Abstract: Objective To evaluate ^99mTc-HYNIC-TOC somatostatin receptor and ¹³¹I-MIBG imaging in clinical diag- nostic of pheochromocytoma and paraganglioma (PPGL). Methods This was a retrospective study.359 PPGL patients diagnosed by pathology microscopy were included. The diagnostic sensitivity and influencing factors on ^99mTc-HYNIC-TOC somatostatin receptor and ¹³¹I-MIBG imaging were analyzed. Results The positive rate of ^99mTc-HYNIC-TOC somatostatin receptor scintigraphy was 57.7%(184/319)and ¹³¹I-MIBG imaging was 83.2%(232/279). The positive rates of ^99mTc-HYNIC-TOC somatostatin receptor imaging in the adrenal glands, retroperitoneum, head and neck, heart and mediastinum, pelvis and bladder were 53.3%, 62.5%, 95.0%, 66.7%, 50.0% and 11.0% respectively and the positive rates of ¹³¹I-MIBG imaging were 86.7%, 88.5%, 45.4%, 50.0% ,75.0% and 33.3% respectively. The positive rate of the two imaging did not showed difference among patients with different genetic backgrounds (SDH,VHL,RET mutations). The median maximum diameter of tumors was 4.4(3.0, 6.1)cm.and the diagnostic sensitivity of somatostatin receptor imaging and ¹³¹I-MIBG imaging for larger tumors(≥4.4 cm) was significantly higher than those for the smaller tumor group (＜4.4 cm) (64.0% vs. 51.3%; 92.3% vs. 74.1%)(P＜0.01). Tumors in 19 patients (5.3%) failed to uptake neither imaging method. Conclusions This is the largest PPGL cohort in China concerning ^99mTc-HYNIC-TOC somatostatin receptor imaging and ¹³¹I-MIBG imaging. The sensitivity of¹³¹I-MIBG imaging is higher than that of ^99mTc-HYNIC-TOC somatostatin receptor imaging, but for some tumors, such as head and neck paraganglioma, the latter has obvious advantages. These two imagings technologies are complementary and the choice of them should depend the individual situation of patients.

Key words: pheochromocytoma, paraganglioma, ^99mTc-HYNIC-TOC somatostatin receptor imaging, ¹³¹I-MIBG imaging, diagnostic sensitivity