The parents of a 6-week-old boy come to the clinic for evaluation because the infant has been vomiting. The parents report that the vomiting has been increasing in frequency and forcefulness over the last week. The mother says, "Sometimes, it seems like it just bursts out of his mouth." A diagnosis of hypertrophic pyloric stenosis is suspected. When performing the physical examination, what would the nurse most likely find?

A. Sausage-shaped mass in the upper midabdomen: A sausage-shaped mass is more characteristic of intussusception rather than hypertrophic pyloric stenosis. Intussusception typically presents with intermittent abdominal pain, currant jelly stools, and a palpable tubular mass. Projectile vomiting without bile is not the classic presentation for this finding. B. Hard, moveable, olive-shaped mass in the right upper quadrant: Hypertrophic pyloric stenosis classically presents with a firm, olive-shaped mass in the right upper quadrant or epigastric area. This mass represents the hypertrophied pyloric muscle and is most often palpated during feeding. Progressive, forceful projectile vomiting is a hallmark feature supporting this finding. C. Tenderness over the McBurney point in the right lower quadrant: McBurney point tenderness is associated with acute appendicitis, which is rare in infants this young. Appendicitis presents with localized right lower quadrant pain, fever, and guarding rather than projectile vomiting. D. Abdominal pain in the epigastric or umbilical region: Diffuse or localized abdominal pain is more typical of conditions such as gastroenteritis or early appendicitis. Infants with pyloric stenosis usually appear hungry after vomiting and do not typically demonstrate abdominal pain. The key finding is a palpable mass rather than pain.