A nurse is caring for a newborn who may have pyloric stenosis. Which of the following manifestations should the nurse expect?

Pyloric stenosis involves hypertrophy of the pyloric sphincter, causing gastric outlet obstruction. Understanding the mechanical nature of this obstruction is necessary to identify the classic signs of retrograde flow and the resulting nutritional and fluid volume deficits in infants. Choice A rationale Dance sign refers to a physical finding in intussusception where the right lower quadrant feels empty. It is not associated with pyloric stenosis, which typically presents with an olive-shaped mass in the right upper quadrant instead. Choice B rationale Projectile vomiting occurs because the hypertrophied pylorus prevents gastric emptying into the duodenum. Pressure builds within the stomach until the contents are forcefully expelled, typically occurring shortly after feeding and lacking bile in the emesis. Choice C rationale Infants with pyloric stenosis are typically hungry and eager to feed immediately after vomiting. Because the food cannot pass into the small intestine for absorption, the child remains in a state of constant caloric deprivation. Choice D rationale Excessive weight gain is impossible in pyloric stenosis due to the inability to digest and absorb nutrients. Most infants present with significant weight loss, dehydration, and failure to thrive because of the persistent, forceful vomiting.