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 Published: 29/11/2011

Necrtotising enterocolitis

Modified Bell Staging Definite NEC NEC with Portal Venous Gas Suspicious (but not) NEC

Necrotising enterocolitis (NEC) is a severe disease of the intestinal tract, typically involving small and/or large bowel.  Diagnosis is made with a combination of clinical features and radiographic findings, although sometimes a firm diagnosis may not be made until laparotomy.  The cause is unclear but is probably related to a complex interplay between intestinal ischaemia, injury, and infection.  The incidence is inversely proportional to gestational age, and the risk of developing NEC continues longer in smaller infants.  Other infants at risk include asphyxiated infants, infants following cardiac surgery, and following exchange transfusion.  It is rare in infants who have not been enterally fed.

The incidence in infants <32 weeks is in the region of 5-10%, depending on the diagnostic criteria used.   The survival for infants with non-surgical NEC is good, whereas up to 50% of infants who require laparotomy may die.  Extensive resection of bowel may be associated with short bowel syndrome.

Modified Bell Staging

Modified from: Walsh MC, Kliegman RM.  Necrotizing enterocolitis: treatment based on staging criteria.  Pediatr Clin North Am 1986; 33:179:

Modified
Bell Staging
Classification Systemic
Signs
Abdominal
Signs
Radiological
Signs
I A Suspected NEC
  • Temperature instability
  • Apnoea
  • Bradycardia
  • Lethargy
  • Aspirates
  • Mild abdominal distension
  • Positive faecal occult blood
  • Normal
  • Mild intestinal dilatation
  • Mild ileus
I B Suspected NEC

As above

  • Fresh blood PR

As above

II A Proven NEC -
mildly ill

As above

As above, plus

  • Absent bowel sounds
  • +/- abdo tenderness
  • Intestinal dilatation
  • Ileus
  • Pneumatosis intestinalis
II B Proven NEC -
moderately ill

As above, plus

  • mild metabolic acidosis
  • mild thrombocytopenia

As above, plus

  • absent bowel sounds
  • definite tenderness
  • +/- abdominal cellulitis
  • RLQ mass

As above, plus

  • Portal vein gas
  • +/- ascites
III A Advanced NEC -
severely ill, bowel intact

As above, plus

  • Hypotension
  • Bradycardia
  • Severe apnoea
As above, plus
  • Signs of generalised peritonitis
  • Marked tenderness
  • Marked distension

As above, plus

  • Definite ascites
III B Advanced NEC -
severely ill, bowel perforated
As above As above

As above, plus

  • Pneumoperitoneum

Definite Radiographic NEC

AXR - NEC - florid.jpg (24993 bytes)

Severe NEC lateral shoot through.jpg (162222 bytes)

These radiographs demonstrate the classic intramural gas (pneumatosis intestinalis) appearance of necrotising enterocolitis (NEC).  Lucency within the bowel wall is seen throughout the abdomen.  In this supine view, no free intraperitoneal air is seen but a lateral decubitus view is necessary to exclude a bowel perforation.

The intramural gas may show as thin lines within the bowel wall, or as a series of coalesced "cysts".

NEC Severe.jpg (277478 bytes) Definite NEC 1.JPG (62074 bytes) Definite NEC 2.JPG (54499 bytes)


NEC with Portal Venous Gas

  Portal venous gas may be seen if gas produced by organisms in the intestinal wall tracks through into the portal circulation.  It can be a subtle finding.
NECwithPortalGasAP1.jpg (24141 bytes) In the image to the left, there is extensive pneumatosis involving several areas of the bowel.  There is distension of the stomach.  There is also lucency in the liver, representing portal venous gas.

Suspicious but not NEC

  Sometimes the diagnosis of NEC can be difficult to make on both clinical and radiological grounds.  In this circumstance, repeating the radiographs may help in establishing diagnostic certainty.  Occasionally, faecal loading of the large bowel may have appearances of NEC.
Suspicious but not NEC 1.JPG (53628 bytes)

This initial film demonstrates a suspicious area in the right upper quadrant.  The baby had no clinical signs suggestive of NEC but had passed a small amount of rectal blood.

Suspicious but not NEC 2.JPG (51836 bytes) On a film the following day, there appeared to be cystic abnormalities of the bowel in a similar area.  The baby remained well, with no changes on the full blood count, no abdominal distension or signs, and no bileous aspirates.  He was however commenced on treatment for NEC on the basis of suspicion about the radiological findings.
Suspicious but not NEC 3.JPG (63694 bytes) He then passed a large bowel motion.  A follow-up film was reassuringly normal and, in the absence of any significant clinical or haematological indicators of NEC, treatment was stopped at 48 hours.  He remained clinically well and tolerated full oral feeds without incident.