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

Rationale: A newborn with pyloric stenosis will exhibit projectile vomiting after feedings due to the obstruction at the pylorus, causing an increase in pressure within the stomach. This is a key clinical manifestation. Absent bowel sounds (B) are not typically associated with pyloric stenosis. Increased sodium levels (C) may be seen in dehydration from vomiting but are not specific to pyloric stenosis. A golf ball-sized mass over the left quadrant (D) is not a typical finding in pyloric stenosis. Therefore, option A is the correct answer as it aligns with the characteristic symptom of projectile vomiting.