Analysis of pelvic ^131I uptake after ^131I whole body scan in patients with thyroid cancer

Objective To analyze and explore the possible mechanism for pelvic ^131I uptake after ^131I post treatment whole body scan （RX-WBS）in patients with differentiated thyroid cancer. Methods （1）Data were retrospectively reviewed from 168 female patients with differentiated thyroid cancer（everyone has a RX-WBS ）. （2）46 patients were accepted by analyzing the characteristics of Rx- WBS and combing with some inclusion criteria, and then followed up. Results Among the 46 patients（46 positions accumulated 131I）with significant pelvic 13q uptake, 6 patients had two reasons leading to pelvic 131I uptake, and 2 patients had no specific reason. Among the 50 reasons for pelvic 131I uptake, 41 reasons related with uterus, 3 reasons related to rectum, 5 related to bladder and 1 related to ovarian chocolate cyst. Among the 41 reasons related to uterus, by combining the examinations of SPECT/CT, ultrasound, CT and the follow-up results, 18 were uterine leiomyomas, 9 were intrauterine devices, 2 were endometrial thickening, 3 were uterine cavity effusion, 7 were menstrual periods, 1 were uterine adenomyosis, 1 were gestational sac. Conclusions （1）In the Rx-WBS of female, the sig- nificant pelvic 131I uptake is generally caused by uterus, but not bladder. And it usually means gynecological disease, especially uterine leiomyomas when excluding physiological factors. （2）It is generally easy to differentiate bladder from rectum because they have different characteristic features of the pelvic 131I uptake. （3）SPECT/CT plays a very important role in locating 131I uptake in uterus. Key words: Thyroid neoplasms;  Iodine radioisotopes;  Whole body imaging;  Pelvic uptake