancement of CNs that pass through.

Answer 15

1. Post radiation neuritis—limited to radiation field. 2. Ischaemic—diabetics, vasculopaths; transient enhancement followed by gradual atrophy. CN II, III and VI.

Answer 16

1. Collateralization due to proximal progressive steno-occlusive disease. (a) Moyamoya disease—idiopathic, progressive occlusion of the proximal intracranial arteries. ‘Puff of smoke’—angiographic appearance of small abnormal net-like collateral vessels. ‘Ivy sign’—pial collaterals have serpentine sulcal FLAIR hyperintensity and enhancement. (b) Moyamoya-like syndromes—other proximal intracranial artery steno-occlusive diseases that mimic Moyamoya disease, e.g. post radiation, NF1, Down’s syndrome, SCD and atherosclerosis. 2. Secondary to a distal ‘sump’ effect. (a) AVM—tangle of abnormal vessels with feeding arteries and draining veins. Often multiple dilated vessels, no stenoses (cf. Moyamoya). (b) Tumour—vascular tumours recruit increased arterial flow to both tumour and surrounding parenchyma/leptomeninges. 3. Sturge-Weber*—phakomatosis; facial cutaneous and leptomeningeal haemangiomas. Steal phenomenon causes atrophy of subjacent cortex and WM + ‘tram-track’ calcification

Answer 17

1. Nonspecific and age-related—small peripheral lesions in nontypical locations for an inflammatory cause (see following). Greater number reported in patients with migraine. Spare subcortical U-fibres (SCUF). Some authors arbitrarily say one lesion per decade is within normal limits. 2. Vascular. (a) Small-vessel disease (SVD)—periventricular WM lesions (>3 mm from surface, cf. MS) and deep WM lesions; tends to spare corpus callosum (cf. MS). Varies from punctate to confluent. Spares SCUF due to end-arterial distribution. (b) Hypertensive encephalopathy—ganglionic lacunar infarcts and microhaemorrhages. Interrelated with SVD. (c) Multi-infarct encephalopathy—SVD + additional embolic cortical and pontine infarcts. (d) Cerebral amyloid angiopathy—see Section 13.4. 3. Inflammatory. (a) Multiple sclerosis (MS)—perivenous distribution, periventricular (contacting surface, cf. SVD), infratentorial, cortical/juxtacortical with involvement of SCUF (cf. vascular aetiologies). Involves corpus callosum at callososeptal interface. Incomplete ring enhancement (cf. infection). Short segment spinal cord lesions. (b) Neuromyelitis optica (NMO)—often indistinct/fluffy lesions, classic locations: periaqueductal grey matter and area postrema (posterior medulla abutting fourth ventricle) + optic neuritis. Long segment spinal cord lesions (cf. MS). (c) Vasculitis—wide spectrum of vasculitides defined by size of vessel involvement and whether confined to CNS arteries or systemic. Multiple infarctions, usually bilateral in different vascular territories. Angiography demonstrates multifocal stenoses and occlusions. Black-blood contrast MRI may show enhancing inflammatory tissue cuffing arteries. (d) Sarcoidosis*—see Section 13.15. (e) Connective tissue disease (CTD)—can be indistinguishable from MS, e.g. SLE (associated with infarcts), Sjögren’s. Other signs of CTD. 4. Miliary metastases—e.g. lung, melanoma, breast. Often at GWMJ. Greater mass effect and perilesional oedema. Callosal involvement very rare (cf. MS). 5. Infection—granuloma, septic emboli; ± punctate restricted diffusion, microhaemorrhages, complete ring enhancement 6. Diffuse axonal injury (DAI)—shear-related injuries often with microhaemorrhage; common locations GWMJ, splenium and middle cerebellar peduncles.

Answer 18

1. Neoplastic—e.g. glioma, lymphoma, metastases. Generally have more mass versus other differentials (see Section 13.8). 2. Vascular—same as above due to coalescence of multiple vascular insults. 3. Hypotensive cerebral infarction—deep and superficial watershed territories, typical signs of infarction if acute. 4. Infection. (a) Encephalitis—HSV predilection for medial temporal lobes; other non-herpes encephalitides can involve basal ganglia (BG), thalamus, brainstem and cerebellum. Ill-defined, variable enhancement and restricted diffusion. Acute presentation with fevers, seizures, reduced Glasgow Coma Scale (GCS) and nonspecific neurology. (b) Progressive multifocal leukoencephalopathy (PML)—JC polyomavirus opportunistic infection causing demyelination in immunocompromised patients (HIV, patients on immunotherapy). Multifocal periventricular and subcortical lesions involving SCUF. No contrast enhancement. Late cavitation/cystic change. (c) PML-immune reconstitution inflammatory syndrome (PML-IRIS)—paradoxical deterioration in PML due to exaggerated inflammatory reaction after reconstitution of immune system. Classically seen in HIV patients on therapy, but also recognized with MS immunotherapies. Associated with mass effect and irregular enhancement (cf. PML). (d) Lyme disease—resembles MS but greater abnormalities in BG and brainstem ± CN enhancement. 5. Inflammatory. (a) MS, NMO, vasculitis, sarcoidosis*—see earlier. (b) Tumefactive demyelination—large demyelinating lesion with relatively little mass effect or oedema, often unifocal. Open-ring enhancement, low CBV on perfusion (cf. tumour). Like MS often perivenous in distribution. (c) Acute disseminated encephalomyelitis (ADEM)— monophasic demyelination following infection/vaccination, usually in children or adolescents. Bilateral asymmetrical subcortical lesions, spare callososeptal interface (cf. MS). 6. Osmotic myelinolysis—acute demyelination from rapid change in serum osmolality (classically rapid correction of hyponatraemia). Typically a round or trident-shaped lesion in central pons, but can be extrapontine, e.g. symmetrical in BG and/or WM. 7. Radiation necrosis—s

Answer 19

1. Vascular 2. Neoplastic—diffuse glioma. 3. Inflammatory. (a) MS, NMO, vasculitis, sarcoidosis (b) Rasmussen encephalitis—children and young adults with intractable seizures; chronic encephalitis of one hemisphere with ipsilateral patchy WM lesions and volume loss. 4. Leukoencephalopathies—all tend to cause symmetric, multifocal lesions. Most present in childhood. (a) Inherited—early adult onset. (i) CADASIL—recurrent lacunar and subcortical infarcts, especially in anterior temporal and frontal lobes (see (ii) COL4A1—small-vessel disease, dilated perivascular spaces, microhaemorrhages and intracerebral haemorrhages. SCUF spared. (iii) X-linked adrenoleukodystrophy—adult-onset phenotype, frontal lobe and genu of corpus callosum involvement predominates (cf. child onset, which has a predilection for occipitoparietal regions). (iv) Krabbe disease—adult-onset phenotype, slower progression. CT: hyperdense thalami, cerebellum and caudate nuclei. Periventricular abnormal WM signal. (b) Toxic–metabolic—dependent on cause, typically symmetrical and often involve splenium + corresponding restricted diffusion. (c) HIV encephalopathy—symmetric periventricular and deep WM lesions + volume loss. 5. Degenerative—e.g. frontotemporal lobar degeneration and corticobasal degeneration; associated volume loss 6. Radiation leukoencephalopathy—diffuse confluent lesions with volume loss and evidence of indications for radiotherapy, e.g. intracranial or head and neck tumour. U-fibre sparing

Answer 20

1. Agenesis/dysgenesis—CC develops from anterior to posterior; early embryonic insult = CC agenesis, late embryonic insult = CC dysgenesis limited to rostrum or splenium. Complete agenesis = parallel (‘racing car’) lateral ventricles, WM tracts paralleling the interhemispheric fissure (Probst bundles), high-riding third ventricle. Associated with pericallosal lipoma, dermoid and interhemispheric arachnoid cysts. 2. Atrophy—small-vessel ischaemia, radiation therapy, leukodystrophy. Extensive abnormal WM signal and volume loss beyond CC

