Pituicytoma.

Pituicytoma is a rare, low-grade neoplasm that originates in the neurohypophysis of the pituitary gland. We report the clinicopathologic features of a pituicytoma arising in a 52-year-old man who presented with a mass and panhypopituitarism, clinically suggestive of a pituitary adenoma. The tumor was marked by a proliferation of elongated cells arranged in bundles and interlacing fascicles. The tumor demonstrated positive staining with S-100 protein and glial fibrillary acid protein antibodies. The tumor did not stain with antibodies to cytokeratin, synaptophysin, chromogranin, anterior pituitary hormones, or p53. An MIB-1 labeling index of 1.1% was observed. The tumor was subtotally resected and recurred 11 months after the initial surgery. The literature on this rare tumor will be reviewed and differential diagnosis discussed.