What condition involves a narrowing of the pylorus in infants?

Pyloric stenosis is a condition in which the pylorus, the opening from the stomach to the small intestine, becomes narrowed. This typically occurs in infants and leads to severe projectile vomiting and dehydration as the narrowed pylorus obstructs the passage of food from the stomach.

In this condition, hypertrophy of the pyloric muscle narrows the channel, resulting in difficulties with gastric emptying and leading to feeding issues. Infants with pyloric stenosis often present between the ages of 3 weeks and 12 weeks, and the characteristic "olive-like" mass may be palpable in the right upper quadrant of the abdomen during a physical examination.

The recognition of pyloric stenosis is crucial in pediatrics as prompt diagnosis and surgical intervention can significantly improve outcomes for affected infants. The other conditions listed do not specifically refer to a narrowing of the pylorus, making pyloric stenosis the correct choice.