Background: Cushing’s syndrome due to ectopic production of ACTH has been recognized for many years. Bronchial carcinoid tumor is one of the most common cause of this syndrome. Herein we report an additional case of ectopic ACTH syndrome, who underwent unsuccessful hypophysectomy because the anatomic and hormonal studies are insufficient to distinguish it from pituitary-dependent Cushing’s syndrome and soon after treated successfully with right lower lobectomy. Case Report: A 24-year-old woman with biochemical findings including high levels of plasma cortisol, very high plasma ACTH level and urinary free cortisol, as well as negative response to supression test and ovine corticotropin-releasing hormone stimulation test was referred for further evaluation of persistent Cushing’s syndrome. Selective venous ACTH sampling showed no pituitary gradient. Thoracic CT demonstrated a tumor mass within the right lower lobe. Right lower lobectomy was performed. Postoperatively, her Cushingoid appearance disappeared, plasma ACTH value and serum cortisol concentration declined to normal levels.Conclusions: Although the clinical features of the ectopic ACTH syndrome differ from the classic Cushing’s syndrome and metabolic derangements are usually seen more often in the ectopic ACTH syndrome, unnecessary pituitary surgery can be performed in some cases with occult ectopic ACTH-dependent Cushing’s syndrome. Invasive radiologic techniques, especially inferior petrosal sinus, peripheral ACTH sampling and contrast-enhanced chest CT may help to establish a precise diagnosis. Biochemical features must be assessed with careful consultation between the radiologist, endocrinologist and the surgeon in order to prevent patients from unsuccessful and unnecessary treatment modalities.

Keywords: ACTH, bronchial carcinoid, paraneoplastic syndrome, dexamethasone supression test, CRH stimulation test, inferior petrosal sinus sampling