Pituicytoma incidentally found at autopsy.

Pituicytoma is a rare benign neoplasm, occurring in the sellar and suprasellar regions. Reported herein is a case of asymptomatic pituicytoma, discovered at autopsy, in a 54-year-old Japanese woman. This is the first case report of pituicytoma, found incidentally at autopsy (incidentaloma), in which whole-mounted sections are available for histological and immunohistochemical studies. Grossly, the bisected pituitary gland revealed a round, white to light tan, 7 mm-diameter nodule. Microscopically, whole-mounted sections revealed a well-circumscribed nodule with no fibrous capsule, located mainly in the neurohypophysis and partially compressing the adenohypophysis. The tumor was composed primarily of bipolar, occasionally unipolar, cells with syncytial fibrillary cytoplasm, arranged in short curvilinear fascicles and/or storiform patterns. Unusual histological features were seen, which included a few groups of large pleomorphic tumor cells with abundant, glassy, eosinophilic cytoplasm, occasionally associated with multinucleated giant tumor cells, and scattered Herring bodies within the tumor. Immunohistochemically, the tumor showed diffuse strong expression of glial fibrillary acidic protein, S-100 protein, and vimentin. Epithelial membrane antigen immunoreactivity was focally observed, mainly in the large tumor cells. Distinction from other intrasellar tumors (granular cell tumor and pilocytic astrocytoma) is important. Because the immunohistochemical profiles of these tumors are similar, histological findings are crucial for distinction.