Radioiodine accumulation in a large adnexal cystadenofibroma

Posttherapy or diagnostic whole-body radioiodine (131I) scans are conducted to observe metastases of differentiated thyroid carcinomas. Sometimes, false-positive scans occur due a variety of lesions. Here we report a patient with marked radioiodine accumulation in a large adnexal cystadenofibroma, a benign ovarian tumor.

A 51-year-old woman underwent subtotal thyroidectomy due to an enlarged-multinodular goiter that caused mild compression to trachea. In her preoperative neck ultrasonography, there were mixed cystic-solid nodules without suspicious ultrasound features that were smaller than 1 cm. Pathologic examination revealed multifocal papillary thyroid carcinoma. The residual thyroid tissue was ablated with 3.7 GBq radioiodine (131I) when the serum thyroglobulin concentration was 28.7 ng/mL and the serum thyroid-stimulating hormone level was 50 microIU/mL. A posttherapy whole-body scan on the 10th day after ablation revealed well-demarcated, circumscribed radioiodine uptake in the right pelvic region. Pelvic ultrasonography revealed a solid-cystic lesion with a diameter of 9 cm in the right pelvic region. Six months later, the lesion accumulated marked radioiodine in the whole-body scan (with 185 MBq 131I). The patient underwent total abdominal hysterectomy and bilateral salpingo-oophorectomy. Pathologic examination revealed a benign cystadenofibroma without any coexisting thyroid tissue.

As far as we can ascertain, this is the first report of a radioiodine-accumulating cystadenofibroma. The mechanism for radioiodine accumulation in this patient's tumor is unclear.