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Pyloric stenosis is a condition where the muscular valve (pylorus) between the stomach and small intestine becomes abnormally thickened and narrowed, preventing food from passing through normally. This obstruction typically presents in infants 2-8 weeks of age with progressive non-bilious vomiting and failure to thrive.
The pyloric muscle undergoes hypertrophy and hyperplasia, causing narrowing of the pyloric channel and functional gastric outlet obstruction. This leads to forceful gastric contractions as the stomach attempts to push contents through the narrowed opening, resulting in the characteristic projectile vomiting and eventual gastric distension.
Diagnosis is suspected in infants with progressively worsening non-bilious projectile vomiting, dehydration, and a palpable 'olive-shaped' mass in the epigastrium. Ultrasound showing pyloric wall thickness >3mm and pyloric channel length >15mm confirms the diagnosis, while metabolic alkalosis from persistent vomiting supports the clinical picture.
Key imaging focus: Pyloric muscle thickness >3mm, length >15mm, target sign