*Riglers sign* , which is also known as the double-wall sign or the bas-relief sign , both sides of the bowel wall can be visualized on a radiograph of the abdomen obtained with the patient in the supine position.Gas normally outlines only the luminal surface of the bowel wall and not the serosal surface, which has a degree of opacity similar to that of adjacent peritoneal contents. When at least a moderate amount offree intraperitoneal air exists, however, this free air is more likely to accumulate between bowel loops,thus permitting visualization of the outer walls of the bowel.
