MICROSCOPIC DESCRIPTION: 1&2. Sections show a piece of neural tissue composed of grey and white matter. At one edge of the biopsy the white matter demonstrates aggregates of foamy macrophages, enlarged hyperchromatic reactive astrocytes and oligodendroglial ground glass intranuclear inclusions.
Immunohistochemical results confirm positive staining for SV40/BK virus, consistent with JC virus infection.
DIAGNOSIS: Brain, left parietal lesion: JC virus infection (progressive multifocal leukoencephalopathy).