Paraffin sections show fragments of white matter with scatterd mature neurones. There is an angiocentric pattern of accumulation of small lymphoid cells which are predominantly T cells (CD3+, CD4+, CD8+) with smaller numbers of CD20+ B lymphocytes. There are also prominent CD68+ monocyte-macrophages both adjacent to small calibre blood vessels and within the intervening parenchyma. Foci of incipient necrosis are also noted and there is prominent reactive astrocytic gliosis. An occasional poorly formed granuloma composed of CD68+ monocyte-macrophages and lymphocytes is present adjacent to a blood vessel. The majority of blood vessels show distortion of their structure with swollen reactive endothelial cells. Some vessels show fibrinoid necrosis. In situ hybridization and immunohistochemistry for EBV are negative.

DIAGNOSIS: Features favour granulomatous cerebral angiitis (reviewed by a number of neuropathologists)