Specific Imaging Findings

Manifestations of cryptococcal CNS infection are varied and include: (1) meningoencephalitis, (2) gelatinous pseudocysts, (3) parenchymal or intraventricular miliary nodules/cryptococcomas, or (4) a combination of these findings. Imaging studies (especially CT) may frequently be normal or show just ventriculomegaly, which is the most common radiologic abnormality. Meningoencephalitis appears as cortical and subcortical hyperintensity on FLAIR images with associated leptomeningeal (often nodular) enhancement. Gelatinous pseudocysts appear as rapidly enlarging, well-demarcated, cystic lesions in the basal ganglia and deep white matter of low density on CT, and signal similar to cerebrospinal fluid (CSF) on T2- and T1-weighted MRI, without contrast enhancement. On FLAIR images, the lesions may be hyperintense to CSF. The finding of multiple cysts/dilated perivascular spaces in an immunosuppressed patient is highly suspicious for cryptococcal infection. Cryptococcomas appear as enhancing nodular intraaxial lesions (usually in the deep gray matter and cerebellum) or as intraventricular lesions with enlarged choroid plexus (choroid plexitis), leading to hydrocephalus. They are T2 hyperintense similar to pseudocysts, range in size from a few millimeters to several centimeters, and may have surrounding edema.

Pertinent Clinical Information

The CNS and the lung are the two primary sites of infection with Cryptococcus neoformans. Patients with CNS cryptococcosis typically present with nonspecific signs of subacute or chronic meningitis or meningoencephalitis, including headaches, fever, lethargy, nausea, vomiting, or memory loss over a period of several weeks. The diagnosis is confirmed by encapsulated yeast cells on direct microscopic examination of the CSF with India ink, positive CSF cultures for C. neoformans, or detection of the cryptococcal capsular polysaccharide antigen in the CSF. Without appropriate antifungal treatment, cryptococcal meningitis is uniformly fatal.