Brain biopsy:
The sections contain cerebral cortex and white matter. There are atypical lymphoid cells surrounding some of the cerebral blood vessels. They are at least medium-sized. They have enlarged hyperchromatic nuclei, angulated nuclear contour, focal conspicuous nucleoli and scanty cytoplasm. A few associated mitoses are noted. Small mature lymphocytes are also seen. The blood vessels show no fibrinoid necrosis or thrombosis. There are no macrophages to suggest demyelination. No viral inclusions are seen. There are no granulomas. No spongioform change is present.
The atypical lymphocytes are CD20, PAX-5, bcl-2, bcl-6 and MUM1 positive. These atypical lymphoid cells are also seen in the parenchyma, as highlighted by the B-cell markers. The Ki-67 index is more than 75%. They are CD3, CD10 and EBER-CISH (EBV) negative. Immunostain for polyomavirus (SV40/BKV) is negative. Beta-amyloid immunostain shows no amyloid plaques.
The features are those of diffuse large B-cell lymphoma, with activated B-cell-like phenotype.
FINAL DIAGNOSIS: Diffuse large B-cell lymphoma.