A case of asymptomatic cortisol producing adrenal adenoma.

We describe a man without the clinical findings of Cushing's syndrome, but who harbored an incidentally found cortisol-producing adrenal adenoma. On adrenal 131I-adsterol imaging, there was good uptake to the nodule, but no visualization of the contralateral adrenal. No abnormalities were found in the basal plasma cortisol, ACTH, urinary free cortisol and 17OHCS. However, dynamic hormone assessment revealed the existence of abnormal cortisol secretion: no suppression to dexamethasone, incomplete response to human corticotropin-releasing hormone, and lack of diurnal variation in plasma cortisol. Left adrenalectomy was performed with the diagnosis of cortisol-producing adrenal tumor. The pathological finding was an adrenal adenoma, and the perifusion of the excised tissues revealed a negligible response of the tumor tissue to ACTH though the residual normal cortex responded. Postoperative course was uneventful without replacement therapy with cortisol. It is suggested that the tumor autonomously produced a small amount of cortisol not only insufficient to provide clinical Cushing's syndrome, but also to provide typical suppression of hypothalamo-pituitary corticotroph-adrenal system.