What are the clinical features of Necrotizing Enterocolitis (NEC)?

Clinical Features of Necrotizing Enterocolitis (NEC)

NEC presents with a constellation of gastrointestinal and systemic findings, with abdominal distention, feeding intolerance with bilious gastric residuals, bloody stools, and systemic signs of sepsis being the cardinal features, though these signs can be nonspecific and may appear late in the disease course. 1, 2

Primary Clinical Manifestations

Gastrointestinal Signs

• Abdominal distention is one of the most common presenting features 2, 3
• Feeding intolerance with bilious or non-bilious vomiting and increased gastric residuals 4, 3
• Bloody stools (either gross or occult blood) with mucus and leukocytes on stool examination 1, 4
• Abdominal tenderness with a firm, "woody" feel to the abdomen in advanced cases 3
• Diarrhea may be present, though not universal 3

Systemic Signs

• Lethargy and altered mental status indicating systemic toxicity 1, 2
• Temperature instability (hypothermia or fever) 3
• Apnea and bradycardia episodes, particularly in preterm infants 3
• Hypotension and signs of shock in severe cases, with odds ratios >2.0 for hypotension in confirmed NEC 2
• Pallor related to anemia and hemodynamic compromise 1

Laboratory Abnormalities

Hematologic Changes

• Thrombocytopenia is common and may be progressive 2
• Leukocytosis with left shift or leukopenia, mimicking sepsis 1, 2
• Anemia in chronic presentations 1
• Thrombocytosis reported in 65% of acute cases in some series 1

Metabolic Derangements

• Metabolic acidosis due to hemodynamic shifts and tissue hypoperfusion 1, 2
• Hypokalemia with odds ratios >2.0 in confirmed NEC 2
• Hypophosphatemia associated with NEC diagnosis 2
• Hyponatremia serves as a predictor of NEC development (hazard ratio >1.5) 2
• Hyperglycemia is also a predictor (hazard ratio >1.5) 2

Other Laboratory Findings

• Hypoalbuminemia in chronic cases 1
• Methemoglobinemia may occur due to hemodynamic shifts 1

Radiographic Features

Plain Abdominal Radiography

• Pneumatosis intestinalis (gas within the bowel wall) is the pathognomonic finding, seen in 50-60% of cases 1, 5, 3
• Portal venous gas indicates advanced disease and carries poor prognosis 1, 6, 3
• Pneumoperitoneum (free intraperitoneal air) indicates perforation and is an indication for surgical intervention 1, 4
• Intestinal ileus with dilated, fixed bowel loops 3, 7
• Bowel wall thickening and separation of bowel loops 3

Ultrasound Findings (Increasingly Important)

• Bowel wall thickening >4 mm is abnormal, with thickness >10 mm associated with 60% mortality versus 4.2% for ≤10 mm 1, 8, 6
• Pneumatosis intestinalis detected with higher sensitivity than plain radiography 1, 5
• Absent or reduced bowel peristalsis on real-time assessment 1, 5, 3
• Free peritoneal fluid with or without debris 1, 4, 5
• Portal venous gas visualization 1, 4
• Decreased or absent vascular perfusion on Doppler assessment 5

Risk Factors and Epidemiology

• Prematurity is the strongest risk factor, affecting 6-10% of infants weighing <1500g at birth 5
• Risk decreases by 11-30% for every 100g increment in birth weight and single week increment in gestational age 2
• Very low birth weight (VLBW) infants have prolonged hospital stays with higher NEC risk 3
• Perinatal stress and intestinal ischemia contribute to pathogenesis 3, 7

Timing and Presentation Patterns

• Median age at diagnosis is 14 days in extremely low birth weight infants 2
• Can occur 3 days to 4 months postoperatively in neonates who have undergone surgery 7
• Clinical deterioration occurs 7 hours to 5 days before definitive diagnosis is established 7

Critical Diagnostic Caveats

• Clinical signs are nonspecific until late in disease, making early diagnosis challenging 5, 3
• Pneumatosis and portal venous gas appear relatively late in the disease course 7
• Postoperative NEC is particularly difficult to diagnose because typical signs (distention, bilious residuals, diarrhea) can occur without NEC 7
• Independent radiological adjudication increases NEC recognition compared to local site interpretation alone 2
• Ultrasound may detect early disease when radiographs are inconclusive, providing prognostic value 1, 5

Associated Complications

• Gastrointestinal perforation and obstruction with odds ratios >2.0 2
• Late-onset sepsis occurs at higher rates after NEC diagnosis 2
• Renal complications particularly in smaller infants (<750g) 2
• Overall mortality of 16% in confirmed NEC, with higher rates in larger infants (750-1000g) 2
• Long-term sequelae include short bowel syndrome and impaired neurodevelopment 1