Mature retroperitoneal teratoma in a 6-year-old child with trisomy 21: a case report

Introduction Retroperitoneal teratomas are rare pediatric germ cell tumors, most commonly diagnosed during infancy, and are predominantly histologically mature. Their association with Down syndrome has been reported but remains uncommon. Case presentation A six-year-old girl with trisomy 21 presented with a one-year history of intermittent left flank pain and occasional non-bilious vomiting. Examination revealed a firm, non-tender abdominal mass. Contrast-enhanced CT demonstrated a large, well-circumscribed retroperitoneal mass (150 × 75 × 122 mm) containing macroscopic fat, cystic areas, and calcifications. The mass displaced adjacent structures without invasion and compressed the inferior vena cava without occlusion. Serum AFP and β-hCG were age-appropriate. Complete en-bloc excision was performed, preserving major vessels despite close aortic adherence. Histopathology confirmed a mature teratoma with clear margins, and the postoperative course was uneventful, with no recurrence at one-year follow-up. Conclusion Although rare, mature retroperitoneal teratomas should be included in the differential diagnosis in children with trisomy 21 who are found to have an abdominal mass.