Successful localization of ectopic ACTH-secreting bronchial carcinoid by selective pulmonary arterial sampling

Among patient with ACTH-dependent Cushing's syndrome, about 10-20% of those with ectopic ACTH syndromes (EAS) have occult or unknown tumors. Despite the intensive search for the culprit tumors by dynamic endocrine tests and imaging tests, it is often difficult to localize and confirm the source of occult ectopic ACTH secretion. We report a patient with EAS caused by a small bronchial carcinoid tumor, which was successfully localized by a selective pulmonary arterial sampling for the first time. A 69-year-old woman presented with typical Cushingoid features and elevated plasma ACTH and cortisol levels, which showed lack of circadian rhythm, no suppression by high-dose dexamethasone, and no response to CRH stimulation. No mass lesion was detected by pituitary MRI, and inferior petrosal sinus sampling showed no central to peripheral ACTH gradient. Although CT scan of the chest revealed a very small nodule in the right lung, it could not be confirmed by either somatostatin receptor scintigraphy or fluorodeoxyglucose positron emission tomography. Selective pulmonary arterial sampling of the wedged blood from a pulmonary artery branch affecting the nodule showed a marked ACTH gradient, and the lobectomy of the right middle lung resulted in dramatic decreases in plasma ACTH and cortisol levels. The resected tumor was diagnosed as a bronchial carcinoid tumor with positive immunostaining for ACTH. Thus, selective pulmonary arterial sampling, because of its more site-selective measurement of hormonal secretion, could be one of the useful tools to localize and confirm the ectopic ACTH production by a small pulmonary tumor.