Gas On Abdominal X-ray DDx


Location of gas on the abdominal x-ray may suggest the the underlying cause

  • Intraluminal gas — bowel gas pattern
  • Free intraperitoneal air — pneumoperitoneum
  • Other gas collections — biliary, intramural, etc.

Bowel gas patterns may point to an underlying cause — bowel gas patterns include:

  • Normal
  • Nonspecific
  • Adynamic ileus
  • Mild — localized ileus or “sentinel loop”
  • Severe — “colonic pseudo-obstruction”
  • Small bowel obstruction; central, valvulae conniventes, pliable (“bent finger”)
  • Large bowel obstruction – peripheral, haustra, contains feces



  • Perforated peptic ulcer (usually duodenal)
  • Gastric ulcer perforation (benign or malignant)
  • Intestinal perforation (e.g. large bowel obstruction causing cecal perforation, inflammatory bowel disease)
  • Cecal or sigmoid volvulus
  • Perforated appendicitis or diverticulitis (infrequent)
  • Colonoscopy and biopsy
  • Residual postoperative gas
  • Post-laparoscopy
  • Post-dialysis
  • Penetrating trauma
  • Breakdown of surgical anastomosis
  • Ruptured pneumatosis cystoides intestinalis (e.g. ischemic gut, necrotizing enterocolitis)
  • Gas-forming intra-abdominal infection
  • Extension from the chest (e.g. pneumomediastinum, bronchopleural fistula)
  • Air via uterine tubes (e.g. post-sexual activity, spa bath, water ski-ing)

Mimics of pneumoperitoneum

  • Hepatodiaphragmantic interposition of the colon
  • Idiopathic (Chilaiditi syndrome)
  • Secondary to colonic distention (obstruction or ileus)
  • Rib margin that parallels diaphragm
  • Perihepatic fat

Right upper quadrant gas

  • Gallstone ileus (biliary-enteric fistula) [Rigler triad; Bouveret syndrome]
  • Sphincterotomy or surgical anastomosis
  • Emphysematous cholecystitis
  • Hepatic portal venous gas (bowel infarction)
  • Hepatic or subdiaphragmatic abscess
  • Pneumoperitoneum (overlying liver)
  • Hydrogen peroxide ingestion (or other gas forming substance)


Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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