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.
Patients with cerebral cryptococcosis usually present with signs and symptoms of meningitis/meningoencephalitis including headache, seizures, altered mental state, focal neurological defect, or blurred vision due to raised intracranial pressure 12.
Central nervous system involvement with cryptococcosis 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 depending on which part of the brain is affected:
The disease can have a variety of radiographic presentations and is influenced by the degree of immunocompromise and therapy. As a result, the literature describing features has evolved considerably in parallel to marked improvements in the management of HIV and the availability of HAART.
As a general rule, in patients who are profoundly immunocompromised (and therefore earlier literature), cryptococcosis demonstrates little enhancement. Instead, in patients who are on more effective therapy enhancement is more frequently encountered 13.
The range of appearances includes 1-12
- dilated perivascular spaces coalescing into gelatinous pseudocysts
- leptomeningeal and pachymeningeal enhancement
- cryptococcomas (or torulomas)
- miliary nodules
- choroid plexus (plexitis)
The most common pattern, particularly in profoundly immunocompromised patients is spread along the perivascular spaces, most commonly involving the basal ganglia but also the white matter of the cerebral hemispheres, the brainstem and cerebellum 12.
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 the next most commonly described feature but may relate more to HIV dementia than cryptococcosis 13. Hydrocephalus and mass lesions may also each be present.
MRI is better at assessing dilated perivascular spaces, one of the most frequently described features on MRI, and basal ganglia pseudocysts. These findings are more common in immunocompromised patients. Signal characteristics can vary dependent on the form of infection.
- T1 C+ (Gd): can show leptomeningeal enhancement and pachymeningeal enhancement
- FLAIR C+ (post-contrast FLAIR): high T2 signal in subarachnoid space 12
- T1: low signal
- T2/FLAIR: high signal
- T1 C+ (Gd): variable, ranging from no enhancement 5 to peripheral nodular enhancement 9
- DWI/ADC: variable, may have both facilitated or restricted diffusion 12,13
Dilated perivascular spaces
Dilated perivascular space can coalesce into gelatinous pseudocysts that tend to give a "soap bubble" appearance.
- T1: low to intermediate (from mucin) signal 9
- T2: high signal
- FLAIR: variable signal ranging from full suppression to persistent high signal
- variable; may have both facilitated or restricted diffusion 12,13
- maybe complicated by perforator infarct
Treatment and prognosis
Treatment is with appropriate antifungal (e.g. intravenous amphotericin B or fluconazole). If left untreated it is usually fatal.
General imaging differential considerations include:
- 1. Lanzieri CF, Bangert BA, Tarr RW et-al. Neuroradiology case of the day. CNS cryptococcal infection. AJR Am J Roentgenol. 1997;169 (1): 295, 299. AJR Am J Roentgenol (citation) - Pubmed citation
- 2. Awasthi M, Patankar T, Shah P et-al. Cerebral cryptococcosis: atypical appearances on CT. Br J Radiol. 2001;74 (877): 83-5. Br J Radiol (full text) - Pubmed citation
- 3. Popovich MJ, Arthur RH, Helmer E. CT of intracranial cryptococcosis. AJR Am J Roentgenol. 1990;154 (3): 603-6. AJR Am J Roentgenol (abstract) - Pubmed citation
- 4. Andreula CF, Burdi N, Carella A. CNS cryptococcosis in AIDS: spectrum of MR findings. J Comput Assist Tomogr. 17 (3): 438-41. - Pubmed citation
- 5. Miszkiel KA, Hall-craggs MA, Miller RF et-al. The spectrum of MRI findings in CNS cryptococcosis in AIDS. Clin Radiol. 1996;51 (12): 842-50. - Pubmed citation
- 6. Caldemeyer KS, Mathews VP, Edwards-brown MK et-al. Central nervous system cryptococcosis: parenchymal calcification and large gelatinous pseudocysts. AJNR Am J Neuroradiol. 1997;18 (1): 107-9. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 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
- 11. Offiah CE, Naseer A. Spectrum of imaging appearances of intracranial cryptococcal infection in HIV/AIDS patients in the anti-retroviral therapy era. Clinical radiology. 71 (1): 9-17. doi:10.1016/j.crad.2015.10.005 - Pubmed
- 12. Duarte SBL, Oshima MM, Mesquita JVDA, do Nascimento FBP, de Azevedo PC, Reis F. Magnetic resonance imaging findings in central nervous system cryptococcosis: comparison between immunocompetent and immunocompromised patients. (2017) Radiologia brasileira. 50 (6): 359-365. doi:10.1590/0100-3984.2016.0017 - Pubmed
- 13. Shuang Xia, Xueqin Li, Hongjun Li. Imaging characterization of cryptococcal meningoencephalitis. Radiology of Infectious Diseases Volume 3, Issue 4, December 2016, Pages 187-191 doi:10.1016/j.jrid.2016.05.003
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Infections of the central nervous system
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herpes virus family
- herpes simplex virus 1 (HSV-1) encephalitis
- herpes simplex virus 2 (HSV-2) encephalitis
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