A case of atypical granular cell tumor of the neurohypophysis

A case of granular cell tumor (GCT) arising in the neurohypophysis of a 63- year-old woman is reported. The tumor consisted of ovoid, polygonal or spin dle-shaped cells in a sheet-like or fascicular arrangement. Its abundant cy toplasm contained granules positive for diastase-resistant periodic acid-Sc hiff reaction. Ultrastructurally, the tumor cells contained numerous polymo rphic lysosomes of various densities. Immunohistochemically, the tumor cell s were positive for S-100 protein, glial fibrillary acidic protein and Leu7 , suggesting that the tumor originated from pituicytes that were thought to be modified astrocytes in the neurohypophysis and its stalk. The granular cells showed nuclear atypia, pleomorphism and increased mitotic activity. T herefore, the present tumor was considered as a histologically atypical GCT . Interestingly, proliferating cell nuclear antigen, Ki-67 and p53 were sta ined in a few tumor cells of this case. These findings indicate that the pr esent tumor had a malignant potential.