Metastatic follicular carcinoma arising from struma ovarii

Struma ovarii (SO) is an uncommon monodermal teratoma predominantly composed of mature thyroid tissue. Approximately 5% of SO are malignant; however, metastases are rare. A single female in her 40s, with a medical history of Graves' disease and bilateral cystectomy 10 years prior for right endometriotic cyst and left SO, presented with an enlarging abdominal mass for 4 months. Ultrasound pelvis showed a 13.8 cm left adnexal heterogeneous solid-cystic mass with internal septations and vascularity. She underwent open left salpingo-oophorectomy and resection of fibrous nodules from the right infundibulo-pelvic ligament and fallopian tube. Histology showed highly differentiated metastatic follicular carcinoma. She subsequently underwent total thyroidectomy, total hysterectomy, right salpingo-oophorectomy, tumour debulking and omentectomy followed by radioactive iodine treatment. Four-year follow-up did not show tumour recurrence or metastases. Due to its rarity, there are no well-established guidelines for the management and follow-up of metastatic follicular carcinoma arising from SO.