Fig. 2

Pathological findings of brain biopsy. a-c Hematoxylin-eosin staining revealed diffuse infiltration of atypical cells in cortical gray (a, b) and deep white matter (c). Lymphoma cells show enlarged round nuclei, thin cytoplasmic rims and occasional nucleoli (arrowheads). Mitotic cells (arrow) and reactive astrocytes with eosinophilic cytoplasm (asterisk) are identified (b). Perivascular infiltration of the atypical cells was partly observed (d). Immunohistochemical studies revealed the infiltration of CD20 positive cells in the parenchyma (e, f) and numerous MIB-1 positive cells (g). BCL-6 and MUM-1 immnunostainings highlight a non-germinal center B-cell pattern (h, i)