What is the classic presentation of pyloric stenosis in infants?

The classic presentation of pyloric stenosis in infants is characterized by non-bilious projectile vomiting. This condition typically manifests in infants between 3 and 12 weeks of age and is due to hypertrophy of the pylorus, the muscular valve between the stomach and small intestine. As the muscle thickens, it narrows the opening, which leads to difficulty in emptying the stomach.

The vomiting associated with pyloric stenosis is described as non-bilious because the obstruction occurs before the bile duct entrance into the duodenum. As a result, the vomit contains undigested food from the stomach but no bile, which distinguishes it from vomiting due to other gastrointestinal conditions. The projectile nature of the vomiting occurs because of the strong contractions that attempt to push the food through the narrowed pylorus, resulting in forceful ejection of stomach contents.

In contrast to other symptoms listed, such as persistent diarrhea, abdominal distension, and constipation with fever, these are more indicative of different gastrointestinal disorders. Diarrhea does not occur with pyloric stenosis due to the blockage, abdominal distension may occur but is not as defining as the vomiting, and constipation with fever typically suggests an infection or other pathology rather than pyloric sten