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The newborn abdomen: necrotising enterocolitis and malrotation

  • Finding

Two newborn bowel emergencies: an inflamed, dying gut in premature babies, and a twisted gut from abnormal rotation. Each has its own X-ray and contrast signs.

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What it is

Necrotising enterocolitis (NEC) is inflammation and necrosis of the bowel wall, mainly in premature and low-birth-weight infants after feeds have started, presenting with feeding intolerance, abdominal distension, bloody stools and signs of sepsis. The abdominal radiograph is the key study and is repeated at intervals in the acute phase to look for progression and perforation; ultrasound adds information on bowel wall thickness, blood flow and fluid. Malrotation is failure of the normal rotation and fixation of the midgut in fetal life, which leaves the bowel on a narrow mesentery that can twist (midgut volvulus) and cut off the superior mesenteric blood supply. Its hallmark is bilious vomiting in a newborn, a surgical emergency. The upper gastrointestinal contrast study, which locates the duodenojejunal flexure, is the classic diagnostic test; ultrasound can show twisted mesenteric vessels.

What it looks like

  • NEC, early: dilated, gas-filled loops, thickened bowel walls and a disorganised gas pattern.
  • Pneumatosis intestinalis: bubbly or linear lucencies (gas) within the bowel wall; the hallmark of NEC.
  • Portal venous gas: thin branching lucencies over the liver reaching its periphery; a sign of more severe disease.
  • Pneumoperitoneum (perforation): football sign (a large oval lucency over the abdomen on the supine film), gas on both sides of the bowel wall (Rigler sign), or free gas under the abdominal wall on a cross-table lateral or left lateral decubitus film.
  • A fixed dilated loop that does not change across serial films suggests necrotic bowel.
  • Malrotation on upper GI study: the duodenojejunal flexure does not cross to the left of the left vertebral pedicle or lies lower than the duodenal bulb; jejunum sits in the right abdomen.
  • Midgut volvulus: corkscrew course of the duodenum and proximal jejunum, or a bird's beak tapering at the point of twist; on ultrasound, the whirlpool sign and a superior mesenteric vein lying left of the artery.

Why it looks that way

  • In NEC, gas-forming bacteria enter the damaged mucosa, so gas collects in the bowel wall and can track into the portal veins.
  • In malrotation, the narrow mesenteric base acts as a pivot; when the bowel twists around it the superior mesenteric vessels twist too, giving the whirlpool sign.
  • The plain film in volvulus may be normal early, or show a distended stomach and duodenum with little distal gas, so a normal radiograph does not exclude it.

Differential and pitfalls

  • Pneumatosis can be subtle and mimicked by stool mixed with gas; compare serial films and correlate with the clinical picture.
  • Never give an enema or barium contrast study in suspected NEC: it risks perforation.
  • A normal abdominal radiograph does not exclude malrotation with volvulus; bilious vomiting needs an urgent contrast study or surgery.
  • An unstable infant with suspected volvulus may go straight to the operating room without imaging.
  • Spontaneous intestinal perforation in very premature infants can give free air without pneumatosis; the management differs from NEC.

Next step

  • Suspected NEC: supine abdominal radiograph plus a cross-table lateral or left lateral decubitus film; repeat at intervals in the acute phase.
  • Stop feeds, decompress the stomach, take cultures and inform the neonatologist and paediatric surgeon.
  • Free air, portal venous gas with deterioration, or a fixed loop: call the paediatric surgeon urgently.
  • Bilious vomiting in a newborn: urgent upper GI contrast study and surgical review the same hour if possible.
  • If the infant is unstable or the abdomen is peritonitic, do not wait for imaging: call the surgeon.

Test yourself

Think of the answer, then tap the question to see it.

What radiographic finding is the hallmark of necrotising enterocolitis?

Pneumatosis intestinalis: bubbly or linear gas lucencies within the bowel wall.

Which extra radiograph helps detect perforation in a supine newborn?

A cross-table lateral or left lateral decubitus film, which shows free gas rising under the anterior abdominal wall or over the liver.

Where should the duodenojejunal flexure lie on a normal upper GI contrast study?

To the left of the left vertebral pedicle and at about the level of the duodenal bulb; failure to reach this position suggests malrotation.

Why does a normal abdominal radiograph not exclude midgut volvulus?

Early in volvulus the film can be normal or nearly so; only a contrast study, ultrasound or surgery reliably shows the twist.

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Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: Necrotizing Enterocolitis (StatPearls (NCBI Bookshelf), 2023); Midgut Malrotation (StatPearls (NCBI Bookshelf), 2026).

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