Malignant struma ovarii with thyrotoxicosis

BACKGROUND: Malignant struma ovarii is seldom diagnosed preoperatively due to the rarity of the disease itself and the even rarer complications of thyrotoxicosis. CASE: A 48-year-old woman presented with symptoms of hyperthyroidism and a pelvic tumor raising the possibility of ovarian malignancy. Hormonal findings revealed increased thyroid function, but the thyroid gland was normal in size and texture. Thus, she was diagnosed preoperatively as having a hormone-producing malignant struma ovarii. At surgery, a FIGO stage Ia ovarian papillary adenocarcinoma of the thyroid was found. An immunohistochemical tumor stain for thyroglobulin was positive and the ovarian venous thyroglobulin level was extremely high. Findings of hyperthyroidism disappeared over several weeks. CONCLUSION: Malignant struma ovarii can be diagnosed preoperatively. Complications of thyrotoxicosis should be kept in mind when evaluating an ovarian tumor.