Magnetic resonance imaging and pathological analysis of a pituicytoma: case report.

A case of a pituicytoma is presented that describes the clinical, pathological, and magnetic resonance imaging features of a rare tumor of the neurohypophysis. A 26-year-old woman presented with a 4-month history of dizziness and visual obscuration. A magnetic resonance image revealed a pituitary mass with suprasellar extension. The specimen obtained from a transsphenoidal decompression identified the mass as an astrocytoma of the posterior pituitary (pituicytoma). Immunohistochemical staining was positive for glial fibrillary acidic protein, S-100, and vimentin. Electron microscopy identified intermediate filaments, numerous broad cell junctions, no secretory granules, and two cellular populations with either an electron-dense or lucent cytoplasmic matrix. This case is unique in that other documented cases originating in the posterior pituitary have all been pilocytic astrocytomas, whereas this neoplasm was not a pilocytic variant. This is also the first case in the literature of a pituicytoma documented by magnetic resonance imaging. This report reviews the cytological elements of the neurohypophysis and the origin of pituicytomas and stresses the proper use of the term "pituicytoma" in relation to tumors of the posterior pituitary.