99mTc-HYNIC-TOC Scintigraphy Is Superior to 131I-MIBG Imaging in the Evaluation of Extraadrenal Pheochromocytoma

In this investigation, the efficacy of scintigraphy using Tc-99m-labeled hydrazinonicotinyl-Tyr3-octreotide (HYNIC-TOC) in the evaluation of extraadrenal pheochromocytoma was assessed and compared with I-131-labeled metaiodobenzylguanidine (MIBG) imaging. Methods: Ninety-seven patients who were suspected of having pheochromocytoma but showed no definite adrenal abnormalities on CT were evaluated by both Tc-99m-HYNIC-TOC scintigraphy and I-131-MIBG imaging. The results were compared with pathology findings or clinical follow-up. Results: Of 58 patients proven to be without pheochromocytoma, Tc-99m-HYNIC-TOC and I-131-MIBG imaging excluded 56 and 58 patients, respectively, rendering a specificity of 96.6% for Tc-99m-HYNIC-TOC imaging and 100% for I-131-MIBG imaging. In the evaluation of adrenal pheochromocytoma (14 patients), the sensitivity of Tc-99m-HYNIC-TOC scintigraphy and I-131-MIBG imaging was 50% and 85.7%, respectively. However, in the evaluation of extraadrenal pheochromocytomas (25 patients), the sensitivity of Tc-99m-HYNIC-TOC scintigraphy and I-131-MIBG imaging was 96.0% and 72.0%, respectively. Conclusion: Tc-99m-HYNIC-TOC scintigraphy is more sensitive than I-131-MIBG imaging in the detection of extraadrenal pheochromocytomas.