Necrotizing Enterocolitis

• Unknown cause
• Various degrees of mucosal or transmural necrosis of the intestine
• Incidence 1-5% of admissions to NICU
• Rarely occurs in term infants

Pathology and Pathogenesis

• Development of necrotic segment of intestine, gas accumulation in submucosa of bowel wall (pneumatosis intestinalis), progression of necrosis to perforation, sepsis or death
• Most frequently involved: distal ileum, proximal colon. Fatal cases have gangrene from the stomach to rectum
• Contributions to mucosal injury: polycythemia, hypertonic milk or oral medicines, too rapid feeding protocols. Mucosal injury -> infection -> necrosis
• NEC also occurs in premature infants without stress, particularly during epidemics
• Clustering of cases, suggests infectious agent: most often, no pathogen has been identified, but C perfringens, E coli, S epidermidis, rotavirus have been recovered

Clinical manifestations

• Usually occurs in 1^st 2 weeks, can be as late as 3 mos old in VLBW infants
• Age of onset is inversely proportional to gestational age
• 1^st signs: abdominal distension, with gastric retention, usually after onset of enteric feedings
• grossly  bloody stools in 25%
• Wide spectrum of illness: guiac + stools only, to peritonitis, bowel perf, SIRS, shock, death
• Progression may be rapid, but unusual to progress from mild to severe after 72 hours.

Dx:

• Pneumatosis intestinalis on KUB is diagnostic; portal vein gas signals severe disease; pneumoperitoneum indicates perforation
• Ddx: infxn (systemic or intestinal), obstruction, volvulus; indomethacin may cause focal intestinal perforation (which may also be idiopathic); gastrograffin enema may demonstrate pneumatosis, and should be used if congenital obstruction or midgut volvulus is suspected; hepatic US may be more sensitive than XR for portal venous gas

Stages of NEC

• Stage I -suspected NEC
  • some clinical findings
  • x-ray normal or shows mild ileus or bowel wall edema
• Stage II -definite NEC
  • more obvious clinical findings
  • pneumatosis intestinalis on x-ray
• Stage III -advanced NEC
  • severe clinical findings
  • pneumatosis intestinalis+/-ascites+/-perforation on x-ray

Tx: For suspected or diagnosed cases:

• NPO, NG decompression, IVF
• Careful attn to respiratory status, coag profile, acid-base/electrolyte balance
• Blood cx, then abx: ampicillin or anti-pseudomonal + aminoglycoside
• Remove umbilical catheters
• If distension contributes to hypoxia/hypercapnia, assist ventilation
• If hypotensive: resuscitation with crystalloid, blood, plasma, dopamine
• Monitoring: frequent lateral XR (look for perf), Hct, platelets, lytes, acid-base determinations
• Consult surgery early
• If evidence of perforation (pneumoperitoneum, brown paracentesis): resect necrotic bowel
• Additional indications for ex lap, resection of necrotic bowel, external ostomy diversion: failure to respond to medical management, single fixed bowel loop, erythema of abdominal wall, palpable mass
• Extreme cases of peritonitis and unable to withstand bowel resection? Peritoneal drainage can help.

Px:

• Medical management fails in 20% of pt w/ pneumatosis. Of these, 9-25% die. Strictures develop at the site of the necrotizing lesion in about 10% of patients – resection of this stricture is curative.
• Complications of NEC following massive intestinal resection: short bowel syndrome, TPN related: central catheter sepsis/thrombosis, cholestatic jaundice
• Prevention? Slow advancement of feeds (15-20 cc/kg/day), use of breast milk or formula w/ egg phospholipids.

Nelson 16^th ed.

The age of onset of necrotizing enterocolitis (NEC) is inversely related to gestational age at birth. The mean age at diagnosis of NEC is reported to be approximately 20 days for infants born at 30 or fewer weeks’ gestation, 14 days for those born at 31 to 33 weeks’ gestation, and 5 days for those born at 34 or more weeks’ gestation. The reason for the delayed onset of NEC in more immature infants is unclear.

NEC is more common among neonates convalescing from intensive care than among those undergoing intensive care. At the time of diagnosis of NEC, most affected infants are not receiving mechanical ventilation or continuous positive airway pressure and do not have indwelling arterial or venous catheters. The clinician, therefore, must be alert to the signs and symptoms of NEC in preterm neonates, even long after their initial hospitalization in the intensive care unit.

The earliest radiographic sign of NEC is generalized bowel distension. Other nonspecific findings on abdominal radiographs include bowel wall thickening and the presence of intraperitoneal fluid. Pneumatosis intestinalis represents gas in the bowel wall and usually confirms the diagnosis of NEC. It may present with a bubbly or foamy gas pattern, especially in the right lower abdominal quadrant. Because this gas pattern is similar to the pattern resulting from a mixture of air with meconium or fecal matter, it is not specific for the diagnosis of NEC. A linear or crescentic distribution of gas in the bowel wall is a more specific sign of NEC, and it usually correlates with severe disease. Pneumatosis intestinalis can extend into the portal venous circulation and be visible as linear branching lucencies overlying the liver. Portal venous gas usually is associated with severe disease.

Strictures are the most common long-term gastrointestinal complication of NEC, occurring in 10% to 35% of survivors. Most strictures occur in the large intestine and represent cicatricial scarring of the ischemic bowel. In one third of cases, the strictures are multiple. Although most strictures become symptomatic during the initial hospitalization, some may not become obvious for as long as 6 months after the acute incident.

The incidence of NEC is higher among African-American than Caucasian infants, with the reported ratio varying between 1.7:1.0 and 3.2:1.0. The reason for the increased predisposition of African-American infants to NEC is unclear.

References:
Kanto WP Jr, Hunter JE, Stoll BJ. Recognition and medical management of necrotizing enterocolitis. Clin Perinatol. 1994;21:335-346
Morrison SC, Jacobson JM. The radiology of necrotizing enterocolitis. Clin Perinatol. 1994;21:347-363
Simon NP. Follow-up for infants with necrotizing enterocolitis. Clin Perinatol. 1994;21:411-424
Stoll BJ. Epidemiology of necrotizing enterocolitis. Clin Perinatol. 1994;21:205-218