The spectrum of ACTH-producing pituitary lesions.

The immunohistochemical characterization of 92 surgically resected abnormal pituitaries showed 24 cases with ACTH immunoreactivity. These included two cases of nodular hyperplasias, 20 functional adenomas, and two silent corticotropic adenomas. Both patients with nodular hyperplasia and 19 patients with functional adenomas had Cushing's disease, while one patient with a functional adenoma had Nelson's syndrome. The two silent corticotropic adenomas were not associated with Cushing's disease, although both patients had slightly elevated serum prolactin levels. The tumors, which were stained for beta-endorphin (12 cases) and alpha and beta-MSH (five cases) were all positive for these peptides. These results show that immunohistochemical staining is indispensable in the diagnosis of nodular hyperplasia and silent corticotropic adenomas and that it is extremely helpful in confirming the diagnosis of ACTH-producing adenomas.