MRI differentiation of CNS fungal infections: correlating imaging features with microbiological and histopathological findings.

Purpose: The study aims to evaluate the magnetic resonance (MR) features of central nervous system (CNS) fungal infections and determine the associations between these findings and the type of fungus. Our main objective was to assess whether imaging can serve as a predictor for identifying the specific group of fungi responsible for the infection using microbiology and histopathology as a benchmark.

Materials and methods: A retrospective analysis was done on 50 patients with proven CNS fungal infections. Fungal type was determined and grouped according to microbial classifications into four subtypes: hyalohyphomycetes, mucorales, yeasts and dematiaceous molds. MR findings were compared with histopathology/microbiology and associations between fungal groups were sought.

Results: A total of 37 males and 13 females with a mean age of 39.3 years were included in the study. Aspergillus spp. infection (48%) was the most common. Most patients (54%) had an underlying risk factor for the infection. Pseudo-tumoral mass-like behavior was observed with Aspergillus, and the presence of meningitis was associated with yeast infections (p < 0.001). Of the 19 abscesses, 9 (47.3%) showed a dual rim sign on susceptibility-weighted imaging (SWI), and 10 (52.6%) showed intracavitary dot-like foci of dropouts on SWI. Both findings were statistically significant with dematiaceous molds (p = 0.04 and p = 0.009, respectively).

Conclusion: Although radiological characteristics are non-specific and can overlap with each type of fungi, our study shows that certain MR features can help radiologists point towards the causative type. More specifically, dot-like foci of susceptibility point towards abscesses caused by dematiaceous molds possibly owing to melanin pigment and metal chelation properties.