Intraoperative localization of malignant pheochromocytoma by 123-I-metaiodobenzylguanidine single probe measurement.

Metaiodobenzylguanidine (MIBG) imaging is a well-established method for locating intra- and extraadrenal pheochromocytomas. We investigated whether preoperative injection of 123-I-MIBG might be useful for intraoperative staging of chromaffine tumor cells. This was performed in a 46-year-old patient in whom the diagnosis of a malignant pheochromocytoma had been established by 123-I-MIBG imaging and enhanced catecholamine secretion. The rationale for intraoperative staging in this patient was a discrepancy between computed tomography (CI) of the abdomen and the radionuclide imaging, because scintigraphy revealed a mass with MIBG uptake in the right lower abdomen that could not be visualized by CT. We thus applied a preoperative dose of 4 mCi 123-I-MIBG and determined tissue activity by direct organ measurement. A right abdominal mass was thus identified with an activity of 10 x 10(4) impulses/s as compared to normal tissue (15 x 10(2)). The left-sided tumor was found to be identified correctly by prior CT and MIBG imaging. We thus conclude that intraoperative application of this single probe measurement might help to identify chromaffine tumor cells that have not been located fully by CT.