- 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.
- 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.
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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