Abstract
Struma ovarii is an extremely rare monodermal teratoma of the ovaries that produce thyroid hormone. We report a case of unexplained hyperthyroidism in a female patient that was found to have struma ovarii of the right ovary. A 59-year-old woman with a past medical history of hyperthyroidism was diagnosed 4 years ago. She started taking Methimazole approximately 2 years ago when she developed palpitations and was diagnosed with atrial fibrillation with rapid ventricular response. The patient was being evaluated for Graves' disease with a thyroid scintigraphy scan. The result showed decreased iodine uptake in the thyroid. She was also being evaluated for radioactive iodine ablation. The patient was admitted to the hospital due to atrial fibrillation with rapid ventricular response secondary to hyperthyroidism. Thyroid-stimulating hormone (TSH) was suppressed, free T4 and T3 were elevated. The thyroid ultrasound showed unremarkable findings and the nuclear medicine thyroid uptake scan showed decreased uptake in the thyroid. Thyroid peroxidase antibody (TPO-Ab), thyroid stimulating hormone receptor antibody (TSH-receptor Ab), thyroglobulin antibody, thyroid-stimulating immunoglobulin (TSI) were all negative. Due to unexplained hyperthyroidism, there was a concern about ectopic thyroid hormone production. The patient had pelvic ultrasound which showed a 4.5 x 4.1 x 3.4 cm right ovarian cyst. She underwent salpingo-oophorectomy of the right ovary. Pathology results confirmed struma ovarii. After the surgery, hyperthyroidism resolved, and she was taken off Methimazole. This patient presented with primary hyperthyroidism in the setting of normal thyroid ultrasound, thyroid uptake scan, and negative thyroid antibodies. The possibility of ectopic thyroid-producing tissue or tumor should be considered in the differential diagnosis. Struma ovarii is a specialized or monodermal teratoma predominantly composed of more than 50% of mature thyroid tissue or sufficient thyroid hormone production to cause hyperthyroidism. The most common presenting symptoms at the time of diagnosis was lower abdominal pain and palpable lower abdominal mass, but patients can be asymptomatic on presentation. Struma ovarii may mimic malignant ovarian tumors or sometimes can present with symptoms of hyperthyroidism. The treatment is surgical resection of the tumor. In rare cases, this tumor could be malignant and must be ruled out by histology.
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