Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is an intestinal inflammatory process that can lead to mucosal injury and necrosis. The condition is multifactorial, with underlying risk factors that include prematurity and formula feeding. The clinical presentation varies in severity from feeding intolerance, acute findings on abdominal exam, and systemic symptoms. The diagnosis is based on a clinical suspicion, abnormal abdominal radiographs, and supporting abnormal laboratory results. Management consists of supportive medical care for milder stages and bowel rest and surgical intervention for more advanced stages. Necrotizing enterocolitis and its complications carry a high risk of morbidity and mortality.

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Overview

Definition

Necrotizing enterocolitis (NEC) is an intestinal inflammatory condition associated with focal or diffuse ulceration and necrosis that primarily affects the terminal ileum and colon.

Epidemiology

  • Necrotizing enterocolitis is the most common cause of GI emergencies and intestinal perforation in premature infants.
  • Incidence: 0.3–2.4 per 1000 live births
  • Prevalence: 2%–5% of preterm infants admitted to the NICU

Etiology

  • No single identified cause
  • Multifactorial, with underlying risk factors leading to intestinal inflammatory process:
    • Prematurity: < 32 weeks
    • Low birth weight: < 1500 grams
    • Formula feeding (particularly hyperosmolar feedings)
    • Aggressive advancement of feeding volume
    • Perinatal stress
      • Shock
      • Asphyxia
      • Sepsis
    • Nursery outbreak
    • Maternal illicit drug use (especially of cocaine)
    • Congenital GI defects
    • Congenital heart disease

Pathophysiology and Clinical Presentation

Pathophysiology

  • Multifactorial, with several possible contributing factors:
    • Genetic predisposition
    • Intestinal immaturity
    • Imbalance in intestinal microvascular tone
    • Abnormal intestinal microbial colonization
    • ↑ Immunoreactivity of intestinal mucosa
  • Possible mechanism:
    • Initial ischemic or reperfusion injury → activation of proinflammatory mediators
    • Damage to the intestinal lining → ↑ intestinal permeability → allows bacterial invasion
    • ↑ Feedings → proliferation of luminal bacteria
    • Penetration of bacteria into the intestinal wall → production of hydrogen gas → pneumatosis intestinalis and gas in the portal vein
    • Continued inflammation and intestinal wall destruction → ischemia and necrosis
    • Eventual bowel perforation → peritonitis
  • Most commonly affected sites:
    • Terminal ileum
    • Proximal colon

Clinical presentation

  • Time of symptom onset varies by gestational age:
    • Inverse relationship between gestational age and timing of presentation
    • Preterm: typically in the 2nd to 4th week of life
    • Term or near term: typically in the 1st week of life
  • Clinical course: 
    • Can progress rapidly, within hours
    • Starts as vague signs of feeding intolerance and mild systemic symptoms:
      • Vomiting
      • Increased residual after feeds
      • Temperature instability
      • Decreased activity
      • Fatigue
    • Progresses to acute abdominal symptoms:
      • Hematochezia (bloody stools)
      • Abdominal distention and discoloration
      • Abdominal tenderness
      • Absent bowel sounds
    • Severe systemic involvement:
      • Apnea and respiratory failure
      • Hypotension and shock
      • Unresponsiveness

Diagnosis

The diagnosis of NEC is made primarily by imaging.

Abdominal X-ray

Abdominal X-ray is the method of choice to establish the diagnosis of NEC.

  • Views:
    • Anteroposterior
    • Left lateral decubitus or supine cross-table lateral
  • Findings:
    • Thickened bowel loops
    • Ileus
    • Fixed, dilated bowel loops (does not change with serial imaging studies)
    • Intraperitoneal fluid (ascites):
      • Opacification of the abdomen
      • Absence of intestinal gas (worrisome finding)
    • Pneumatosis intestinalis:
      • Pathognomonic
      • “Train-track” lucency within bowel walls
      • Due to entrapment of air produced by gas-forming bacteria
    • Portal venous gas (pneumatosis hepatis)
    • Pneumoperitoneum: 
      • Large, hyperlucent area above the liver indicating free air below diaphragm
      • Indicative of bowel perforation

