A 3-week-old male infant presents with progressive projectile vomiting and weight loss. On abdominal ultrasound, the structure marked **A** measures 5 mm. Which of the following is the most appropriate next step in management?

Explanation

## Why "Immediate surgical consultation for Ramstedt pyloromyotomy after electrolyte correction" is right The structure marked **A** (pyloric muscle thickness > 4 mm) is the gold-standard diagnostic criterion for hypertrophic pyloric stenosis on ultrasound. A measurement of 5 mm exceeds the diagnostic threshold and confirms the diagnosis. The key clinical anchor is that once pyloric muscle thickness > 4 mm is documented on USG, the diagnosis is confirmed and surgical intervention (Ramstedt pyloromyotomy) is indicated. However, MANDATORY pre-operative metabolic correction is essential — these infants develop hypochloremic, hypokalemic metabolic alkalosis from loss of gastric acid and electrolyte depletion. Electrolytes must be normalized (Cl > 100 mEq/L, K > 3.5 mEq/L, HCO3 < 30 mEq/L) with normal saline and potassium chloride boluses before surgery to prevent perioperative complications. After correction, Ramstedt pyloromyotomy (open or laparoscopic) is curative, with excellent prognosis and feeding resumption within 4–6 hours post-operatively (Nelson 21e; Bailey & Love 28e). ## Why each distractor is wrong - **Trial of proton pump inhibitor therapy for 2 weeks**: Hypertrophic pyloric stenosis is a mechanical obstruction due to muscle hypertrophy, not acid-related disease. PPIs do not address the underlying pathology and delay definitive surgical treatment, risking continued vomiting, dehydration, and electrolyte derangement. - **Contrast-enhanced upper GI study to confirm diagnosis**: Ultrasound is the gold-standard imaging modality for pyloric stenosis diagnosis. Once pyloric muscle thickness > 4 mm is documented, the diagnosis is confirmed and contrast studies are not routinely needed. Contrast studies add unnecessary radiation and delay surgical intervention. - **Reassurance and observation for spontaneous resolution**: Hypertrophic pyloric stenosis does not resolve spontaneously. Observation without intervention leads to progressive dehydration, electrolyte imbalance, and metabolic alkalosis. Surgery is mandatory once the diagnosis is confirmed. **High-Yield:** Pyloric muscle thickness > 4 mm on ultrasound = confirmed HPS; proceed to pre-operative electrolyte correction, then Ramstedt pyloromyotomy. No contrast studies needed. [cite: Nelson Textbook of Pediatrics 21e; Bailey & Love's Short Practice of Surgery 28e]