Primary extra-adrenal pheochromocytoma: positive I-123 MIBG imaging with negative I-131 MIBG imaging.

I-131 metaiodobenzylguanidine (I-131 MIBG) is a well established imaging agent that reliably detects pheochromocytoma. In some patients, however, I-131 MIBG may fail to localize pheochromocytoma. I-123 MIBG has several potential advantages over I-131 MIBG, and these advantages may enable locating pheochromocytomas which have eluded other techniques, including I-131 MIBG imaging. A patient with primary extra-adrenal pheochromocytoma is described who illustrates the superiority of I-123 MIBG for the imaging of pheochromocytoma.