Impact of ¹²³I-MIBG Scintigraphy on Clinical Decision-Making in Pheochromocytoma and Paraganglioma

Context: Cross-sectional imaging with CT or MRI is regarded as a first-choice modality for tumor localization in patients with pheochromocytoma and paraganglioma (PPGL). ¹²³I-labeled metaiodobenzylguanidine (¹²³I-MIBG) is widely used for functional imaging but the added diagnostic value is controversial. Objective: To establish the virtual impact of adding ¹²³I-MIBG scintigraphy to CT or MRI on diagnosis and treatment of PPGL. Design: International multicenter retrospective study. Intervention: None. Patients: Two hundred thirty-six unilateral adrenal, 18 bilateral adrenal, 48 unifocal extra-adrenal, 12 multifocal, and 26 metastatic PPGL. Main Outcome Measures: Patients underwent both anatomical imaging (CT and/or MRI) and ¹²³I-MIBG scintigraphy. Local imaging reports were analyzed centrally by two independent observers who were blinded to the diagnosis. Imaging-based diagnoses determined by CT/MRI only, ¹²³I-MIBG only, and CT/MRI combined with ¹²³I-MIBG scintigraphy were compared with the correct diagnoses. Results: The rates of correct imaging-based diagnoses determined by CT/MRI only versus CT/MRI plus ¹²³I-MIBG scintigraphy were similar: 89.4 versus 88.8%, respectively (P = 0.50). Adding ¹²³I-MIBG scintigraphy to CT/MRI resulted in a correct change in the imaging-based diagnosis and ensuing virtual treatment in four cases (1.2%: two metastatic instead of nonmetastatic, one multifocal instead of single, one unilateral instead of bilateral adrenal) at the cost of an incorrect change in seven cases (2.1%: four metastatic instead of nonmetastatic, two multifocal instead of unifocal and one bilateral instead of unilateral adrenal). Conclusions: For the initial localization of PPGL, the addition of ¹²³I-MIBG scintigraphy to CT/MRI rarely improves the diagnostic accuracy at the cost of incorrect interpretation in others, even when ¹²³I-MIBG scintigraphy is restricted to patients who are at risk for metastatic disease. In this setting, the impact of ¹²³I-MIBG scintigraphy on clinical decision-making appears very limited.