Pathology
MICROSCOPIC DESCRIPTION: 1&2: Paraffin sections show fragments of brain parenchyma which are densely infiltrated by a population of atypical large lymphoid cells mixed with smaller mature lymphocytes. The large cells have convoluted vesicular nuclei, many with conspicuous nucleoli and a varying amount of pale cytoplasm. Both populations are arranged in diffuse sheets as well as cuffs around blood vessels. The walls of some vessels are obliterated by the infiltrate. Immunohistochemistry shows positive staining in tumour cells for CD20 and CD5. Scattered atypical cells show positive staining for MUM-1. Atypical cells are negative for CD3, CD10, CD23, cyclin D1, CD30, bcl-2, bcl-6 and EBV-LMP. Moderate numbers of small mature CD3+ T lymphocytes are mixed with the large atypical B cells. The features are of non-Hodgkin's large B cell lymphoma. DIAGNOSIS: "Right frontal brain lesion": non-Hodgkin's diffuse large B cell lymphoma.