How does pyloric stenosis typically present itself in infants?

Pyloric stenosis is a condition that affects infants, characterized by a narrowing of the pylorus, the outlet of the stomach into the small intestine. This narrowing prevents the normal passage of food, leading to a specific symptom profile.

The hallmark presentation of pyloric stenosis is projectile vomiting after meals. The vomiting occurs because the narrowed pylorus obstructs the flow of gastric contents, causing the baby to expel the stomach's contents forcefully. This vomiting can often occur right after feeding, and it tends to be more intense and voluminous compared to typical reflux or vomiting in infants.

In addition to projectile vomiting, infants with pyloric stenosis may display signs of dehydration and malnutrition due to inadequate calorie intake. The condition tends to cluster around infants between the ages of three to twelve weeks and is often recognized in first-born males more frequently.

The other choices, while possible symptoms of various conditions, do not specifically align with the clinical presentation of pyloric stenosis.