Tanycytic ependymoma of the filum terminale with pleomorphic giant cells.

A tanycytic ependymoma measuring 1.5 cm in maximal dimension, which involved the filum terminale and conus medullaris of a 55-year-old woman, is reported. The tumor consisted of a compact fascicular proliferation of spindle cells having long bipolar cytoplasmic processes, and immunohistochemical and ultrastructural studies demonstrated the ependymal features of neoplastic cells. The most prominent finding was an appearance of many atypical and pleomorphic, often monstrous, giant cells, which was not associated with an increase in proliferative activity. Remarkable nuclear atypism and pleomorphism with formation of giant cells have not been documented previously in tanycytic ependymoma. These nuclear changes are considered essentially degenerative in nature and probably do not portend a worse prognosis despite their worrisome appearance. This tumor could be appropriately termed "giant cell tanycytic ependymoma."