False-positive diagnosis of a pheochromocytoma with I-123 metaiodobenzylguanidine.

The rare case of a false-positive scintiscan with I-123 labelled metaiodobenzylguanidine (MIBG) in a patient with suspected pheochromocytoma is reported. Focal accumulation of the tracer in the upper right abdomen, primarily thought to represent a right-sided pheochromocytoma, was subsequently proven to be caused by an ampullary renal pelvis. In cases of unexplained MIBG accumulation the possibility of prolonged retention of the tracer, because of an abnormality of the renal pelvis, should be considered and excluded by ultrasound.