131-I-MIBG scintigraphy in the evaluation of suspected pheochromocytoma

131-I-metaiodobenzylguanidine (131-I-MIBG) scintigraphy was performed on 25 patients with suspected pheochromocytoma. Nine surgically proven pheochromocytoma masses (4 intra-adrenal, 5 extra-adrenal) occuring in 7 patients were all demonstrated on the 131-I-MIBG scintigrams. Sensitivity by 131-I-MIBG scintigraphy was 100 %, while sensitivities by CT scan and ultrasonography were 67 % and 63 % respectively. Our study confirmed the superiority of 131-I-MIBG scintigraphy in localizing pheochromocytoma. There were no false positives, though a slight uptake of 131-I-MIBG was shown in 27 % of normal adrenal gland. To make possible a more objective evaluation of 131-I-MIBG uptake in the adrenal gland, we studied the count ratios between the tumor and the background and between the normal adrenal gland and the background. The ratio of the former had a range greater than 1.5 while the latter was less than 1.3. (author)