Answer 21

1. Demyelination—MS, NMO. Lower border of CC at callososeptal interface (see Section 13.20). 2. Vascular—e.g. embolic infarcts, Susac syndrome. Asymmetric, adjacent to the midline. Callosal lesions are characteristic in Susac syndrome and typically spare the callososeptal interface, ± restricted diffusion and enhancement if acute; patients are typically young adult females presenting with a clinical triad of encephalopathy, bilateral sensorineural hearing loss and branch retinal artery occlusions. 3. DAI—asymmetric involving both midline and borders of CC + microhaemorrhage on SWI (see Section 13.20). 4. Marchiafava-Bignami syndrome—chronic alcoholics with vitamin B deficiency. Body of CC > genu/splenium. Large lesions in the central layer of CC

Answer 22

1. Butterfly glioma—high grade glioma, symmetric midline-crossing lesion most common in frontal lobes crossing and expanding genu, heterogeneous enhancement + central necrosis. 2. Lymphoma*—hypercellular (dense on CT), homogeneous restricted diffusion and solid enhancement (cf. butterfly glioma)

Answer 23

1. Cytotoxic lesions of the corpus callosum—transient cytotoxic oedema of the splenium; well-defined, oval, in the midline. T2 hyperintense + restricted diffusion but no enhancement. Many causes: seizures, metabolic (hypoglycaemia, sodium imbalance), infections, drugs and toxins

Answer 24

1. Corpus callosum impingement syndrome—impingement of CC against falx due to severe chronic hydrocephalus; abnormal signal + atrophy in rostral CC. 2. Post shunt decompression—typically diffuse oedema in CC occurring after shunt insertion for chronic severe hydrocephalus

Answer 25

1. Age-related—incidence of GP calcification increases with age. Increased iron deposition causes reduced T2 signal in GP and putamen (see Section 13.24). 2. Perivascular spaces (PVS)—CSF signal on all sequence

Answer 26

1. Lacunar infarct—well-defined CSF density/intensity lesions + surrounding high signal rim evident on FLAIR. 2. Hypertensive haemorrhage—background of DGM lacunes, enlarged PVS and microhaemorrhages. 3. Global hypoxic ischaemic injury—bilateral infarcts in regions of high metabolic demand: GP, posterior putamen, ventrolateral thalami, perirolandic regions, occipital cortex and hippocampal formations. 4. Venous infarction—due to internal cerebral vein thrombosis; bithalamic involvement (see Section 13.25). Marked swelling from venous congestion. 5. Central variant PRES—can involve brainstem.

Answer 27

1. Parkinson’s—18F-DOPA PET scan: loss of normal comma-shaped tracer uptake in the corpus striatum with full stop-shaped uptake only seen in the caudate head. 2. Multiple system atrophy-Parkinson’s type (MSA-P)—reduced putamen volume with reduced T2 signal relative to globus pallidus. High T2 rim surrounding putamen (‘putaminal rim’ sign) at 1.5T. (MSA-C- hot cross bun sign -pontocerebellar tracts) 3. Huntington’s disease—atrophy of caudate heads, ‘boxcar’ frontal horns.

Answer 28

1. Chronic bilirubin encephalopathy (kernicterus)—increased T1 and T2 signal in GP. 2. Hypermanganesaemia—e.g. total parenteral nutrition, haemodialysis, liver failure. High T1 signal in BG. 3. Exogenous toxins. (a) Carbon monoxide—GP. (b) Methanol—putamen. (c) Cyanide—corpus striatum and perirolandic cortex

Answer 29

1. Uraemic encephalopathy—bilateral basal ganglia, thalamus and midbrain. ‘Lentiform fork’ sign—T2 hyperintense internal and external capsule. 2. Hyperammonaemic/hepatic encephalopathy—acute liver failure. Symmetric insular, thalamic and posterior limb of internal capsule (PLIC) T2 hyperintensity. 3. Hypoglycaemia—symmetric high T2 and restricted diffusion in basal ganglia, PLIC, splenium and parietooccipital cortex.

Answer 30

1. Wilson’s disease—copper deposition disease. High T2 and volume loss in striatum and ventrolateral thalamus. ‘Face of giant panda’ sign in midbrain and ‘miniature panda’ sign in pons—‘double panda’ sign if both are present. 2. Mitochondrial cytopathies. (a) Kearns-Sayre syndrome—GP and cortical calcification. (b) Leigh syndrome—putamen, thalamus and periaqueductal grey matter. 3. Lipid storage disorders—Krabbe disease (see Section 13.20). 4. Amino acid disorders—e.g. methylmalonic acidaemia; selective necrosis of GP. 5. Neurodegeneration with brain iron accumulation (NBIA)—see Section 13.24. 6. Fahr disease—symmetrical calcification of basal ganglia, dentate nuclei and subcortical WM

Answer 31

1. Variant CJD (vCJD)—‘hockey stick’ sign: T2 hyperintensity in pulvinar and dorsomedial thalamus (cf. sporadic CJD which spares thalamus).

Answer 32

1. Methaemoglobin—hypertensive haemorrhage, haemorrhagic infarction. Includes haemorrhagic necrosis, e.g. in carbon monoxide (GP) or methanol (putamina) poisoning. 2. Copper—Wilson’s disease. 3. Manganese—parenteral nutrition, haemodialysis, liver failure. 4. Calcification—some crystalline forms of calcium cause T1 shortening (e.g. Fahr, hypoparathyroidism). 5. Chronic bilirubin encephalopathy (kernicterus)—increased T1 and T2 signal in GP. 6. Prior administration of linear gadolinium chelates

Answer 33

1. Diabetic striatopathy—non-calcific hyperdensity is a characteristic feature; typically manifests with hemiballism-hemichorea caused by nonketotic hyperglycaemia. due to Zn or manganese deposition 2. Fabry disease—typically pulvinar T1 hyperintensity (cf. vCJD with T2 hyperintensity). Associated with posterior circulation infarcts. 3. NF1—focal areas of signal intensity (FASI), high on T1 and T2, in the basal ganglia; most common neuroimaging feature of NF1

Answer 34

1. Neurodegeneration with brain iron accumulation (NBIA)— group of progressive neurological disorders that feature prominent extrapyramidal symptoms and iron deposition. Reduced signal in GP on T2/T2*/SWI sequences with central high signal: ‘eye of the tiger’ sign. Most common is pantothenate kinase-associated neurodegeneration (PKAN), which has abnormalities restricted to the GP and substantia nigra. Presence of pigmentary retinopathy is strongly suggestive of PKAN and is not seen in other forms of NBIA. 2. Huntington’s disease—atrophy of caudate heads.

Answer 35

1. Artery of percheron infarct—variant solitary arterial trunk that arises from one of the posterior cerebral arteries supplying both paramedian thalami and rostral midbrain. 2. Basilar tip thrombosis—hyperdense thrombus/loss of flow void in the basilar tip. 3. Internal cerebral venous infarct—look for deep cerebral vein thrombus on CT (hyperdense) and MRI (loss of T2 flow void). Greater local swelling than arterial infarcts. SWI may show serpiginous thrombosed deep medullary veins and associated microhaemorrhage. 4. Hypertensive haemorrhage. 5. Hypoxic ischaemic encephalopathy.

Answer 36

1. Encephalitis—caused by arboviruses transmitted by mosquito or tick bites, e.g. Japanese encephalitis (Asia), West Nile encephalitis (Middle East), Murray Valley encephalitis (Australasia), St Louis encephalitis (USA). Bilateral thalamic involvement is typical ± extension into brainstem or basal ganglia; usually haemorrhagic. Fevers and fulminant course. 2. Variant CJD—see Section 13.22.Skull and brain 413 13 3. Acute necrotizing encephalitis—haemorrhagic parainfectious syndrome in young children. Thought to be an immune overreaction to a mild antecedent viral infection.

Answer 37

1. Carbon monoxide poisoning—bilateral GP and thalamus. 2. Wernicke’s encephalopathy—triad of mental status, gait and oculomotor dysfunction. Due to thiamine deficiency. Symmetric abnormal signal in thalami, mammillary bodies, tectal plate and periaqueductal areas. 3. Mitochondrial cytopathies—Leigh, Kearns-Sayre 4. Fabry disease (F-foam/febrile, A-angiokeratoma, B-Burning pain/Boys, R-renal failure, Y- Xlinked, C - CV disease/ceramide) 5. Wilson’s disease

Answer 38

1. Bithalamic glioma—low-grade astrocytoma in children and young adults; expansile and often nonenhancing tumour ± obstructive hydrocephalus

Answer 39

1. MSA-cerebellar type (MSA-C)—symmetrical high T2 signal and volume loss in MCPs, ‘hot cross bun’ sign in pons: cross of abnormal signal due to selective degeneration of pontocerebellar tracts. 2. Fragile X—lesions in MCPs and splenium

Answer 40

1. Wilson’s disease. 2. Cirrhotic liver disease. 3. Adrenoleukodystrophy—see Section 13.20. 4. Hypoglycemia. 5. Solvent abuse. 6. Heroin inhalation—symmetrical involvement of PLIC and cerebellar WM.

