# Pneumatosis Intestinalis > Pneumatosis intestinalis for NEET-PG Surgery: gas in the bowel wall, benign versus ischaemic causes, portal venous gas and the management logic. - Canonical URL: https://prepelephant.com/topics/neet-pg/surgery/pneumatosis-intestinalis - Exam / course: NEET-PG · Subject: Surgery - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Pneumatosis Intestinalis", PrepElephant, https://prepelephant.com/topics/neet-pg/surgery/pneumatosis-intestinalis ## Direct answer Gas within the bowel wall is a radiological sign, never a diagnosis by itself. Pneumatosis intestinalis divides into a benign primary form (pneumatosis cystoides intestinalis) and a secondary form that shadows serious disease — mesenteric ischaemia, necrotising enterocolitis, COPD, corticosteroid or checkpoint-inhibitor use. The CT forces one question: is this bowel dying, or are these inert gas cysts in a comfortable patient? Portal venous gas, non-enhancing wall, peritoneal signs and a rising lactate push towards laparotomy; a well patient with cystic wall collections needs a cause hunt and observation, not a scalpel. ## What you must remember - **The 85-15 split:** roughly 85% of cases are secondary to another condition and 15% are primary (pneumatosis cystoides intestinalis) — benign subserosal or submucosal gas cysts in colon and jejunum with no wall disease. - **Secondary causes to list:** mesenteric ischaemia, necrotising enterocolitis, COPD, connective tissue disease, coeliac disease, leukaemia, trauma, intestinal obstruction and infections; drug associations include corticosteroids and immune checkpoint inhibitor colitis. - **CT pattern:** gas conforming exactly to the bowel wall, often with a "double halo" or target sign when mural oedema alternates with gas; hepatic portal venous gas must be hunted deliberately. - **Red flags that convert the scan into an operation:** localised peritonism, free fluid, absent wall enhancement, metabolic acidosis with rising lactate, leucocytosis with fever. - **The gas is fermentative:** hydrogen produced by intraluminal bacteria maintains the cysts — the physiological basis for oxygen therapy, which washes the gas out over days. - **Benign management:** high-concentration oxygen (or hyperbaric oxygen) for days to weeks, metronidazole in some regimens, and treatment of the underlying cause; cysts rupture harmlessly and resorb. - **The neonate is a different disease:** pneumatosis in a sick preterm infant is necrotising enterocolitis — serial imaging, cessation of feeds, and surgery for perforation or progressive deterioration. ## Reading the scan against the patient's pulse Two adults, one CT finding. A 68-year-old on treatment for atrial fibrillation arrives with three hours of diffuse pain; his scan shows pneumatosis of the jejunum, patchy non-enhancement, portal venous gas and free fluid, and his lactate is 3.4 mmol/L. Every red flag is present — this is advanced mesenteric ischaemia, and the correct move is resuscitation and laparotomy, not a wait-and-see. The second patient, a 45-year-old with COPD scanned for renal colic, has gas cysts along a well-enhancing sigmoid and feels entirely well. His pneumatosis is secondary to his lung disease with no surgical implication; he needs a search for the cause and discharge. Between these poles sit the genuinely difficult cases — a patient on nivolumab with diarrhoea, wall thickening but full enhancement and a normal lactate is managed medically for immune-related colitis with the surgical team alerted. The discipline is to let wall enhancement, portal gas and the metabolic state, not the pneumatosis itself, choose the pathway. ## Where students slip The commonest error is treating every pneumatosis as ischaemia and opening an abdomen that never needed opening; the opposite error is dismissing pneumatosis with portal gas in a genuinely septic patient. A quiet viva favourite is the free air question: ruptured gas cysts produce pneumoperitoneum without peritonitis — benign free air — and the examiner expects you to resist an automatic laparotomy when the patient is asymptomatic. In infants, remember that contrast enemas are avoided once NEC is suspected; the pneumatosis there is a marker of disease activity to be tracked radiologically, while in adults it is a decision point built from the whole clinical picture. ## Frequently asked questions ### What is the double halo sign? Alternating rings of gas and oedematous wall on contrast CT produce a target-like appearance, the classic radiological signature of pneumatosis. ### When does pneumatosis intestinalis demand laparotomy? Peritoneal signs, absent bowel wall enhancement, portal venous gas with lactate or acidosis — findings suggesting transmural ischaemia — mandate operative exploration. ### Why does oxygen therapy help the benign form? A high inspired oxygen gradient washes out fermentative hydrogen from the cysts, so they shrink and resorb over days to weeks. ### Which drugs are classically associated? Corticosteroids and immune checkpoint inhibitors are the textbook drug associations; both cause secondary pneumatosis through different mechanisms. ### Can pneumatosis cause pneumoperitoneum? Yes — rupture of a subserosal cyst releases free intraperitoneal gas in an asymptomatic patient, the well-known benign pneumoperitoneum.