Description

• Progressive narrowing of the pyloric canal, occurring in infancy
• Synonym(s): Infantile hypertrophic pyloric stenosis (IHPS)

Epidemiology

• Predominant age: Infancy:
  • Onset usually at 3–6 weeks of age; rarely in the newborn period or as late as 5 months of age
• Considered the most common condition requiring surgical intervention in the 1st year of life
• A recent decline in its incidence has been reported in a number of countries (1).
• Predominant sex: Male > Female (4:1)

Incidence
In Caucasian population, 2–5:1,000 babies; less common in African American and Asian populations

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

Risk Factors

• Incidence higher in firstborn boys
• 5× increased risk with affected 1st-degree relative
• Strong familial aggregation and heritability (2)

Genetics
Recent studies have identified linkage to chromosome 11 and multiple loci and chromosome 16 (3).

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 vomiting.

Etiology

• The exact cause remains unknown, but multiple genetic and environmental factors have been implicated (3,4).
• A recent surveillance study of a population-based birth defects registry identified an association between pyloric stenosis and the use of fluoxetine in the 1st trimester of pregnancy, even after adjustment for maternal age and smoking. The adjusted odds ratio was 9.8 (95% CI: 1.5–62) (5).

Commonly Associated Conditions

Associated anomalies present in ∼4–7% of infants with pyloric stenosis:

• Hiatal and inguinal hernias (most commonly)
• Other anomalies include:
  • Congenital heart disease
  • Esophageal atresia
  • Tracheoesophageal fistula
  • Renal abnormalities
  • Turner syndrome and trisomy 18
  • Cornelia de Lange syndrome
  • Smith-Lemli-Opitz syndrome
• A common proposed genetic link between breast cancer, endometriosis, and pyloric stenosis has been observed in families.