A Case Report of a Giant Mucinous Cystadenoma Suspected to Be Associated with Ovarian Remnant Syndrome After Bilateral Adnexectomy: Diagnostic Pitfalls and Implications for Clinical Management.

Background: Mucinous cystadenoma of the ovary is one of the common benign ovarian neoplasms. Nevertheless, when a huge pelvic mass develops years after bilateral adnexectomy, determining its tissue origin and establishing a differential diagnosis poses substantial challenges, complicating the clinical management of such secondary pelvic lesions. Case Presentation: This study reports a rare case of a giant pelvic mass occurring many years after bilateral adnexectomy in a 65-year-old Han Chinese female. Intraoperative exploration and postoperative histopathology confirmed the lesion as an ovarian mucinous cystadenoma, which was presumed to arise from residual ovarian tissue after previous surgery, consistent with ovarian remnant syndrome (ORS). However, the ovarian origin of this lesion was comprehensively determined based on prior surgical records, intraoperative findings, and histopathological morphology, without further confirmation by definitive immunohistochemical staining. Conclusion: Ovarian remnant syndrome should be considered in the differential diagnosis of de novo pelvic masses following bilateral salpingo-oophorectomy. A review of prior surgical records is essential for tracing the origin of such lesions. For pelvic mucinous lesions, gastrointestinal and appendiceal origins should be prioritized for exclusion, accompanied by comprehensive characterization of pathological features. To minimize the risk of long-term postoperative lesions, complete resection of all ovarian tissue should be pursued during bilateral salpingo-oophorectomy in routine clinical practice.