Necrotizing enterocolitis (NEC) is the leading gastrointestinal emergency of the premature infant. In many cases, it happens in apparently healthy premature infants who have no other medical problems. Although it affects mostly premature infants, 10% of affected infants are born at term. Its incidence varies between 0.3 and 2.4 infants/1000 births and between 3.9% and 22.4% amongst infants of less than 1500 g. Males and females are equally affected.
Most infants develop NEC within the first 2 weeks of life (KRasNa et al. 1996). Its precise cause remains unclear, but it is thought that factors such as ischemia, decreased mucus production, and diminished immune response of the premature infant may lead to invasion of the intestinal mucosa by intestinal flora resulting in air entering the submucosa and mucosa. Some experimental work suggests that translocation of intestinal flora across an incompetent mucosa may play a role in spreading the disease and systemic involvement. Such a mechanism would account for the apparent protection breastfed infants have against fulminant NEC (H0Rt0N 2005). The terminal ileum and the proximal colon are most commonly affected, though any portion of the intestines may be involved.
The clinical signs are nonspecific and consist of feeding intolerance, increased gastric retention, vomiting, abdominal distension, and the presence of blood in the stools.
The mainstay of diagnostic imaging is abdominal radiography. Because of the possibility of perforation of the necrotic bowel, the supine film should be supplemented with a cross-table lateral or left-lateral decubitus radiograph. The radiograph findings of NEC are nonspecific, especially in early stages. Diffuse nonspecific gaseous distension and thickened bowel walls (suggesting edema/inflammation) is the most common pattern (FottER and SoRaNtiN 1994; KRasna et al. 1996) (Fig. 1.35). An asymmetric bowel air pattern or distension localized to focal loops only may also be seen. Radiographs can sometimes reveal scarce or absent intestinal air, which is more worrisome than diffuse distension that changes over time. But the pathognomonic finding of NEC is pneumatosis intestinalis, consisting of submucosal or subserosal air (Bu0N0m0 1999). Pneumatosis intestinalis appears as a characteristic train-track lucency configuration within the bowel wall and may be linear or cystic (Figs. 1.36 and 1.37). The cystic collections are usually subsero-sal, whereas the linear form is usually submucosal. Pneumatosis intestinalis is due to the production of small bubbles of hydrogen by bacteria within the intestinal wall (AlbaNESE and Rowe 1998). Intramural air bubbles may also represent extravasated air from within the intestinal lumen. These changes might not be detectable on digitalized images due to the suboptimal resolution, and a printed X-ray film is often necessary (M0RRiS0N and Jac0bS0N 1994). Serial radiographs help assess disease progression.
Abdominal free air is ominous and usually requires emergency surgical intervention (Fig. 1.38). The presence of abdominal free air can be difficult to discern on a flat radiograph, which is why decubitus radiographs are recommended at every evaluation. The football sign is characteristic of intraperitoneal air on a flat plate and manifests as a subtle oblong lucency over the liver shadow. It represents the air bubble that has risen to the most anterior aspect of the abdomen in a baby lying in a supine position and can be demonstrated by left lateral decubitus imaging (Bu0N0m0 1999). Although free air in the a
Fig. 1.35a,b. Necrotizing enterocolitis. a Photograph of a 3-week-old premature neonate showing important abdominal distension. b Plain abdominal radiograph shows diffuse nonspecific gaseous distension of the bowel loops b a
Fig. 1.35a,b. Necrotizing enterocolitis. a Photograph of a 3-week-old premature neonate showing important abdominal distension. b Plain abdominal radiograph shows diffuse nonspecific gaseous distension of the bowel loops
Fig. 1.36a-c. Pneumatosis intestinalis in a 1-week-old infant. Anteroposterior (a) and lateral (b) plain radiographs show small and large bowel loops sharply outlined by collections of gas in bowel wall. Most of these collections of gas are linear, indicating a submucosal location. c Surgical image of the same patient demonstrates diffuse bowel necrosis
Fig. 1.37. Pneumatosis intestinalis in 12-day-old infant. Abdominal radiograph demonstrates increase in the amount of gas in the small bowel. Pneuma-tosis intestinalis is identified as cystic lucencies in the right upper and lower quadrant. These cystic lucencies are usually subserosal
Fig. 1.38. Pneumoperitoneum complicating necrotizing enterocolitis. Supine in a 1-month-old premature infant radiograph shows intramural gas in the small bowel and free intraperitoneal air secondary to bowel perforation. The central lucency and the falciform ligament are observed
Fig. 1.38. Pneumoperitoneum complicating necrotizing enterocolitis. Supine in a 1-month-old premature infant radiograph shows intramural gas in the small bowel and free intraperitoneal air secondary to bowel perforation. The central lucency and the falciform ligament are observed abdominal cavity confirms it, bowel wall perforation might be present in the absence of free air in one third of the cases.
