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.
AXR of pneumoperitoneum
Right lateral decubitus radiograph of the abdomen shows a large amount of free air within the abdomen.
AXR of pneumoperitoneum due gastrostomy tube malposition causing gastric perforation
Supine AXR (left) shows a gastrostomy tube projecting appropriately over the stomach with a triangular lucency superior to the stomach. Left lateral decubitus AXR (above right) again shows the triangular lucency superior to the stomach but does not show air between the abdominal wall and liver. Cross-lateral AXR (below right) shows air between the anterior abdominal wall and liver.
AXR of pneumoperitoneum due to malposition of gastrojejunostomy tube outside of bowel
Supine AXR (above) shows the tip of the gastrojejunostomy tube extending deep into the pelvis. Left lateral decubitus AXR (below) shows air between the abdominal wall and the liver.
AXR and gastrojejunostomy tube injection of pneumoperitoneum due to malposition of the gastrojejunostomy tube outside of the bowel
Supine (above left) and left lateral decubitus (above right) AXR show no evidence of air between the abdominal wall and the liver but on the decubitus view several concerning air bubbles project over the liver and appear extra-lumenal. The gastrojejunostomy tube was exchanged for a gastrostomy tube and AP image from a gastrostomy tube injection with water soluble contrast (below) shows contrast extravasating inferiorly out of the duodenum at the junction of the second and third parts of the duodenum.
AXR of esophageal perforation from nasogastric tube placement
Supine AXR (above) shows increased lucency in the upper abdomen. The cross-table lateral AXR (below) shows air between the anterior abdominal wall and the bowel. The nasogastric tube follows a very straight course and does not curve towards the stomach. Note on both views that the tip of the nasogastric tube does not project over the stomach. US performed subsequently showed the tip of the nasogastric tube was in the retroperitoneum and not in the stomach.
AXR of gastric perforation from nasogastric tube placement
Supine AXR (left) shows a large amount of air within the abdomen and air outlining both sides of bowel wall (Rigler’s sign) in the right lower quadrant. Supine AXR taken later after pulling back of the nasogastric tube out of the stomach shows visualization of the falciform ligament over the spine (American football sign)
AXR of gastric perforation from nasogastric tube placement
Supine AXR (above) shows increased lucency throughout the central abdomen and left lateral decubitus AXR (below) shows air between the abdominal wall and the liver. On both views the tip of the nasogastric tube projects inferior to the gas-filled stomach.
AXR of gastric perforation from nasogastric tube placement
Supine and left lateral decubitus AXR (left) show a nasogastric tube with its tip deep in the pelvis without evidence of free air. Supine AXR taken after pulling the nasogastric tube back into the stomach (above right) shows increased lucency throughout the central abdomen and left lateral decubitus AXR taken at same time (below right) shows air between the abdominal wall and the liver.