Cryptococcosis is the most common CNS fungal infection in AIDS, occurring in 8.7-13% of patients. Cryptococcus neoformans has a peculiar propensity to affect individuals with cell mediated immunity, and it usually produces a meningitis. CSF antibody titers are not always reliable for diagnosis because the immune response in AIDS patients is so variable. Imaging studies may be negative or show only mild ventricular dilatation. Since cerebral atrophy is common in AIDS patients, distinguishing central atrophy from hydrocephalus is not always easy, and sometimes followup studies or correlation with the clinical picture is necessary. The cryptococcal organisms may enter the brain via the VR spaces at the base of the brain. Proliferation of the organisms within the VR spaces produces gelatinous pseudocysts of variable size to give a mottled appearance on imaging studies. Meningeal enhancement is not often present unless a chronic inflammation has developed. A chronic relapsing infection can result in cryptococcal brain abscesses. Endnote

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