NECROTIZING ENTEROCOLITIS IMAGING STUDIES

necrotizing enterocolitis imaging studies:
• The mainstay of diagnostic imaging is abdominal radiography. An anteroposterior (AP) abdominal radiograph and a left lateral decubitus radiograph (left side down) are essential for initially evaluating any baby with abdominal signs. Perform these abdominal radiographs serially at 6-hour or greater intervals, depending on presentation acuity and the preferences of the attending medical team, including any involved surgeons.

o Characteristic findings on an AP abdominal radiograph include an abnormal gas pattern, dilated loops, and thickened bowel walls (suggesting edema/inflammation). Serial radiographs help assess disease progression. A fixed and dilated loop that persists over several examinations is especially worrisome. o Radiographs can sometimes reveal scarce or absent intestinal gas, which is more worrisome than diffuse distention that changes over time.

o Pneumatosis intestinalis is a radiologic sign pathognomonic of NEC. It appears as a characteristic train-track lucency configuration within the bowel wall. Intramural air bubbles represent extravasated air from within the intestinal lumen. Analysis of gas aspirated from these air bubbles reveals that it consists primarily of hydrogen, suggesting that these are caused by bacterial fermentation of undigested intraluminal substrates. Carbohydrate (often lactose) fermentation by intestinal flora yields hydrogen and carbon dioxide and a series of short-chain organic acids, which can promote inflammation.

o Abdominal free air is ominous and usually requires emergency surgical intervention. 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.

o Portal gas is a subtle and transient finding that was originally thought to be ominous when detected but is now considered less ominous. Portal gas, which is not usually captured in serial radiographs, appears as linear branching areas of decreased density over the liver shadow and represents air present in the portal venous system. Portal gas is much more dramatically observed on ultrasonography.

o 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 appreciated on ultrasonography.

o Left side down (left lateral) decubitus radiography allows the detection of intraperitoneal air, which rises above the liver shadow (right side up) and can be visualized easier than on other views. Obtain this view with every AP examination until progressive disease is no longer a concern.

• Abdominal ultrasonography is a relatively new technology for evaluating suspected NEC in neonates.
o Advantages
􀂃 Available at bedside
􀂃 Noninvasive imagery of intra-abdominal structures

o Disadvantages
􀂃 Limited availability at some medical centers
􀂃 Requires extensive training to discern subtle ultrasonographic appearance of some pathologies

o With abdominal ultrasonography, a skilled physician can identify a larger amount of diagnostic information faster and with less risk to the baby than with the current o tandard evaluation methods.

o Abdominal air (easily observed on ultrasonography and in grossly distended patients) can interfere with assessing intra-abdominal structures.

o 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 gas or a fixed area of radiographic density.

o Ultrasonography is excellent for distinguishing fluid from air, so ascites can be identified and quantified. Serial examinations can be used to monitor the progression of ascites as a marker for the disease course.

o Portal air can be easily observed as bubbles present in the venous system. This finding has been termed informally the "champagne sign" because of its similar appearance to a champagne flute.

o Recent data suggest that ultrasonographic assessment of major splanchnic vasculature can help in the differential diagnosis of NEC from other more benign and emergent disorders.

• The orientation of the superior mesenteric artery in relationship to the superior mesenteric vein can provide information regarding the possibility of a malrotation with a subsequent volvulus. If a volvulus is present, the artery and vein are twisted and, at some point in their courses, their orientation switches. This abnormality can be detected, even if the rotation is 360 degrees, if the full path of the vessels can be observed.

• 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 clinical study from Europe and a recent small series in the United States demonstrate markedly increased peak flow velocity (>1.00) of arterial blood flow in the celiac and superior mesenteric arteries in early NEC. 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.