Answer 41

1. PRES (central variant)—typically precipitated by drugs or hypertension. 2. Anterior inferior cerebellar artery (AICA) infarction—look for restricted diffusion and signs of vertebral artery occlusion or dissection

Answer 42

1. MS. 2. Behçet’s*—may involve bilateral basal ganglia, brainstem and thalamus. 3. ADEM. 4. HIV. 5. Japanese encephalitis—bilateral thalamic involvement. 6. PML and PML-IRIS.

Answer 43

1. Lymphoma*. 2. Brain stem glioma. 3. Meningeal carcinomatosis—leptomeningeal enhancement and FLAIR sulcal hyperintensity

Answer 44

1. Pituitary adenoma—mildly T2 hyperintense and T1 hypointense relative to normal gland. (a) Microadenoma—<10 mm, shows slightly delayed (60 secs) enhancement relative to normal gland.Skull and brain 415 13 (b) Macroadenoma—>10 mm, often demonstrates suprasellar and/or cavernous sinus extension, ± cystic degeneration and high T1 signal from internal haemorrhage or proteinaceous material. Sellar expansion from gradual remodelling. 2. Pituitary hyperplasia—enlarged normal signal gland. (a) Physiological—pregnancy, postpartum, lactation and postpubertal females. (b) Pathological—end-organ failure, e.g. hypothyroidism. 3. Pituitary haemorrhage/infarction—associated with macroadenoma. Blood-fluid levels, dense intrasellar mass on CT and variable signal and diffusion on MRI. ‘Apoplexy’ when haemorrhage/infarction is associated with acute clinical symptoms—headache, sudden vision loss and oculomotor palsy. 4. Intracranial hypotension—slightly swollen convex pituitary often extending just above sella, due to negative intracranial pressure (see Section 13.16). 5. Inflammatory hypophysitis—these can involve anterior and/or posterior pituitary and/or infundibulum, typically causing enlargement and avid homogeneous enhancement, but without sellar remodelling (cf. adenoma). Pituitary dysfunction is common. If the posterior pituitary is involved the normal T1 ‘bright spot’ is absent. (a) Lymphocytic hypophysitis—typically in late pregnancy or postpartum. (b) Granulomatous hypophysitis—e.g. sarcoid, TB, Wegener’s. (c) IgG4-related hypophysitis—as part of systemic IgG4-related disease. 6. Metastasis—rare, males = lung, females = breast. Pituitary or infundibulum. Normal fossa size, bony destruction, dural thickening and irregular margins (cf. adenoma). 7. Pituitary abscess—rare, cystic lesion + peripheral enhancement, likely associated meningitis. Fever, meningism

Answer 45

1. Meningioma—sphenoid, diaphragma sellae or cavernous sinus. Typically projects into sella displacing diaphragma sellae inferiorly + enhancing dural tail ± skull hyperostosis (cf. macroadenoma). 2. Rathke’s cleft cyst—also known as pars intermedia cyst, typically lies between anterior and posterior pituitary. Usually <1 cm but can be large. 50% have intracystic nodule. ‘Claw sign’ of normal displaced pituitary. 3. Craniopharyngioma—purely intrasellar rare, usually suprasellar and sellar.

Answer 46

1. Metastases—e.g. from lung or breast 2. Lymphoma*—may present as isolated stalk thickening or periventricular enhancing masses. Seen in primary and secondary CNS involvement. 3. Leukaemia—acute/chronic myeloid leukemia. Diagnosis usually known prior to infundibular involvement. Look for dural and optic nerve sheath deposits. 4. Germ cell tumours—children/young adults. Germinoma most common, other types: embryonal carcinoma, yolk sac tumour, choriocarcinoma, teratoma and mixed. Hyperdense on CT, homogeneous solid enhancement and restricted diffusion. 5. Craniopharyngioma. (a) Adamantinomatous (90%)—children > adults, 90% cystic, 90% calcified and 90% enhance. Multilocular, large with high T1 (oily) contents. (b) Papillary (10%)—adults, typically a solid enhancing mass. Small water-signal cysts, minimal enhancement. Calcification is rare. 6. Langerhans cell histiocytosis (LCH)*—children/young adults, stalk thickening and enhancement ± meningeal and choroid plexus involvement. Posterior pituitary bright spot absent. Look for lung, bone and skin disease. 7. Pituicytoma—benign, men in 40–50s. Enhances homogeneously. No sellar enlargement. ( neurohypophysis cells) 8. Other primary tumours—gliomas, choristomas (normal tissue in abnormal location - benign) and tanycytomas ( new type of tumour-hypothal/suprasellar from tancyte) (encase circle of Willis). 9. Pituitary adenoma—may occasionally arise in the infundibular region (pars tuberalis)

Answer 47

1. Neurosarcoid—enhancing stalk granuloma, which often involves adjacent optic pathways and floor of third ventricle. Check for dural, leptomeningeal and CN involvement. Consider systemic involvement. 2. Lymphocytic infundibuloneurohypophysitis (LINH)—variant of lymphocytic hypophysitis that predominantly affects infundibulum; 3. Other granulomatous hypophysitis—TB, Wegener’s, Erdheim-Chester, Whipple’s disease. In isolation generally indistinguishable from sarcoidosis. TB associated with basal meningitis. Wegener’s associated with sinonasal disease 4. Ectopic posterior pituitary—T1 bright spot located on median eminence of hypothalamus ± pituitary stalk/gland hypoplasia. Look for other midline abnormalities, e.g. deficient septum pellucidum. 5. Infundibular cysts—pars intermedia cysts may rarely be confined to the stalk.

Answer 48

1. Meningioma—see Section 13.27. 2. Granulomatous—TB, sarcoid, LCH. Enhancing granulomas may be T2 hypointense

Answer 49

1. Saccular aneurysm—giant aneurysms (>25 mm) may erode bone in the supra or parasellar region, appearances may be complicated by thrombus and flow void. Look for pulsation artefact in phase encoding direction. Angiographic imaging essentia

Answer 50

1. Pituitary lesions—with suprasellar extension. 2. Infundibular masses—especially craniopharyngioma (often large, making it difficult to verify infundibular origin). 3. Hypothalamic hamartoma—arises from tuber cinereum; T2 iso/ hyperintense to cerebral cortex, no enhancement. Gelastic seizures, precocious puberty and developmental delay. 4. Germ cell tumours. 5. Metastases/lymphoma*

Answer 51

1. Hypothalamic chiasmatic glioma—pilocytic astrocytoma typically arising from optic nerve/chiasm with variable involvement of hypothalamus. Variable enhancement. Associated with NF1. 2. Chiasmal optic neuritis—NMO, MS. High T2 signal and swelling. Signs of demyelinating disease elsewhere.

Answer 52

1. Epidermoid—paramidline cystic lesion, CSF density (CT) and T1/ T2 signal (MRI). Incomplete signal suppression on FLAIR and characteristic restricted diffusion enable differentiation from arachnoid cyst. 2. Dermoid—midline cystic lesion with fat content and capsular calcification. Look for subarachnoid ‘fat droplets’ to indicate rupture which is associated with chemical meningitis and hydrocephalus. 3. Teratoma—multiloculated, heterogeneous mixed soft tissue, fat and calcification. 4. Lipoma—fat density/signal lesion, calcification rare in suprasellar location (cf. dermoid and interhemispheric lipomas). 5. Arachnoid cyst—well-defined cyst of variable size. Isointense to CSF, nonenhancing, noncalcified.

