Necrotizing Enterocolitis

  • Etiology:
    — Combination of immaturity, enteral feeding, ischemia, infection which leads to mucosal damage which leads to intestinal ischemia which leads to necrosis
    — Involves any portion of intestine but distal ileum and proximal colon most common
  • Imaging AXR:
    — Early see diffusely dilated air-filled loops of bowel and ileus or asymmetrically focally dilated loop of bowel
    — Later see classic triad of pneumatosis intestinalis, portal venous gas, free air
    — Fixed bowel 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 such as pneumatosis intestinalis and portal venous gas
    — Bubbly pneumatosis intestinalis = submucosal gas, curvilinear pneumatosis intestinalis = subserosal gas
    — Note: Biliary air is more central in liver, portal venous gas is more peripheral in liver
    — Note: Portal venous gas when seen with pneumatosis intestinalis is forewarning of more severe bowel ischemia
  • Imaging US:
    — Complicated ascites and free air are signs of perforation
    — Portal venous gas appears as echogenic bubbles in portal veins
    — Pneumatosis intestinalis
  • DDX:
  • Complications: Strictures in 25% which are more common in colon than small bowel, especially in descending colon
  • Treatment: Surgical intervention when there is free air due to bowel perforation
  • Clinical:
    — Mainly seen in premature infants with feeding intolerance, abdominal distension, bloody stools
    — Up to 10% of cases occur in term infants who are stressed (after cardiac surgery)
    — Is most common cause of portal venous gas in a neonate
    — Is most common cause of pneumatosis intestinalis in children
  • Note: Stricture should be suspected in an infant with a persistently distended abdomen after treatment for necrotizing enterocolitis

Imaging US:

  • US can help when AXR is unremarkable, AXR has paucity of bowel gas or is gasless, AXR shows dilated fixed loop of bowel which leads to check its perfusion and peristalsis
  • US most helpful findings – free air, absent peristalsis, complex ascites, focal fluid collections
  • Findings:
    — Bowel wall thickening (greater than 2.7 millimeters) or thinning (less than 1 millimeters)
    — Pneumatosis intestinalis, portal venous gas, ascites, fluid collection, peristalsis, zebra pattern of prominent valvulae conniventes
    — US Doppler of superior mesenteric artery and celiac trunk – increased peak systolic velocity, hyperemia or no flow
  • Progression of bowel wall findings:
    — Start with normal bowel wall
    — Which leads to bowel distension and hyperemia with or without echogenic mucosa
    — Which leads to bowel wall thickening with or without hyperemia, with or without intramural gas with or without loss of gut signature with or without loss of bowel wall distinctness
    — Which leads to bowel wall thinning and bowel distension and bowel contents with debris with or without intramural gas

Approach to necrotizing enterocolitis:

  • On AXR and 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 or abscess, intraluminal gastrointestinal fluid and 2) bowel wall – thickness and echogenicity, peristalsis (real time), perfusion (Doppler)

Radiology Cases of Necrotizing Enterocolitis

Radiology Cases of Diffusely Dilated Loops of Bowel in Necrotizing Enterocolitis

AXR of necrotizing enterocolitis
Supine AXR shows diffusely dilated loops of bowel throughout the abdomen. There is no evidence of pneumatosis intestinalis, portal venous gas, or free air.

Radiology Cases of Pneumatosis Intestinalis in Necrotizing Enterocolitis

AXR of necrotizing enterocolitis
Supine AXR shows linear pneumatosis intestinalis involving several loops of bowel in the left lower quadrant of the abdomen.

Radiology Cases of Portal Venous Gas in Necrotizing Enterocolitis

AXR of necrotizing enterocolitis
Supine AXR shows numerous branching linear lucencies throughout the liver consistent in appearance with portal venous gas.

Radiology Cases of Bowel Perforation in Necrotizing Enterocolitis

AXR of necrotizing enterocolitis
Supine AXR (left) shows free air underneath the diaphragm while the left lateral decubitus AXR (right) shows free air between the abdominal wall and liver and a small amount of portal venous gas.

Radiology Cases of Bowel Stricture After Necrotizing Enterocolitis

Enema of necrotizing enterocolitis
AP image from an enema shows two fixed strictures in the colon, the first at the junction of the sigmoid colon and descending colon, and the second at the splenic flexure.
Enema of colonic strictures after necrotizing enterocolitis
AXR AP (left) shows multiple dilated loops of bowel throughout the abdomen. AP image from early in a barium enema (above right) shows a fixed narrowing in the sigmoid colon while AP image from later in the enema (below right) shows additional areas of fixed narrowing beneath the splenic flexure, at the splenic flexure and beneath the hepatic flexure.
Enema of colonic strictures after necrotizing enterocolitis
AXR (left) shows dilated loops of bowel throughout the abdomen. AP image from an enema (above right) shows narrowing of the colon at the rectosigmoid colon, splenic flexure and cecum. AP image from later in the exam (below right) shows dilated loops of small bowel filled with contrast above the level of the narrowing in the cecum.
Enema of post necrotizing enterocolitis stricture of the colon
AP image from an enema (left) shows a transition zone in the lower right of the image from a narrow sigmoid colon to a more dilated descending colon above it. Spot image from the enema (right) shows the narrowed colonic lumen filled with contrast connecting those two parts of the colon.
CT and enema of colonic stricture after necrotizing enterocolitis
AXR (above left) shows an extremely dilated structure in the mid abdomen filled with air and small radiopaque objects. Axial CT without contrast of the abdomen (above right) shows the dilated structure to be a loop of bowel containing stool and radiopaque foreign bodies. AP image from an enema (below left) shows a dilated ascending colon, an extremely dilated transverse colon, and normal caliber of the descending colon and sigmoid colon. Oblique views of the splenic flexure (not provided) showed a very tight stricture there.

Radiology Cases of Enterocutanous Fistula After Necrotizing Enterocolitis

Upper GI of enterocutaneous fistula in necrotizing enterocolitis
AP image from an UGI exam (left) shows contrast opacifying the proximal jejunum. An image obtained a minute later (right) shows contrast entering the surgical drain in the left lower quadrant of the abdomen.

Surgery Cases of Necrotizing Enterocolitis

Surgical image of necrotizing enterocolitis
Surgical image shows the bowel was white and necrotic throughout its entire length from the duodenum to the colon. There was no salvageable bowel.

Surgery Cases of Bowel Stricture After Necrotizing Enterocolitis

Surgical image of colonic stricture due to necrotizing enterocolitis
Surgical image (above left) shows a massively dilated transverse colon (held between the fingers) and massively dilated small bowel to the left of the image. Examination of the splenic flexure of the colon (above right) reveals a transition zone between the transverse colon and descending colon (center of image). Further dissection near the transition zone shows a tight stricture at the transition zone (below in the center of the image).