Infantile hypertrophic pyloric stenosis (IHPS) is characterized by hypertrophy of the pylorus, with elongation and thickening, eventually progressing to near-complete obstruction of the gastric outlet.
Infantile hypertrophic pyloric stenosis (IHPS) occurs in approximately 2 to 3.5 in 1000 live births, although rates and trends vary markedly from region to region [1-7]. It is more common in males than females (4:1 to 6:1) [1,7-11]. Approximately 30 percent of cases occur in firstborn children (approximately 1.8-fold increased risk) [8,9,12], and it is less common in infants of older mothers . Symptoms usually begin between 3 and 5 weeks of age, and very rarely occur after 12 weeks of age .
The etiology of infantile hypertrophic pyloric stenosis (IHPS) is obscure but probably is multifactorial, involving genetic predisposition and environmental factors. Neonatal hypergastrinemia and gastric hyperacidity may have a role , as may increased vascularity .
Environmental factors — Maternal smoking during pregnancy increases the risk for IHPS by 1.5 to 2.0-fold [13,16,17]. Several studies have suggested that bottle-feeding rather than breast-feeding increases the risk for IHPS [18-20]. In particular, a large population-based study from Denmark found that bottle-feeding during the first four months of life increased the risk for IHPS more than four-fold (hazard ratio 4.62, 95% CI 2.78-7.65), and a similar increase in risk was seen for infants that were both bottle- and breast-fed . Most of the included subjects used formula for bottle-feeds rather than expressed breast milk, so the study did not determine whether the increased risk is related to the formula or to the mechanism of bottle-feeding. Similarly, a large study from Washington state also found that bottle-feeding increased the risk for IHPS, after adjustment for sex and maternal smoking (OR 2.31, 95% CI 1.81-2.95) .
Genetic factors — Familial aggregation of pyloric stenosis was examined in a large population registry from Denmark . Significant familial aggregation was noted, with a nearly 200-fold higher rate among monozygotic twins, and a 20-fold increase among dizygotic twins or siblings, as compared with individuals with no affected relatives. The heritability estimate from this study was 87 percent. The maternal and paternal contributions to heritability were similar, suggesting that the intrauterine environment was not an important causal factor.