A 3-week-old first-born male infant presents with non-bilious projectile vomiting immediately after every feeding. He appears avidly hungry after vomiting. Physical examination reveals mild dehydration and a palpable olive-shaped firm mass in the right upper quadrant. Serum chemistry shows hypochloremic hypokalemic metabolic alkalosis. What is the diagnosis?

Answer and explanation

Correct answer: D. Infantile hypertrophic pyloric stenosis

  1. Step 1: Analyze patient demographics and symptoms: 3-week-old male with projectile non-bilious emesis and hunger following feeds.
  2. Step 2: Identify pathognomonic physical finding: A palpable 'olive-like' mass in the epigastrium/right upper quadrant.
  3. Step 3: Recognize classic metabolic derangement: Persistent loss of gastric hydrochloric acid causes hypochloremic, hypokalemic metabolic alkalosis.
  4. Step 4: Confirm diagnosis: Infantile hypertrophic pyloric stenosis.
Answer
Infantile hypertrophic pyloric stenosis.
Why not the others: 'Duodenal atresia' causes bilious vomiting presenting within the first 24 to 48 hours of life, showing a 'double-bubble' sign on X-ray; 'Gastroesophageal reflux' causes effortless regurgitation without metabolic alkalosis or palpable masses; 'Midgut volvulus' presents with acute bilious emesis and abdominal catastrophe.

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