Coexistence of Pituitary Adrenocorticotropin-Dependent Cushing's Syndrome with a Solitary Adrenal Adenoma*

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Abstract
A 45-yr-old woman presented with a 2-yr history of Cushing's syndrome. Baseline cortisol and ACTH levels were elevated and lacked a normal circadian rhythm. Dynamic testing of her pituitary-adrenal function revealed positive responses to metyrapone and synthetic ACTH and suppression with high doses of dexamethasone. The finding of asymmetrical adrenal uptake of 6-[131I]methyl-19-nor-cholesterol and a tumor image in the right adrenal on venography led to the preoperative diagnosis of pituitary ACTH-dependent adrenal hyperfunction coexisting with a right adrenal adenoma. Surgical resection of the right adrenal demonstrated a solitary 39-g nodule, 4 cm in diameter. There were no additional nodules present in the surrounding cortex. When incubated in vitro, both the adenoma and the surrounding tissue were functional and responsive to ACTH. This was in contrast to the lack of response to ACTH in vitro of similar tissues removed from two other patients with ACTH-independent adrenal adenomas. We suggest that this case represents a transition between pituitary ACTH-dependent bilateral adrenocortical hyperfunction and solitary adrenal adenoma.