Cure of Cushing's disease by transsphenoidal removal of a microadenoma from a pituitary gland despite a radiographically normal sella turcica.

A 37-year-old woman had symptoms of Cushing's disease for two years. Galactorrhea was present. The diagnosis was confirmed by finding intermittently elevated urinary 17-hydroxysteroids, absent circadian rhythm, and elevated plasma ACTH. Plasma prolactin was slightly elevated. Films of the sella turcica were normal. A 9 mm basophilic microadenoma was removed by the transphenoidal approach. Immunocytochemical and electron-microscopic studies showed that the tumor was composed exclusively of ACTH secreting cells. Endocrine re-evaluation one year later revealed normal adrenal function. Serum prolactin had returned to normal. This case provides further evidence that Cushing's disease can be caused by a pituitary microadenoma insufficient in size to deform the sella.