Limitations of 131I-MIBG scintigraphy in locating pheochromocytomas.

131I-metaiodobenzylguanidine (131I-MIBG) scintigraphy for the location of pheochromocytomas has proved to be a major advance in patient management. In combination with computerized tomographic scanning, nearly all pheochromocytomas can be located before surgery and invasive investigations are now indicated only in exceptional cases. However, there are still lessons to be learned concerning the optimal administration and interpretation of 131I-MIBG scintigraphy. With careful attention to detail and an awareness of isotope distribution, false positive studies should be extremely rare. While the incidence of false negative studies is uncommon, these certainly occur. A patient with sporadic bilateral adrenal medullary hyperplasia, bilateral pheochromocytomas, and additional benign pheochromocytomas arising in paraganglia tissue anterior to the abdominal aorta is presented. The right adrenal pheochromocytoma was not identified on 131I-MIBG imaging. We conclude that even with current locating techniques, the traditional surgical approach to pheochromocytoma should not be abandoned. This involves transabdominal exploration of both adrenal glands and careful examination of all possible sites of extra-adrenal pheochromocytomas.