The extent of mucosal or transmural intestinal necrosis varies. Pneumatosis progresses from the submucosa through the muscular layer to the subserosa. The distal ileum and proximal colon are most frequently involved.
Both feeding and bacterial overgrowth may injure an already compromised mucosal barrier. This results in the shunting of blood away from the terminal submucosal vessels. Ischemia then impairs gut mobility and barrier function, which results in amplified cytokine release.
Predisposing factors include prematurity, stressful delivery, respiratory distress syndrome, hypoxia, shock, hypothermia, hyperosmolar feedings, too early feedings, sepsis, hypoglycemia, polycythemia, congenital heart disease, umbilical catheterization, exchange transfusion, and drugs such as methylxanthines and indomethacin.
In most neonatal ICUs, the incidence of necrotizing enterocolitis ranges from 1% to 5%. Affected infants typically present in the first 2 weeks of life with lethargy, gastric retention, vomiting, ileus, abdominal distention, and bloody stools. Bradycardia, apnea, and hypothermia are signs of progressive deterioration. Erythema and edema of the abdominal wall and a fixed abdominal mass suggest bowel necrosis. Guarding indicates intestinal perforation.
Suggestive radiographic findings include distended loops of bowel, portal venous gas, and pneumatosis intestinalis (Figure). Radiographic signs of bowel infarction or perforation include free air in the peritoneum, free intraperitoneal fluid, fixed dilated intestinal loops, and diminished bowel gas with asymmetric loops. Hepatic ultrasonography may detect portal venous gas even if abdominal radiographs are normal.
Laboratory findings may include leukocytosis with bands and toxic granulations, anemia, thrombocytopenia, metabolic acidosis, electrolyte disturbances, hypoalbuminemia, and hypoglycemia.
Treatment in uncomplicated cases is mainly conservative; it includes cessation of feeding, nasogastric decompression, repletion of intravascular volume with intravenous fluids, total parenteral nutrition, correction of acid-base and electrolyte imbalances, ventilatory support as indicated, appropriate blood cultures, and parenteral administration of antibiotics (ampicillin, gentamicin, and clindamycin).
Indications for surgical intervention include intestinal perforation as evidenced by pneumoperitoneum, erythema of the abdominal wall, a palpable abdominal mass, presence of portal venous gas, a persistent fixed loop on repeated abdominal radiographs, paracentesis that is positive for fluid (especially fecal material), and clinical deterioration. Patients with ischemic necrosis and perforated bowel at laparotomy require bowel resection. Ideally, bowel resection is performed when the intestine is gangrenous but not perforated. Resection and primary anastomosis are generally advisable if the lesion is localized. Exteriorization of the transected ends of the viable bowel with reanastomosis at a later date is indicated for infants with diffuse intestinal involvement or physiologic instability.