CNS cryptococcosis produces a wide variety of MRI features that may vary depending on the immunological status of the patient.
The MRI findings range from single to multiple alterations such as hydrocephalus,
leptomeningeal/pachymeningeal enhancement,
dilated perivascular spaces,
miliary nodules,
plexitis (via hematogenous dissemination),
and pseudotumor (cryptococcoma),
occurring in isolation or concomitantly with other MRI findings.
Chronic granulomatous reactions caused by C.
neoformans are more common in immunocompetent hosts than in those with immunosuppression.
On T1-weighted images,
cryptococcal granulomas appear as hypointense lesions,
with or without homogenous enhancement.
The most common MRI findings in immunocompetent patients are variable-sized masses with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images,
accompanied by ring or nodular enhancement and vasogenic edema.
Dilatation of the perivascular spaces is a common finding in both immunocompetent and immunocompromised patiets. The perivascular space is defined as a potential space that involves a vessel and is an extension of the subarachnoid space.
Most commonly located in the basal ganglia,
white matter,
cerebellum,
and brainstem,
with a "soap bubble appearance",
gelatinous round masses within the perivascular spaces appear as round foci with intermediate to low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
Coalescence of the perivascular spaces is often seen,
leading to a mild mass effect.
Vasogenic edema is not present,
and there may be little or no enhancement at the periphery of these lesions.
Cryptococcomas (accumulations of fungi,
inflammatory cells,
and gelatinous mucoid material) arise during infection and can extend to the parenchyma as focal masses,
having a tumor-like appearance. The correct diagnosis of cryptococcomas,
particularly in immunocompetent individuals,
is challenging because these lesions may show a very high choline/N-acetylaspartate ratio in proton magnetic resonance spectroscopy and may require a biopsy to confirm the diagnosis. Cryptococcomas usually have low signa on T1, high signal on T2/FLAIR and variable enhancement,
ranging from no enhancement to peripheral nodular enhancement.
Choroid plexus disease is a rare manifestation of CNS cryptococcal infection.
It is characterized by a multilobulated cystic appearance and abnormal hyperintense signal in T2-weighted FLAIR sequences,
with intense enhancement on gadolinium-enhanced T1-weighted images.