Retroperitoneal hematomas in children without an antecedent history of trauma are a diagnostic challenge. They may be a coincidental finding at the time of autopsy or may present as a problem in the differential diagnosis of an abdominal mass. X-ray film of the abdomen, intravenous pyelogram, and barium enema are helpful in evaluation, but only with laparotomy can one exclude neoplasm.
Johnson CF, Reyes HM, Replogle RL. Chronic Retroperitoneal Hematomas in Children. Arch Surg. 1971;102(3):214-215. doi:10.1001/archsurg.1971.01350030052015