Hyperthyroidism due to struma ovarii: Diagnostic pitfalls and preventing thyroid storm.

We report struma ovarii in a case that had hyperthyroidism and was treated with laparoscopic tumor resection. A 40-year-old Japanese woman presented with tachycardia, finger tremor, and weight loss. Although blood examination showed hyperthyroidism, test results for thyroid stimulating hormone receptor antibody and thyroid stimulating antibody were negative, and thyroid scintigraphy showed no abnormal findings. Because she was diagnosed with an ovarian tumor, and whole-body scintigraphy showed that iodine uptake was detected in the pelvic space, we diagnosed her with an ovarian tumor, which caused excessive thyroid hormone secretion. After controlling the thyroid hormone level, we resected the ovarian tumor laparoscopically. The thyroid hormone level was within the normal range postoperatively without any medications. Based on our experience, physicians need to remember that ovarian tumors can cause hyperthyroidism. Controlling the thyroid hormone level preoperatively by using antithyroid drugs and performing minimally invasive laparoscopic surgery is considered useful for preventing thyroid storm.