The paediatric abdominal X-ray

Written by the X-Ray Atlas editorial team from the sources listed below · Medical review pending · Updated 24 October 2026 · Level: Advanced

The abdominal X-ray (AXR) in a newborn or infant answers different questions from the adult film. In neonates it looks for necrotising enterocolitis, congenital obstruction and perforation. In older infants and toddlers it is sometimes requested for intussusception, where ultrasound is the better test. Two rules frame everything on this page: bilious (green) vomiting in a neonate is malrotation with volvulus until proven otherwise, and a normal AXR does not exclude malrotation or intussusception. This page explains the normal infant gas pattern, the key signs, and when to move straight to another test.

1. The normal infant gas pattern

• Swallowed air appears in the stomach within minutes of birth, fills the small bowel over the first few hours and normally reaches the rectum within about the first day. A lack of distal gas at an age when it should be there suggests obstruction (or a baby who is ventilated, sedated or nil by mouth).
• In infants, small and large bowel are hard to tell apart. Haustra are poorly developed, and the bowel loops look similar. Describe the pattern ("multiple dilated loops", "gas-less abdomen") rather than forcing the adult labels from reading an adult AXR.
• A normal infant abdomen has a polygonal, mosaic-like gas pattern of many loops of similar size. Loss of this pattern, with some loops much larger than others, is abnormal.
• Most neonatal films are supine AP. A left lateral decubitus or cross-table (horizontal beam) lateral is added to look for free gas.

2. Necrotising enterocolitis (NEC)

NEC is inflammation and necrosis of the bowel wall, mainly in premature infants, usually in the first weeks of life. Babies develop feed intolerance, abdominal distension and bloody stools. Serial films are used to monitor the disease.

• Dilated bowel loops, sometimes with thickened, separated walls (bowel wall oedema).
• A fixed, dilated loop that does not change on serial films, which raises concern for necrosis.
• Pneumatosis intestinalis: gas within the bowel wall, either bubbly (like faeces, but in a baby who is not yet passing formed stool) or linear lines parallel to the bowel wall. This is the hallmark of established NEC.
• Portal venous gas: branching lucencies over the liver that extend to its periphery.
• Pneumoperitoneum, indicating perforation.

Modified Bell stage	Meaning
I	Suspected NEC: non-specific signs, X-ray normal or mild dilatation.
II	Definite NEC: pneumatosis, with or without portal venous gas.
III	Advanced NEC: critically ill infant, or perforation.

3. Free gas in a baby

On a supine film, large amounts of free gas collect in the front of the abdomen:

• Football sign: a large, oval lucency over the whole abdomen, sometimes with the falciform ligament outlined as a vertical line (the "laces").
• Rigler's sign: both sides of the bowel wall visible because gas lies inside and outside it.
• Gas outlining the liver edge or triangles of gas between loops.

A left lateral decubitus film (gas rises over the liver) or a cross-table lateral (gas under the anterior abdominal wall) confirms small amounts. Perforation is a surgical emergency. See pneumoperitoneum for the adult signs.

4. Congenital obstruction: high or low?

Count the gas-filled loops. A few dilated bubbles suggests a high (proximal) obstruction; many dilated loops suggests a low (distal) one.

Condition	AXR	Notes and next test
Duodenal atresia	Double bubble (stomach and duodenal cap) with no distal gas.	Associated with Down syndrome in a substantial minority (about 30% in many series; figures vary). Gas beyond the duodenum means incomplete obstruction, such as a web, stenosis or malrotation with volvulus, which needs urgent contrast study.
Jejunal atresia	A "triple bubble" or a few dilated proximal loops.	Surgical referral.
Ileal atresia	Many dilated loops.	Contrast enema shows a small, unused colon (microcolon).
Meconium ileus	Many dilated loops, few air–fluid levels, a "soap-bubble" appearance of meconium mixed with gas in the right lower quadrant.	Strongly associated with cystic fibrosis. Contrast enema shows a microcolon and may be therapeutic.
Hirschsprung disease	Distal obstruction with many dilated loops; delayed passage of meconium.	Contrast enema may show a transition zone and a rectum narrower than the sigmoid (rectosigmoid index below 1). Rectal biopsy is diagnostic. Watch for enterocolitis, which can be life-threatening.