Answer 53

1. Pituitary macroadenoma—can invade the CS via lateral extension, causing bulging of the CS. Signal difference most appreciable on pre- and postcontrast T1. Tumour extension beyond the intercarotid line suggestive of invasion. ICA encased but not typically narrowed (cf. meningioma). May invade skull base, mimicking a primary bone lesion

Answer 54

1. Meningioma—avidly enhancing mass with thickened dural tail; other meningiomas may be present. More often associated with venous congestion, and if ICA is encased it is often narrowed (cf. macroadenoma). 2. Granulomatous/inflammatory infiltration (a) Sarcoidosis*—additional dural and nerve deposits, signs of systemic sarcoid in lungs. (b) TB*—with basal meningitis ± tuberculomas. (c) Idiopathic orbital inflammatory syndrome—also known as orbital pseudotumour. Most commonly involves extraocular muscles with rapid onset unilateral proptosis. Mass is ill-defined and T2 hypointense due to fibrosis (cf. lymphoma, which is more lobular with intermediate T2 signal). Involvement of the orbital apex and cavernous sinus with painful ophthalmoplegia is termed Tolosa-Hunt syndrome; may also narrow the ICA and extend to superior orbital fissure. Linked to many autoimmune diseases, including: (i) IgG4-related disease*—associated with pachymeningitis, hypophysitis and salivary/lacrimal gland enlargement. (ii) Wegener’s*—look for sinonasal disease with abnormal soft tissue, osseous erosions and nasoseptal perforation. (iii) Churg-Strauss*—with lung involvement. 3. Defect—meningocoele/encephalocoele. Often due to raised intracranial pressure (ICP), clues include a partially empty sella (from arachnoid herniation flattening pituitary) and enlarged Meckel’s caves. 4. Invasive fungal sinusitis—Aspergillus; immunocompromised and diabetic patients. Extension from paranasal sinuses. Hyperdense opacification of paranasal sinus on CT, with susceptibility signal dropout on T2-weighted MRI.

Answer 55

1. Haematogenous. (a) Lymphoma*—homogeneous enhancement and restricted diffusion (more than pseudotumour). (b) Metastases—irregular, heterogeneous infiltrative enhancing tissue. 2. Direct extension—from malignant sphenoid sinus and nasopharyngeal tumours, with osseous erosion. 3. Perineural spread—squamous cell and adenoid cystic carcinomas; review skull base spaces, fissures and optic pathways. Abnormally thickened and enhancing nerve

Answer 56

1. Schwannoma—may involve CPA, Meckel’s cave and pterygomaxillary fissure. Variably solid and cystic, ‘dumbbell’ shaped, avidly enhancing with skull base remodelling.

Answer 57

1. Carotico-cavernous fistula—look for associated venous congestion in/around orbit (± proptosis, muscle swelling and chemosis clinically) and central skull base. May be direct, due to rupture of intracavernous ICA (e.g. traumatic or aneurysmal), or indirect, due to small AV shunts (associated with venous sinus thrombosis and subsequent revascularization). 2. Aneurysm—traumatic (pseudoaneurysm) and nontraumatic; prominent flow void and phase artefacts. May be partially thrombosed ± fistula. 3. Cavernous sinus thrombosis—nonenhancing thrombus in enlarged sinus ± adjacent dural enhancement and venous congestion. Often due to orbitofacial sepsis. 4. Cavernous haemangioma—multilobular, well-defined, very T2 bright heterogeneous mass, which can expand/erode into the adjacent sphenoid sinus without hyperostosis. May show gradual filling enhancement on dynamic contrast imaging (DDx - schwannoma, meningioma, chordoma, macroadenoma, chondrosarcoma)

Answer 58

1. Chordoma—older males, in midline at sphenooccipital synchondrosis. Well-defined, very T2 bright + septa. Encases vessels without narrowing. 2. Chondrosarcoma—osseous erosion with calcified chondroid matrix. Greater risk of ophthalmoplegia (cf. chordoma). 3. Myeloma/metastases/lymphoma*—lytic/sclerotic lesion with variable soft-tissue component

Answer 59

1. Optic neuritis—triad of visual impairment, pain and abnormal colour vision. T2 hyperintensity within optic nerve substance (cf. optic perineuritis). (a) Inflammatory. (i) MS—usually unilateral retrobulbar optic neuritis and papillitis with variable enhancement and classical WM lesions in the brain (see Section 13.20). (ii) NMO—usually bilateral with longer segment abnormal signal and enhancement and clinically more severe visual loss (cf. MS). Fewer intracranial WM lesions. (iii) SLE/sarcoid/Wegener’s*—optic perineuritis > neuritis (see later). SLE also associated with acute ischaemic optic neuropathy (abrupt severe visual loss). (b) Infective—herpes zoster, Lyme disease, syphilis and TB. (c) Post vaccination—ADEM ( (d) Radiation-induced. 2. Optic perineuritis—idiopathic, SLE, sarcoid, Wegener’s, infective. Characterized by thickening of the ONS (‘doughnut’ sign) in the intraorbital segment with surrounding fat stranding and less/no abnormal signal in the optic nerve (cf. optic neuritis). 3. Ischaemic optic neuropathy. (a) Anterior (AION)—intraocular segment/optic nerve head; associated with papilloedema, suggested by flattening or bulging of the optic nerve head on MRI. Imaging generally not indicated. (i) Arteritic—due to giant cell/temporal arteritis. >70 years, history of jaw claudication and polymyalgia rheumatica. Greater risk of bilateral involvement. Temporal artery wall thickening + periarterial enhancing fat stranding. (ii) Non-arteritic—associated with vascular risk factors (hypertension, diabetes mellitus, smoking), >50 years, no optic nerve enhancement. (b) Posterior (PION)—all segments of optic nerve posterior to intraocular. No papilloedema. Watershed ischaemia due to hypoxia and/or hypovolaemia. Intracanalicular segment most severely affected due to optic nerve swelling and compartment syndrome within bony canal. 4. Traumatic. (a) Direct—direct nerve disruption, e.g. penetrating injury or fracture fragment (especially in the optic canal). (b) Indirect—transmitted forces cause shear stress on the nerve. The intracanalicular segment is most susceptible as the ONS at this point is tightly adherent to the periosteum of the optic canal. 5. Neoplastic. (a) Optic nerve glioma—rare, typically in children, often with NF1. Intraorbital segment most commonly involved and expanded with central isointense (to WM) signal + perineural high signal due to arachnoidal gliomatosis. Variable enhancement; may extend to optic chiasm ± hypothalamus. (b) Optic nerve sheath meningioma—‘tram-track’ sign: avidly enhancing mass surrounding a nonenhancing optic nerve, ± calcification ± adjacent bony hyperostosis. Adults > children, associated with NF2. (c) Leukaemia/lymphoma*—optic nerve and ONS are important review areas for potential CNS deposits. 6. Extrinsic compression—from adjacent lesion in the orbit, orbital apex, optic canal or suprasellar cistern

Answer 60

1. Pineal cyst—common incidental finding, well-defined CSF intensity unilocular cyst, often slightly T1 hyperintense with incomplete FLAIR suppression ± slight rim enhancement. Rarely haemorrhagic. 2. Pineal germ cell tumours—all tend to ‘engulf’ normal pineal calcification; associated with CSF seeding. (a) Germinoma (85%)—children and young adults; homogeneous hyperdense enhancing mass. Presence of pineal calcification in children is suspicious. (b) Others—e.g. mixed (commonest), teratoma (fat, calcification and cysts), embryonal carcinoma, choriocarcinoma and yolk sac tumour. All heterogeneously enhancing. Elevated αFP and/ or ß-hCG, depending on type. 3. Pineal parenchymal tumours—tend to disperse (‘explode’) pineal calcification. (a) Pineocytoma—typically adults; well-defined noninvasive enhancing mass. May be entirely cystic mimicking a benign pineal cyst; any nodular enhancement is suggestive. (b) Pineoblastoma—typically children; large, aggressive, locally invasive mass with CSF seeding. Hyperdense on CT (hypercellular), heterogeneous signal with restricted diffusion on MRI. Associated with retinoblastoma.

