C. Pathological Changes:
1. General description:
Multiple and/or widespread areas of CNS involvement occur, as opposed to localized nature of abscess formation. Specific viruses affect specific anatomic areas or subpopulations of cells, a phenomenon called "tropism". An example of this is the predilection of herpes simplex virus to produce lesions in the limbic system, and infection of lower motor neurons by poliovirus. Microscopic changes include: perivascular cuffing by lymphocytes and plasma cells; neuronal necrosis; inclusion bodies; microglial proliferation and glial nodules; hemorrhagic necrosis (common in Herpes simplex encephalitis). Calcification can be detected in some neonates infected in utero with encephalitis-producing agents like CMV and HIV viruses.