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

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.

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 ). 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 SPECT of the pelvis showing a large and heterogeneous radioiodine accumulation ultrasonography showing a right adnexal mass measuring 126 mm with a double tissue and cystic components HEx250: mucinous adenocarcinoma of the ovary, mucinous glands in a fibrous stroma

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 ].

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.