Primary Retroperitoneal Mucinous Tumor with Borderline Malignancy

Background: Primary Retroperitoneal Mucinous Tumors (PRMTs) are extremely rare neoplasms, with only a limited number of cases reported in the literature.They are classified into mucinous cystadenomas, mucinous borderline tumors, and mucinous cystadenocarcinomas. Case Presentation:We report the case of a 78-year-old female who presented with fatigue, knee pain, and tingling sensations.MRI of the lumbar spine incidentally revealed Grade IV hydronephrosis on the right side.A subsequent CT scan suggested a large renal cell carcinoma, leading to an open radical nephrectomy through a transperitoneal approach.Histopathological examination identified a primary retroperitoneal tumor with borderline malignancy adherent to the kidney.The patient's postoperative course was initially uneventful; however, she developed paralytic ileus requiring conservative management.Additionally, a persistent pulmonary lesion prompted a segmentectomy, confirming an in-situ adenocarcinoma of the lung.Discussion: To our knowledge, including this case, only 35 case reports of primary retroperitoneal mucinous borderline tumors have been published.PRMTs with borderline malignancy are predominantly found in women, with a median age of 42.4 years.Their clinical presentation varies.Imaging studies lack specific diagnostic criteria, and tumor markers are inconsistently elevated.Complete surgical resection remains the primary treatment, yielding an excellent prognosis.Due to the absence of standardized follow-up guidelines, individualized surveillance strategies are recommended. Conclusion:Primary retroperitoneal mucinous tumors are a rare but a potential differential diagnosis for retroperitoneal masses.Given their excellent prognosis early recognition and complete resection are crucial.Further case studies are necessary to establish standardized management and follow-up protocols.