Fungal Infections

Abstract

The manifestations of fungal infections result in life-threatening conditions and the major role of the neuroradiologist is to recognize the manifestation and make an educated guess as to the type of pathogen. Magnetic resonance imaging is the imaging modality of choice, and administration of gadolinium contrast is essential to identify areas of enhancement that may be subtle. In principle, fungal CNS infections can lead to meningitis (with secondary hydrocephalus), meningoencephalitis, vasculitis, and formation of abscesses and granulomas. The small yeast forms (Coccidioides, Histoplasma, Cryptococcus) usually reach the small arterioles and capillaries. They cause leptomeningitis and subpial ischemic lesions as they have access to the microcirculation from which they seed the subarachnoid space. The large hyphal forms (Aspergillus and Zygomyces) obstruct larger arteries and thus cause large infarcts. A ring-enhancing inhomogeneous lesion with irregular walls and projections into the cavity with low apparent diffusion coefficient and without contrast enhancement of these projections carries a high probability of being a fungal abscess. Due to the lack of inflammatory response, neuroradiological findings in fungal infections are often atypical and thus hard to interpret.