What is necrotising enterocolitis?
Necrotising enterocolitis (NEC) is a life-threatening inflammatory disease of the neonatal intestine. Inflammation of an immature gut allows bacterial invasion of the bowel wall, which leads to ischaemia, coagulative necrosis and, if unchecked, perforation, peritonitis and sepsis. StatPearls calls it the most common life-threatening gastrointestinal emergency in the neonatal intensive care unit, with mortality reported up to 50%.
The exact trigger is still unknown. The working model combines four ingredients: an immature intestinal barrier (prematurity), disturbed gut flora, enteral feeding (especially formula) and reduced splanchnic blood flow. Gas produced by bacteria inside the wall is what creates the hallmark X-ray sign, pneumatosis intestinalis.
Who gets NEC — what are the risk factors?
StatPearls lists prematurity, low birth weight and formula feeding as the primary risk factors, with high-osmolality formula specifically implicated. The worldwide incidence ranges from 0.3 to 2.4 per 1,000 live births; nearly 70% of cases occur in infants born before 36 weeks, and NEC affects 2–5% of all premature infants.
| Category | Increases risk | Reduces risk |
|---|---|---|
| Infant | Prematurity, low birth weight | — |
| Feeding | Formula (especially high-osmolality) feeds | Mother's own breast milk (dose-dependent); donor milk if own milk is unavailable |
| Blood flow | Placental insufficiency (hypertension, pre-eclampsia, maternal cocaine); PDA, cardiac disease, hypotension | — |
| Term infants | Hypoxic events, e.g. cyanotic congenital heart disease — onset in the first few days | — |
| Medicines | Empirical antibiotics for more than 5 days; H2 blockers | Antenatal corticosteroids |
| Microbiome | Dysbiosis | Probiotics reduce incidence in trials (product choice debated) |
The Turkish Neonatal Society guideline calls breast milk feeding the most effective protective intervention: giving more than half of enteral feeds as breast milk in the first 2 weeks lowers NEC significantly, and each further 10% lowers it further. In one study, NEC rose by 7% for each extra day of empirical antibiotics, which is why units try to stop empirical antibiotics within 5 days. Among PDA drugs, a Cochrane analysis found less NEC with ibuprofen than with indomethacin.
How does NEC present clinically?
Early signs are non-specific and subtle, which is why staging starts at 'suspected'. Signs fall into two groups:
- Abdominal (intestinal) signs: feed intolerance with increased gastric residuals, vomiting (often bilious), abdominal distension, tenderness, occult or gross blood in stool, absent bowel sounds, visible loops, a palpable mass (often right lower quadrant) and, in advanced disease, abdominal wall erythema, oedema and induration.
- Systemic signs: temperature instability, apnoea, bradycardia, lethargy, then respiratory failure, hypotension and shock. About 20–30% of infants with NEC have associated bacteraemia.
Laboratory tests support but do not make the diagnosis. Common findings are thrombocytopenia, neutropenia (leukopenia), metabolic acidosis and hyponatraemia. StatPearls notes that a white cell count below 1,500 per microlitre strongly suggests established sepsis, and that blood cultures are usually negative. Falling platelets and worsening acidosis are markers of progression.
What are the modified Bell stages of NEC?
Bell (1978) introduced a three-stage system — suspected, definite, advanced. Walsh and Kliegman (1986) modified it by splitting each stage into A and B using systemic, intestinal, radiological and laboratory findings. The modified Bell staging is still the most widely used tool to define, stage and guide treatment of NEC.
| Stage | Systemic signs | Abdominal signs | Radiograph |
|---|---|---|---|
| IA — suspected | Temperature instability, apnoea, bradycardia, lethargy | Gastric retention, mild distension, emesis, occult (heme-positive) blood in stool | Normal, or mild ileus / dilatation |
| IB — suspected | Same as IA | Grossly bloody stool | Same as IA |
| IIA — definite, mildly ill | Same as stage I | Absent bowel sounds ± tenderness | Ileus, dilated loops, pneumatosis intestinalis (focal) |
| IIB — definite, moderately ill | Plus mild metabolic acidosis and thrombocytopenia | Definite tenderness ± abdominal wall cellulitis or right lower quadrant mass | Extensive pneumatosis, early ascites ± portal venous gas |
| IIIA — advanced, bowel intact | Plus hypotension, severe apnoea, combined respiratory and metabolic acidosis, DIC, neutropenia | Peritonitis, marked tenderness and distension | Prominent ascites, fixed bowel loop, no free air |
| IIIB — advanced, bowel perforated | Same as IIIA (further deterioration, shock) | Evidence of perforation | Pneumoperitoneum |
What does the X-ray show — pneumatosis, portal venous gas and free air?
