Cryptococcosis
- Cryptococcus neoformans: a yeast that spreads from lungs and intrathoracic lymph nodes to blood, commonly infecting CNS
- Most cases occur in patients with low cell mediated immunity (HIV, steroid therapy, organ transplant recipients, reticuloendothelial malignancies, sarcoidosis,TB, and multiple myeloma).
- MRI findings: large Virchow-Robin spaces (< 3mm) due to mucoid gelatinous material produced by the capsule ('gelatinous pseudocysts') in basal ganglia or midbrain which may progress to cryptococcomas (> 3mm); Cryptococcomas: granulomatous tissue invasion, are more common in immunocompetent.
- Lesions are T1 hypointense, T2/FLAIR bright, no enhancement, dark on DWI and show high lipid/lactate with low NAA, Cho, Cr, MI on MRS.
- Other features: pial enhancement, choroid plexitis, focal enhancing lesion, hydrocephalus, infarcts and, rarely, arachnoid cysts.
- Normal MRI does not exclude it; typical features seen in 40% of patients.
- Definitive diagnosis: positive identification of yeasts on India ink staining, CSF culture;'high cryptococcal antigen latex agglutination titers in CSF and blood; positive results in blood cultures.
