False-positive radioiodine accumulation in a huge pelvic mass after thyroidectomy for papillary carcinoma, a case report from Syria

Abstract

Iodine has always been connected to thyroid gland, and the fact that thyroid tissue traps, organificates and stores iodine more than other tissues is well known, hence the use of radioiodine as a diagnostic and therapeutic tool for thyroid disorders. However, false-positive cases do occur. We present a case of a 34-year-old patient who underwent total thyroidectomy for papillary carcinoma. Results of follow up TSH, thyroglobulin and thyroglobulin antibody tests after surgery lead to two rounds of radioactive iodine. After that, a radioiodine whole-body scan showed high uptake in the pelvis above bladder. Computed tomography scan showed a pelvic heterogeneous mass with some calcifications. Surgical removal and subsequent pathology confirmed the absence of metastasis. The final pathological diagnosis was serous cystadenoma, endometriosis cyst and leiomyoma. As the real cause behind false-positive iodine uptake by these tissues has yet to be determined, careful assessment should be considered in any suspicious case.

Causes of False-Positive Radioactive Iodine Uptake in Patients with Differentiated Thyroid Cancer

“…Benign tumors may have unexpected uptake of RAI. The mechanism can be due to functional physiologic NIS expression in the parenchymal tissues, such as in salivary gland tumors [109][110][111][112], breast fibroadenomas [113], and ovarian tumors [114][115][116][117]. Tumors with high vascularity, such as meningiomas [118,119] and angiomas/hemangiomas [120][121][122][123][124] can cause RAI pooling and uptake on RAI-WBS.…”

Incidental Finding of Endometrioid Adenocarcinoma of the Ovary on 131I Whole-Body Scan

“…Ovarian uptake of 131 I has been reported in the literature, which can either be from benign or malignant etiology 1,2 . Benign 131 I uptake entails benign struma ovarii, 3,4 mucinous cystadenoma, 5 serous cystadenoma, 6 cyst adenofibroma, 7 endometrial cyst, 6,8 leiomyoma, 6,9 and mature cystic teratoma 10 . Malignant causes include granulosa cell tumor, 11 mucinous adenocarcinoma, 12 and ovarian metastasis from papillary thyroid carcinoma 13 .…”