Pneumoperitoneum

  • Etiology: barotrauma (pneumothorax or pneumomediastinum dissecting into abdomen), nasogastric tube perforating stomach, indomethacin used to close patent ductus arteriosus causing gastric ulcer, necrotizing enterocolitis, obstruction, blunt abdominal trauma
  • CXR upright: air beneath diaphragm
  • AXR upright: air beneath diaphragm
  • AXR left lateral decubitus: air above the liver (air between abdominal wall and liver)
  • AXR cross-table lateral: for small amounts of air see tell-tale triangle sign of air between bowel loops, for large amounts of air see air superiorly between abdominal wall and viscera
  • AXR supine: overall increased lucency of abdomen, American football sign of falciform ligament, inverted Y of umbilical artery ligaments, Rigler’s sign (see air outlining both sides of bowel wall)
  • Note: in inflamed abdomen (due to necrotizing enterocolitis or other forms of perforation), pneumoperitoneum may be loculated and not be classically seen on upright / decubitus / cross-table lateral views, may appear as fixed air collection that does not appear to conform to bowel

Cases of Pneumoperitoneum

CXR of pneumoperitoneum
Upright CXR shows free air beneath the diaphragm.
AXR of pneumoperitoneum
Left lateral decubitus AXR shows free air between the right abdominal wall and the liver.
AXR of pneumoperitoneum
Cross-table lateral AXR shows a large amount of free air superiorly in the abdomen outlining some of the bowel loops and compressing the rest posteriorly.
AXR of pneumoperitoneum
Supine AXR shows increased lucency in the upper abdomen without clear demonstration of the football sign of the falciform ligament being outlined by free air.
AXR of pneumoperitoneum
Supine AXR shows increased lucency in the upper abdomen with clear demonstration of the football sign of the falciform ligament being outlined by free air.
AXR of pneumoperitoneum
Supine AXR obtained during an intussusception reduction shows air outlining both the inner and outer walls of the small bowel (Rigler’s sign).
AXR of pneumoperitoneum
Supine (left) and upright (right) AXR show a central fixed air collection that does not appear to conform to bowel and does not demonstrate any of the classic signs of free air.