Pneumatosis and portal venous gas are the specific signs; a fixed loop across serial films is the one that is easy to dismiss.
Orient first
- NEC is a clinical and radiological diagnosis in a preterm neonate. The radiograph is read SERIALLY — the change between films carries as much information as any single film.
- PNEUMATOSIS INTESTINALIS (gas in the bowel wall) is the specific sign. It looks like a bubbly or curvilinear lucency following the bowel contour and can be mistaken for stool, which a preterm baby on minimal feeds rarely has.
- PORTAL VENOUS GAS appears as branching lucencies extending to the PERIPHERY of the liver — the periphery is what distinguishes it from pneumobilia, which is central.
- Free gas means perforation and is a surgical indication.
Acquire the study
- Supine abdominal radiograph as the baseline, repeated at intervals set by the clinical course.
- Add a LEFT LATERAL DECUBITUS or a cross-table lateral when perforation is suspected — a supine film alone is poor for free gas, and these babies cannot sit up.
- Ultrasound is a valuable adjunct: it detects pneumatosis, portal venous gas, free fluid and bowel wall perfusion, and can show findings before the radiograph does.
- Include the lines and tubes in the assessment — UAC/UVC position is part of this report.
The manoeuvre
- Assess the overall bowel gas pattern: is it generally distended, is the distribution disordered, are loops separated by fluid?
- Look specifically for PNEUMATOSIS — bubbly or linear lucency in the bowel wall, most often right lower quadrant.
- Look at the LIVER for branching lucencies reaching the periphery.
- Compare with the previous film for a FIXED, unchanging dilated loop — a persistent loop in the same position across serial films suggests a compromised segment.
- Look for free gas: the football sign, Rigler sign, the falciform ligament sign, and gas outlining the liver edge on a decubitus film.
- Assess for ascites and loop separation suggesting fluid or peritonitis.
- On ultrasound: bowel wall thickness, wall echogenicity, pneumatosis, portal venous gas, free fluid and its echogenicity, and wall perfusion on Doppler — absent perfusion suggests necrosis.
- Check line positions and report them.
What confirms it
- Pneumatosis intestinalis in the right clinical setting is diagnostic of NEC.
- Portal venous gas is a marker of severity.
- Free gas indicates perforation and is a surgical finding.
What licenses you to exclude it
- ⚠️ A NORMAL OR NON-SPECIFIC FILM DOES NOT EXCLUDE NEC, particularly early. Serial imaging is the answer, and the report should say when the next film is indicated.
- Never write a reassuring conclusion on a single early film in a deteriorating baby.
The classic misread
- Dismissing pneumatosis as faecal mottling in a preterm baby who is barely fed.
- Confusing pneumobilia (central) with portal venous gas (peripheral).
- Missing perforation because only a supine film was obtained.
- Reporting each film in isolation without comparing to the previous one.