CNS cryptococcosis

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:

  • meningitis
  • cryptococcomas
  • 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

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

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.

Meningeal disease
Cryptococcomas
  • T1: low signal
  • T2 / FLAIR: high signal
  • T1 C+ (Gd): variable, ranging from no enhancement 5 to peripheral nodular enhancement 9
Gelatinous pseudocysts

Tend to give a "soap bubble" appearance.

  • T1: low to intermediate (from mucin) signal 9
  • T2: high signal
  • FLAIR: low signal

Treated with intravenous amphotericin B or fluconazole. It is fatal if left untreated.

Complications

General imaging differential considerations include:

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Article Information

rID: 10825
Section: Pathology
Synonyms or Alternate Spellings:
  • CNS cryptococcal infection
  • Central nervous system cryptococcal infection
  • CNS manifestations of cryptococcosis

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