What is necrotizing enterocolitis?

Necrotizing Enterocolitis (NEC)

Necrotizing enterocolitis is a life-threatening gastrointestinal emergency primarily affecting premature and very low birth weight infants, characterized by inflammation and necrosis of the intestinal wall that can lead to perforation, sepsis, and death. 1

Definition and Epidemiology

• A severe inflammatory disease of the intestine resulting in necrosis of the bowel wall
• Most common in premature infants, especially those with very low birth weight (<1500g)
• Occurs in approximately 5-10% of all very low birth weight infants 2
• Mortality rate is high, reaching up to 40-90% when the entire bowel is involved 3
• Survival rate is close to 95% when NEC is limited to portions of the bowel 3

Pathophysiology

NEC develops through a complex interplay of factors:

1. Intestinal immaturity: Premature infants have underdeveloped intestinal barrier function
2. Altered microbiome: Dysbiosis of gut bacteria contributes to pathogenesis 3
3. Ischemia and reperfusion injury: Compromised blood flow to intestinal tissue
4. Excessive inflammatory response: Abnormal immune activation in the intestinal mucosa
5. Feeding practices: Formula feeding increases risk compared to human milk 4

Clinical Presentation

Symptoms and Signs

• Early signs: Often vague and nonspecific

  • Feeding intolerance
  • Abdominal distention
  • Bilious vomiting or gastric residuals
  • Lethargy
  • Temperature instability
  • Apnea and bradycardia episodes

• Progressive signs:

  • Abdominal wall discoloration
  • Visible intestinal loops
  • Bloody stools
  • Signs of sepsis (thrombocytopenia, neutropenia)
  • Metabolic acidosis

Diagnostic Criteria

NEC is typically diagnosed using modified Bell's staging criteria:

• Stage I: Suspected NEC - Mild systemic illness, feeding intolerance, abdominal distention
• Stage II: Definite NEC - Moderate systemic illness, pneumatosis intestinalis on imaging
• Stage III: Advanced NEC - Severe systemic illness, bowel perforation, peritonitis

Diagnosis

Laboratory Tests

• Complete blood count (may show thrombocytopenia, neutropenia)
• Blood cultures
• Electrolytes and acid-base status
• Coagulation studies

Imaging

• Abdominal radiographs: Primary imaging modality

  • Pneumatosis intestinalis (air in the bowel wall) - pathognomonic
  • Portal venous gas
  • Fixed, dilated intestinal loops
  • Pneumoperitoneum (indicating perforation)

• Abdominal ultrasound: Can detect bowel wall thickening (>4mm is abnormal) 3

  • Wall thickness >10mm associated with higher mortality (60% vs 4.2% for ≤10mm) 3

Management

Medical Management

1. Bowel rest and decompression:

   • NPO (nothing by mouth)
   • Nasogastric tube decompression

2. Antimicrobial therapy:

   • Broad-spectrum antibiotics for 7-14 days
   • Recommended regimens 3:
     • Ampicillin, gentamicin, and metronidazole
     • Ampicillin, cefotaxime, and metronidazole
     • Meropenem as monotherapy

3. Supportive care:

   • Fluid resuscitation
   • Correction of electrolyte abnormalities
   • Respiratory and cardiovascular support as needed
   • Parenteral nutrition

Surgical Management

Indications for surgical intervention 3:

• Pneumoperitoneum (indicating perforation)
• Clinical deterioration despite maximal medical therapy
• Fixed dilated intestinal loop
• Abdominal wall erythema or discoloration

Surgical options:

• Peritoneal drainage: May be used as temporizing measure in very low birth weight infants
• Laparotomy: With resection of necrotic bowel and creation of ostomies or primary anastomosis

Prevention Strategies

1. Feeding practices:

   • Human breast milk: Strongly preferred over formula 4
   • Standardized feeding protocols with slow advancement
   • Donor human milk when mother's milk unavailable

2. Probiotics:

   • Administration of probiotics (particularly Lactobacillus and Bifidobacterium species) has shown benefit in reducing NEC incidence 4
   • Consider in high-risk premature infants

3. Other preventive measures:

   • Antenatal corticosteroids for fetal lung maturation also benefit gut maturation
   • Avoid histamine-2 receptor antagonists and proton pump inhibitors 5
   • Restrictive antibiotic use to preserve normal microbiome development

Prognosis and Complications

• Short-term complications:

  • Sepsis
  • Short bowel syndrome
  • Intestinal strictures
  • Malabsorption

• Long-term complications:

  • Growth failure
  • Neurodevelopmental delays
  • Chronic intestinal dysfunction

Key Distinctions from Other Conditions

NEC must be differentiated from other causes of enterocolitis 3:

• Infectious gastroenteritis
• Sepsis
• Food protein-induced enterocolitis syndrome
• Hirschsprung's disease
• Volvulus or intestinal obstruction
• Neutropenic enterocolitis (in older patients receiving chemotherapy)

Clinical Pearls

• The classic triad of NEC includes abdominal distention, bilious emesis/gastric residuals, and bloody stools
• Early recognition and aggressive management are critical for improving outcomes
• Approximately 70% of NEC cases can be managed non-operatively 3
• Probiotics show promise for prevention but optimal strains and dosing remain under investigation
• The combination of prematurity, formula feeding, and dysbiosis creates the "perfect storm" for NEC development