Infections of the Central Nervous System

This chapter describes and illustrates the different lesions observed in CNS infections. A wide variety of pathogenic infectious organisms may affect the CNS. They can be classified as “pathogenic” (causing disease in every individual) or “opportunistic” (affecting only patients with immunodeficiency). Bacteria may cause pyogenic infections or so-called “specific infections,” in which the morphology of the lesions is suggestive of a specific agent. Mycoses and parasitic infections used to be uncommon, restricted to certain countries; however, due to increasing incidence of immunodeficiency conditions and intercontinental travel, they are now more frequently encountered. Viral infections of the CNS cause nonspecific lesions due to immune-mediated reactions or more specific encephalitides. In AIDS, infection by the human immunodeficiency virus causes a unique encephalitis and immunodeficiency with a wide range of secondary opportunistic infections.