Necrotising Enterocolitis

Summary
Introduction
Risk factors
Clinical Presentation
Differential Diagnosis of suspected NEC
Radiographic findings
Management
Complications
Prevention

Summary

NEC (necrotising enterocolitis) is the most common GI emergency in neonates
NEC can present late in tiny babies
early or ‘possible’ NEC is difficult to diagnose – if in doubt treat early and conservatively (nil by mouth and broad spectrum antibiotics)
babies with ‘definite’ NEC should be referred to a NICU
babies with ileostomies
- need supplemental sodium
- can become rapidly dehydrated with gastroenteritis
strictures can present many weeks after NEC

Introduction

Necrotising enterocolitis (NEC) is the most common gastrointestinal (GI) emergency in neonates. Ninety percent of babies with NEC are preterm. It is predominantly a disease of the very low birthweight infant and is most common in babies < 1000 g or those that are both preterm and growth restricted. The incidence of NEC is inversely proportional to birthweight. In general, the age of onset is inversely proportional to gestation; therefore smaller babies present later.

Approximately 50% of babies developing NEC require surgery. The mortality rate of NEC is 20-40%. Of those who survive, approximately 25% develop long term sequelae.

Early or suspected NEC is often difficult to diagnose as the clinical signs and symptoms are often non-specific, as are the radiological and laboratory findings. As babies with definite NEC should be transferred to a level III unit, this topic will concentrate mainly on the presentation and diagnosis of NEC as well the level II management of a baby who has had previous NEC.

Risk factors

prematurity
enteral feeding (although approx. 10% of cases occur in infants never fed)
formula feeding (6 times more common than if only breast milk fed)
often occurs in clusters (although organisms vary)
bowel ischaemia
in term infants
- polycythaemia
- cardiac surgery
- abdominal surgery (esp. gastroschisis, intestinal atresia)
- endocrine abnormalities

Clinical Presentation

clinical signs and symptoms are highly variable but include

GI dysfunction
- abdominal distention
- vomiting
- bilious drainage from enteral feeding tubes
- blood in stool

systemic
- temperature instability
- apnoea and/or bradycardia
- lethargy
- hypotension

the severity, radiology and management of NEC is best exemplified by the ‘Modified Bell’s Staging Criteria’

Modified Bell’s Staging Criteria for Necrotizing Enterocolitis

STAGE	SYSTEMIC SIGNS	INTESTINAL SIGNS	RADIOLOGIC SIGNS	TREATMENT
I. Suspected
A	Temperature instability, apnoea, bradycardia	Elevated pregavage residuals, mild abdominal distension, occult blood in stool	Normal or mild ileus	NPO, antibiotics x 3 days
B	Same as IA	Same as IA, plus gross blood in stool	Same as IA	Same as IA
II. Definite
A: Mildly ill	Same as IA	Same as I, plus absent bowel sounds, abdominal tenderness	Ileus, pneumatosis intestinalis	NPO, antibiotics x 7 to 10 days
B: Moderately ill	Same as I, plus mild metabolic acidosis, mild thrombocytopenia	Same as I, plus absent bowel sounds, definite abdominal tenderness, abdominal cellulitis, right lower quadrant mass	Same as IIA, plus portal vein gas, with or without ascites	NPO, antibiotics x 14 days
III Advanced
A: Severely ill, bowel intact	Same as IIB, plus hypotension, bradycardia, respiratory acidosis, metabolic acidosis, disseminated intravascular coagulation, neutropenia	Same as I and II, plus signs of generalised peritonitis, marked tenderness and distension of abdomen.	Same as IIB, plus definite ascites	NPO, antibiotics x 14 days, fluid resuscitation, inotropic support, ventilator therapy, paracentesis
B: Severely ill: bowel perforated	Same as IIIA	Same as IIIA	Same as IIB, plus pneumoperitoneum	Same as IIA, plus surgery

NB: Permission to us the Modified Bell's Staging Criteria has been given by Paediatrics in Review. The Modified Bell’s Staging Criteria chart is available as a .pdf file for printing. If you do not have a copy of Acrobat Reader to view this file, the latest version is available for free download from www.adobe.com

Differential Diagnosis of suspected NEC

dysmotility of prematurity
septic ileus
bowel obstruction
gastroenteritis
anal fissure
cow’s milk protein sensitive enterocolitis

Radiographic findings

nonspecific
- diffuse gaseous distension
- asymmetric, disorganised bowel pattern
- ‘featureless’ loops
- dilated bowel loops
- bowel wall thickening
- increased peritoneal fluid
diagnostic signs
- persistent loop
- pneumatosis intestinalis (virtually pathognomonic)
  - submucosal – bubbly or cystic appearance (may be confused with stool, although stool usually moves on serial x-rays)
  - subserosal – linear or curvilinear appearance
- portal venous gas
- pneumoperitoneum (although may not be due to NEC)

Management

see ‘Modified Bell’s Staging Criteria’ for duration
nil by mouth
gastric tube on free drainage
blood culture
antibiotics
- vancomycin
- gentamicin
- metronidazole ( only for definite NEC)
cases of definite NEC should be referred to a level III NICU for management, as the following (may be) required
- gut rest for 10-14 days
- total parenteral nutrition
- fluid management
- inotropes
- ventilation
- analgesia
- frequent radiographs
- surgery (25% to 50% of cases)

Complications

surgery requiring ileostomy
- require supplemental sodium even when well
- high risk of rapid dehydration with gastroenteritis
stricture
- 20-30%
- most commonly in large bowel
- 80% on left side
- may not develop for weeks to months post-NEC
- presents with recurrent abdominal distension
- surgical consultation and contrast enema required

Prevention

antenatal corticosteroids
early intervention (nil orally) for suspected NEC
breast milk
infection control practices may limit the size of disease clusters

Areas of uncertainty

effect of rate of feed upgrade in the prevention of NEC
prophylactic antibiotics (proven to reduce NEC risk but concern re development of antibiotic-resistant organisms)
enteral IgA (enteral IgG refuted)

References

Taeusch HW, Ballard RA. Avery’s Diseases of the Newborn 7^th Ed. W.B. Saunders Company, Philadelphia. 1998

Chandler JC, Hebra A. Necrotizing enterocolitis in infants with very low birth weight. Sem Pediatr Surg 2000;9:63-72

Buonomo C. The radiology of necrotizing enterocolitis. Radiol Clinics North Amer 1999;37:1187-98