CNS cryptococcosis results from infection of the central nervous system with the yeast-like fungus Cryptococcus neoformans. It is the most common fungal infection and second most common opportunistic infection of the central nervous system.
For a general discussion of infection with this organism, please refer to the article cryptococcosis.
The disease tends to be predominant in immunocompromised individuals such as those with AIDS. In immunocompetent patients, there is usually history of close contact with birds.
They usually present with meningitis or meningoencephalitis, headache, seizure or blurred vision due to raised intracranial pressure.
It typically results from haematogenous spread from the lungs (which is usually the primary site). In HIV/AIDS patients cryptococcal infection of the CNS usually occurs when the CD4+ count drops below 100 cells/µL. The disease can have either meningeal or parenchymal involvement with the former being the primary manifestation 6. With meningeal involvement, a grayish, mucinous exudate accumulates over the involved brain surface.
There are three dominant CNS forms to the disease which are:
- gelatinous pseudocysts
The disease can have a variety of radiographic presentations.
One of the most common finding is hydrocephalus. There is a tendency for the disease to spread along the perivascular spaces. With parenchymal involvement, there can be often formation of parenchymal cryptococcomas (or torulomas) that commonly involve the midbrain and basal ganglia 2. Gelatinous pseudocysts and choroidal ependymal granulomas may also develop.
CT findings can be often non-specific and with normal scans seen in a significant proportion of patients (reported up to ~40% 3). Diffuse atrophy is usually next most commonly described feature. Hydrocephalus and mass lesions may also each be present in ~10% of cases.
MRI is better at assessing dilated perivascular spaces, one of the most frequently described feature on MRI, and basal ganglia pseudocysts. These findings are more common in immunocompromised patients. Signal characteristics can vary dependant on the form of infection.
- T1 C+ (Gd): can show leptomeningeal enhancement
- T1: low signal
- T2 / FLAIR: high signal
- T1 C+ (Gd): variable, ranging from no enhancement 5 to peripheral nodular enhancement 9
Tend to give a "soap bubble" appearance.
- T1: low to intermediate (from mucin) signal 9
- T2: high signal
- FLAIR: low signal
Treatment and prognosis
Treated with intravenous amphotericin B or fluconazole. It is fatal if untreated.
General imaging differential considerations include:
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- 7 Vender JR, Miller DM, Roth T et-al. Intraventricular cryptococcal cysts. AJNR Am J Neuroradiol. 1996;17 (1): 110-3. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 8 Kumari R, Raval M, Dhun A. Cryptococcal choroid plexitis: rare imaging findings of central nervous system cryptococcal infection in an immunocompetent individual. Br J Radiol. 2010;83 (985): e14-7. doi:10.1259/bjr/50945216 - Pubmed citation
- 9. Smith AB, Smirniotopoulos JG, Rushing EJ. From the archives of the AFIP: central nervous system infections associated with human immunodeficiency virus infection: radiologic-pathologic correlation. Radiographics. 28 (7): 2033-58. doi:10.1148/rg.287085135 - Pubmed citation
- 10. Grant LA, Grant LA, Griffin N. Grainger and Allison's Diagnostic Radiology Essentials. Elsevier Health Sciences. (2013) ISBN:0702034487. Read it at Google Books - Find it at Amazon