The key investigation is a plain abdominal radiograph — anteroposterior plus left lateral decubitus views. StatPearls recommends repeating films serially (often every 6 hours) to track progression until the course is clear.
- Early, non-specific: dilated bowel loops, ileus pattern, bowel-wall oedema.
- Pneumatosis intestinalis — linear or bubbly ('cystic') gas inside the bowel wall, produced by bacteria. StatPearls calls it pathognomonic for NEC; it defines stage II.
- Portal venous gas — fine branching lucencies over the liver extending to its periphery, from gas travelling in the portal venous radicles. It is fleeting (reported in 10–30%) and is a poor prognostic sign.
- Pneumoperitoneum (free air) — the sign of perforation. On supine films look for the football sign, Rigler sign (both sides of the bowel wall visible) and the falciform ligament sign; the left lateral decubitus view shows air over the liver.
- Fixed, persistently dilated loop on serial films and ascites (sometimes a gasless abdomen) suggest necrotic bowel.
How is NEC managed medically?
Medical management starts as soon as NEC is suspected and is given to every infant, including those who later need surgery. It rests on four pillars plus close monitoring:
- Stop enteral feeds (NPO / bowel rest). The guideline suggests about 7 days for stage II and about 14 days for stage III.
- Gastric decompression with an orogastric or nasogastric tube on intermittent suction until the ileus and pneumatosis resolve.
- Broad-spectrum IV antibiotics after cultures, covering gram-negative and anaerobic gut flora — StatPearls cites ampicillin + gentamicin + clindamycin or metronidazole. For stage II or worse, treatment usually runs 10–14 days even if cultures are negative; suspected stage I may stop after 48–72 hours.
- Total parenteral nutrition through a central line, plus fluid, electrolyte, cardiovascular and respiratory support (ventilation, inotropes) as needed.
- Serial examination, blood counts, gases and radiographs to detect deterioration early, with early surgical consultation.
When does a baby with NEC need surgery?
About 30–50% of infants with definite NEC eventually need an operation. The only universally accepted absolute indication is pneumoperitoneum (bowel perforation). Other findings are relative indications, used together with the clinical trajectory:
| Type | Finding |
|---|---|
| Absolute | Pneumoperitoneum on imaging (perforation, stage IIIB) |
| Relative | Clinical deterioration despite maximal medical therapy (worsening acidosis, thrombocytopenia, shock) |
| Relative | Positive paracentesis — more than 0.5 mL of brown or yellow-brown fluid with bacteria on Gram stain |
| Relative | Fixed, persistently dilated loop on serial radiographs |
| Relative | Abdominal wall erythema, palpable abdominal mass, portal venous gas |
Laparotomy is the standard operation. The surgeon is as conservative as possible: resect only clearly necrotic or perforated bowel, try hard to preserve the ileocaecal valve, and usually create a diverting stoma, reversed after recovery. For extremely small, unstable babies, primary peritoneal drainage — a drain placed at the bedside under local anaesthesia — can stabilise the infant, although many later need a laparotomy.
What are the complications and outcome of NEC?
- Intestinal stricture — reported in 9–36% of survivors, more often after non-operative treatment; about 80% involve the colon, presenting weeks later with obstruction.
- Short bowel syndrome — the most common cause of intestinal failure after extensive resection.
- TPN-associated liver disease (cholestasis), central-line sepsis, adhesive obstruction.
- Neurodevelopmental impairment and poor growth, more frequent after surgical NEC.
The Turkish guideline reports overall mortality of 20–30%, higher with surgery, lower gestational age and growth restriction. StatPearls quotes a range of 10–50%, approaching 100% in the most severe cases with perforation, peritonitis and sepsis.