Primary borderline retroperitoneal mucinous cystic neoplasm and situs inversus totalis: a case report

Primary retroperitoneal mucinous cystic neoplasms (PRMCNs) are rare tumors classified into cystadenoma, PRMCN with borderline malignancy (PRMCN-BM), and cystadenocarcinoma. We report a 60-year-old woman with left flank abdominal pain whose MRI revealed situs inversus totalis alongside a complex cystic lesion in the left retroperitoneum measuring 4.8 × 5.2 × 4.5 cm. She underwent laparotomy with complete resection of the lesion, and histopathology confirmed a primary retroperitoneal neoplasm with borderline malignancy, with an uneventful postoperative course and no recurrence after 8 months. To date, only 35 cases of mucinous cystadenomas with borderline malignancy have been documented in the literature. Clinical presentation is variable, imaging lacks specific diagnostic criteria, and serum tumor markers have no diagnostic value. Surgical resection remains the curative therapeutic approach, and histopathology is essential for the definitive diagnosis, which continues to pose a preoperative challenge.