Follicular variant of papillary carcinoma thyroid occurring in struma ovarii

We present the case of a 35-year-old female who presented with abdominal pain and irregular menstrual bleeding. The patient was found to have a left adnexal lesion on ultrasonography and contrast-enhanced computed tomography. Based on the preoperative imaging and biochemical workup, a left ovarian cystectomy was done. Histopathology (HPE) revealed follicular variant of papillary carcinoma thyroid in a background of struma ovarii. The patient then underwent total thyroidectomy. HPE showed no malignancy in the thyroid gland. After achieving the desired level of thyroid-stimulating hormone, postoperatively, the patient underwent a diagnostic I-131 whole-body scan (WBS) which revealed remnant thyroid tissue in the neck only. The patient's remnant thyroid tissue was ablated with I-131. Follow-up at 6-month interval revealed normal ultrasound pelvis, no abnormal uptake in diagnostic I-131 WBS and serum thyroglobulin (Tg), and anti-Tg antibody levels within normal range.