Microscopic examination revealed a massive leptomeningeal inflammatory infiltrate composed of polymorphonuclear leukocytes, lymphocytes, and numerous histiocyte-like cells (Figure 4, arrow; x600). There was marked leptomeningeal congestion. The inflammatory infiltrate extended into the cerebral parenchyma, perivascularly in places (Figure 5; x40). The hippocampus also revealed leptomeningeal and intraparenchymal inflammatory infiltrates which also involved the choroid plexus of the temporal horn. Basal ganglia displayed massive inflammatory infiltration throughout (Figure 6; x400 and Figure 7; x1000). There was an extremely massive leptomeningeal inflammatory infiltrate in the cerebello-pontine angle and inflammatory infiltration of the pontine parenchyma. Sections of the cerebellum showed similar histopathologic changes. The inflammatory infiltrate involved ependyma and subependyma of the fourth ventricle. It also filled the outlet foramina of the lower brainstem (Figure 8; x1.3 and Figure 9; x40) and extended into cranial nerve X root (Figure 10; x40). Special stains for bacteria and fungi were negative.