Dilated bowel loops on an abdominal radiograph in patient with necrotizing enterocolitis

Image: “A report of a rare congenital malformation in a Nepalese child with congenital pouch colon: a case report” by Shakya VC, Agrawal CS, Koirala R, Khaniya S, Poudel P, Adhikary S. License: CC BY 3.0

Ultrasonography

  • Less commonly used
  • Can be used as an adjunct if radiography yields nonspecific findings
  • Findings:
    • Changes in bowel wall thickness and echogenicity
    • Pneumatosis intestinalis
    • Portal venous gas
    • Changes in bowel wall perfusion
    • Ascites
    • Absent peristalsis
    • Abdominal free air

Laboratory evaluation

The following studies are nonspecific, but they may support the diagnosis and demonstrate the severity of the disease.

  • Positive stool occult blood test
  • CBC:
    • Anemia
    • Leukocytosis with left shift or leukopenia
    • Thrombocytopenia
  • Blood cultures:
    • Obtained before giving antibiotics
    • Most do not grow any organisms
  • Metabolic panel:
    • Hyponatremia
    • ↓ Bicarbonate → metabolic acidosis
    • ↑ Lactic acid
  • Blood gas:
    • Confirms a metabolic acidosis
    • Evaluate for hypoventilation (↑CO2)
  • Coagulation:
    • ↑ PT and PTT
    • ↑ D-dimer
  • Inflammatory markers:
    • ↑ ESR
    • ↑ CRP

Modified Bell’s staging criteria for NEC

The following table provides staging criteria used to enhance recognition of NEC and assess its severity.

StageClassificationClinical signsRadiologic signs
IASuspected NEC
  • Abdominal distention
  • Emesis or gastric residuals
  • Lethargy
  • Apnea
  • Bradycardia
  • Temperature instability
  • Heme-positive stool
Normal to mild intestinal dilation
IBIn addition to the above findings: hematochezia
IIA
  • Definite NEC
  • Mildly ill
In addition to the above findings:
  • Absent bowel sounds
  • +/– Abdominal tenderness
  • Intestinal dilation
  • Ileus
  • Pneumatosis intestinalis
IIB
  • Definite NEC
  • Moderately ill
In addition to the above findings:
  • Abdominal tenderness
  • Metabolic acidosis
  • Thrombocytopenia
  • +/– Abdominal cellulitis
  • +/– RLQ mass
In addition to the above findings:
  • Portal venous gas
  • +/– Ascites
IIIA
  • Advanced NEC
  • Severely ill
  • Bowel intact
In addition to the above findings:
  • Marked distention and tenderness
  • Generalized peritonitis
  • Hypotension
  • Severe apnea
  • Combined metabolic and respiratory acidosis
  • Disseminated intravascular coagulation (DIC)
  • Neutropenia
In addition to the above findings: ascites
IIIB
  • Advanced NEC
  • Severely ill
  • Bowel perforated
In addition to the above findings: pneumoperitoneum

Management

Early and aggressive treatment is necessary.

Medical management:

  • Indicated for stages I and II
  • Resuscitation:
    • Assess airway, breathing, and circulation
    • Cardiovascular and respiratory support
    • IV fluid resuscitation
    • Correct acidosis
  • Initial interventions:
    • Discontinue enteral feedings immediately.
    • Gastric decompression using intermittent nasogastric suction
    • Broad-spectrum IV antibiotics:
      • Can be modified later based on culture results
      • Duration of therapy is dependent on stage.
    • Correct electrolyte abnormalities.
    • Correct coagulopathy.
    • Total parenteral nutrition (TPN)
  • Monitoring:
    • Serial clinical exams every 2 hours
    • Serial abdominal radiography every 6–12 hours

Surgical intervention:

  • Indications: 
    • Perforation
    • Clinical worsening despite medical therapy
  • Options:
    • Primary peritoneal drainage
    • Laparotomy with necrotic bowel resection and enterostomy

