3) CNS disorders, brain infection, tumours

Question 1

Pyogenic meningitis (CT, MRI)

Answer 1

• Bacterial infectious infiltration of meninges
• CT: usually normal in uncomplicated PM, but CT is useful for detecting complications such as hydrocephalus
• MRI: High SI, meningeal enhancement in C+

Question 2

Tuberculous meningitis (CT, MRI)

Answer 2

• CNS involvement is seen in 5% of TB cases
• CT: obliteration of basal cisterns by isodense or slightly hyperdense exudates. Multiple “ring” like appearance. Sometimes hydrocephalus
• MRI: more sensitive than CT for above signs

Question 3

Tuberculous granuloma/tuberculoma (CT, T1, T2, T1+con)

Answer 3

• Benign tumour
• CT: small rounded lesion which are isodense or hyperdense to brain, variable surrounding oedema, homogeneous enhancement in solid lesions, rim enhancement in lesions w/ central caseation or liquefaction
• MRI: Ring enhancement seen w/ caseation
  T1) low SI
  T2) high SI, low SI with caseation
  T1+gad) solid lesions have homogeneous enhancement

Question 4

Herpes encephalitis (CT, T2)

Answer 4

• Viral infection of brain tissue (usually glial cells)
• drowsiness, fever, chills, vomiting
• CT: normal in first 3-5 days, followed by low attenuation in ateromedial lobe
• MRI: T2) high SI w/ in the anteromedial lobe in first 2 days of onset

Question 5

Brain abscess (CT, T1, T2)

Answer 5

• Encapsulated accumulation of puss within brain resulting from cranial infection, penetrating head wound or infection spreading through blood stream
• fever, headache, nausea, vomiting
  Radiological features
• usually subcortical or periventricular
• Rim enhancing mass is non-specific finding
• CT: Central low attenuation puss. Following contrast, rim enhancement corresponds to abscess capsule
• T1: hypointense mass with isointense capsule (hyperintense capsule with contrast)
• T2: Hyperintensity in mass and surrounding oedema

Question 6

Multiple sclerosis (T1, T2, T1+con)

Answer 6

Radiological features
- MS lesions are located in subependymal periventricular white matter, typically ovoid lesions
- Dawson fingers are radiographic feature depicting demyelinating plaques
- MRI:
T1) isointense or hypointense plaque
T2) Hyperintense signal plaques
T1 + con) solid or ring enhancement of acute lesions

Question 7

Alzheimers disease (CT, MRI, T2)

Answer 7

CT: usually normal, sometimes cerebral atrophy and ventricular enlargement
MRI: similar to CT. Periventricular high intensity on T2

Question 8

Tumour classification

Answer 8

Intra-axial tumours

• tumours arising from within the brain parenchyma
• glioma: broad category which includes tumours that arise from astrocytes, oligodendrocytes, ependymal cells, mostly malignant

Extra-axial tumours

• Tumours arising from tissues covering brain
• more frequent in adults than children
• Meningioma: usually slow growing and benign

Question 9

Intra-axial and extra-axial differentiation

Answer 9

Extra-axial tumour

• meningioma often has a bone reaction
• grey/white matter junction preserved

Intra-axial tumour

• Rarely has bony changes
• grey/white matter junction destroyed

Question 10

Glioma/glioblastoma (T1, T2, CT)

Answer 10

• MRI
  T1) masses of low SI (or isointensity)
  T2) masses of high SI
  -CT: thick heterogeneous hyperdense margins, hypodense centre

Question 11

Meningioma (T1 & T2, T1 & T2 w/ con, CT)

Answer 11

• MRI
  T1 & T2) isointense
  T1 & T2 + con) hyperintense
• CT: rounded, well circumscribed, hyperdense