Pneumoperitoneum: subdiaphragmatic free air

Pneumoperitoneum is gas within the peritoneal cavity. Interpretation depends on clinical history and any recent procedure.

Check position, quality and diaphragmatic domes. Distinguish gas between liver and diaphragm from bowel lumina with visible walls.

The image shows a lucent band beneath the right hemidiaphragm, separate from the bowel gas marked by blue arrows.

Investigate possible bowel perforation. Recent surgery can also account for free gas; the clinical course remains decisive.

Colonic interposition beneath the diaphragm can mimic this sign. Look for haustra and walls; use CT when necessary.

Assess sudden pain, guarding or rigidity, fever and haemodynamic deterioration. Establish recent surgery, endoscopy or trauma.

Peritonitis or shock requires urgent surgical assessment and stabilisation; do not delay referral merely to complete imaging.

A radiograph without visible free air does not exclude perforation. This isolated view cannot localise the bowel source.

Identify free gas, then integrate clinical and procedural context; CT often clarifies the cause, site and complications.

• Tarasconi et al. Perforated and bleeding peptic ulcer: WSES guidelines (2020) ↗
• Sartelli et al. WSES/GAIS/SIS-E/WSIS/AAST global clinical pathways for patients with intra-abdominal infections (2021) ↗

Documentary review: 2026-10-15