Abstract
Teratoma is a type of germ cell tumor layer that appears in the gonadal, sacrococcygeal, mediastinal, and retroperitoneal regions. Primary retroperitoneal teratoma is rare and asymptomatic but can present with symptoms due to a mass effect on neighboring organs. These tumors have to be considered in the differential diagnosis of a mass in the abdominal cavity of children to distinguish between Wilms' tumor, neuroblastoma, and other intra-abdominal lesions. We presented an infant boy with protrusion of the left upper quadrant of the abdomen and a palpable abdominal mass that had progressively enlarged. An abdominal computed tomography scan revealed a large retroperitoneal cystic, solid mass on the left side of the abdominal cavity, causing pressure on the left ureter. Also, hydronephrosis of the left kidney was seen with a decreased enhancement of the left kidney due to obstruction uropathy. The mass was suspicious on imaging for a retroperitoneal teratoma. The patient underwent laparotomy, and excision of the huge retroperitoneal mass was done. The final diagnosis was an immature teratoma grade 3, and the patient was discharged in good condition. Retroperitoneal teratomas are rare tumors in infants. These tumors would be an incident diagnosis or diagnosed by the mass effect of giant tumors on other organs. They must be considered in the differential diagnosis of intra-abdominal tumors in children. Hydronephrosis and obstructive uropathy can be rare consequences of the mass effects of these tumors.