Hypertrophic pyloric stenosis (HPS) causes a functional gastric outlet obstruction as a result of hypertrophy and hyperplasia of the muscular layers of the pylorus. In infants, HPS is the most common cause of gastric outlet obstruction and the most common surgical cause of vomiting. Hypertrophic pyloric stenosis is a condition characterised by hypertrophy of two muscle layers of pylorus,l enghthening of canal, thickening of pylorus which becomes oedematous causing functional obstruction of gastric outlet. The gastric outlet obstruction due to the hypertrophic pylorus impairs emptying of gastric contents into the duodenum. As a consequence, all ingested food and gastric secretions can only exit via vomiting, which can be of a projectile nature. While the exact cause of the hypertrophy remains unknown, one study suggested that neonatal hyperacidity may be involved in the pathogenesis.

Keywords: Hypertrophic pyloric stenosis (HPS); Hyperplasia.