Pitfall of I-131 whole body scan: a mucinous adenocarcinoma of the ovary.

False positive radioiodine uptake following thyroidectomy for differentiated thyroid cancer has been reported in some cases. A 57-year-old female patient was referred for ablative radioiodine treatment four weeks after undergoing total thyroidectomy for papillary thyroid carcinoma. Posttherapeutic I-131 scintigraphy showed uptake in the neck and large focus in the lower abdomen and pelvis. Pathology revealed a mucinous adenocarcinoma of the right ovary. © Ali Sellem et al.

Introduction

Radioiodine is used for treating differentiated thyroid carcinoma [1]. The presence of uptake sites on the whole body scanning (WBS) following iodine 131 (I-131) may be caused by physiological radioiodine uptake, thyroid remnants or metastasis. However, the presence of unusual lesions may cause a false-positive results on radioiodine WBS; therefore, it is imperative to carefully evaluate abnormal scans in order to appropriately manage patients with differentiated thyroid cancer (DTC) [1]. We herein report an interesting case of false positive radioiodine uptake on an ovarian mucinous adenocarcinoma.

Patient and observation

A 57-year-old female patient underwent total thyroidectomy. Histopathology revealed a follicular thyroid carcinoma (pT1bNxMx). Four weeks later she received, with thyroid hormone withdrawal, 3.7 GBq of 131I as a treatment. At this time, the serum thyroglobulin level was 2.7 ng/mL, TSH was 73 µIU/ml and antithyroglobulin antibody level was less than 20 IU/mL. Five days after the treatment, WBS (Figure 1) showed mild uptake in the neck, representing thyroid remnants, and a large and a high heterogeneous radioiodine accumulation in the median lower abdomen and pelvis confirmed by Single Photon Emission Computed Tomography (SPECT) (Figure 2). An ultrasound showed a right adnexal mass measuring 126 mm with a double tissue and cystic components with heterogeneous vascularization on color Doppler (Figure 3). The patient underwent a hysterectomy with bilateral oophorectomy. Pathological examination found a mucinous adenocarcinoma of the right ovary (Figure 4).

Figure 1

post-therapeutic whole body scanning showing a mild uptake in the neck (thyroid remnants), and a large radioiodine accumulation in the median lower abdomen and pelvis

Figure 2

SPECT of the pelvis showing a large and heterogeneous radioiodine accumulation

Figure 3

ultrasonography showing a right adnexal mass measuring 126 mm with a double tissue and cystic components

Figure 4

HEx250: mucinous adenocarcinoma of the ovary, mucinous glands in a fibrous stroma

Discussion

Ovarian radioiodine uptake at post-therapy WBS may occur in benign or malignant conditions [2-4]. Pathology examination is the only way to differentiate between the two conditions. The benign pathological diagnosis can be a benign thyroid tissue (struma ovarii) [2], a benign mucinous ovarian cystadenoma [5, 6] and an ovarian endometriosis cyst [2]. The malignant conditions were metastasis of thyroid cancer cells to ovary and thyroid cancer originating from embryonic thyroid tissue in the ovary, which may also result in focal ovarian uptake [2]. To our knowledge, this is the first case of false-positive radioiodine uptake in an ovarian mucinous adenocarcinoma. The suggested mechanisms of radioiodine uptake in the ovarian cystadenoma include increased vascularity and capillary permeability [7].

Conclusion

It is important to recognize the physiological and pathological aetiologies (unrelated to thyroid) that demonstrate 131 I uptake and may lead to false positif 131 I scan in patients of DTC.