Answer 61

1. Pineal cyst—see earlier. Located below internal cerebral veins. 2. Cavum velum interpositum (CVI)—enlarged CSF space behind the foramen of Monro, beneath the columns of the fornices and above the internal cerebral veins (cf. pineal cyst). 3. Cyst of the velum interpositum—when the CVI is >1 cm in axial dimensions with convex bowed margins and mass effect

Answer 62

1. Tectal glioma—low grade astrocytoma in childhood, expands tectal plate and causes hydrocephalus. 2. Infarct—prominent restricted diffusion. 3. Metastasis—heterogeneous enhancement + vasogenic oedema. 4. Demyelination—NMO

Answer 63

1. Vein of Galen malformation—presents in neonatal period with high output cardiac failure; dilated median prosencephalic vein, which appears as a large midline posterior vessel. 2. Internal cerebral vein thrombosis—hyperdense vein, loss of normal flow void on MRI, surrounding oedema/infarct ± haemorrhage. Other 1. Meningioma—displaces pineal calcification rather than engulfing or dispersing it. Homogeneous enhancement ± calcification.

Answer 64

1. Xanthogranuloma—degenerative cyst common in elderly. May be hyperintense on T1, FLAIR and DWI due to protein, lipid and blood products. 2. Cyst—CSF signal. 3. Papilloma—lobulated, frond-like avidly enhancing intraventricular mass with hydrocephalus (either obstructive or due to CSF overproduction). 4. Carcinoma—young children; variable-appearing lesion with heterogeneous enhancement, necrosis, calcification and local parenchymal invasion. 5. Metastasis—renal, melanoma, breast, lymphoma. Local invasion ±additional parenchymal/dural metastases

Answer 65

1. Central neurocytoma—young adults. In lateral ventricle, arises from septum pellucidum near foramen of Monro. Hyperdense, calcified and T2 bright bubbly mass with heterogeneous enhancement. 2. Meningioma—usually lateral ventricle. Avidly enhancing mass ± calcification. 3. Ependymoma—rare in adults; see Section 13.11. 4. Subependymoma—elderly, fourth ventricle; see Section 13.11. 5. Subependymal giant cell astrocytoma—young patient with tuberous sclerosis; see Section 13.6. 6. CNS lymphoma*—periventricular hypercellular mass with homogeneous enhancement and restricted diffusion.

Answer 66

1. Colloid cyst—anterior roof of third ventricle. Well-defined nonenhancing cyst, hyperdense on CT. More likely to be symptomatic if >1 cm. 2. Ependymal cyst—often CSF intensity with mass effect. 3. Neurocysticercosis—in ventricles or parenchyma; see Part 2

Answer 67

1. Intraventricular haemorrhage—haematomas can form solid casts of the ventricles. 2. Epidermoid—CSF-like signal intensity on MRI except for restricted diffusion and incomplete suppression on FLAIR. 3. Cavernous malformation—rare; T2 hyperintense, mildly T1 hyperintense globular lesion with blood degradation products on SWI/T2* imaging

Answer 68

1. Vestibular schwannoma—ovoid, intracanalicular, heterogeneous T2 bright mass with avid enhancement. Small lesions solid, larger lesions may be cystic and haemorrhagic. Expands internal auditory meatus. Bilateral schwannomas diagnostic for NF2. 2. Meningioma—solid uniformly enhancing mass ± calcification and dural tail. 3. Epidermoid—CSF signal on T1 and T2, incomplete suppression on FLAIR + restricted diffusion. Multilobular lesion, no enhancement. 4. Ependymoma—usually plastic-like extension from fourth ventricle, but can be purely in CPA; see Section 13.11. 5. Arachnoid cyst—isointense to CSF on all sequences. 6. Vascular. (a) Aneurysm—variable signal depending on degree of thrombosis. (b) Ectasia—tortuous, dilated vascular flow void. 7. Other schwannomas. (a) Trigeminal—enhancing lesion in Meckel’s cave extending into CPA. (b) Facial—same location as vestibular schwannoma, along the path of CN VII. 8. Lipoma—isointense to fat; may encase facial nerve. 9. Dural/leptomeningeal metastasis.Skull and brain 425 13 10. Granuloma—dural sarcoid, TB, and Wegener’s. 11. Neurenteric cyst—usually prepontine, lobular mass. Slightly denser than CSF, variable signal (proteinaceous material). No enhancement or restricted diffusion. 12. Paraganglioma—hypervascular mass extending from jugular foramen with erosive changes in skull base on CT and MRI. Flow voids and foci of blood degradation products give ‘salt and pepper’ appearance on MRI

Answer 69

1. Cortical ischaemia/infarction—cortical high T2 signal and restricted diffusion, caused by arterial occlusions or hypoxic/ hypotensive episodes (watershed areas). 2. Encephalitis. (a) HSV—mesial temporal lobes ± insula and lateral temporal lobe involvement, haemorrhage common (cf. autoimmune). Fever and rapid course. (b) Autoimmune—mesial temporal lobes + basal ganglia involvement, haemorrhage rare (cf. HSV). Subacute to gradual onset. (c) Paraneoplastic—indolent onset, other features of malignancy. 3. Encephalopathy—drugs, toxic, metabolic and vasculopathic. Multifocal cortical T2 hyperintensities ± restricted diffusion. Includes hypoglycaemia, PRES and hypertensive encephalopathy. 4. Post ictal/status epilepticus—GM or subcortical WM signal change ± restricted diffusion. Rapid onset and quick resolution of imaging findings. 5. Cortical contusion—blood degradation products. Typically in orbitofrontal and anterior temporal regions. 6. Cortical-based tumour—look for mass effect; see Section 13.10. 7. Cortical malformations—e.g. focal cortical dysplasia, cortical tubers; see Section 13.10. 8. CJD—gyriform cortical T2 hyperintensity and persistent restricted diffusion. vCJD is also associated with bithalamic abnormal signal (‘pulvinar’ and ‘hockey stick’ sign).

Answer 70

1. Subarachnoid haemorrhage—hyperdense blood on CT, SWI signal dropout. 2. Ruptured dermoid—fat droplets, high T1 signal.

Answer 71

1. Bacterial meningitis—leptomeningeal enhancement, purulent exudate also shows restricted diffusion; check for ventriculitis. 2. Aseptic meningitis—sarcoid, Wegener’s and rheumatoid arthritis. 3. Leptomeningeal carcinomatosis. (a) Primary CNS—glioblastoma, medulloblastoma, ependymoma. (b) Metastatic—breast, lung, melanoma, lymphoma, leukaemia. 4. Meningeal melanomatosis—rare primary melanocytic tumour of the CNS, associated with cutaneous melanocytic lesions and hydrocephalus; hyperdense leptomeninges with high T1 signal.

Answer 72

1. Thrombosis of cortical veins—hyperdense vein and loss of flow void + local cerebral swelling from venous congestion. 2. Dilated leptomeningeal perforators—Moyamoya 3. Slow flow in sulcal arteries—secondary to stenoses/occlusions

Answer 73

1. Hyperoxygenation. 2. CSF flow and pulsation artefact. 3. Recent gadolinium administration—especially if there is adjacent pathology causing breakdown of the blood-brain barrier

Answer 74

1. Fat—e.g. lipid-laden macrophages in cortical laminar necrosis, fat-containing lesions . 2. Methaemoglobin—subacute haemorrhage, thrombus and cavernoma. 3. Proteinaceous material—colloid cyst, posterior pituitary (normal), mucinous adenocarcinoma metastases, Rathke’s cleft cyst and craniopharyngioma. 4. Gadolinium enhancement—look for normal mucosal and vascular enhancement. 5. Melanin—melanoma metastases, meningeal melanomatosis. 6. Minerals—manganese (hepatic encephalopathy), copper (Wilson’s), iron (NBIA). 7. Calcification—only with diamagnetic calcium salts especially in Fahr disease. 8. Flow artefact—CSF or slow vascular flow.

Answer 75

1. Turbulent/rapid flow—vessels, aneurysms, CSF flow. Absent normal vascular flow voids may reflect thrombosis or stenosis. 2. Air—paranasal sinuses, mastoid air cells and pneumocephalus. 3. Cortical bone. 4. Metallic prosthesis. 5. Haemoglobin breakdown products—see following table. 6. Proteinaceous material—colloid cyst, Rathke’s cleft cyst, sinus secretions. T2 signal reduces with increasing protein concentration. 7. Highly cellular lesions—medulloblastoma, lymphoma, high grade gliomas. 8. Minerals—calcium, copper and iron deposition. 9. Melanin—melanoma metastases, meningeal melanomatosis. 10. Fungal hyphae—invasive fungal sinusitis. 11. Gadolinium—causes T2 relaxation. Applied in dynamic susceptibility contrast enhanced perfusion imaging.

