"The pseudo-Rigler sign is an important form of pseudopneumoperitoneum, and a mimicker of the classic Rigler (double wall) sign, that can be encountered normally on abdominal radiographs."
"The pseudo-Rigler sign can result from omental or mesenteric fat, or oral contrast media outlining the bowel loops, or due to overlapping gas-filled bowels making the wall contours more striking 1-3."