Struma ovarii is a specialized or monodermal teratoma predominantly composed of mature thyroid tissue . Thyroid tissue must comprise more than 50 percent of the overall tissue to be classified as a struma ovarii. Struma ovarii accounts for approximately 5 percent of all ovarian teratomas [2-4]. Depending on the histologic features, struma ovarii can be classified as benign or malignant . The clinical presentation, diagnosis, and management of struma ovarii will be reviewed here. Ovarian teratomas are reviewed in detail elsewhere. (See "Ovarian germ cell tumors: Pathology, clinical manifestations, and diagnosis", section on 'Teratomas'.)
The clinical manifestations of struma ovarii are based upon single case reports and small case series [2-7]. Struma ovarii is most common between the ages of 40 and 60 years. Women with struma ovarii usually present with pain and/or a pelvic mass and less frequently with ascites. In case series of 20 to 30 patients with histologically confirmed struma ovarii, abdominal pain was present in 20 to 42 percent and a palpable lower abdominal mass in 23 to 58 percent [4,8]. In one series, no definite symptoms were present in 14 patients (41.2 percent), in whom the presence of an ovarian tumor was incidentally noted on ultrasonography performed for other reasons . Ascites was present in 12 to 17 percent of patients. CA-125 was elevated in 4 of 13 women in whom it was measured (one of three who were found to have malignant struma ovarii).
Clinical and biochemical features of hyperthyroidism are uncommon in women with struma ovarii, occurring in less than 5 to 8 percent of cases [3,5,8-10]. In hyperthyroid patients, the serum TSH is low and free T4 and/or T3 are elevated. The thyroid gland typically is not enlarged, but serum thyroglobulin is elevated. Radioiodine uptake is low or absent in the thyroid gland, but present in the pelvis. Rarely, women with struma ovarii and hyperthyroidism also have a goiter . There are at least two possible explanations for this association:
●The coexistence of Graves' disease and struma ovarii, which has been reported rarely in the literature [11,12]. Serum thyroid-stimulating immunoglobulins (thyrotropin-receptor antibodies) would be expected to stimulate function of thyroid tissue in the ovary as well as in the neck.
●A toxic nodular goiter with parallel formation of thyroid autonomy in an ovarian teratoma.