NeuroradiologyCryptococcosis
mycotic infection, caused by an encapsulated yeast-like fungus, the most common
CNS mycotic infection.
Cryptococcus neoformans is an ubiquitous organism found in mammal and bird faeces, particularly pigeon droppings.
CNS cryptococcosis is believed to result from haematogenous dissemination from the lung. Although the infection may occur in immunocompetent persons, many patients have an underlying chronic illness such as diabetes mellitus, collagen
vascular disease, chronic
renal disease, alcoholism or
malignant neoplasms, particularly lymphoreticular disorders, or are on immunosuppressive medication. Around 615% of AIDS patients will develop cryptococcosis during the course of their disease.
CNS cryptococcosis commonly presents with nonspecific manifestations of meningitis and encephalitis, such as headache, mental deterioration, low-grade fever, meningismus, and evidence of increased intracranial pressure. The course of the disease may be fulminant or chronic and insidious depending on the host's resistance and the inoculum of infection. Organisms may be detected by microscopic examination and culture. A greyish, mucinous exudate accumulates over the brain surface. Infection of the
meninges may spread to the adjacent brain through the subarachnoid space or along the ependymal surface. As the infection spreads along the VirchowRobin spaces that accompany perforating arteries, the perivascular spaces may become distended with mucoid, gelatinous material that originates from the organism's
capsule. Larger collections of organisms and gelatinous capsular material have been termed gelatinous pseudocysts. Mass lesions representing cryptococcomas may occur, particularly in the deep grey matter.
Imaging findings are primarily the manifestations of meningitis. Hydrocephalus often develops as a result of meningeal scarring. Punctate hyperintensities, representing dilated perivascular spaces or cryptococcomas, are frequently seen in the basal ganglia, thalami and midbrain on T2-weighted MR images. CT (Fig.1) may show cystic nodules with an enhancing capsule and central core.
Proliferating masses of organisms and gelatinous material may distend the subarachnoid spaces. Granulomas may be seen throughout the brain, along the ependyma, in the choroid plexus, and along the spinal cord and spinal nerve roots. Contrast enhancement of the meninges and cryptococcomas may or may not occur and is frequently absent in AIDS-related cryptococcosis.
Calcification of cryptococcomas is rare.
FS