[¹²³I]metaiodobenzylguanidine and [¹¹¹In]octreotide uptake in benign and malignant pheochromocytomas

Selecting the appropriate approach for resection and follow-up of pheochromocytomas (PCCs) is highly dependent upon reliable localization and exclusion of multifocal, bilateral, or metastatic disease. Metaiodobenzylguanidine (MIBG) scintigraphy was developed for functional localization of catecholamine-secreting tissues. Somatostatin receptor imaging (SRI) has a high sensitivity for localizing head and neck paragangliomas, but studies of intraabdominal PCCs are rare. In this study we review our experience of [¹²³I]MIBG and SRI, performed since 1983 and 1989, respectively, in the work-up of primary and recurrent PCCs. Scintigraphic results were correlated with catecholamine secretion, size and site, malignancy, associated tumor syndromes, and morphological features. [¹²³I]MIBG scans were performed in a total of 75 patients, in 70 cases before resection of primary PCCs and in 5 cases because of recurrent disease. Ninety-one PCCs were resected. The overall detection rates were 83.3% and 89.8% for PCCs larger than 1.0 cm. Multifocal disease was detected in 4 patients with [¹²³I]MIBG. [¹²³I]MIBG uptake correlated with greater size of PCC (r = 0.33; P = 0.008) and greater concentration of plasma epinephrine (r = 0.32; P = 0.006). [¹²³I]MIBG-negative PCCs (n = 14) had significantly (P = 0.01) smaller diameters than [^123I]MIBG-positive tumors. Furthermore, [¹²³I]MIBG uptake was significantly higher in unilateral (P = 0.02), benign (P = 0.02), sporadic (P = 0.02), intraadrenal (P = 0.02), and capsular invasive (P = 0.03) PCCs than in bilateral, malignant, MEN2A/2B-related, extraadrenal, and noninvasive PCCs, respectively. The detection rate of SRI was only 25% (8 of 32) for primary benign PCCs. In 14 patients metastases occurred, which were effectively visualized with [¹²³I]MIBG in 8 of 14 cases. SRI was able to detect metastases in 7 of 8 cases, including 3 [¹²³I]MIBG-negative metastatic cases. In addition, [¹²³I]MIBG and SRI detected 2 recurrences. In conclusion, [¹²³I]MIBG uptake is correlated with the size, epinephrine production, and site of PCCs. Its role in bilateral and MEN2A/2B-related PCCs seems limited. In cases of recurrent elevation of catecholamines, localization of metastases and/or recurrence should be attempted with [¹²³I]MIBG scintigraphy. In suspicious metastatic PCCs, SRI might be considered to supplement [¹²³I]MIBG scintigraphy.