The importance of renal localization with MIBG scintigraphy.

Although I-123 metaiodobenzylguanidine (MIBG) imaging is a well-validated technique for identification and evaluation of a pheochromocytoma, accurate interpretation can be confounded by tracer retention within the renal pelvis. The authors report two cases of abnormal MIBG accumulation in which renal localization was essential. In the first case, renal localization revealed uptake inferomedial to the left kidney in what was proved to be an extra-adrenal paraganglioma. In the second case, MIBG uptake in a similar location on the right was caused by uptake in the renal pelvis, a physiologic finding. When the location of MIBG uptake in the upper abdomen is uncertain, a renal scan should be obtained to exclude the possibility of radiolabeled MIBG tracer retention within the collecting system, a potential false-positive diagnosis of pheochromocytoma.