Rigler's sign, also known as the double wall sign, is a radiologic sign seen on an x-ray of the abdomen when air is present on both sides of the intestine; a Rigler's sign is present when air is present on the inside (luminal side) and the outside (peritoneal side). Air in the peritoneum is considered abnormal, unless the patient had a recent abdominal surgery.
Double wall sign. This is a secondary sign of pneumoperitoneum. Patient is supine, and air within the abdomen and lumen of the bowel accentuate both sides of the bowel wall.
A false double wall sign can result from two loops of bowel being in contact with one another.