Pyloric Stenosis



  • 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)


  • 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)

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

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].

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

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