Gangrenous torsion of a giant benign mucinous ovarian cystadenoma mimicking malignancy in a postmenopausal woman: a rare case report

Giant mucinous cystadenomas are rare in postmenopausal women and may mimic ovarian malignancy, particularly when complicated by torsion or ischemic necrosis. Conventional tools such as the risk of malignancy index (RMI) and ovarian-adnexal reporting and data system (O-RADS) can be misleading in these situations. Although accurate distinction is desirable, when preoperative evaluation suggests high malignant potential, comprehensive staging surgery is justified to ensure oncologic safety, even if the lesion proves benign. A 75-year-old postmenopausal woman presented with 10 days of progressive abdominal distension, dull diffuse abdominal pain, anorexia, and weight loss. Examination revealed a large abdominopelvic mass corresponding to a 32-week gravid uterus. Tumor markers were normal (CA-125:32.1 U/ml< 35; CEA: 1.85 ng/ml<3). Ultrasonography and CT demonstrated a 20 cm multiloculated complex cystic adnexal mass with irregular mural nodules but no ascites or lymphadenopathy. Risk assessment suggested high malignant potential (elevated RMI score and O-RADS 4 category). A staging laparotomy was performed. Intraoperatively, a 30 cm torsed, gangrenous mucinous cystadenoma of the left ovary with intact capsule was identified. Surgical management included total abdominal hysterectomy, bilateral salpingo-oophorectomy, pelvic lymphadenectomy, and omentectomy. Frozen section and final histopathology confirmed a benign mucinous cystadenoma with extensive gangrenous changes. This case highlights the diagnostic dilemma of differentiating complicated benign adnexal tumors from malignancy in elderly women. It emphasizes the limitations of preoperative risk models when torsion or necrosis distorts imaging features and supports comprehensive surgical staging in high-risk profiles, even when pathology is benign, thereby ensuring oncologic safety.