A 3-week-old boy is brought to the physician by his parents, who report that he vomits forcefully immediately after nursing. Physical examination reveals an "olive-like" palpable mass and visible peristaltic movements within the infant's abdomen. What is the most likely cause of projectile vomiting in this infant?

Congenital pyloric stenosis is a concentric enlargement of the pyloric canal that obstructs the outlet of the stomach. The disorder is the most common indication for abdominal surgery in the first 6 months of life. Congenital pyloric stenosis has a familial tendency, and the condition is more common in identical twins than in fraternal ones. The only consistent microscopic abnormality is hypertrophy of the circular muscle coat. Projectile vomiting is not characteristic of the other choices, particularly in neonates.Diagnosis: Congenital pyloric stenosis