Figure 8b. Free retroperitoneal air in a 7-year-old boy after a motor vehicle accident. Copies of CT scans (marks included) from the referring institution show not only free intraperitoneal air (arrows) but also free retroperitoneal air (arrowheads). Free intraperitoneal fluid (F in b) and mesenteric stranding (M in b) are also seen. At surgery, perforations were found in the distal duodenum and the hepatic flexure of the colon.