Necrotizing Enterocolitis | Pediatric Radiology Reference Article | Pediatric Imaging

Etiology: combination of immaturity, enteral feeding, ischemia, infection -> mucosal damage -> intestinal ischemia -> necrosis, involves any portion of intestine but distal ileum + proximal colon most common
AXR: early (diffusely dilated loops of bowel / ileus, asymmetrically dilated loop of bowel), later (classic triad of pneumatosis intestinalis, portal venous gas, free air), fixed loop can be sign of impending perforation, some perforations (15-20%) can be walled off due to surrounding inflammation and not show free air on AXR, many cases have no AXR findings as some findings of necrotizing enterocolitis on AXR are transient (pneumatosis intestinalis + portal venous gas)
— Bubbly pneumatosis = submucosal gas, curvilinear pneumatosis = subserosal gas
— Note: biliary air is more central in liver, portal venous gas is more peripheral in liver
US: complicated ascites + free air are signs of perforation, portal venous gas appears as echogenic bubbles in portal veins, pneumatosis intestinalis
Complications: strictures in 25%, more common in colon than small bowel, especially in descending colon
Clinical: mainly in premature infants: feeding intolerance, abdominal distension, bloody stools, can also affect older stressed infants (after cardiac surgery)
Note: stricture should be suspected in an infant with a persistently distended abdomen after treatment for necrotizing enterocolitis

US:

Bowel wall thickening (>2.7 mm) or thinning (<1 mm), pneumatosis intestinalis, portal venous gas, ascites, fluid collection, doppler of SMA + celiac trunk – increased peak systolic velocity, hyperemia or no flow, peristalsis, zebra pattern of prominent valvulae conniventes
Normal bowel wall -> bowel distension / hyperemia +/- echogenic mucosa -> bowel wall thickening +/- hyperemia, +/- intramural gas +/- loss of gut signature +/- loss of bowel wall distinctness -> bowel wall thinning / bowel distension / bowel contents with debris +/- intramural gas
US can help when AXR unremarkable, AXR has paucity of bowel gas or is gasless, AXR shows dilated fixed loop of bowel -> check its perfusion and peristalsis
US helpful finding – free air, absent peristalsis, complex ascites, focal fluid collections

Approach to necrotizing enterocolitis:

On AXR + US look for 1) gas – intraluminal bowel gas – dilated / pattern, intramural gas, portal venous gas, free gas and 2) calcification – peritoneal, mural, luminal
On US look for 1) fluid – free fluid, focal fluid / abscess, intraluminal GI fluid and 2) bowel wall – thickness / echogenicity, peristalsis (real time), perfusion (Doppler)