A 3-week-old infant is brought to the emergency department with a history of forceful, projectile vomiting after feedings and signs of weight loss. On assessment, the nurse palpates a small, olive-shaped mass in the upper abdomen. Which condition does this clinical picture most likely indicate?

A. Intussusception is incorrect because this condition typically presents with intermittent abdominal pain, drawing up of the legs, and “currant jelly” stools caused by blood and mucus. Vomiting may occur, but the presence of a palpable olive-shaped mass and projectile vomiting is not characteristic. B. Pyloric stenosis is correct. Pyloric stenosis occurs when the pyloric muscle hypertrophies, causing gastric outlet obstruction. It usually presents in infants around 3–6 weeks of age with forceful, projectile vomiting immediately after feedings, signs of weight loss or poor weight gain, dehydration, and a palpable, firm, olive-shaped mass in the right upper abdomen. Vomiting is non-bilious because the obstruction is proximal to the duodenum. C. Gastroesophageal reflux (GER) is incorrect because GER typically causes spitting up or regurgitation, which is usually non-forceful and not associated with an olive-shaped mass or significant weight loss. GER is common in infants and often resolves spontaneously. D. Hirschsprung's disease is incorrect because it presents with chronic constipation, abdominal distension, and delayed passage of meconium in the newborn period. Projectile vomiting and a palpable pyloric mass are not typical features.