Malignant Struma Ovarii Requiring Emergency Surgery for Acute Abdomen: A Case Report and Literature Review

Abstract

Malignant struma ovarii is an extremely rare tumor, accounting for ≤0.1% of all mature cystic teratomas and 0.01% of all ovarian tumors. We herein describe a case involving a patient who underwent emergency surgery for suspected torsion of a mature cystic teratoma that was later diagnosed as malignant struma ovarii. A 23-year-old woman was brought to our hospital with the main complaint of acute lower abdominal pain. Computed tomography revealed a 10-cm-diameter right ovarian tumor with findings suggestive of a mature cystic teratoma. Based on the computed tomography and clinical findings, torsion of the ovarian tumor was suspected; therefore, emergency laparoscopic-assisted surgery was performed. On histopathological examination, the tumor was composed of cells with clear basophilic cytoplasm and a round nucleus. The cells were organized in thyroid follicle-like structures or funicular and solid honeycomb structures, and they exhibited slight nuclear atypia, proliferation, and vascular invasion. The tumor was diagnosed as malignant struma ovarii, and additional surgical resection of the right adnexa with partial omentectomy by laparotomy was performed on a later date. No malignant cells were found in the subsequently resected tissues, and cytologic examination of the ascitic fluid was negative. Because no residual tumor was found, the patient was followed up at the outpatient clinic without additional treatment. No signs of recurrence had been detected at the time of this writing. We herein present this case along with a literature review.