Another pathognomonic sign of NEC is portal vein air. Portal vein air is more frequent and less ominous than was previously thought. It is seen as finely branching radiolucencies extending from the porta hepatis to the periphery of the liver (Fotter and SoraNtiN 1994) (Fig. 1.39). Ascites is a late finding that usually develops some time after perforation when peritonitis is present. Ascites is observed on an AP radiograph as centralized bowel loops that appear to be floating on a background of density. It is better observed on ultrasonography (AlbaNesE and Rowe 1998).
Abdominal ultrasonography is a relatively new technology for evaluating suspected NEC in neo-nates. Ultrasonography can be used to identify areas of loculation and/or abscess consistent with a walled-off perforation when patients with indolent NEC have scarce air or a fixed area of radiographic density. Ultrasonography is excellent for identifying and quantifying ascites. Serial examinations can be used to monitor the progression of ascites as a marker for the disease course. Portal air may be demonstrated on ultrasound as bright, shifting echogenic foci within the portal vein (MorrisoN et al. 2004) (Fig. 1.40). This finding has been termed informally the "champagne sign" because of its similar appearance to a champagne flute. Sonogra-phy can also show thickened bowel loops, and bowel air pneumatosis (Fig. 1.41). Recent data suggests that Doppler study of the splanchnic arteries early in the course of NEC can help distinguish developing NEC from benign feeding intolerance in a mildly symptomatic baby. A markedly increased peak flow velocity (> 1.00) of arterial blood flow in the celiac and superior mesenteric arteries in early NEC has been demonstrated (Deeg et al. 1993). Such a finding at the presentation of symptoms can further aid in diagnosis and therapy, potentially sparing those individuals at low risk for NEC from unnecessary interventions. Recently, color Doppler US has been used to evaluate bowel wall perfusion. Early stages of the disease show increase in color Doppler signals in the bowel wall and mesentery, reflecting marked a
Fig. 1.39a,b. Portal vein air. Plain radiographs. a Air is observed within the portal vein branches complicating pneuma-tosis intestinalis in a 3-week-old premature infant. b Another premature infant with pneumatosis intestinalis and air within the portal b
Fig. 1.39a,b. Portal vein air. Plain radiographs. a Air is observed within the portal vein branches complicating pneuma-tosis intestinalis in a 3-week-old premature infant. b Another premature infant with pneumatosis intestinalis and air within the portal a
Fig. 1.40a-c. Portal vein air. a,b Transverse sonograms of the liver show multiple echogenic areas (arrows) corresponding to air within the portal vein branches. c Air is also observed within the hepatic veins
Fig. 1.40a-c. Portal vein air. a,b Transverse sonograms of the liver show multiple echogenic areas (arrows) corresponding to air within the portal vein branches. c Air is also observed within the hepatic veins b a b a
b a b hyperemia due to vasodilatation. Absence of blood flow in the bowel wall reflecting absence of perfusion to the involved loop, has been correlated with necrotic bowel (Faingold et al. 2005).
NEC mortality ranges from 9% to 28% and is due to refractory shock, disseminated intra-vascular coagulation, multiple organ failure, intestinal perforation, sepsis, extensive bowel necrosis, and complication of short bowel syndrome. Proper selection of patients for medical versus surgical managements has resulted in significant improvement in survival of infants with NEC. The only universally accepted indication for surgery is the presence of perforation, which may manifest as pneumoperitoneum or free fluid in the peritoneal cavity. Unfortunately, only
50%-75% with perforation have free air detectable on decubitus or horizontal beam radiographs. The presence of intraperitoneal fluid at US, particularly if it is complex or echogenic, is suggestive of perforation (Miller et al. 1993). About 20% of patients treated medically or surgically develop one or multiple strictures, at previously affected sites, especially in the large bowel. The strictures may be asymptomatic but also may cause bowel obstruction several weeks or months after the episode of NEC (Hofman et al. 2004; Pierro and Hall 2003) (Fig. 1.42). Strictures may develop even in patients whose NEC was not severe. Therefore, any patient with symptoms of obstruction after completion of treatment for necrotizing enterocolitis should undergo a contrast enema.
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