Prevention

  • Antenatal corticosteroids for < 34 weeks of gestation
  • Preferential use of breast milk for feedings
  • Standardized feeding protocols:
    • Timed initiation of low-volume trophic feedings
    • Slow advancement of feedings
  • Avoidance of agents that reduce gastric acidity
  • Avoidance of prolonged courses of antibiotics

Additional complications

  • Peritonitis
  • Sepsis occurs in 20%–30%.
  • Death:
    • Mortality rate: 20%–50%
    • Increased mortality with advanced stage and earlier gestational age
  • Intestinal strictures and obstruction
  • TPN-associated cholestasic liver disease
  • Short bowel syndrome:
    • Necrotizing enterocolitis is the most common cause.
    • Due to shortened bowel after surgical resection
    • Causes malabsorption and nutritional deficiencies
  • Neurodevelopmental disorders

Differential Diagnosis

  • Spontaneous intestinal perforation (SIP): an isolated perforation without demonstrable cause in an otherwise normal small bowel: In contrast to NEC, SIP typically presents in the 1st week of life and is not dependent on the risk factor of enteral feedings. Spontaneous intestinal perforation presents with abdominal distention and vomiting. Exam may show a bluish discoloration of the abdomen. The condition is diagnosed by abdominal radiography showing pneumoperitoneum but not pneumatosis intestinalis. Spontaneous intestinal perforation is managed surgically.
  • Intestinal obstruction: In the neonatal period, obstruction may be due to various underlying causes, including meconium ileus, intestinal atresias, Hirschsprung’s disease, intussusception, and volvulus. Obstruction will present as abdominal distention, vomiting, and possibly delayed passage of meconium. Abdominal imaging will provide the diagnosis. Management is surgical.
  • Infectious enteritis: a viral or bacterial infection of the intestines that can also present with vomiting and bloody stools: The diagnosis is often clinical, and bacterial causes may be confirmed by stool culture. Management is supportive.
  • Anal fissure: a tear or ulceration of the anal canal that may lead to blood in stool with none of the other associated clinical findings of NEC: Diagnosis is by visualization on exam. Management is generally supportive.
  • Cow’s milk protein intolerance: an abnormal response by the immune system to cow’s milk; the most common food allergy in early life: This intolerance typically presents later than NEC and can progress to bloody stools and vomiting. The diagnosis is clinical and supported by improvement in symptoms with avoidance of cow’s milk. Management includes transition to a protein hydrolysate or elemental amino acid formula.

References

  1. Neu J, Walker W. (2011). Necrotizing enterocolitis. New England Journal of Medicine 364:255–264. https://dx.doi.org/10.1056%2FNEJMra1005408
  2. Bell MJ, Ternberg JL, et al. (1978). Neonatal necrotizing enterocolitis: Therapeutic decisions based upon clinical staging. Annals of Surgery 187:1–7. https://dx.doi.org/10.1097%2F00000658-197801000-00001
  3. Charu T, Sandals G, Jayaswal S, Shah H. (2015). Spontaneous Intestinal Perforation in Neonates. Journal of Neonatal Surgery 4(2):14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4447467/
  4. Kim J. Neonatal necrotizing enterocolitis: Clinical features and diagnosis. Retrieved March 5, 2021, from: https://www.uptodate.com/contents/neonatal-necrotizing-enterocolitis-clinical-features-and-diagnosis
  5. Kim J. Neonatal necrotizing enterocolitis: Management. Retrieved March 5, 2021, from: https://www.uptodate.com/contents/neonatal-necrotizing-enterocolitis-management
  6. Cochran WJ. (2020). Necrotizing enterocolitis. MSD Manual Professional Version. Retrieved March 6, 2021, from https://www.msdmanuals.com/professional/pediatrics/gastrointestinal-disorders-in-neonates-and-infants/necrotizing-enterocolitis
  7. Springer SC, Annibale DJ. (2017). Necrotizing enterocolitis. In Aslam M (Ed.). Medscape. Retrieved March 6, 2021, from https://emedicine.medscape.com/article/977956-overview
  8. Ginglen JG. (2020). Necrotizing enterocolitis. StatPearls. Retrieved March 6, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK513357/

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