Which is a classic symptom of pyloric stenosis?

Projectile vomiting is a classic symptom of pyloric stenosis, particularly in infants. This condition involves a thickening of the pylorus, the opening from the stomach to the duodenum, which leads to gastric outlet obstruction. As a result, when food cannot pass through the narrowed pylorus, it creates increased pressure in the stomach. This pressure can cause forceful expulsion of stomach contents, leading to projectile vomiting.

This vomiting is often described as occurring shortly after feeding and can be quite severe, leading to significant dehydration and electrolyte imbalances if not addressed promptly. The nature of the vomitus is typically non-bilious, indicating that the obstruction is before the duodenum, where bile mixes with the stomach contents.

Other symptoms associated with pyloric stenosis can include dehydration, weight loss, and a characteristic "olive-like" mass felt on physical examination; however, projectile vomiting remains the hallmark symptom that often leads to a diagnosis. While other gastrointestinal symptoms such as diarrhea, gastroesophageal reflux, and constipation may be observed in different contexts, they are not characteristic of pyloric stenosis and do not reflect the underlying pathological process involved in this condition.