Pyloric Stenosis

A 3-week-old who eats hungrily then vomits across the room isn't spitting up — that forceful trajectory is the hallmark clue to a surgical emergency.

Pyloric stenosis is hypertrophy of the circular muscle at the pylorus, creating a near-complete gastric outlet obstruction. It classically presents between 2 and 6 weeks of age, more common in firstborn males. The signature finding is projectile, nonbilious vomiting that occurs shortly after feeding. The vomit is nonbilious because the obstruction is proximal to the ampulla of Vater — bile never reaches the stomach. Despite vomiting, the infant remains hungry and feeds eagerly immediately afterward ("hungry vomiter"). On exam, you may palpate an olive-shaped mass in the right upper quadrant during or just after a feeding, and visible gastric peristaltic waves may travel left to right across the epigastrium. Ultrasound confirms the diagnosis by showing a pyloric muscle thickness ≥3 mm or channel length ≥16 mm. Repeated vomiting of gastric acid causes a classic metabolic alkalosis with hypochloremia and hypokalemia. Surgical correction is a pyloromyotomy (Ramstedt procedure). Before surgery, the priority is correcting fluid and electrolyte imbalances — IV fluids with potassium replacement are given until alkalosis resolves. Anesthesia with uncorrected alkalosis is dangerous. Postoperatively, feedings are reintroduced gradually in small, frequent amounts. Some vomiting after the first feeds is expected and does not indicate surgical failure.

Key Distinctions

Don't confuse pyloric stenosis (nonbilious, projectile vomiting, hungry infant) with intussusception (bilious vomiting, currant jelly stools, episodic pain). Students mix up the electrolyte picture: pyloric stenosis causes metabolic alkalosis from HCl loss, not acidosis. The olive-shaped mass is RUQ, not LLQ — wrong location points to a different diagnosis entirely.

Clinical Pearl

Nonbilious + projectile + hungry after = pyloric stenosis. If the vomit is green, the obstruction is below the bile duct — think somewhere else.