Necrotising Enterocolitis (NEC)

Definition and Epidemiology

• Affects 1-5% of all NICU admissions and 4-13% of very-low-birth-weight (VLBW) infants (<1500 g)
• Incidence is inversely proportional to gestational age - peak incidence at ~32 weeks corrected gestational age
• Approximately 2,500 cases per year in the United States (Robbins Pathologic Basis of Disease)
• Mortality: 10-30% overall; up to 50% in infants requiring surgery
• Occurs in about 10% of preterm babies on NICUs; virtually always after initiation of feeds (Bailey & Love's Surgery, 28th Ed.)

Pathophysiology

Pathophysiology Diagram (Fischer's Mastery of Surgery)

• Immature mucosal barrier and immune system
• Poor motility and digestion
• Impaired circulatory regulation

• Alterations in the gut microbiome with overgrowth of pathogenic bacteria
• TLR4 (Toll-like receptor 4) activation on gut mucosa increases mucosal ischaemia in response to pathogenic bacteria
• No single bacterial pathogen has been definitively linked

• Release of pro-inflammatory cytokines and chemokines
• Platelet-activating factor (PAF) promotes enterocyte apoptosis, compromises tight junctions, and increases mucosal permeability
• ET-1 (endothelin-1) causes vasoconstriction; relative deficiency of NO (nitric oxide) contributes to ischaemia
• Once mucosal barrier breaks down: transluminal bacterial migration → vicious cycle of inflammation → necrosis → sepsis → shock

Risk Factors

Anatomy of Involvement

• Most commonly: terminal ileum, caecum, and right colon (ascending colon)
• Less commonly: jejunum
• Rarely: duodenum
• In severe cases: NEC totalis - entire GI tract affected

Clinical Features

• Temperature instability
• Lethargy, apnoea, bradycardia
• Hypotension, mottled skin (poor peripheral perfusion)
• Septic shock in advanced disease

• Feed intolerance, bilious aspirates, vomiting
• Abdominal distension
• Rectal bleeding (occult or gross)
• Abdominal wall erythema, oedema, discolouration (blue-grey in perforation due to thin abdominal wall)
• Palpable abdominal mass (matted ischaemic bowel)

• Thrombocytopenia
• Leukocytosis or leukopenia
• Elevated CRP, lactate
• Metabolic and/or respiratory acidosis
• Coagulopathy in late disease

Bell Staging (Modified Bell Criteria)

Investigations

Radiology (Plain X-ray - key findings)

• Pneumatosis intestinalis - pathognomonic finding; air within the intestinal wall from bacterial (hydrogen gas) fermentation of luminal substrates
• Portal venous gas - linear echogenicities in the liver on X-ray or USS; indicates severe disease
• Pneumoperitoneum - free intraperitoneal air; absolute indication for surgery; best seen on left lateral decubitus or cross-table lateral view
• Fixed loop - persistent dilation of a specific bowel loop suggests ischaemia/perforation
• Bowel loop separation - due to bowel wall oedema

Ultrasound

• Complex ascites (suggests perforation)
• Bowel wall thickening
• Portal venous gas (multiple linear echogenicities extending to liver periphery)

Macroscopic Pathology

• Mucosal or transmural coagulative necrosis
• Ulceration
• Bacterial colonisation
• Submucosal gas bubbles (pneumatosis intestinalis)
• Reparative changes: granulation tissue, fibrosis (post-acute phase)

Management

Medical (>50% of cases managed non-operatively)

1. Nil by mouth (NBO) - bowel rest
2. Orogastric tube decompression
3. IV fluid resuscitation
4. Broad-spectrum antibiotics (covering Gram-negative organisms, anaerobes)
5. Total parenteral nutrition (TPN)
6. Serial abdominal X-rays (every 6-8 hours initially)
7. Close monitoring for deterioration

Surgical Indications

• Pneumoperitoneum (free air on plain X-ray)

• Clinical deterioration despite medical management
• Persistent metabolic acidosis
• Abdominal wall cellulitis / erythema
• Palpable abdominal mass
• Fixed bowel loop on serial radiographs
• Portal venous gas
• Worsening obstruction

Surgical Options

1. Peritoneal drain (bedside):
   • Especially in extremely low birth weight (<1500 g) premature infants too unstable for theatre
   • Removes feculent ascites, decompresses abdomen, improves ventilation
   • ~2/3 of infants subsequently require laparotomy
   • A multicenter RCT established equivalence in survival, need for PN, and hospital stay vs. laparotomy for infants <1500 g
2. Laparotomy:
   • Allows full assessment of disease extent
   • General principles: resect all non-viable bowel, preserve maximum intestinal length
   • Options for focal disease: repair, resection with anastomosis, or resection with stoma (preferred due to risk of anastomotic leak)
   • For patchy/extensive disease: staged resection with second-look laparotomy (24-48 hours later)
   • "Clip and drop": in the sickest neonates - resect dead bowel, close open ends with clips, leave abdomen open (laparostomy) with vacuum dressing on low suction; definitive surgery after stabilisation
   • For pan-intestinal necrosis (NEC totalis): extremely poor prognosis, often palliation considered
3. Primary anastomosis is occasionally done in rare stable infants with focal isolated perforation and minimal contamination, though anastomotic leak and stricture risks limit enthusiasm.

Complications

Prevention

Key Points Summary

• NEC = most common GI surgical emergency in neonates; almost exclusive to premature, enterally-fed infants
• Pathognomonic finding: pneumatosis intestinalis (air in bowel wall on X-ray)
• Pneumoperitoneum = absolute surgical indication
• Staging: Bell criteria (I suspected → III advanced/perforated)
• Medical management succeeds in >50%; surgery reserved for deterioration or perforation
• Protective: breast milk, antenatal steroids, gradual feeding advancement
• Key long-term complication: intestinal stricture (commonest at splenic flexure) and short bowel syndrome
• Mortality: 10-30% overall, up to 50% in surgical cases