Atypical inflammatory histiocytic tumor of the cerebellum. A histological, immunohistochemical, and ultrastructural study.

We report a primary histiocytic tumor involving the cerebellum. Microscopically, the tumor was composed of nests of pleomorphic cells surrounded by thin vascular septa invaded by lymphocytes. Immunocytochemistry and electron microscopy confirmed the histiocytic origin of the tumor. Although we considered several diagnoses, we ultimately concluded that "atypical inflammatory histiocytic tumor of the cerebellum" best characterized the lesion. This case represents another example of the diversity of histiocytic tumors and shows that they can occur in the central nervous system.