5. Malrotation with volvulus

In malrotation, the bowel has not rotated and fixed normally during development, leaving the small bowel hanging on a narrow mesentery that can twist (midgut volvulus). This cuts off the blood supply to most of the small bowel within hours.

• The classic presentation is bilious vomiting in a neonate, but it can occur at any age.
• The AXR is often normal. It may show a partial double bubble with little distal gas, or a gasless abdomen. Late signs (dilated, thick-walled loops) mean ischaemia.
• The test is an urgent upper GI contrast study. The duodenojejunal (DJ) flexure normally lies to the left of the left vertebral pedicle at about the level of the duodenal bulb. A low or midline DJ flexure, or a "corkscrew" duodenum, indicates malrotation or volvulus.
• Ultrasound may show a whirlpool sign or an inverted relationship of the superior mesenteric vein and artery, but a normal ultrasound does not exclude it.

6. Intussusception

A segment of bowel telescopes into the next, most often at the ileocolic junction. It typically affects children aged about 3 months to 3 years, with a peak at about 6–18 months. Classic features are colicky pain with drawing up of the legs, vomiting, pallor and lethargy, and later "redcurrant jelly" stool, but many children do not have the full picture.

• Ultrasound is the test of choice, with very high sensitivity in experienced hands: a target or doughnut sign in cross-section and a pseudokidney sign in long section.
• AXR signs are insensitive: a soft-tissue mass (often in the right upper quadrant), a crescent of gas outlining the head of the intussusception, a target of concentric fat rings, an empty right iliac fossa with no caecal gas, and features of small bowel obstruction.
• A normal AXR does not exclude intussusception. Its main use is to look for free gas, which contraindicates enema reduction.
• Treatment is usually reduction by air or contrast enema in a specialist centre with surgical support.

7. Pyloric stenosis and constipation

• Hypertrophic pyloric stenosis causes projectile non-bilious vomiting at about 2–8 weeks of age, more often in first-born boys, with a hypochloraemic metabolic alkalosis. Ultrasound is the test: pyloric muscle thickness of 3 mm or more and channel length of about 15–17 mm or more are commonly used thresholds (they vary between sources). An AXR, if done, may show a large gas-filled stomach, sometimes with peristaltic waves ("caterpillar sign").
• Constipation: NICE advises against using a plain AXR to diagnose idiopathic constipation in children. Faecal loading on the film correlates poorly with symptoms, and the X-ray adds radiation without changing management.

Red flags: act now

What to focus on, by role

Role	Priorities
Medical student	Double bubble, pneumatosis, the football sign, and the rule about bilious vomiting.
Neonatal / paediatric nurse	Report green vomit, distension, feed intolerance and bloody stool promptly; recognise a sudden deterioration.
Junior doctor	Know which test answers which question: contrast study for malrotation, ultrasound for intussusception and pyloric stenosis. Do not be reassured by a normal AXR.
Radiographer	Add the horizontal beam or decubitus view when free gas is the question, include the whole abdomen including the hernial orifices, and minimise repeats.
Advanced / FRCR	Subtle pneumatosis, DJ flexure position on contrast studies, meconium ileus versus ileal atresia, and Hirschsprung transition zones.

Practise on paediatric X-rays →

References

1. Radiopaedia. Necrotising enterocolitis. radiopaedia.org
2. Bell MJ, et al. Neonatal necrotizing enterocolitis: therapeutic decisions based upon clinical staging. Ann Surg 1978;187(1):1–7.
3. Radiopaedia. Intussusception. radiopaedia.org
4. Radiopaedia. Pneumoperitoneum. radiopaedia.org
5. National Institute for Health and Care Excellence. Constipation in children and young people: diagnosis and management (CG99). nice.org.uk
6. Royal College of Radiologists. iRefer: making the best use of clinical radiology. irefer.org.uk

For education only. Not a substitute for a formal report, senior review or your local policy. Never use this page to make decisions about a real patient.