Nabothian cyst associated with high false-positive incidence of iodine-131 uptake in whole-body scans after treatment for differentiated thyroid cancer

OBJECTIVE This study aimed to analyze the focal uptake of iodine-131 (131I) in the upper pelvis superior to the urinary bladder on whole-body images of patients who underwent this treatment after thyroidectomy for differentiated thyroid cancer. METHODS Between June 2012 and March 2013, 205 patients (72 men and 133 women, with an average age of 47.9 ± 11.7 years) who underwent 131I radioactive treatment after thyroid cancer surgery were analyzed retrospectively. Pathological findings confirmed papillary thyroid carcinoma. A whole-body scan was acquired 5 days after 100-120 mCi sodium iodide was administered orally to the patients. Single-photon emission computed tomography/computed tomography (SPECT/CT) scanning was carried out to locate the lesion; this showed abnormal intense activity in the upper pelvis superior to the urinary bladder, which was further evaluated by ultrasonography. RESULTS Using 131I-SPECT scanning, five (3.76%) female patients were shown to have abnormal focal radioactivity in the lower abdomen. Subsequent SPECT/CT examination showed that the radioactivity was located in the cervix in four of the five patients and in the sigmoid colon in one patient. Transvaginal ultrasonography was performed in the former four patients, which revealed several echo-free regions in the cervix. These findings are consistent with the diagnosis of a nabothian cyst. Three of these patients were administered a second course of radioiodine therapy. Radioactive uptake was still visible at the same sites on whole-body imaging. CONCLUSION Nabothian cyst should be considered in cases in which abnormal uptake in the upper pelvis superior to the urinary bladder is detected on 131I whole-body scans after differentiated thyroid cancer resection.