Stages of Necrotizing Enterocolitis (NEC)
NEC is classified using the modified Bell's staging criteria, which divides the disease into three progressive stages (I, II, and III) based on clinical, radiographic, and laboratory findings, with each stage reflecting increasing severity from suspected disease to advanced necrosis with perforation. 1
Stage I: Suspected NEC
Stage I represents early, non-specific signs where NEC is suspected but not confirmed 1:
- Clinical presentation includes feeding intolerance, increased gastric residuals, abdominal distension, and lethargy 2
- Early symptoms may include increased episodes of apnea and bradycardia 3
- Gastrointestinal signs include bilious emesis and occult blood in stools 3
- Systemic signs are mild and non-specific 1
- Radiographic findings show non-specific intestinal dilation with normal or mildly abnormal gas patterns 1
Approximately 57% of NEC cases present at Stage I 4. Birth asphyxia is significantly more common in Stage I cases (35.7% vs 10.3% in advanced stages) 4.
Stage II: Definite NEC
Stage II confirms the diagnosis with clear pathognomonic findings 1:
- Clinical presentation includes persistent or worsening abdominal distension, absent bowel sounds, and definite bloody stools 3
- Abdominal wall changes may include focal erythema or edema 3
- Systemic signs include thrombocytopenia, neutropenia, and metabolic acidosis (particularly if bowel ischemia is present) 3
- Radiographic hallmark is pneumatosis intestinalis (air in the bowel wall), which is the definitive diagnostic finding 2
- Portal venous gas may also be present 3
Stage II accounts for approximately 23% of NEC cases 4, with a survival rate of 78% 4.
Stage III: Advanced NEC
Stage III represents the most severe form with intestinal necrosis and perforation 1:
- Clinical presentation includes signs of peritonitis with marked abdominal distension and tenderness 1
- Hemodynamic instability with signs of septic shock requiring vasopressor support 3
- Severe metabolic derangements including profound acidosis, disseminated intravascular coagulation, and multi-organ dysfunction 1
- Radiographic findings include pneumoperitoneum (free air indicating perforation) 5
- Surgical intervention is required, typically involving bowel resection with creation of stomas or reanastomosis 3
Stage III accounts for approximately 20% of NEC cases 4, with a dramatically reduced survival rate of only 13% 4.
Clinical Timing and Presentation
- Age at presentation averages 4.9 ± 4.8 days, with 96% of cases presenting during the first 14 days of life 4
- The disease typically strikes premature infants during the first 2 weeks of life 2
- The ileum and colon are the usual sites of intestinal necrosis 2
Prognostic Implications by Stage
Overall survival for NEC is approximately 95% unless the disease involves the entire bowel, which occurs in ~25% of cases and carries a mortality rate of 40-90%. 3, 6, 7
- Nonoperative management is successful in approximately 70% of cases 3, 7
- Approximately 50% of infants with NEC develop intestinal gangrene or perforation requiring surgery 2
- Mortality rates among neonates requiring surgery are estimated at 20-30% 5
- Intestinal stricture occurs in 15-35% of recovered infants as the most common late complication 2
Risk Stratification by Gestational Age
The incidence of NEC varies significantly by gestational age 8:
- 23-24 weeks' gestation: 10-20% incidence 8
- 25-27 weeks' gestation: 5-10% incidence 8
- ≥28 weeks' gestation: <5% incidence 8
Very low birth weight (VLBW) infants have a significantly higher incidence (5.7% vs 0.25% in non-VLBW infants) 4, and preterm infants <32 weeks have markedly increased risk (5.2% vs 0.09%) 4.