Neuroimaging

Question 1

What is the role of imaging in CNS infections?

Answer 1

Not diagnostic, but look for complications:
1) Abscess/empyema → drainage
2) ↑ICP/hydrocephalus → decompress + CANNOT LP

Question 2

How does a subdural abscess appear on CT?

Answer 2

Crescentic
- limited by dural reflections

Question 3

How does an epidural abscess appear on CT?

Answer 3

Biconvex
- contained by cranial sutures

Question 4

What is the most likely source of a supratentorial empyema?

Answer 4

Sinusitis

Question 5

What is the most common source of an infratentorial empyema?

Answer 5

Otomastoiditis

Question 6

How does an empyema present on a CT?

Answer 6

Extra-axial, iso-to hyperdense to CSF

Question 7

How does an empyema present on a MRI?

Answer 7

1) Restricted diffusion (DWI)
2) Marginal enhancement (T1+C)
3) Iso- to hyperintense to CSF (T2)
4) Hyperintense to CSF (FLAIR)
5) Enhance of adjacent brain parenchyma (cerebritis/abscess)
6) Leptomeningeal enhancement (meningitis)

Question 8

What are 8 causes of intracranial ring-enhancing lesions on CT?

Answer 8

MAGIC DR
Metastasis
Abscess
Glioblastoma
Infarct (subacute)
Contusion
Demyelinating disease
Radiation necrosis

Question 9

What is a “dual rim” sign?

Answer 9

Early cerebritis capsule
- Outer low-signal intensity rim
- Inner high-signal intensity rim
- VERY specific for abscess

Question 10

How are pyogenic abscess differentials differentiated?

Answer 10

1) Pyogenic
- smooth enchancement
- restricted diffusion
- double rim sign

2) Glioblastoma
- thick nodular enhancement
- haemorrhage

3) Metastasis
- Thick walled, centrally necrotic mass
- multiple, marked edema

4) Demyelinating disease
- incomplete ring enhacement

Question 11

How does ventriculitis/ependymitis appear on MRI?

Answer 11

Purulent material with dependent layering and restricted diffusion

Question 12

How does herpes simplex encephalitis appear on MRI?

Answer 12

1) Abnormal signal in limbic system with DWI restriction
2) Temporal lobes, insula, subfrontal area, cingulate gyri
3) Bilateral but asymmetric
4) Gyriform enhancement 1 week after initial symptoms

Question 13

What are 2 DDx of herpes simplex encephalitis?

Answer 13

1) Status epilepticus
- temporal lobe epilepsy hyperperfusion
- no haemorrhage

2) Limbic encephalitis
- 1° (often lung)
- bilateral
- no haemorrhage

Question 14

How is a MRI with abnormal signal in limbic system with DWI restriction in Temporal lobes, insula, subfrontal area, cingulate gyri confirmed to be herpes simplex encephalitis?

Answer 14

CSF PCR → start IV acyclovir immediately if suspected

Question 15

What are 3 CNS forms of TB infection?

Answer 15

1) Tuberculous meningitis (basal cisterns)
2) Tuberculoma (multiple round masses)
3) TB abscess (large, solitary)

Question 16

How does tuberculous meningitis present on MRI?

Answer 16

Marked meningeal enhancement with basilar prominence

Question 17

What are 3 complications of CNS tuberculomas?

Answer 17

1) Hydrocephalus
2) Acute infarcts (basal ganglia and internal capsule due to involvements of lenticulostriate arteries)
3) Cranial neuropathy (CN3, 4, 6)

Question 18

How does a tuberculous abscess present on MRI?

Answer 18

Mutliloculated ring enhancement

Question 19

How does a tuberculoma present on MRI?

Answer 19

Ring enhancement with necrotic core

Question 20

How does toxoplasmosis appear on MRI?

Answer 20

1) Ring nodular enhancement
2) Basal ganglia, corticomedullary junction, thalamus, cerebellum
3) Target sign
- enhancing nodule within enhancing rim

Question 21

What are the 4 pathological stages of cerebritis?

Answer 21

1) Early (1-2days)

2) Late (2-7 days)

3) Early capsule (5-14 days)

4) Late capsule (>2weeks)

Question 22

What are the 4 pathologic stages of neurocysticercosis?

Answer 22

1) Vesicular
- quiescent, cyst + scolex

2) Colloidal vesicular
- dying larva, intense inflammation + edema

3) Granular nodular
- healing, cyst involutes

4) Nodular calified
- healed, fibrocalcified, nodule
- no edema

Question 23

How does neurocysticercosis appear on MRI?

Answer 23

1) Cysts with “dot” inside (scolex)
2) Convexity subarachnoid spaces
3) Calcifications (late stage)

Question 24

How does cryptococcosis appear on MRI?

Answer 24

1) Dilated perivascular spaces
- mucoid material deposition
- no enhancement

2) Cryptococcoma
- ring-like/solid enhancement

Question 25

How does CMV encephalopathy appear on MRI?

Answer 25

1) 1/3 Migration disorders
a) Lissencephaly
b) Pachygyria
c) Polymicrogyria

2) Calcification
3) Anterior temporal cysts