Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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June 25, 2015
CNS Cryptococcosis
- Background: In patients with AIDS, cryptococcosis (Cryptococcus neoformans) is the third most common CNS infection, with only HIV encephalopathy and toxoplasmosis being more common. Cryptococcus proliferates in the subarachnoid spaces and spreads into the perivascular spaces, dilating them. The confluence of dilated perivascular spaces leads to the formation of gelatinous pseudocysts, usually in the basal ganglia and dentate nuclei regions. Cryptococcomas, which are proper parenchymal infections, differ from gelatinous pseudocysts. Infection of the choroid plexus resulting in a choroid plexitis may also occur.
- Clinical Presentation: Most patients present with symptoms or signs of subacute meningitis or meningoencephalitis, with fever, malaise, nausea, vomiting, lethargy, and altered mental status.
- Key Diagnostic Features: Classic MR findings are clusters of small hyperintense T2-weighted lesions in the basal ganglia showing subtle peripheral
enhancement, representing the dilated perivascular spaces (as seen in the companion case). In cases with larger pseudocysts,
high T2-FLAIR signal can be seen as the gelatinous material has different relaxation times than CSF, and therefore will not
be suppressed.
- In the absence of parenchymal lesions, communicating hydrocephalus (subacute to chronic cases) may raise suspicion.
- In patients with AIDS and a CD4 count below 200 cells/mm3, meningeal enhancement, cryptococcomas, and choroid plexitis or gelatinous pseudocysts are a rare finding probably due to 1) the patient’s inability to mount an immune response to the organisms, and 2) the organism's thick mucoid capsule that isolates it from the patient’s inflammatory cells.
- The diagnosis should be confirmed with the patient's serum or CSF agglutination test for cryptoccocal polysaccharide antigen, Indian ink stain of CSF and CSF cultures.
- DDx: Other opportunistic infections (eg, toxoplasmosis, TBC), although these lesions are parenchymal rather than located in the subarachnoid space, and also elicit a more pronounced inflammatory reaction.
- Treatment: Therapy is based on antifungal drugs (amphotericin B or fluconzole) and HAART to improve the patient's immune status.
- Teaching Point: Case 1 illustrates the potential value of DWI in the diagnosis of CNS cryptoccocal meningitis in patients with AIDS. Restricted diffusion in the subarachnoid spaces, in the absence of meningeal enhancement or parenchymal enhancement, should be a strong indicator of this disease. The distribution of the lesions and the absence of focal neurologic deficits or an embolic source suggested that these lesions were not secondary to ischemia.
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