Answer 76

1. Hypoxic-ischaemic (a) Acute cerebral infarction—variable distribution: vascular territorial, watershed and lacunar patterns. Causes: thrombotic, embolic or vasculitic. (b) Hypoxic ischaemic injury—due to global hypoperfusion or hypoxia, e.g. cardiac arrest and drowning. Watershed and DGM infarcts. 2. Post ictal—cortex and hippocampi. 3. PRES—parietooccipital and superior frontal gyri. 4. Encephalitis/cerebritis 5. DAI—GWMJ, splenium and middle cerebellar peduncles + microhaemorrhages. 6. Hypoglycaemia—bioccipital and splenium. 7. CJD—insula and pulvinar (largest nucleus of thalamus - pulvinar sign - Fabry) 8. MR artefact—due to susceptibility artefact; affects cortex close to skull, paranasal sinuses and mastoid air cells.

Answer 77

1. Infection. (a) Abscess—ring-enhancing, ‘dual rim’ sign on SWI and T2 (hypointense outer rim and hyperintense inner rim). (b) Empyema—extraaxial collection + rim enhancement. (c) Ventriculitis—pus dependent in ventricles (occipital horns). 2. Hypercellular neoplasms. (a) Lymphoma*—periventricular, homogeneous enhancement. (b) Medulloblastoma—fourth ventricle/cerebellum, in children. (c) Germinoma—children/young adults. Avid enhancement, midline. (d) Glioblastoma—high grade components show restricted diffusion. 3. Acute demyelination—active lesions only; restricted diffusion typically conforms to the incomplete ring enhancement. 4. Epidermoid—lobular, insinuating cisternal lesion. Restricted diffusion is the main feature differentiating this from arachnoid cyst. 5. Mucoid degeneration—e.g. choroid plexus cyst, Rathke’s cleft cyst. 6. Haemorrhage/haematoma—blood degradation products induce signal changes on DWI due to susceptibility effect. 7. Osmotic myelinolysis—central pons.

Answer 78

1. Lipoma—interhemispheric fissure (± callosal dysgenesis) > suprasellar > pineal region > CPA. 2. Dermoid cyst—midline fatty mass with chemical shift artefact ± calcification. Can rupture causing chemical meningitis. 3. Teratoma—midline multiloculated cystic mass with fat, soft-tissue and calcified components. 4. Postsurgical fat plugs—e.g. following pituitary surgery. 5. White epidermoids—rare variant containing triglycerides causing T1 hyperintensity (normally CSF signal). Restricts diffusion (cf. dermoid). 6. Lipomatous degeneration of tumours—rare, has been reported in meningiomas and small round blue cell tumours, e.g. medulloblastoma

Answer 79

1. Mega cisterna magna—enlarged retrocerebellar CSF space communicating with fourth ventricle and basal CSF spaces. Normal vermis, cerebellum and fourth ventricle. 2. Dandy-Walker spectrum—variable hypoplasia of vermis, cystic dilatation of fourth ventricle (displacing cerebellar hemispheres anterolaterally) ± enlarged posterior fossa with torcula-lambdoid inversion (torcula above lambdoid suture). If all features are present, it is termed a Dandy-Walker malformation. 3. Blake’s pouch cyst—posterior diverticulum of the fourth ventricle due to failed opening of the foramen of Magendie in utero, resulting in hydrocephalus of all four ventricles. Cyst communicates with fourth ventricle but not with cisterna magna. Vermis is of normal size but is displaced superiorly. 4. Arachnoid cyst—CSF signal + mass effect on vermis, which is of normal size. Hydrocephalus is rare. 5. Epidermoid cyst—restricted diffusion and incomplete suppression on FLAIR. 6. Pilocytic astrocytoma—in children; cystic cerebellar mass + enhancing mural nodule and walls. 7. Cerebellar hemangioblastoma—in adults; cystic cerebellar mass + enhancing mural nodule, but no wall enhancement. Surrounding abnormal vessels. 8. Trapped fourth ventricle—secondary to haemorrhage or ventriculitis. Typically noted after persistent fourth ventricular dilatation despite successful shunting of lateral ventricles. Associated with diplopia and ataxia 9. Neuroglial/neurenteric cyst—CSF signal parenchymal cyst. No enhancement or restricted diffusion. 10. Neurocysticercosis—most commonly in fourth ventricle; can cause obstructive hydrocephalus (see Part 2).

Answer 80

1. Normal ageing—0.5% total brain volume loss per year is normal, >1.0% is likely abnormal. 2. Cerebrovascular disease—background of small-vessel disease 3. Drugs. (a) Alcohol—additional cerebellar vermian atrophy. (b) Steroids—short use: transient reduced volume, which recovers. Chronic use: irreversible volume loss. 4. Postinflammatory—MS and other inflammatory WM diseases; lesions with WM volume loss and variable cavitation related to chronic lesions. 5. Posttraumatic—if severe and especially if widespread DAI. 6. Whole brain radiotherapy—can also be regional if radiotherapy is confined; ± coexistent radiotherapy-induced meningiomas and cavernomas 7. HIV encephalopathy—diffuse symmetric periventricular abnormal WM signal and volume loss.

Answer 81

1. Postinfarction—wedge-shaped cortical and subcortical volume loss, limited to vascular territory. 2. Posttraumatic—contusion or haematom in typical locations (orbitofrontal and anterior temporal regions). 3. Postinfective—encephalitis and meningitis

Answer 82

1. Alzheimer’s disease. (a) Classical—old age onset (70–80s), memory impairment with hippocampal and temporoparietal atrophy. (b) Posterior cortical atrophy—usually younger age onset (50–60s). Visual agnosia and apraxia with occipitoparietal volume loss. 2. Parkinson disease—tremor, rigidity, bradykinesia ± dementia. NB: in dementia with Lewy bodies, cognitive decline and visual hallucinations precede parkinsonism. Generalized cerebral atrophy and atrophy of substantia nigra with relative sparing of hippocampi. Increased putaminal iron (reduced T2 signal). Loss of normal ‘swallowtail’ appearance of substantia nigra on SWI. 3. Frontotemporal lobar degeneration—inappropriate behaviour and apathy with frontotemporal atrophy. 4. Progressive supranuclear palsy—reduced cognition, supranuclear vertical gaze palsy. Reduced area of midbrain relative to pons in sagittal plane. Midbrain has ‘mickey mouse’ appearance on axial and ‘hummingbird’ sign on sagittal imaging (the latter is subjective and of limited utility). 5. Corticobasal degeneration—apraxia and dystonia. Asymmetric atrophy of superior parietal lobules and paracentral gyri. 6. MSA-P—reduced putamen volume with reduced T2 signal relative to GP. High T2 rim surrounding putamen (‘putaminal rim sign’). 7. Huntington’s disease—autosomal dominant, progressive choreoathetoid movements with atrophy of caudate heads. 8. Post encephalitis—chronic volume loss in regions affected, e.g. mesial temporal lobes in both HSV and autoimmune limbic encephalitis.

