Imaging can

1. Help diagnose infection e.g., encephalitis, toxoplasmosis, TB
2. Differentiate abscess from tumour
3. Look for source of infection e.g., meningitis secondary to inner ear or mastoid infection
4. Look for complications: cerebral oedema, hydrocephalus, cerebral abscess, herniation
5. Screen patients for risk of brain herniation prior to lumbar puncture

Japanese encephalitis

hyperintense signal involving bilateral thalami, caudate nuclei, pons, midbrain, left occipital lobe and bilateral cerebellar hemispheres. Patchy focal areas of blooming seen in thalami and pons, suggestive of haemorrhage.

Meningitis

• In most patients, lumbar puncture followed by early initiation of antibiotics is essential

• CT of the brain (looking for abscess, hydrocephalus, cerebral oedema, haemorrhage, thrombosis, herniation) is recommended before LP in these patients:

  • Immunocompromised
  • History of CNS disease (e.g., mass lesion, stroke, or focal infection)
  • New onset seizure (within one week of presentation)
  • Papilloedema
  • GCS < 10
  • Focal neurological deficit

• Treatment should not be delayed while waiting for a CT. Unless contraindicated or an alternate diagnosis is found, an LP should be performed following CT in these patients

  

  Enlargement of the temporal horns indicating increased intracranial pressure (horizontal open large arrow). The closed arrowhead shows small intracerebral haemorrhage foci on the right temporal lobe, and the curved arrow shows the effect of increased intracranial pressure on the cerebellum

Brain Abscess

• May be visible on noncontrast CT as hypodense regions, occasionally with air within them.

  

• may be nonspecific, consider ddx of toxoplasmosis, mass with vasogenic oedema, central nervous system lymphoma depending on clinical scenario.