RESUMEN
Introduction and importance: Primary Retroperitoneal mucinous cystadenoma (PRMC) is an extremely rare benign tumor, predominantly occurring in women, with unclear pathogenesis. Case presentation: A 31-year-old woman, with no medical or surgical history, presented with left flank pain. Clinical discussion: An abdominal computed tomography (CT) scan revealed an 11cm retroperitoneal cyst. Due to its large size, percutaneous CT-guided drainage followed by a laparotomy surgical resection, were performed. Post-operative course was uneventful. Histological and immunohistochemical findings were consistent with PRMC. The patient was disease-free after a 6-month follow-up. Conclusion: Mucinous cystadenoma is a very odd finding in the retroperitoneum. Multiple differential diagnoses are to be considered beforehand, as most of cystic lesions in this anatomical region are malignant and require a different surgical approach. Radical resection, by laparotomy or laparoscopy, is the treatment of choice.
