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Cryptococcosis

Last Updated: July 5, 2021

Open Table of Contents: Cryptococcosis

Figure 1: In this HIV-positive patient, there is a cluster of dilated perivascular spaces and pseudocysts with signal isointense to CSF on T1-weighted (top  left), T2-weighted (top right), and FLAIR (middle left) imaging. (Middle Right) The medial-most lesion demonstrated more heterogeneous signal with a solid enhancing component along the medial margin. (Bottom Left and Bottom Right) The majority of these lesions in the basal ganglia demonstrate normal or increased diffusivity on DWI/ADC, a common finding in many atypical infections.

Figure 1: In this HIV-positive patient, there is a cluster of dilated perivascular spaces and pseudocysts with signal isointense to CSF on T1-weighted (top  left), T2-weighted (top right), and FLAIR (middle left) imaging. (Middle Right) The medial-most lesion demonstrated more heterogeneous signal with a solid enhancing component along the medial margin. (Bottom Left and Bottom Right) The majority of these lesions in the basal ganglia demonstrate normal or increased diffusivity on DWI/ADC, a common finding in many atypical infections.

Description

  • Opportunistic fungal infection (Cryptococcus neoformans)
  • Strongest risk factor is T-cell dysfunction and, thus, is seen most commonly in patients with HIV/AIDS

Pathology

  • Encapsulated, yeast-like fungus that is found in animal droppings
  • Infection in the lung spreads through the perivascular spaces into the deep gray nuclei, midbrain, and cerebellum

Clinical Features

  • Signs and symptoms
    • Headache is most common
    • Seizure, blurred vision, focal deficits
    • Hydrocephalus
  • Gender
    • Male > female
  • Prognosis
    • Mortality rates approach 100% in the untreated population; improves significantly with treatment to 15% to 30%

Imaging

  • General features
    • Most common finding is nonspecific meningitis
    • A more specific finding is usually small gelatinous pseudocysts in the deep gray nuclei, cerebellum, and white matter along the perivascular spaces
    • Cryptococcoma can simulate a tumor in the cerebral or cerebellar parenchyma or brainstem
  • Modality specific
    • CT
      • Often normal
    • MRI
      • T1WI
        • Dilated perivascular spaces and pseudocysts isointense to cerebrospinal fluid (CSF)
        • Cryptococcoma: hypointense
      • T2WI
        • Dilated perivascular space isointense to CSF
        • Pseudocysts will have a hypointense ring surrounding a hyperintense center
        • Cryptococcoma: hyperintense
      • DWI
        • Normal diffusivity
      • Contrast
        • If the patient is immunocompetent, the lesion might demonstrate low-level enhancement
        • Cryptococcomas demonstrate solid or rim enhancement
      • Gelatinous pseudocyst
        • T1-hypointense, T2-hypointense ring surrounding a hyperintense center
  • Imaging recommendations
    • Standard protocol MRI (including DWI) with intravenous contrast
  • Mimic
    • Can be difficult to distinguish between tuberculous and toxoplasma infections, but for a patient with AIDS with dilated perivascular spaces, this should be at the top of the differential diagnosis; when in the form of a cryptococcoma, will mimic all other ring-enhancing lesions

For more information, please see the corresponding chapter in Radiopaedia, and the Cryptococcosis chapter within the Cerebral Infectious Diseases subvolume in The Neurosurgical Atlas.

Contributor: Sean Dodson, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.02.13

References

Caldemeyer KS, Mathews VP, Edwards-Brown MK, et al. Central nervous system cryptococcosis: parenchymal calcification and large gelatinous pseudocysts. Am J Neuroradiol 1997;18:107–109.

Miszkiel KA, Hall-craggs MA, Miller RF, et al. The spectrum of MRI findings in CNS cryptococcosis in AIDS. Clin Radiol 1996;51:842–850. doi.org/10.1016/s0009-9260(96)80080-8

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 2008;28:2033–2058. doi.org/10.1148/rg.287085135

Takasu A, Taneda M, Otuki H, Oku K. Gd-DTPA-enhanced MR imaging of cryptococcal meningoencephalitis. Neuroradiology 1991;33:443–446. doi.org/10.1007/BF00598622

Vender JR, Miller DM, Roth T, et al. Intraventricular cryptococcal cysts. AJNR Am J Neuroradiol 1996;17:110–113.

Zerpa R, Huicho L, Guillen A. Modified India ink preparation for Cryptococcus neoformans in cerebrospinal fluid specimens. J Clin Microbiol 1996;34:2290–2291. doi.org/10.1128/jcm.34.9.2290-2291.1996

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