Necrotizing Enterocolitis (NEC)

Necrotizing enterocolitis is an inflammatory and ischemic injury of the intestine that occurs most often in premature or very-low-birth-weight infants. Very low birth weight means less than 1500 g, while extremely low birth weight means less than 1000 g. The immature bowel has a fragile mucosal barrier, underdeveloped immune regulation, and less reliable perfusion. These vulnerabilities make it less able to tolerate a fall in blood flow or an exaggerated response to intestinal bacteria. NEC reflects interacting intestinal immaturity, altered bacterial colonization, inflammation, enteral feeding, and impaired perfusion rather than one proven cause. Reduced perfusion can injure the mucosa; bacteria can cross a damaged barrier and intensify inflammation. Gas within the bowel wall appears as pneumatosis intestinalis. If injury progresses through the full thickness of the bowel, perforation, peritonitis, sepsis, and shock may follow. Prematurity and very low birth weight are the strongest background risks. Formula feeding is associated with greater risk than human milk, while human milk is preferred when enteral feeding is clinically appropriate. Other conditions that compromise perfusion or intestinal resilience, such as severe systemic illness, may...