Neonatal Necrotizing Enterocolitis (NEC)

Definition:

Acute intestinal necrosis with concurrent inflammation and infarction of the intestines (usually terminal ileum and colon) generally seen after ischemic injury. This is usually followed by secondary bacterial invasion with subsequent perforation of the bowel.

Epidemiology

Rare in healthy, full-term infants
1%-5% of all infants admitted to NICUs develop NEC
75% of infants with NEC were born at < 37 weeks gestational age with birth weights < 2000 g.
Prognosis is generally good, with mortality at 30%.

Etiology/Pathogenesis:

NEC is usually seen secondary to bowel wall injury that results from perinatal asphyxia. Using formula or human milk introduced with feeding, bacteria then invade the bowel wall leading to tissue damage and perforation. Pneumatosis intestinalis, a radiographic finding seen as a result of gas production in the bowel wall, is pathognomonic for NEC.

Prenatal/maternal risk factors include…

Maternal age > 35 years
Maternal infection that required antibiotic treatment
PROM
Cocaine exposure

Perinatal risk factors include…

Birth asphyxia (most common)
Maternal anesthesia
RDS
Systemic hypotension
Depressed Apgar at 5 minutes

Postnatal risk factors include…

PDA
CHF
Umbilical vessel catheterization (umbilical artery)
Polycythemia
Exchange transfusion
Use of hyperosmolar formula
Rapid advancement of the feeding volume

Clinical features/presentation:

Presentation of NEC usually occurs within the first 5 days of life and generally within 4 weeks of life. The earliest signs are feeding intolerance with associated regurgitation, vomiting, and abdominal distention. Gastric aspirates may be bilious in nature. Diarrhea occurs infrequently. Two types of NEC are classified, medical and surgical.

Medical NEC is the more common, more favorable clinical pattern. It does not require surgery. The course of the disease is characterized by feeding intolerance, abdominal distention, occult blood in the stool, dilated bowel loops radiographically, and decreased bowel sounds. It generally improves rapidly with treatment.
Surgical NEC is a rapidly progressing, severe clinical pattern of disease. Gross blood in the stool, extreme abdominal tenderness and discoloration, hyperglycemia, severe metabolic acidosis, sepsis, shock, DIC, temperature instability, and ineffective respiratory effort are usually seen.

Lab/Studies:

Laboratory findings include leukocytosis or neutropenia and thrombocytopenia. In order to distinguish between NEC and other intestinal disorders, C-reactive protein, a ₁-acid glycoprotein, lysosomal acid hydrolase, and urinary D-lactate levels can be checked and are increased in NEC.

Abdominal radiograph findings include dilated, thickened bowel loops, pneumatosis intestinalis usually starting in the right lower quadrant, portal venous gas, and pneumoperitoneum.

Barium contrast studies are specifically contraindicated due to risk of perforation.

CBC and differential do not generally contribute to the diagnosis.

Treatment:

Upon suspicion of NEC oral feedings should be immediately discontinued. Gastric drainage and IV fluids should then follow. TPN may be required. Following procurement of blood cultures, systemic antibiotics (e.g. ampicillin, gentamicin, clindimycin) should be given. Surgical resection of the necrotic bowel is indicated in severe, downwardly-progressive disease or if intestinal perforation is either imminent or has already occurred.