A 3-week-old first-born male infant presents with forceful, projectile non-bilious vomiting immediately following every breastfeed. The infant appears eager to feed again after vomiting. Abdominal examination reveals a small, firm, olive-shaped palpable mass in the right upper quadrant. What is the underlying pathophysiology?
Answer and explanation
Correct answer: D. Hypertrophy of the pyloric circular smooth muscle layer
- Step 1: Infantile hypertrophic pyloric stenosis typically presents between 3 and 6 weeks of age with non-bilious projectile vomiting.
- Step 2: Hypertrophy and hyperplasia of the circular pyloric sphincter muscle obstructs gastric emptying, causing the palpable 'olive mass' and hypochloremic hypokalemic metabolic alkalosis.
Answer
Hypertrophy of the pyloric circular smooth muscle layer.
Why not the others: 'Midgut volvulus' causes acute bilious vomiting and bowel ischemia; 'Duodenal atresia' presents in the first 24 hours of life with bilious vomiting and 'double bubble' sign on X-ray; 'Hirschsprung disease' causes distal intestinal obstruction and failure to pass meconium.
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