Hyperthyroidism due to coexistence of graves' disease and struma ovarii

Objective: To report an unusual case of persistent thyrotoxicosis after treatment of Graves' disease, because of coexistence of struma ovarii. Methods: We report the clinical history, imaging studies, laboratory and pathologic data, and treatment in a patient with persistent hyperthyroidism after surgical treatment of Graves' disease. In addition, we discuss some aspects of the pathogenesis of hyperthyroidism due to functioning struma ovarii. Results: A 42-year-old woman underwent near-total thyroidectomy for treatment of Graves' disease. Post-operatively, hyperthyroidism was still present. Methimazole was administered again, and performance of a ¹³¹I whole-body scan demonstrated a focus of intense uptake in the pelvis. Pelvic ultrasonography revealed a mass (11 by 8 by 7.1 cm) arising from the right ovary, with both solid and cystic components. Abdominal surgical exploration was performed, and the final histologic diagnosis was struma ovarii. The symptoms of hyperthyroidism diminished, and 3 weeks postoperatively, the thyroid hormone levels were in the hypothyroid range. Conclusion: In patients with refractory hyperthyroidism after thyroid surgical treatment, radioiodine scanning should be performed to diagnose or exclude the functioning profile of ovarian masses.