What is the Rigler sign?
“Rigler” sign is named after the radiologist Leo Rigler, MD, who described a sign of pneumoperitoneum in 1941. Normally, gas outlines only the luminal side of a bowel loop. The soft tissue side of the bowel is not visible as a sharp edge because there is no difference in density between the soft tissue of the bowel wall and the remainder of the abdomen. When free intraperitoneal gas abuts a gas-filled loop of bowel, gas surrounds both sides of the bowel wall. If the interfaces of gas and bowel wall are perpendicular to the x-ray beam, the bowel wall is visible and appears as a thin stripe of soft tissue