Pathogenesis circular muscle of pylorus becomes hypertrophied pyloric sphincter fails to open causing obstruction of gastrointestinal tract stomach cannot drain becomes fuller and stretches until emesis occurs jaundice seen in 1%-2% of infants with IHPSPathogenesis ◼ circular muscle of pylorus becomes hypertrophied ◼ pyloric sphincter fails to open causing obstruction of gastrointestinal tract ◼ stomach cannot drain, becomes fuller and stretches until emesis occurs ◼ jaundice seen in 1%-2% of infants with IHPS