Pneumatosis Intestinalis
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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.