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- Progressive narrowing of the pyloric canal, occurring in infancy
- Synonym(s): infantile hypertrophic pyloric stenosis (IHPS)
- Predominant age: infancy
- Onset usually at 3 to 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 incidence has been reported in a number of countries.
- Predominant sex: male > female (4 to 5:1)
In Caucasian population, 2 to 5:1,000 babies; less common in African American and Asian populations
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 vomiting.
- The exact cause remains unknown, but multiple genetic and environmental factors have been implicated.
- Breast versus bottlefeeding—increased vasoactive intestinal peptide in breast milk may mediate pyloric relaxation and increase gastric emptying, whereas bottlefeeding may cause higher serum levels associated with pylorospasm (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
- Multiple gestation—200-fold increased risk if monozygotic twin diagnosed and 20-fold increased risk if dizygotic twin diagnosed
- Breastfeeding protective versus bottlefeeding where risk is increased
- Postnatal macrolide use (i.e., erythromycin, azithromycin)—erythromycin agonist of motilin, which might cause continuous contraction of the pyloric muscle (1)[C]
- A recent surveillance study of a population-based birth defects registry identified association between pyloric stenosis and the use of fluoxetine in the 1st trimester, even after adjustment for maternal age and smoking. The adjusted odds ratio was 9.8 (95% CI 1.5–62) (2)[B].
Commonly Associated Conditions
Associated anomalies present in ~4–7% of infants with pyloric stenosis
- Hiatal and inguinal hernias (most commonly)
- Other 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
- A common proposed genetic link between breast cancer, endometriosis, and pyloric stenosis has been observed in families.