Answer 83

. Normal ageing. 2. Chronic alcoholism. 3. Drugs—phenytoin, chemotherapy, lithium, benzodiazepines. 4. Chronic vertebrobasilar ischaemia/insufficiency—posterior circulation steno-occlusive disease with multiple infarcts. 5. Chronic temporal lobe epilepsy—independent of antiseizure medication. 6. Cerebellitis—in children, post infection/vaccination. Acute: generalized cerebellar swelling with cortical T2 hyperintensity + obstructive hydrocephalus. Chronic: generalized cerebellar volume loss. 7. MSA-C—‘hot cross bun’ sign in pons; see Section 13.26. 8. Olivopontocerebellar atrophy—atrophy of olivary nuclei and cerebellar peduncles, associated with MSA-C. 9. Superficial siderosis—recurrent SAH with haemosiderin depositions associated with deafness and ataxia. Susceptibilityrelated signal dropout lining cerebellar folia, best seen on SWI. 10. Post radiation therapy.432 Aids to Radiological Differential Diagnosis 11. Inherited ataxias. (a) Friedreich ataxia—AR, adolescent onset. Dorsal cervical cord volume loss + hypertrophic cardiomyopathy. (b) Ataxia telangiectasia—AR; multiple telangiectasia, ataxia and lung infections. Vermian volume loss and cerebral WM T2 hyperintensities. (c) Spinocerebellar ataxia syndromes—wide range of inherited syndromes characterized by atrophy of the spinal cord and cerebellum. 12. Paraneoplastic cerebellar degeneration—lung, breast and ovarian cancer. 13. Gluten ataxia—gluten sensitivity, improves with gluten-free diet. 14. Crossed cerebellar diaschisis—unilateral, due to contralateral supratentorial gliosis

Answer 84

1. Radiotherapy. 2. Inflammatory. (a) MS—midbrain/pons > medulla. (b) NMO—medulla > midbrain/pons. (c) Behçet’s*—oedematous lesions + perivascular enhancement. 3. Wallerian degeneration—atrophy and signal change downstream of a supratentorial lesion (e.g. infarct, haemorrhage, demyelination). Diffuse or focal depending on extent of insult. 4. Infectious rhombencephalitis—encephalitis of the hindbrain (brainstem and cerebellum), e.g. by Listeria or enterovirus. Acute: swollen with enhancing WM lesions and cranial nerve enhancement. Chronic: generalized volume loss. 5. Infarction. 6. Spinocerebellar ataxia—see Section 13.43. 7. Inherited leukoencephalopathies—rare, child/young adult onset

Answer 85

1. Midbrain—progressive supranuclear palsy, Wilson’s disease. 2. Pons—MSA-C. 3. Medulla—hypertrophic olivary degeneration (late feature), adult onset Alexander’s disease

Answer 86

1. Parietal foramina—usually bilateral and symmetrical, anterior to lambdoid suture. If enlarged (>5 mm) then may be linked to genetic syndromes and other intracranial anomalies. 2. Normal ageing calvarium. 3. Fontanelle—anterior (closes <18 months), posterior (closes <3 months), anterolateral ×2, posterolateral ×2

Answer 87

1. Myeloma—multiple lytic lesions (pepper pot skull); can involve mandible (where metastases are very rare). 2. Metastases—e.g. lung, breast, renal, thyroid and leukaemia. 3. Paget’s sarcoma—osteosarcoma, chondrosarcoma, fibrosarcoma. Lytic, blastic or mixed lesion with cortical destruction and soft-tissue component on a background of Paget’s disease. Usually little/no periosteal reaction; suspect in an area of Paget’s that has undergone rapid change on serial imaging

Answer 88

1. Metastases—neuroblastoma, leukaemia and sarcoma. 2. Langerhans cell histiocytosis*—especially parietal bone; may be an isolated well-defined lesion with a beveled edge due to unequal involvement of inner and outer tables (also known as eosinophilic granuloma), or multiple coalescent lesions with a geographic appearance (LCH). May contain central sequestrum of residual bone. Enhances avidly

Answer 89

1. Fracture—easy to mistake for normal suture. If involving suture, check for diastasis. 2. Leptomeningeal cyst—also known as growing fracture. Skull fracture with trapped meninges; CSF pulsation causes progressive widening and scalloping. Usually in young children. 3. Burr hole—typically a perfect circle, often frontal or parietal location, ± evidence of gliosis in the subjacent brain parenchyma.

Answer 90

1. Osteoporosis—generalized reduced bone density most appreciable on CT. Vertebral insufficiency fractures common. 2. Hyperparathyroidism*—multiple foci of lucency and sclerosis (‘salt and pepper’ skull) ± a discrete brown tumour: expansile lytic lesion, which causes cortical thinning without cortical destruction or periosteal reaction, ± fluid-fluid levels on MRI.

Answer 91

1. Acute pyogenic osteomyelitis—from sinusitis (frontal bones), mastoiditis (temporal bones), penetrating head trauma or postsurgical. Look for cortical breach of the inner table to suggest intracranial involvement. Complications: intracranial empyema, abscess, meningitis, cerebritis, venous thrombophlebitis (especially with mastoiditis extending into sigmoid sinus). 2. TB*—rare, punched-out lesion with sequestrum + an overlying soft-tissue component. 3. Hydatid cyst—expansile loculated lesion centered in the diploic space. 4. Syphilis*—moth-eaten appearance.

Answer 92

1. Haemangioma—expansile lesion with ‘sunburst’ pattern of radiating spicules, avid enhancement. 2. Sinus pericranii—congenital, traumatic or spontaneous venous malformation of the scalp characterized by an abnormally enlarged skull emissary vein, which connects the dural venous sinuses and extracranial veins. Soft tissue mass + an underlying serpiginous vascular channel in the skull

Answer 93

1. Osteoporosis circumscripta—lytic phase of Paget’s disease; usually a large, well-defined lytic lesion most commonly in the inferior frontal or occipital bones (rarer at vertex); can cross sutures, ± separate regions of sclerosis reflecting later stage of Paget’s. 2. Neurofibroma—can be secondary to both mesodermal dysplasia and skull erosion by an adjacent neurofibroma. 3. Intradiploic arachnoid cyst—very rare, CSF density/signal.

Answer 94

1. Venous channels—transcalvarial serpiginous channels containing emissary veins connecting venous sinuses to extracranial veins. 2. Venous lakes—enlarged veins with a round or ovoid morphology, avid enhancement post contrast. Often connect to venous channels.Skull and brain 435 13 3. Arachnoid granulations—arachnoid projections into skull; round, well-defined lucencies often in region of venous sinuses with disruption of inner table. CSF signal on MRI. Generally a normal variant but if multiple consider chronically raised ICP

Answer 95

1. Epidermoid—intradiploic rare; well-defined, scalloped margins, similar to CSF on T1/T2 but with restricted diffusion and incomplete FLAIR suppression. 2. Meningocoele/encephalocoele—protrusion of meninges ± brain through skull defect. Can be congenital, following trauma/surgery or related to chronically raised ICP.

Answer 96

1. Langerhans cell histiocytosis*—in healing phase; | 2. Treated lytic metastasis

Answer 97

1. Chronic osteomyelitis—staphylococci, pseudomonas and fungal. Same locations and risks as acute osteomyelitis (see Section 13.45). Greater association with soft-tissue masses and dural thickening. 2. Frontal sinus mucocoele—completely opacified and expanded frontal sinus containing mucus with variable signal due to protein content. Thinning of sinus walls with variable resorption. Others 1. Fibrous dysplasia—variable appearance, commonly exhibits a ground-glass matrix but can be an entirely lytic, expanded, well-defined lesion with preserved overlying bone. Monostotic > polyostotic.

Answer 98

1. Paget’s disease*—in the elderly. Multiple islands of dense bone, loss of clarity of inner and outer tables, thickened skull vault, ± basilar impression. 2. Sclerotic metastases—breast (especially post treatment), prostate. 3. Fibrous dysplasia—younger age group than Paget’s; see Section 13.46. 4. Myelofibrosis—diffuse sclerosis without architectural distortion. Associated with extramedullary haematopoiesis, intracranially this may be indicated by dural thickening. 5. Renal osteodystrophy*—osteosclerosis in 25%; mimics Paget’s.436 Aids to Radiological Differential Diagnosis 6. Acromegaly*—enlarged frontal sinuses, prognathism and thickened skull vault, ± an enlarged sella due to the underlying pituitary adenoma. 7. Chronic haemolytic anaemias—expansion of medullary spaces due to red marrow hyperplasia causing ‘hair-on-end’ appearance (see Section 13.51); variable sclerosis also related to hyperplastic red marrow (as opposed to bone infarcts). 8. Sclerosing bone dysplasia. (a) Osteopetrosis—infantile (AR) and adult (AD) forms. Infantile form more severe with life expectancy <10 years. Diffusely sclerotic and thickened skeleton with fractures. Associated with narrowing of skull foramina with compression of traversing CNs and vessels. Orbital crowding + proptosis. Poorly pneumatized paranasal sinuses. (b) Pyknodysostosis—especially skull base; multiple wormian bones, wide sutures from delayed closure, frontoparietal bossing. (c) Craniometaphyseal dysplasia—diffusely thickened skull with compromise of foramina (like osteopetrosis), flared metaphyses in long bones. 9. Prolonged phenytoin treatment—skull thickening and osteosclerosis + cerebellar volume loss (see Section 13.43). 10. Fluorosis—due to excessive fluoride ingestion. Osteosclerosis and ossification of tendons/ligaments

