Necrotizing Enterocolitis - Types, Causes, Diagnosis, and Treatment

What Is Necrotizing Enterocolitis?

Necrotizing enterocolitis (NEC) is a bacterial infection that mostly affects the neonatal population, with a high mortality of over 50 percent. As the nomenclature suggests, the infection causes inflammation and necrosis of the colon and the intestine leading to life-threatening complications, even causing death in more than half of the infected babies. The condition is mostly seen in preterm-delivered babies with low birth weights.

What Are the Types of Necrotizing Enterocolitis?

Clinicians have classified NEC into four categories based on the time of onset of symptoms. The classifications are:

1. Classic: Most common NEC occurs in infants born before 28 weeks of pregnancy. Onset is sudden and is between three to six weeks of age.

2. Transfusion Associated: About 30 percent of premature babies who require blood transfusion for anemia may develop NEC.

3. Atypical: Rare category, onset is during the first week of birth or before the first breastfeeding.

4. Term Infant NEC: NEC is usually seen in full-term babies with birth defects like congenital heart conditions, gastroschisis, and low oxygen levels at birth.

Who Is Susceptible to Necrotizing Enterocolitis?

Necrotizing enterocolitis is the most common fatal gastrointestinal tract infection seen in neonatal intensive care unit (NICU) babies (almost 70 percent prevalence). The onset is usually during the second or third week after birth, occurring in about one baby per 1000 premature births. Full-term babies are at a lower risk, with an incidence of one in 10,000 term deliveries and a global incidence of 0.3 to 2.4 per 1000 live births. NEC is most common in babies weighing less than 3.25 pounds (4 ounces or 1.5 kilograms). Incidence is rare in older, healthier, and larger babies. The smaller the baby, the greater the risk of NEC. NEC affects about two to five percent of all premature and over eight percent of NICU admissions. Mortality rate ranged between 10 to 50 percent, with the most severe cases having mortality close to 100 percent.

What Are the Risk Factors for Necrotizing Enterocolitis?

With the highest prevalence in preterm neonates, certain additional conditions increase the risk of NEC development. The risk factors are as follows:

• Formula feeding.

• Low oxygen saturation at birth.

• Intestinal infection.

• Too many RBCs (red blood cells) in circulation.

• Pre-existing gastrointestinal infections.

• Babies with blood transfusion.

• Similar outbreaks in the nursery.

• Injury to the intestinal lining.

• Heavy bacterial growth in the intestine.

What Causes Necrotizing Enterocolitis?

The exact cause of NEC still evades recognition. Still, it is hypothesized to be secondary to a multifactorial etiology, including a drop in bowel perfusion and exaggerated activation of proinflammatory intracellular cascades. Clusters of microbes, including gram-positive and gram-negative bacteria, viruses, and fungi, have been identified in some affected babies, which supports the pathogenic hypothesis.

Some research also suggests that the translocation of intestinal microflora across intestinal barriers may render the gastrointestinal tract vulnerable to ischemia, immunologic immaturity, and immunological dysfunction. There is significant inflammation of the gastrointestinal tissues, an increase in inflammatory mediators and intraluminal bile acids, and a decrease in cellular growth factors leads to varying degrees of tissue damage.

Genetic studies also point towards a possible genetic component of NEC onset. An association between carbamoyl-phosphate synthetase I (an enzyme involved in urea production), functional SNP (single-nucleotide polymorphisms) IL-6 (interleukin-6), TRIM21 (a protein-coding gene), TGFβ-1 (transforming growth factor β-1) genes, and NEC. While the first two upregulate the risk, the latter decreases the association. Babies with certain medications have been prone to NEC. The medications include Theophylline, Aminophylline, Indomethacin, vitamin E, gastric acid inhibitors, and in-utero exposure to magnesium sulfate.

All the etiologies lead to bowel perforation (micro or frank) and leakage of the infection and bowel components into the abdominal space, which infects the entire peritoneal cavity.

What Are the Clinical Features of Necrotizing Enterocolitis?

The signs and symptoms of NEC include the following features:

• Abdominal pain.

• Abdominal swelling.

• Unstable heart rate.

• Fluctuating blood pressure.

• Changes in body temperature.

• Breathing changes.

• Diarrhea.

• Hematochezia (bloody stool).

• Green or yellow vomit.

• Lethargy.

• Lack of appetite.

• Inability to gain weight.

• Pneumatosis intestinalis (air within the intestinal wall).

• Bowel perforation.

• Peritonitis (infection of the peritoneal cavity).

• Visible intestinal loops.

• Decreased bowel sounds.

• Palpable abdominal mass.

• Erythema of the abdominal wall.

Systemic signs include:

• Respiratory failure.

• Circulatory collapse.

• Decreases peripheral perfusion.

How Is Necrotizing Enterocolitis Diagnosed?

Premature babies, who form the bulk of this illness, are under constant observation in the NICU. Any suspected deviation from normal vitals, feeding, and growth can alert the physician, who can order several tests to diagnose the underlying cause.

Plain X-rays (anterior-posterior and left lateral decubitus views) of the abdomen show bubbling, which is evidence of gas bubbles produced by bacteria. Dilated loops of the bowel, pneumatosis intestinalis, and portal venous air findings are diagnostic of NEC. Portal venous air is a rare finding, but it severely degrades the prognosis. It is advisable to repeat the series of radiographs every six hours until definitive treatment is achieved.

Laboratory studies reveal WBC (white blood cell count) below 1500 per microliter, hyponatremia, low serum bicarbonate, and thrombocytopenia. Stool cultures are also done to detect occult blood. Rarely, the hydrogen breath test may turn out positive.

How to Treat Necrotizing Enterocolitis?

The treatment protocol begins with the cessation of all gastrointestinal feeding and engaging nasogastric or orogastric drainage to remove air and fluid from the abdomen, intestine, and stomach. Fluid replacement is done by intravenous administration along with antibiotics. Regular monitoring of the abdomen and blood is essential to track the progress or remittance. Severe cases with perforation or peritonitis would require surgery to either remove the dead bowel or perform a colostomy or ileostomy. The baby is provided with supplemental oxygen and respiratory support.

What Is the Prognosis of Necrotizing Enterocolitis?

The prognosis of NEC depends on the time of onset and severity. Overall mortality is quite high, between 10 to 50 percent. However, in neonates with advanced NEC (full-thickness destruction of the intestinal wall), mortality is close to 100 percent. Early aggressive treatment may help improve the outcomes.

What Are the Complications of Necrotizing Enterocolitis?

The complications of NEC include

• Short bowel syndrome.

• Intestinal failure.

• Liver failure.

• Intestinal stricture.

• Nutritional deficiencies.

• Defects in growth and development.

• Sepsis.

What Is the Differential Diagnosis of Necrotizing Enterocolitis?

The differential diagnosis of NEC includes the following:

• Hypoplastic left heart syndrome.

• Intestinal malrotation.

• Intestinal volvulus.

• Bacterial meningitis.

• Neonatal sepsis.

• Omphalitis.

• Prematurity.

• Urinary tract infection.

• Volvulus.

• Pyloric stenosis.

• Duodenal atresia.

• Tracheoesophageal fistula.

• Gastroschisis.

• Gastroenteritis.

• Pneumonia.

• Testicular torsion.

Conclusion

Although it is beyond prevention, the mother should ensure the breastfeeding of the infants. Mothers should be counseled about the dangers of preterm deliveries. Management of antenatal and postnatal complications can also decrease the chance of NEC.