Detection of ACTH-producing bronchial carcinoid tumors: MR imaging vs CT.

Adrenocorticotrophic hormone (ACTH)-producing bronchial carcinoid tumors tend to occur in the middle third of the lung adjacent to pulmonary vessels. Because they cause signs and symptoms when quite small (by virtue of their ACTH production), they may not be detected by CT. MR imaging was performed in 10 consecutive patients with surgically proved ACTH-producing bronchial carcinoid tumors in order to test the ability of MR to clarify equivocal or indeterminate findings on CT examinations. All bronchial carcinoid tumors had high signal intensity on T2-weighted and short-inversion-time inversion-recovery images, facilitating their distinction from pulmonary vasculature. In eight patients, the CT and MR images were equivalent in the detection of bronchial carcinoid tumors. In two patients, MR showed tumors in the middle third of the lung that were equivocal on CT. MR imaging may distinguish small bronchial carcinoid tumors from adjacent pulmonary vessels in the central third of the lung at a time when the CT study is nondiagnostic or equivocal.