Most cases of NEC occur in premature infants born before 34 weeks’ gestation who have been fed enterally. Prematurity is associated with immaturity of the gastrointestinal tract, including decreased integrity of the intestinal mucosal barrier, depressed mucosal enzymes, suppressed gastrointestinal hormones, suppressed intestinal host defense system, decreased coordination of intestinal motility, and differences in blood flow autoregulation, which is thought to play a significant role in the pathogenesis of NEC. More than 90% of infants diagnosed with NEC have been fed enterally, but NEC has been reported in infants who have never been fed. Feeding with human milk has shown a beneficial role in reducing the incidence of NEC. In addition, probiotics may offer potential benefits for the preterm infant by increasing mucosal barrier function, improving nutrition, upregulating the immune system, and reducing mucosal colonization by potential pathogens. It also is theorized that compromised intestinal blood flow contributes to NEC.
Early clinical signs of NEC include abdominal distention,feeding intolerance/increased gastric residuals, emesis, rectalbleeding, and occasional diarrhea. As the disease progresses,patients may develop marked abdominal distention, biliousemesis, ascites, abdominal wall erythema, lethargy, temperatureinstability, increased episodes of apnea/bradycardia, disseminated intravascular coagulation, and shock. With abdominalperforation, the abdomen may develop a bluish discoloration.
The white blood cell count can be elevated, but often it is depressed. Thrombocytopenia is common. In addition, infants may develop coagulation abnormalities along with metabolic derangements, including metabolic acidosis, electrolyte imbalance, and hypoglycemia and hyperglycemia. No unique infectious agent has been associated with NEC; bacteriologic and fungal cultures may prove helpful but not conclusive.
Radiographic imaging is essential to the diagnosis of NEC.The earliest radiographic finding is intestinal ileus, often associated with thickening of the bowel loops and air-fluid levels. Thepathognomonic radiographic finding is pneumatosis intestinalis caused by hydrogen gas production from pathogenic bacteria present between the subserosal and muscularis layers ofthe bowel wall. Radiographic findings also may include a fixedor persistent dilated loop of bowel, intrahepatic venous gas, andpneumoperitoneum seen with bowel perforation.
The differential diagnosis of NEC includes sepsis with intestinal ileus or a volvulus. Both conditions can present with systemic signs of sepsis and abdominal distention. The absence of pneumatosis on abdominal radiographs does not rule out the diagnosis of NEC; other causes of abdominal distention and perforation (gastric or ileal perforation) should be considered and investigated. Patients diagnosed with Hirschsprung enterocolitis or severe gastroenteritis may present with pneumatosis intestinalis.