Necrotising Enterocolitis

Necrotising enterocolitis is a life-threatening gastrointestinal emergency with high mortality rate almost exclusively affecting neonates, characterised by inflammation and necrosis of the bowel, which is apparent as dilated bowel loops with pneumotosis intestinalis.

Description

Necrotising enterocolitis is a life-threatening gastrointestinal emergency in neonates, primarily affecting premature infants and typically develops within the first two weeks of life. It is characterised by variable injury to the intestinal tract, ranging from mucosal injury to full-thickness necrosis and perforation.

Pathogenesis

The exact pathogenesis is complex and multifactorial, involving immature gut barrier function, abnormal bacterial colonisation, and exaggerated inflammatory response. Ischaemia-reperfusion injury also plays a significant role.

Epidemiology, Risk Factors & Associations

• Predominantly occurs in preterm infants, particularly those with very low birth weight.
• 10% may occur in term neonates.
• Risk factors include prematurity (50-80%), enteral feeding practices, and bacterial colonisation.
• Associated with other conditions like congenital heart disease and perinatal asphyxia.

Clinical Features

• Abdominal distension and tenderness.
• Bloody stools.
• Feeding intolerance and vomiting.
• Signs of sepsis and shock in severe cases.

Complications

• Intestinal perforation and peritonitis.
• Sepsis and multiorgan failure.
• Strictures (can be seen on barium enema) and short bowel syndrome post-recovery.
• Neurodevelopmental impairment in survivors.

Pathological Features

Histopathology

• Macroscopic: Segmental intestinal necrosis, pneumatosis intestinalis.
• Microscopic: Coagulative necrosis, bacterial overgrowth, and transmural inflammation.

Radiological Features

General Features

• Supine abdominal XR is mainstay of diagnosis
• Pneumatosis intestinalis, portal venous gas, and bowel wall thickening.
• Pneumoperitoneum

XR

• Abdominal X-ray:
  • Pneumatosis intestinalis (intramural gas) appears as mottled lucencies within the bowel wall
  • Portal venous gas appears as branching lucency overlying the liver
  • Pneumoperitoneum – free air indicating perforation.
    • Best visualised on cross-table lateral or left-lateral decubitus (to separate normal gastric bubble (downside) from free intraperitoneal gas (upside))
    • Supine pneumoperitoneum may be detected as the following signs:
      • Hyperlucent liver sign
      • Lower density of the large free gas anterior to the ventral hepatic surface replacing the brightness of the hepatic shadow
      • Rounded area of lucency within the central abdomen
      • Falciform ligament sign, a visible longitudinal linear density of the falciform ligament outlined by gas
      • Rigler sign, also known as the double-wall sign, the bowel wall outlined by gas both inside and outside

US

• B-mode:
  • Can demonstrate bowel wall thickening
  • Pneumatosis – hyperechoic intramural rounded foci with posterior acoustic shadowing
  • Free fluid possibly containing echogenic debris – suggests perforation
  • Pneumoperitoneum – stacked echogenic lines outside the bowel lumen
  • Portal venous gas – shadowing hyperechoic foci within the portal venous system
• Colour Doppler: Assesses bowel wall perfusion
  • Hypervascularity may be seen in early stage
  • Diminished perfusion indicates severe disease with possible infarction.

Grading and Staging

Based on Bell’s criteria, which categorise NEC into stages I, II, and III based on clinical and radiological findings.

• Stage I (Suspected NEC): Mild, nonspecific symptoms and radiographic findings.
• Stage II (Definite NEC): More pronounced systemic and intestinal symptoms with distinctive radiographic signs.
• Stage III (Advanced NEC): Severe disease with complications like intestinal perforation.

Diagnosis

• Clinical assessment and abdominal radiographs are primary diagnostic tools.
• Laboratory tests may show signs of infection and inflammation.
• Exclusion of other causes of neonatal distress and abdominal pathology.

Differential Diagnosis

• Spontaneous intestinal perforation: Typically involves a single perforation without extensive pneumatosis.
• Sepsis without NEC: Similar systemic symptoms but without specific intestinal signs.
• Other causes of neonatal abdominal distension (e.g., meconium ileus, volvulus).

Management

• Immediate cessation of enteral feeds and initiation of broad-spectrum antibiotics (Stage I and II)
• Supportive care including fluid management, respiratory support, and surgery in cases of perforation (Stage III) or refractory disease.
• Long-term follow-up for nutritional support and monitoring of developmental progress.