Clinical History
A 54-year-old male patient, who displays lethargy. A lumbar puncture with elevated pressures. Hydrocephalus was ruled out.
Imaging Findings
MRI shows confluent diffusion abnormalities identified in the inferior cerebellar hemispheres projecting mostly in the medial cerebellar folia, lateral recesses of the fourth ventricle adjacent to the nodulus and medial right more than left inferior cerebellar cortical
margins. The supratentorial compartment shows round diffusion signal abnormalities in the medial occipital, left of the midline splenium, subcortical parietal, bilateral left more than right basal ganglia and thalamic distributions behaving as multiple gelatinous cysts with a high protein-related diffusion signal abnormality. Additional lesions are also identified in the interhemispheric subarachnoid spaces along the pericallosal and
callosomarginal sulci on both sides of midline, the superior margin of the
left lenticulate nucleus and on the right posterior cingulate gyrus.
There are a few punctate susceptibility signal loss changes matching the
areas of diffusion restriction in the left supraventricular posterior
frontal centre semiovale that may represent microhaemorrhages or
microcalcifications in cryptococcal granulomas.
Discussion
Cryptococcosis is the most common fungal infection in the CNS caused by an encapsulated ubiquitous yeastlike fungus in the genus Cryptococcus, found in soil contaminated by bird excrement. Approximately 95% of cryptococcal infections are caused by Cryptococcus neoformans, and less frequently by Cryptococcus gattii [1].
Cryptococcosis is the third most common cause of CNS infection in AIDS patients after HIV and Toxoplasma, especially when the CD4 count is less than 100.
The organism enters through the lungs via inhalation and disseminates haematogenous to various organ systems with a predilection for the CNS.
Clinically, CNS cryptococcosis presents as subacute meningitis or, less frequently meningoencephalitis. About 50% of patients also develop elevated intracranial pressure, which may result in papilloedema.
A diagnosis is made with cryptococcal antigen testing, examination of the CSF with India ink stain, and serum antigen testing.
Magnetic resonance imaging is superior in detecting the presence and extent of cryptococcal lesions as compared to CT.
The radiologic manifestations of cryptococcosis are hydrocephalus, meningoencephalitis, pseudocysts, and cryptococcomas [2].
Hydrocephalus is the most frequent, although nonspecific, finding of cryptococcal infection it can be communicating or noncommunicating. Meningoencephalitis causes T2 hyperintensity within the region of involvement, and leptomeningeal enhancement but the inflammatory response in AIDS patients is present in less than 10% of patients on MRI due to an ineffective inflammatory response in HIV patients.
The fungus spreads along the subarachnoid space through the perivascular Virchow-Robin spaces; these spaces may coalesce into larger lesions referred to as gelatinous pseudocysts, which have a classic "soap-bubble" appearance and occur in the basal ganglia, thalamus, and midbrain.
Fungal invasion into the brain parenchyma in an immunocompetent patient results in a cryptococcoma, a chronic granulomatous reaction, however this is very rare. [2, 3]
Cryptococcal lesions do not have reduced diffusion at DWI, a finding that helps distinguish them from pyogenic abscesses. [3]
Treatment consists of amphotericin B and flucytosine followed by fluconazole. The mortality rate is around 20%, and untreated disease is fatal.
Differential Diagnosis List
CNS cryptococcosis
CNS Toxoplasmosis
CNS Tuberculosis
CNS Lymphoma
