= ubiquitous soil fungus Cryptococcus neoformans infects lungs followed by hematogenous spread

Organism: unicellular yeast

Transmission: inhalation of reproductive spores found in bird feces (eg, pigeon droppings)

• Most common cause of opportunistic fungal infection in immunocompromised + AIDS patients
• Most common fungal disease of CNS

Path: choroid plexitis, meningitis, encephalitis (lack of anticryptococcal factors in CSF)

Incidence: 5% of all patients with AIDS

• headache, malaise, fever, nausea, vomiting

Location: from base of brain extension along Virchow-Robin spaces

• hydrocephalus + cortical / central atrophy (with inadequate immune response)
• abnormal nodular leptomeningeal enhancement (with sufficient immune response), most pronounced at base of brain
• enlargement of Virchow-Robin spaces = distension of perivascular spaces ← budding yeast + mucoid material from organism's capsule
• gelatinous pseudocysts frequently in basal ganglia, thalami and midbrain
• miliary (<3 mm) / larger parenchymal cryptococcoma

CT:

• frequently normal: edema + enhancement may be attenuated in immunodeficiency / corticosteroid therapy
• pseudocystic perivascular lesions in region of basal ganglia

MR:

• low T1 + high T2 signal intensities without enhancement in lenticulostriate region (= gelatinous pseudocyst = budding yeast + mucoid material from organism's capsule)
• hyperintense lesions on FLAIR
• restricted diffusion if contents of high viscosity
• leptomeningeal enhancement

Dx: detection of cryptococcal antigen in CSF

Cx: hydrocephalus ← acute meningeal exudate / meningeal adhesions

Prognosis: mean survival of 2–3 months

DDx: enlarged Virchow-Robin spaces (hypointense on FLAIR)