51-year-old woman with double vision.

A 51-year-old woman presented with a 2-month history of double vision and numbness around her left ear. She subsequently became unsteady on her feet and developed further cranial nerve abnormalities, before complaining of headache, nausea and vomiting. Imaging revealed features suggestive of two intracranial lesions; one non-contrast-enhancing high-signal area in the cerebellum with associated calcification, and a second contrast-enhancing low-signal area in association with the fourth ventricle, and at surgery there were two apparent components to the tumor. The histopathological features were those of a low-grade, focally calcified tumor comprising atypical ganglion and glial cells with interspersed Rosenthal fibres. Mitotic figures were not seen, and there was no necrosis. An infiltrate of small reactive lymphocytes was interspersed among the neoplastic cells. Immunohistochemistry revealed expression of synaptophysin by many of the dysplastic ganglion cells, with some co-expressing neurofilament protein and occasionally glial fibrillary acidic protein (GFAP). Several of the dysplastic ganglion cells also expressed CD34. The glial cell population was highlighted by GFAP. Ki-67 (MIB-1) activity was not noted among the neoplastic populations--the few positive nuclei in these areas were those of interspersed reactive CD3-positive T lymphocytes. In addition, at the edge of one of the biopsies was a dense infiltrate of mitotically-active large atypical CD 20-positive B lymphocytes, among which the Ki-67 (MIB-1) labeling index reached 80%. The final diagnosis was diffuse large B cell lymphoma arising within a ganglioglioma of the cerebellum, and this is believed to be the first reported case.