Neuroradiology

Question 1

Features of T1

Answer 1

Basic properties:
Fat & myelin are bright (White matter is white; grey matter is grey)
Water is dark

Pathological brightness:
1) Paramagnetic substances
Subacute hematoma
Copper, calcium, iron, melanin (e.g., metastatic melanoma)
2) Fat (including myelin)
3) Some proteinaceous material

Pathological darkness:
1) Chronic, fluid-filled lesions (similar to CT scan)
2) Edema
3) demyelination
4) Chronic hematoma

Question 2

Features of T2

Answer 2

Basic features:
Fat is dark
Water is bright
Flow in vessels is dark

Pathological brightness:
1) Any type of edema:
Cytotoxic edema of ischemic stroke
Vasogenic edema (metastases, abscess, inflammation)
Interstitial edema due to hydrocephalus
2) Demyelination, axonal loss
3) Hyperacute hematoma, or late subacute hematoma.
4) Subacute to chronic infarcts

Pathological darkness
Fat; protein-rich masses.
Paramagnetic substances (iron, copper, melanin, calcium)
Acute hematoma or early-subacute hematoma
Air

Question 3

Notable causes of bright signal on DWI

Answer 3

1) Acute ischemic stroke (the ischemic core of the stroke is bright on DWI)
2) Thick purulent material (within an abscess or subdural empyema). This helps differentiate abscesses from necrotic tumors (which do not show diffusion restriction)
3) Hematoma that is either hyperacute or late-subacute (similar to the appearance of hematoma on T2 sequences)
4) Seizure-related cortical restriction
5) Hypoxic-ischemic injury
6) Tumefactive necrosis
7) Lymphoma, or high-grade glioma
8) Creutzfeldt-Jakob disease
9) Epidermal cysts

Question 4

Usefulness of ADC

Answer 4

because there is a component of the image derived from T2 signal, some tissues that are bright on T2 will appear bright on DWI images without there being an abnormal restricted diffusion.

This phenomenon is known as T2 shine through.

Apparent diffusion coefficient maps (ADC) are images representing the actual diffusion values of the tissue without T2 effects.

Question 5

Can DWI discriminate vasogenic from cytotoxic edema

Answer 5

DWI images must always be compared to the T2 and ADC images
If the bright signal is similar in DWI and T2 sequences, then this doesn’t necessarily represent cytotoxic edema (but instead it could reflect vasogenic edema present on the T2 image, aka “T2 shine-through”)
If a bright signal is present on DWI that isn’t as prominent on T2, then this indicates cytotoxic edema (true diffusion restriction)
ADC is even better at verifying the presence of cytotoxic edema

Question 6

GRE and SWI usefulnes

Answer 6

MRI sequences used to detect paramagnetic substances (blood, calcium, metals), which appear black.
These sequences are largely used to look for hemorrhage. All stages of hemorrhage appear dark (unlike T1 and T2 sequences, where the appearance of blood varies over time).

SWI is a more modern version of GRE, with greater sensitivity.

Question 7

Causes of excessive pachyminengitis

Answer 7

Question 8

Differential of ring -enhancing lesions

Answer 8

The differential for peripheral or ring enhancing cerebral lesions includes:

cerebral abscess
tuberculoma
neurocysticercosis
metastasis
glioblastoma
subacute infarct/hemorrhage/contusion
demyelination (incomplete ring)
tumefactive demyelinating lesion (incomplete ring)
radiation necrosis
postoperative change
lymphoma - in an immunocompromised patient
leukemia
thrombosed aneurysm
necrotizing leukoencephalopathy after methotrexate
Baló concentric sclerosis

Mnemonic DR MAGICAL

D: demyelinating disease (classically incomplete rim of enhancement)
R: radiation necrosis or resolving hematoma
M: metastasis
A: abscess
G: glioblastoma
I: infarct (subacute phase) or inflammatory (neurocysticercosis, tuberculoma)
C: contusion
A: AIDS-related CNS disease (e.g. toxoplasmosis, cryptococcosis)
L: lymphoma (this appearance is more common in immunocompromised)

Question 9

Difference between pachymeningitis and leptomeningitis

Answer 9

Pachymeningitis involves the dura-arachnoid
Leptomeningitis affects the pia and subarachnoid spaces

Question 10

Pulvinar sign

Answer 10

The pulvinar sign refers to bilateral FLAIR hyperintensities involving the pulvinar thalamic nuclei. It is classically described in variant Creutzfeldt-Jakob disease.
It is also described in other neurological conditions:

• Fabry disease: the hyperintense signal is seen on T1 rather than T2
• bilateral thalamic infarcts
• acute disseminated encephalomyelitis (ADEM)
• status epilepticus