A nurse is assessing a newborn. Which of the following should the nurse understand is a clinical manifestation of pyloric stenosis?

Rationale: A. Absent bowel sounds is incorrect because bowel sounds are typically present and hyperactive in newborns with pyloric stenosis due to obstruction. Absent bowel sounds suggest paralytic ileus or peritonitis, which are not characteristic of pyloric stenosis. B. Increased sodium levels is incorrect because infants with pyloric stenosis often develop hypochloremic metabolic alkalosis due to vomiting of gastric contents, leading to low chloride and sodium, not increased levels. C. Golf ball-sized mass over the left quadrant is incorrect because the palpable mass associated with pyloric stenosis is typically located in the right upper quadrant of the abdomen. This mass is often described as an "olive-shaped" mass representing the hypertrophied pylorus. D. Projectile vomiting after feedings is correct because this is the classic clinical manifestation of pyloric stenosis. The vomiting is non-bilious and forceful due to the narrowing of the pyloric sphincter, which prevents gastric emptying. Infants may appear hungry after vomiting and may experience weight loss, dehydration, and signs of malnutrition if the condition is untreated.