Description

• Acquired narrowing of the pyloric canal due to progressive hypertrophy of pyloric muscle leading to obstruction, usually occurs in the first 2 to 12 weeks of life
• Synonym(s): infantile hypertrophic pyloric stenosis (IHPS)

Epidemiology

• Onset almost always between 2 and 12 weeks of age
• Highest incidence found in first-born infants.
• May be more common in bottle-fed infants
• The most common condition requiring surgical intervention in the 1st year of life
• A recent decline in incidence has been reported in a number of countries.
• Predominant sex: male > female (4 to 5:1)

Incidence
In Caucasian infants, 2 to 5:1,000 babies; less common in African American and Asian babies

Prevalence
National prevalence level is 1 to 2:1,000 infants, ranging from 0.5 to 4.21:1,000 live births.

Etiology and Pathophysiology

• Abnormal relaxation of the pyloric muscles leads to hypertrophy.
• Redundant mucosa fills the pyloric canal.
• Gastric outflow is obstructed, leading to gastric distension and forceful projectile postprandial vomiting.
• The exact cause remains unknown, but multiple genetic and environmental factors have been implicated.
• Increased vasoactive intestinal peptide in breast milk may mediate pyloric relaxation and increase gastric emptying, protecting from pyloric stenosis.
• Formula feeding may cause higher serum levels associated with pylorospasm, increasing rates of pyloric stenosis (1)[C].

Genetics
Recent studies have identified linkage to chromosomes 3, 5, 11, and 19.

Risk Factors

• 5 times increased risk with affected first-degree relative
• Strong familial aggregation and >80% heritability
• Premature birth is NOT a risk factor.
• Multiple gestation
  • 200-fold increased risk if monozygotic twin affected
  • 20-fold increased risk if dizygotic twin affected
• Maternal white ethnicity
• Maternal alcohol and cigarette use perinatally
• Perinatal risk factors include C-section and first born.
• Postnatal macrolide antibiotics, especially erythromycin, could potentially cause sustained contraction of pyloric muscle.
• Formula feeding increases risk.

General Prevention

Breastfeeding appears to be protective.

Commonly Associated Conditions

Associated anomalies present in ~4–7% of infants with pyloric stenosis.

• Hiatal and inguinal hernias (most common)
• Rare associated anomalies include the following:
  • Congenital heart disease
  • Esophageal atresia
  • Tracheoesophageal fistula
  • Renal abnormalities
  • Turner syndrome and trisomy 18
  • Cornelia de Lange syndrome
  • Smith-Lemli-Opitz syndrome