Chapter 57

Necrotizing enterocolitis (NEC) is the most common life-threatening disorder of the gastrointestinal tract among neonates, primarily occurring in infants born prematurely. It is characterized by inflammation and patchy necrosis of the bowel wall that may rapidly progress to systemic sepsis, bowel perforation, and death. Despite decades of research, the underlying etiology remains poorly understood, preventive strategies are inconsistent, and treatment options are controversial.

The incidence of NEC is reported between 0.72 and 1.1 cases per 1000 live births.1,2 Its occurrence is inversely related to birth weight and gestational age, the most important and consistent risk factors in its development. Preterm infants comprise the overwhelming majority of cases, with near-term and term infants accounting for between 5% and 25%.3,4 For very-low-birth-weight (VLBW) infants born at less than 1500 grams, the incidence reported from large multicenter studies ranges from approximately 5% to 12% of VLBW live births.1,5,6 Reports from individual institutions, however, range widely, from as low as 0.8% to 22%.6-8 Timing of disease onset is inversely related to gestational age, with near-term and term infants typically developing disease in the first week of life, while onset is more common after the first or second week for earlier gestational ages as shown in eFigure 57.1.9

###### eFigure 57.1.

Relationship of gestational age to onset of necrotizing enterocolitis. The inverse relationship between gestational age at birth and average age of necrotizing enterocolitis onset is demonstrated. Term and near-term infants tend to develop disease within the first week of life, while lower gestational ages develop the disease after the first week. The earlier the gestation age, the later the typical onset of disease.

(Source: Neu J, Chen M, Beierle E. Intestinal innate immunity: How does it relate to the pathogenesis of necrotizing enterocolitis? Semin Ped Surg. 2005;14:137-144.)

Mortality from NEC is related to gestational age, extent of bowel involvement, and surgical intervention. In 2000, the in-hospital US mortality across all weight categories was estimated to be 15.2% of all NEC cases.1 Among very-low-birth-weight infants, mortality from NEC varies from 12% to 30%,1,2 with rates as high as 50% for extremely low-birth-weight infants born at less than or equal to 1000 grams.10,11 Mortality increases with the need for surgical intervention to as high as 50% and is directly related to length of remaining intact bowel. Recent data from Blakely and colleagues11 reported 75% survival for infants with more than 80 cm of normal bowel at the time of surgical intervention, 46% for infants with 10 to 80 cm of normal bowel, and no survival in infants with less than 10 cm of normal bowel present.11 Most large multicenter studies have shown no significant change in NEC incidence over the past 3 decades.2,5,...

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