Discussion of Necrotizing enterocolitis
- Necrotizing enterocolitis (NEC) is one of the most common acquired, life-threatening gastrointestinal diseases in the newborn, affecting 1%–5% of neonatal intensive care unit admissions and up to 10% of neonates under 1500 g.
- The incidence of NEC is inversely proportional to the gestational age.
- Of term infants, congenital heart disease is the main risk factor in this group. Other risk factors include perinatal asphyxia, patent ductus arteriosus, indomethacin therapy, and decreased umbilical flow in utero.
- NEC most commonly manifests within the first or second week of life.
- The symptoms referable to the gastrointestinal tract include feeding intolerance, vomiting, diarrhea, and blood in the stool. However, there may also be non-specific generalized symptoms including lethargy, temperature and blood pressure instability, and apnea.
- Physical signs include abdominal distention.
- Prompt institution of therapy, which includes bowel rest with a nasogastric tube, antibiotics, and adequate hydration (total parenteral nutrition), is essential to limit clinical progression and the development of complications.
- The overall mortality rate in NEC is between 20% and 40% and is higher in neonates of very low birth weight.
- Because of the higher mortality rate following perforation, earlier detection of severely ischemic or necrotic loops of bowel before perforation occurs could potentially improve the morbidity and mortality in NEC.
 Imaging Findings for Necrotizing enterocolitis
 Plain film
- Plain abdominal radiography is the current modality of choice for the evaluation of neonates suspected of having NEC.
- The timing of follow-up plain abdominal radiographs depends on the severity of the NEC and may vary from 6 to 24 hourly.
- The main observations to be made on the plain abdominal radiograph relate primarily to the presence, amount, and distribution of gas, which includes intraluminal gas, pneumatosis, portal venous gas, and pneumoperitoneum.
- In normal neonates, gas is most often present through most of the small and large bowel and each gas-filled loop causes an impression on adjacent loops. The loops develop a multifaceted configuration, giving the gas pattern a "mosaic" appearance.
- Dilatation with loss of the mosaic pattern and the development of rounded or elongated loops is more suggestive that an abnormality is present.
 Bowel Gas Pattern
- In NEC, bowel dilatation is a nonspecific finding best appreciated on the plain abdominal radiograph and may be the only sign present in many patients with either mild or severe forms of the disease. The dilatation is usually due to an ileus and may be generalized or focal, depending on the extent of bowel involvement. It is the commonest sign, being present in over 90% of patients, with the remaining 10% showing only minor or nonspecific disturbances of bowel gas pattern.
- Dilatation of bowel is an early sign and may even precede the clinical features of NEC by several hours.
- The degree of dilatation usually correlates well with the clinical severity of the disease and the distribution of the dilated loops in serial examinations is related to clinical progression.
- Worrisome if the dilated loops maintain the same appearance as fixed loops on follow-up plain abdominal radiographs. This suggests the development of full-thickness necrosis and may precede clinical deterioration including signs of peritonitis.
- Pneumatosis is also an early sign that may precede clinical signs.
- Although intramural gas may be present in other neonatal conditions, it is most commonly seen in NEC and thus has been considered a virtually pathognomonic sign of NEC.
- Pneumatosis is more commonly present in the distal small bowel and large bowel and is therefore most commonly seen in the right lower quadrant.
- On plain abdominal radiographs, intramural gas may be diffuse or localized and appears as linear or rounded radiolucencies.
- The linear lucencies often appear curvilinear; they represent intramural gas in the subserosa and appear as black lines on the radiograph, which can occasionally be confused with overlapping bowel loops filled with gas.
- A clue to differentiating intramural gas from overlapping loops are the white lines that often accompany the black lines of intramural gas. The white lines represent the mucosa and submucosa, which are lifted off the serosa and are contrasted by the subserosal intramural gas and the intraluminal gas.
 Portal venous gas
- In NEC, portal venous gas is an extension of intramural gas that enters the veins of the bowel wall and passes into the portal venous system.
- Portal venous gas has been reported on plain abdominal radiographs in up to 30% of neonates with NEC, and these are usually, but not always, the more severely affected cases. Portal venous gas is not always associated with a fatal outcome.
- On a supine plain abdominal radiograph, portal venous gas appears as branching, linear, radiolucent vessels that may extend from the region of the main portal vein toward the periphery of both hepatic lobes, and the extent depends on the amount of portal venous gas present.
- Free gas in the peritoneal cavity results from bowel perforation, which most commonly occurs in the distal ileum and proximal colon.
- It is the only universally accepted radiologic indication for surgical intervention.
- On the cross-table lateral view, free gas may appear as triangular lucencies between loops of bowel anteriorly just beneath the abdominal wall or as small bubbles or linear gas collections anterior to the liver.
- On the left lateral decubitus view, small amounts of gas may be seen between the right lobe of the liver and the right lateral abdominal wall.
- On the supine view, large amounts of gas may give rise to the football sign, where the gas outlines the whole of the peritoneal cavity, the undersurface of the diaphragm, and the falciform ligament (the lacing of the football).
- Smaller amounts of free gas may give rise to lucency below the diaphragm without giving rise to the full-blown football sign.
- Even on the supine view, smaller amounts of free gas may be detected when both sides of the bowel wall are outlined (Rigler sign).
 See Also
 External Links
- Monica Epelman, Alan Daneman, Oscar M. Navarro, Iris Morag, Aideen M. Moore, Jae Hong Kim, Ricardo Faingold, Glenn Taylor, and J. Ted Gerstle. Necrotizing Enterocolitis: Review of State-of-the-Art Imaging Findings with Pathologic Correlation. RadioGraphics 2007 27: 285-305.