A 3-week-old boy is brought to the physician by his parents, who repo 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?

Infantile hyperophic pyloric stenosis: - Associated with Trisomy 18 Trisomy 21 Exposure to erythromycin in 1st 2 weeks of life - Clinical features: Presents at 3-6 weeks after bih New onset regurgitation Nonbilious projectile vomiting after feeding - Diagnosis : by USG - Treatment: Pyloromyotomy Correct electrolyte imbalance before performing surgery.