Abdominal Ultrasound and Abdominal Radiograph to Diagnose Necrotizing Enterocolitis in Extremely Preterm Infants

Abstract

Necrotizing enterocolitis (NEC) is an important contributor towardmortality in extremely premature infants and Very Low Birth Weight(VLBW) infants. The incidence of NEC was 9% in VLBW infants(birth weight 401 to 1,500 grams) in the Vermont Oxford Network(VON, 2006 to 2010, n = 188,703).1 The incidence of NEC was 7%in 1993, increased to 13% in 2008, and decreased to 9% in extremelypreterm infants (22 to 28 weeks gestation) in the Neonatal ResearchNetwork Centers (1993 to 2012).2 The incidence of surgically treatedNEC varies from 28 to 50% in all infants who develop NEC.3 SurgicalNEC occurred in 52% in the VON cohort.1 In this cohort, the odds ofsurgery decreased by 5% for each 100 gram increase in birth.The incidence of surgical NEC has not decreased in the pastdecade.4 The mortality from NEC is significantly higher in infantswho need surgery compared to those who did not (35% versus 21%).1The case fatality rate among patients with NEC is higher in thosesurgically treated (23 to 36%) compared to those medically treated (5to 24%).3 In addition to surgery, NEC mortality rates are influencedby gestational age, birth weight,1,2,5 assisted ventilation on the day ofdiagnosis of NEC, treatment with vasopressors at diagnosis of NEC,and black race.6,7Extremely preterm infants who survive NEC are at risk for severeneurodevelopmental disability and those with surgical NEC have asignificantly higher risk of such delays (38% surgical NEC versus 24%medical NEC).8 Diagnosis of necrotizing enterocolitis is challengingand it is usually suspected based on non-specific clinical signs. Bell’scriteria and Vermont-Oxford Network criteria help in the diagnosisof NEC.Bell’s criteria, commonly used for diagnosis, staging, and planningtreatment of NEC, were described in 1978 and modified in 1986.9,10Bell’s stage I signs are non-specific: temperature instability, lethargy,decreased perfusion, emesis or regurgitation of food, abdominal distension,recurrent apnea, and on occasion, increased support withmechanical ventilation. Abdominal distension and emesis are morecommon than bloody stools in very preterm infants compared to terminfants.7 Abdominal radiographic findings are an integral part of Bell’scriteria. Identification of Bell’s stage I NEC (early NEC) with abdominalradiograph is challenging, as the features on abdominal radiograph(normal gas pattern or mild ileus) are non-specific. With progressionof NEC to Bell Stage IIA, the symptoms (grossly bloody stools,prominent abdominal distension, absent bowel sounds) and featureson abdominal radiographs (one or more dilated loops and focal pneumatosis)are more specific.On the other hand, the Vermont Oxford Network criteria for NECconsist of at least one physical finding (bilious gastric aspirate oremesis, abdominal distension or occult/gross blood in the stool inthe absence of anal fissure) and at least one feature on abdominalradiograph (pneumatosis intestinalis, hepatobiliary gas, or pneumoperitoneum).1 These features correspond to Bell Stage IIA or StageIIB and are not features of early NEC. Thus relying solely on abdominalradiograph for diagnosis of early NEC, as is practiced currently,has significant drawbacks especially in extremely premature infants.7Ultrasound has been suggested to improve the percentage of infantsdiagnosed with early NEC.11 However, this imaging modality is notused routinely in the diagnosis or management of NEC.As the incidence of surgical NEC and mortality from NEC continuesto be high, the literature to demonstrate the shortcomings ofabdominal radiographs and promise of abdominal ultrasound in diagnosisof NEC is reviewed.