Answer 99

1. Hyperostosis frontalis interna—older females; benign symmetrical overgrowth of the inner table of the frontal bone, often lobulated. Can involve other skull bones and be diffuse. 2. Tumour. (a) Sclerotic metastasis—prostate (men), breast (women) and neuroblastoma (children). (b) Osteoma—benign well-defined bone lesion. Two main types: ivory (homogeneously very dense) and mature (has central marrow). Also commonly seen in paranasal sinuses (associated with Gardner syndrome). (c) Treated lytic metastasis. (d) Treated brown tumour of hyperparathyroidism*. 3. Paget’s disease*—see Section 13.45. 4. Fibrous dysplasia—see Section 13.46. 5. Depressed fracture—abrupt cortical irregularity and depression

Answer 100

1. Meningioma—hyperostosis of adjacent bone is common and usually reactive, though occasionally associated with osseous invasion (look for abnormal enhancement extending into the skull). 2. Calcified cephalohaematoma—infants with history of traumatic birth. Well-defined peripherally calcified crescentic lesion overlying outer table of skull. 3. Calcified epidermoid cyst—usually still contains more typical cystic components (

Answer 101

1. Normal variant. 2. Prolonged phenytoin treatment. 3. Acromegaly*. 4. Chronic haemolytic anaemia—see Section 13.51. 5. Microcephaly. 6. Shunted hydrocephalus—secondary to chronic low ICP

Answer 102

1. Normal variant—including hyperostosis frontalis interna. 2. Paget’s disease*. 3. Fibrous dysplasia. 4. Meningioma—due to reactive hyperostosis or osseous invasion. 5. Osteoma. 6. Sclerotic metastasis—prostate

Answer 103

1. Hyperparathyroidism*—see Section 13.45. 2. Chronically raised intracranial pressure—other signs of raised ICP, e.g. ‘empty sella’, multiple arachnoid herniations, hydrocephalus. May produce a ‘copper-beaten skull’ appearance. 3. Osteogenesis imperfecta—associated with wormian bones. Characteristic features: osteoporosis, fractures, blue sclera, dental fragility and hearing impairment. 4. Rickets*—frontal bossing, delayed fusion of cranial sutures and closure of fontanelles. 5. Hypophosphatasia—rare metabolic deficiency of alkaline phosphatase, variable severity and age of presentation. Generalized osteoporosis and premature fusion of cranial sutures. 6. Lacunar skull—bone dysplasia of membranous skull, associated with Chiari 2 malformation. Indentations or pits in frontal and parietal regions that may be full-thickness; defects separated by thin rims of bone; usually resolves by 6 months. Not associated with raised ICP

Answer 104

1. Normal variant. 2. Osteoporosis circumscripta—see Section 13.45. 3. Large intracranial cyst—arachnoid, porencephalic. Causes bony remodelling with smooth, scalloped thinning of the adjacent skull. 4. Slow-growing tumour in cerebral cortex—DNET, ganglioglioma. Also associated with gradual bony remodelling

Answer 105

1. Thalassaemia*—marrow hyperplasia more marked in this than other anaemias. 2. Sickle cell anaemia—initially in frontal region but can involve the whole skull where diploic space (marrow cavity) is present, i.e. above level of internal occipital protuberance. 3. Hereditary spherocytosis and elliptocytosis. 4. Pyruvate kinase deficiency. 5. Glucose-6-phosphate dehydrogenase deficiency

Answer 106

1. Cyanotic heart disease. | 2. Severe childhood iron deficiency anaemia

Answer 107

1. Haemangioma*—‘sunburst’ spicules; see Section 13.45. 2. Meningioma—more suggestive of skull invasion rather than reactive thickening; look for abnormal skull enhancement to support this. Also seen in primary intraosseous meningioma (see Section 13.54). 3. Metastases.

Answer 108

1. Achondroplasia*—rhizomelic dwarfism. 2. Chiari malformations. (a) Chiari 1—peg-shaped cerebellar tonsils extending >5 mm below FM (excluding those caused by raised ICP) ± syrinx ± hydrocephalus. (b) Chiari 2—medulla, fourth ventricle and cerebellar vermis displaced through FM; small posterior fossa, beaked tectum. Nearly always associated with a lumbar myelomeningocoele. (c) Chiari 3—like Chiari 2 but with occipital encephalocoele. 3. Osteogenesis imperfecta—wormian bones

Answer 109

1. Rheumatoid arthritis*—ligamentous softening, erosion of dens and atlantoaxial subluxation. 2. Paget’s—bone softening (see Section 13.45). 3. Osteomalacia—bone softening. 4. Hyperparathyroidism*—bone softening. 5. Localized bone destruction—lytic metastases and destructive infection (e

Answer 110

1. Normal variant. 2. Optic chiasm glioma—if chiasmatic sulcus very depressed (W- or omega-shaped sella), glioma may be bilateral. 3. Neurofibromatosis*. 4. Achondroplasia*. 5. Mucopolysaccharidoses*. 6. Chronic hydrocephalus—enlarged anterior aspect of third ventricle causes remodelling of sella.

Answer 111

1. Epidermal inclusion cyst—also known as ‘sebaceous’ cyst (misnomer as they do not arise from sebaceous glands). Well-defined, usually of homogeneous fluid density on CT ± calcification. Commonly seen on the scalp, face and neck. If multiple, consider Gardner syndrome. 2. Trichilemmal cyst—also known as pilar cyst, originates from hair follicle so common on the scalp. Similar in appearance to epidermal inclusion cyst but calcifies more frequently. 3. Skin tags—pedunculated mass arising from skin; normal subcutaneous layer. 4. Carcinoma—squamous and basal cell, melanoma. Infiltrating, ulcerating soft-tissue mass with variable enhancement. Gorlin-Goltz syndrome: multiple BCCs and odontogenic keratocysts. 5. Skin calcification—associated with acne

Answer 112

1. Lipoma—encapsulated fatty mass, often does not contact skin. If internal soft-tissue component, multiple septations or large (>5 cm) then consider liposarcoma. 2. Haemangioma—early infancy, rapidly grow then involute before adolescence. High T2 signal, avid enhancement and intrinsic flow voids.

Answer 113

1. Subgaleal haematoma—post trauma in adults or children; crescentic haematoma beneath galeal aponeurosis but superficial to periosteum, not confined by cranial sutures. 2. Cephalohaematoma—following birth trauma; subperiosteal lentiform haematoma confined by cranial sutures. Parietal region most common. 3. Dermoid—most commonly midline, associated with sinus tracts. Fat density mass ± remodelling of underlying skull. 4. Plexiform neurofibroma—diagnostic of NF1. Thickening of the nerve sheath across multiple fascicles. Diffuse soft-tissue mass with a branching appearance. High T2 signal with central low signal (‘target’ sign). 10% undergo sarcomatous degeneration. 5. Cirsoid aneurysm—rare AVM of scalp usually fed by the superficial temporal artery

Answer 114

1. Osteoma—dense bone lesion projecting out from skull with no effect on diploic space.Skull and brain 441 13 2. Malignancy—metastasis (lytic or sclerotic), plasmacytoma (expansile and lytic), lymphoma (soft-tissue mass often on both sides of skull with relatively little bone destruction), sarcoma. 3. Pott’s puffy tumour—subperiosteal abscess from frontal bone osteomyelitis secondary to frontal sinusitis or trauma. Opacified frontal sinus with overlying subperiosteal collection and inflammatory stranding. 4. Haemangioma—frontal and parietal bones, outer table involved with sparing of inner table, high T1 and T2 signal + flow voids. 5. Intraosseous meningioma—expands inner and outer tables of skull, dural component not always present. 6. Intraosseous epidermoid—fluid density with variable calcification on CT, high T2 signal and characteristic restricted diffusion. 7. Encephalocoele—defect in the skull and dura with extracranial herniation of intracranial structures. Directly related to trauma/ surgery or secondary to chronic raised ICP. 8. Sinus pericranii—see Section 13.45. 9. Paget’s disease*—skull thickening with expansion of the diploic space and variable sclerosis and lysis

SKULL & BRAIN Flashcards

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