Pituitary adenomas in Cushing's disease. A histologic, ultrastructural, and immunocytochemical study.

Twenty-two pituitary adenomas in Cushing's disease were removed by transsphenoidal surgery. In six patients the pituitary tumor had become manifest following adrenalectomy (Nelson's syndrome). Sixteen tumors were microadenomas measuring from 2 to 9 mm, while two were diffuse invasive adenomas verified at postmortem examination. Light microscopy showed that the tumors were made of basophillic cells containing PAS-positive granules that stained blue with Herlant tetrachrome and lead hematoxylin. Immunocytochemical studies showed that the granules stained positively with antiserum to adrenocorticotrophic hormone (ACTH) or to beta-lipotropic hormone (beta-LPH) and the peroxidase-antiperoxidase complex. Electron microscopic study of the tumor cells showed ACTH and beta-LPH containing granules varying in size, shape, and amount. Perinuclear bundles of 70 A microfilaments constituted a specific ultrastructural finding.