Cushing’s syndrome treated by intrasellar implants of radioactive yttrium
E. Perry McCullagh, M.D.
Department of Endocrinology
Donald F. Dohn, M.D.
Department of Neurologic Surgery
Cushing’s syndrome is due to an excess of circulating cortisol usually from the zona fasciculata and the zona reticularis of the hyperplastic adrenal cortex. In approximately 20 percent of the patients this excessive cortisol production arises from an adrenocortical adenoma. The disorder may also be associated with a chromophobe adenoma of the anterior pituitary which produces an excess of adrenocorticotropic hormone (ACTH), or as a result of hyperproduction of ACTH-like substance from a variety of tumors not of the pituitary, notably thymic tumors and bronchogenic carcinomata.
Cushing1 believed that the pituitary was responsible for the syndrome, but for many years this concept was doubted, and an inherent abnormality in the adrenal cortex was thought to be the cause.2, 3 The probable pathogenetic mechanism in most instances of Cushing’s syndrome is adrenocortical hyperplasia due to an excess of ACTH.
Evidence to support this statement is as follows. Several cases of pituitary tumors occurring after adrenalectomy for Cushing’s syndrome have been reported.4 Although such tumors appear after adrenalectomy for Cushing’s syndrome due to adrenal hyperplasia, they have not been seen after adrenalectomy in patients with metastatic cancer nor in those with spontaneous Addison’s disease.5 This, then, seems to imply strongly that the pituitary is being affected abnormally in Cushing’s syndrome, and raises the possibility of neural stimulation of the pituitary. In some such cases the titer of ACTH in the blood is much higher than that found in patients with Addison’s disease.6 It would seem likely that this propensity to excessive ACTH . . .