Struma ovarii is a rare neoplasm that accounts for approximately 0.3ｵ of ovarian tumors. Due to its ultrasound morphology, which is quite similar to that of malignant ovarian carcinoma, most struma ovarii cases are open operated with laparotomy rather than laparoscopy. We present 3 cases of struma ovarii, which were diagnosed preoperatively by imaging studies and removed by laparoscopic surgery. All patients were premenopausal women between ages 31‒50. The magnetic resonance imaging (MRI) findings were complex masses composed of multiple cysts and solid components with T2-hypointense regions as well as multiple T1-hyperintense cystic areas, findings that are typical for struma ovarii. A combination of plain computed tomography (CT), positron emission tomography (PET)-CT, and scintigraphy was useful for diagnosis. Laboratory examination revealed elevated serum thyroglobulin, which led to the diagnosis of struma ovarii. Laparoscopic surgeries were performed without rupturing the tumors. Although it has been difficult to differentiate between struma ovarii and malignant tumors by conventional methods, recently MRI techniques appear make it possible to diagnose struma ovarii preoperatively from the abovementioned imaging characteristic, together with laboratory data. As for treatment, we think laparoscopy could be successful for struma ovarii, but the surgeon must be careful not to rupture the tumor intra-abdominally in order to prevent dissemination, which could lead to malignancy
