Struma ovarii with massive ascites mimicking ovarian carcinoma treated with conservative laparoscopic surgery: a case report

Struma ovarii is a rare taratoma that accounts for 0.5-1% of all ovarian tumors. It is sometimes difficult to differentiate struma ovarii from ovarian carcinoma. We encountered a case of struma ovarii that was suspected to be malignant due to the accumulation of massive ascites and an elevated CA125 level. It was successfully treated with laparoscopic surgery. A 37-year-old nulliparous woman consulted a local physician with a chief complaint of abdominal distention. Computed tomography (CT) of the abdomen revealed a pelvic tumor with a large amount of ascites. She was referred to our department. Contrast-enhanced magnetic resonance imaging (MRI) and CT showed bilateral ovarian tumors with multicystic and solid components. CA125 level was markedly elevated. Two cytological examinations of ascites showed no malignant cells. Preoperatively, malignancy was strongly suspected, but considering the possibility of a benign ovarian tumor, laparoscopic surgery was scheduled. During laparoscopic surgery, 4,850 mL of ascites were aspirated, and the left adnexa was removed. Intraoperative rapid pathology suggested struma ovarii with no evidence of malignancy. Postoperative pathology showed mature teratoma and struma ovarii. Although struma ovarii is benign in 90-95% of cases, there have been scattered case reports in which suspected malignancy led to unnecessary or excessive surgery. We propose that appropriate preoperative imaging and accurate intraoperative rapid pathology can prevent excessive surgery, conservative or laparoscopic excisions should be considered.