Pituicytoma: ultrastructural evidence of a possible origin from folliculo-stellate cells of the adenohypophysis.

Pituicytoma is a rare neoplasm occurring in the sellar and suprasellar regions. The tumor is currently considered to arise from the pituicyte, a specialized glial cell of the posterior lobe and the stalk of the pituitary gland. The authors describe a case of pituicytoma, focusing on the ultrastructural features. The patient was a 79-year-old woman with hypopituitarism and visual disturbances. Immunohistochemically, the tumor showed strong and diffuse positivity for vimentin, and EMA and GFAP were focally detectable. Ultrastructurally, the lesion was composed of elongated cells containing in the Golgi area aggregates of intermediate filaments in a concentric pathway (fibrous body), and secretory granules. These features intermediate between a pituicytoma and a pituitary adenoma suggest that "pituicytomas" may also arise from the specialized stromal folliculo-stellate cells of the adenohypophysis, which are able to differentiate into endocrine cells.