Necrotising Enterocolitis (NEC) in Neonates

Definition & Epidemiology

• NEC is characterized by intestinal inflammation that can progress to transmural necrosis and perforation.
• Affects 1-5% of all NICU admissions overall; 4-13% of very low birth weight (VLBW) infants (<1500 g).
• Incidence is inversely proportional to gestational age - the more premature the infant, the higher the risk; peak incidence at ~32 weeks corrected gestational age.
• Mortality: 10-30% overall; up to 50% in infants requiring surgery.
• 80% of cases occur in the first month of life, typically after enteral feeds are initiated.

Pathogenesis (Multifactorial)

• NEC is almost exclusively seen in infants who have received enteral feeds, suggesting postnatal bacterial introduction triggers the cascade.
• In term neonates, NEC is often associated with congenital heart disease, perinatal asphyxia, and hypoxia/low-flow states (so-called "term-NEC").

Risk Factors

• Prematurity and low birth weight (most significant)
• Indomethacin tocolysis (especially double-agent tocolytic therapy)
• Protective: antenatal corticosteroid administration

• Formula feeding (vs. human milk)
• Rapid advancement of feeds
• Prolonged antibiotic use
• Multiple blood transfusions
• Hypoxia/ischaemia (especially in term infants with congenital cardiac disease)
• Exposure to enteric pathogens (cluster outbreaks)

Pathology (Morphology)

• Most commonly involves: terminal ileum, cecum, and right colon (any segment can be involved)
• Bowel is distended, friable, congested, or gangrenous
• Perforation and peritonitis may be present

• Mucosal or transmural coagulative necrosis
• Ulceration
• Bacterial colonization
• Submucosal gas bubbles (pneumatosis intestinalis)
• Granulation tissue and fibrosis (in healing phase)

Gross pathology of NEC: (A) Distended, thin-walled small bowel at postmortem. (B) Hemorrhagic infarction of ileum with pneumatosis intestinalis (arrows). - Robbins Basic Pathology

Clinical Features

• Temperature instability
• Lethargy, apnea, bradycardia
• Hypoglycaemia, oxygen desaturation

• Feeding intolerance, increased gastric residuals
• Abdominal distension and tenderness
• Bloody stools (occult or gross)
• Vomiting, diarrhoea

• Abdominal wall erythema and oedema (cellulitis)
• Blue discolouration of the abdomen (perforation)
• Visible dilated bowel loops through thin abdominal wall
• Septic shock, DIC, cardiovascular collapse

• Thrombocytopenia, leukocytosis or leukopenia
• Elevated CRP, elevated lactate
• Metabolic acidosis, respiratory acidosis

Bell Staging Criteria (Bell et al., 1978 - Ann Surg)

Radiological Features

1. Non-specific global bowel dilatation - earliest, non-specific
2. Persistent/fixed bowel loop - on serial X-rays, same loop doesn't change position - poor prognostic sign
3. Pneumatosis intestinalis - pathognomonic; intramural gas (hydrogen from bacterial fermentation); seen as bubbly or linear lucencies in the bowel wall
4. Portal venous gas - branching linear lucencies over liver radiating from porta hepatis; seen in ~30%, indicates severe disease
5. Pneumoperitoneum (free air) - indicates perforation; absolute indication for surgery

Abdominal X-ray in NEC: Note bowel distension and pneumatosis intestinalis (arrow). - Fischer's Mastery of Surgery

Management

Medical (>50% of cases can be managed without surgery)

• Nil per mouth (NPO) - stop all enteral feeds
• Orogastric tube decompression
• IV fluid resuscitation
• Broad-spectrum antibiotics (covering gram-negative organisms and anaerobes)
• Serial abdominal X-rays (every 6-8 hours initially)
• Close monitoring for surgical indications

Surgical Indications

Surgical Options

1. Exploratory laparotomy - resection of all nonviable segments; preserving maximum intestinal length
2. Ostomy creation - common; allows bowel rest and later anastomosis
3. Second-look laparotomy - at 24-48 hours for marginally viable bowel
4. Peritoneal drainage (bedside) - for extremely low birth weight (<1500 g) infants with perforated NEC; effective as temporizing or definitive treatment; outcomes comparable to laparotomy in VLBW infants (established by multicenter RCT)
5. Primary anastomosis - only in rare, very stable infants with focal, isolated perforation

Prevention

• Human breast milk - fourfold decrease in NEC risk (RR 0.25; meta-analysis of RCTs); all mothers of at-risk infants (<32 weeks) should be encouraged strongly
• Antenatal corticosteroids - protective
• Gradual, protocol-based feeding advancement
• Probiotics - evidence is low; not yet standard of care

Complications & Prognosis

• Short bowel syndrome (SBS) - after extensive bowel resection
• Post-NEC strictures - in ~10% of infants (most commonly at the splenic flexure); develop after both medical and surgical management; a contrast enema should be done before ostomy reversal
• Adhesions - may cause late intestinal obstruction
• High mortality, especially in surgical cases (up to 50%)
• NEC totalis (involvement of entire GI tract) - near-universally fatal

Key Points to Remember for Exams

• Most common GI emergency in neonates; most significant risk factor = prematurity
• Pathognomonic finding: pneumatosis intestinalis on X-ray
• Absolute surgical indication: pneumoperitoneum
• Bell staging classifies disease into I (suspected), II (definite), III (advanced)
• Human breast milk is the single most important preventive measure
• Terminal ileum and right colon are most commonly affected
• Portal venous gas is a poor prognostic indicator
• ~10% develop post-NEC strictures even after conservative management