X-Ray of pneumopertoneum

Numerous signs are described for diagnosing pneumoperitoneum on plain radiographs. One of the best known, the Rigler sign (also known as the double-wall or bas-relief sign), is a visualization of the outer surface of a bowel loop wall resulting from free air in the peritoneal cavity. The intraluminal gas provides negative contrast and outlines the internal wall. The cupola sign, typically seen on supine radiographs, is an inverted cup-shaped arcuate lucency overlying the lower thoracic spine and projecting caudally to the heart. This sign is formed as air accumulates anteriorly in the median subphrenic space under the central leaf of the diaphragm. The umbilical ligaments, the urachus, and particularly the falciform ligament are sometimes identified as linear radiopaque structures in the presence of free air.[1,3,5,7]