This scan shows a left frontoparietal hypodense lesion with surrounding oedema and mass effect which shows enhancement with contrast.

In HIV CNS lesions can be divided into those which exhibit mass effect and those that do not.

CNS lesions with mass effect include:

1. toxoplasma encephalitis
2. primary CNS lymphoma
3. tuberculoma (more common in the developing world)
4. other lesions are less common but include brain abscesses secondary to Staph, Strep, Salmonella, Aspergillus, Nocardia, Listeria & cryptococcus

NB: toxoplasmosis and primary CNS lymphoma are the most common

CNS lesions without mass effect are commonly due to progressive multifocal encephalopathy or HIV-associated encephalitis.