A. Primary CNS lymphoma – Explanation

This is a difficult question. Toxoplasmosis is the most common cause of brain lesions in HIV
patients. However, around 80% of toxoplasmosis cases involve multiple lesions and the history is
suggestive of lymphoma. Cerebral tuberculosis is much less common than lymphoma in HIV.
HIV: neurocomplications

Generalised neurological disease

Encephalitis

• may be due to CMV or HIV itself
• HSV encephalitis but is relatively rare in the context of HIV
• CT:oedematous brain

Cryptococcus

• most common fungal infection of CNS
• headache, fever, malaise, nausea/vomiting, seizures, focal neurological deficit
• CSF: high opening pressure, India ink test positive
• CT: meningeal enhancement, cerebral oedema

• meningitis is typical presentation but may occasionally cause a space occupying lesion

Progressive multifocal leukoencephalopathy (PML)

• widespread demyelination

• due to infection of oligodendrocytes by human papovirus (JC virus)
• symptoms, subacute onset : behavioural changes, speech, motor, visual impairment
• CT: single or multiple lesions, no mass effect, don’t usually enhance. MRI is better – high-signal
  demyelinating white matter lesions are seen

AIDS dementia complex

• caused by HIV virus itself
• symptoms: behavioural changes, motor impairment
• CT: cortical and subcortical atrophy

Focal neurological lesions

Toxoplasmosis

• accounts for around 50% of cerebral lesions in patients with HIV
• constitutional symptoms, headache, confusion, drowsiness
• CT: usually single or multiple ring enhancing lesions, mass effect may be seen
• management: sulfadiazine and pyrimethamine

Primary CNS lymphoma

• accounts for around 30% of cerebral lesions
• associated with the Epstein-Barr virus
• CT: single or multiple ring enhancing lesions
  Differentiating between toxoplasmosis and lymphoma is a common clinical scenario in HIV patients.
  It is clearly important given the vastly different treatment strategies. The table below gives some
  general differences. Please see the Radiopaedia link for more details.

Tuberculosis

• much less common than toxoplasmosis or primary CNS lymphoma
• CT: single enhancing lesion