Fig. D and E: Coronal (3D) and sagittal (3E) T1-weighted images of the brain after Gadolinium contrast enhancement show enhancing cryptococomas (black arrows) at base of dilated perivascular spaces on right (black arrow heads).

Discussion: Cryptococcus neoformans is the most common fungus infection involving the CNS. It is particularly important in patients with AIDS, as 5% of AIDS patients develop cryptococcal infection. It is the third most frequent CNS pathogen in AIDS patients, ranking after HIV and toxoplasmosis.[1].

Dilated perivascular spaces in the basal ganglia are the most common imaging findings noted with CNS cryptococcosis. This is better seen on MR than CT. The dilated perivascular spaces often represent several spaces in close proximity to one another. These often contain small cryptococcomas. Typically, the perivascular spaces will follow the normal CSF signal and do not demonstrate enhancement. However, as seen on the right side in this case(Fig. 3), abnormal enhancement may be demonstrated.[2] Additionally, the perivascular spaces may demonstrate signal intensity isointense to the white matter on the T2-weighted images and hypointense relative to CSF. This can be compatible with a cryptococcoma within the perivascular space.[3]

Other imaging findings of CNS cryptococcosis may include rare meningeal enhancement consistent with cryptococcal meningitis and rarely intraparenchymal enhancing lesions compatible with larger cryptococcomas. Again, however, contrast enhancement of cryptococcomas or cryptococcal meningitis is rare. This is most likely due to the underlying immunosuppression of the AIDS patients or the onimmunogenic nature of the polysaccharide capsule of the cryptococcal organism.[4]

In summary, this case demonstrates the finding of dilated perivascular spaces in the basal ganglia bilaterally, a common imaging finding with CNS cryptococcosis. The abnormal enhancement of the right perivascular spaces is a relatively rare finding in CNS cryptococcosis, and represents enhancement of small cryptococcomas within the perivascular spaces. As noted on the T2-weighted images, the right sided perivascular spaces do not follow the signal intensity of CSF as do those on the left.

References:
1. Mathews VP, Piero AL, Glass JD et al. AIDS-related CNS cryptococcosis:
Radiologic-Pathologic correlation. AJNR Sept/Oct 1992;13:1477-1486.

2. Arnder L, Castillo M, Heinz ER, et al. Unusual pattern of enhancement in
cryptococcal meningitis: in vivo findings with postmortem correlation. J Comput Assist
Tomogr Nov/Dec. 1996;20(6):1023-1026.

3. Schmidt S, Reiter-Owonda I, Hotz M, et al. An unusual case of central nervous
system cryptococcosis. Clin Neurol Neurosurg Feb. 1995;97(1):23-27.

4. Takasu A, Taneda M, Otuki H, et al. GD-DTPA-enhanced MR imaging of
cryptococcal meningoencephalitis. Neuroradiology 1991;33(5):443-446.

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