A 3-week-old full-term infant presents with persistent non-bilious projectile vomiting immediately after every feeding. On physical examination, the infant appears mildly dehydrated, and a small, firm, mobile olive-shaped mass is palpable in the right upper quadrant. What is the most likely diagnosis?

Answer and explanation

Correct answer: C. Hypertrophic pyloric stenosis

  1. Step 1: Non-bilious projectile postprandial vomiting at 3-6 weeks of age with a palpable pyloric 'olive' mass is classic for hypertrophic pyloric stenosis.
  2. Step 2: Ultrasound confirms elongation and thickening of the pyloric muscle (> 3 mm thickness, > 14 mm length).
Answer
Hypertrophic pyloric stenosis.
Why not the others: 'Duodenal atresia with annular pancreas' presents within the first 24-48 hours of life with bilious vomiting and a double-bubble sign on radiograph; 'Gastroesophageal reflux disease (GERD)' causes effortless regurgitation rather than projectile vomiting; 'Congenital midgut volvulus' presents with sudden bilious vomiting and abdominal distension.

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