Ectopic pituitary adenoma occurring in the interpeduncular cistern. Case report.

Intracranial ectopic pituitary adenoma occurs most frequently in the suprasellar cistern, usually in continuity with the pituitary stalk. Such tumors probably originate from cells of the pars tuberalis located above the diaphragma sellae or from aberrant anterior pituitary cells of the pituitary stalk. The authors report the case of a 37-year-old woman with Cushing's syndrome caused by an ectopic pituitary adenoma of unique location: the tumor was separate form the pituitary stalk and confined within the interpeduncular cistern. After surgical removal of the tumor, continued improvement in the patient's laboratory results and disappearance of her endocrine symptoms strongly indicated the absence of adenoma cells in the pituitary gland or stalk. The tumor in the present case appears to have arisen from aberrant pituitary cells that were present in the leptomeninges of the basal surface of the hypothalamus.