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Hypertrophy of the muscular layers of the pylorus with elongation and thickening, leading to projectile nonbilious emesis and gastric outlet obstruction
- Usually presents between the 3rd and 10th week of life
- Male-to-female ratio 4:1, with 1st-born males more affected
- More common in Caucasians
~2 to 4 per 1,000 live births in Western populations
- Marked muscle hypertrophy and hyperplasia primarily involving the circular layer and hyperplasia of the underlying mucosa
- Growth of abnormally contorted and thickened nerve fibers and/or lack of neural elements
- Net result is either partial or complete obstruction of the pyloric channel.
- No definitive causative factors have been identified despite considerable research.
- Genetic predisposition evidenced by variability among races, male preponderance, and genetic syndromes with pyloric stenosis
- Children of affected fathers are affected 3–5%, whereas affected mothers are associated with a 7–20% incidence.
- Several growth factors and gastrointestinal (GI) peptides, including gastrin and elevated acid levels, as well as increases in substance P, epidermal growth factor (EGF), transforming growth factor alpha (TGF α), and insulin-like growth factor-1 (IGF-1), have been implicated.
- Erythromycin estolate given for postexposure prophylaxis for pertussis may cause strong gastric and pyloric contractions that induce hypertrophy. Erythromycin exposure to lactating mothers is associated with breastfed infants who have an increased incidence of pyloric stenosis.
- Decreases in nerve differentiation, reduced density of neural elements, and deficiency of nitric oxide–induced muscle relaxation have been implicated.
Commonly Associated Conditions
Esophageal atresia and malrotation was noted in 5% of infants with pyloric stenosis.