A 6-week-old male infant presents with non-bilious, projectile vomiting after every feed for the past 2 weeks. The vomiting occurs immediately after feeding and the infant is always hungry. Examination reveals a palpable olive-shaped mass in the right hypochondrium. Which investigation BEST confirms the diagnosis?
- A Abdominal ultrasound showing pyloric muscle thickness >4 mm and pyloric channel length >14 mm ✓
- B Upper GI barium swallow showing 'string sign'
- C Abdominal X-ray showing double bubble sign
- D Serum amylase
Correct answer: A. Abdominal ultrasound showing pyloric muscle thickness >4 mm and pyloric channel length >14 mm
Explanation
Hypertrophic pyloric stenosis (HPS) is confirmed by abdominal ultrasound, which is the investigation of choice. Diagnostic criteria include pyloric muscle wall thickness ≥4 mm and pyloric channel length ≥14–16 mm. The 'string sign' (narrow pyloric channel) on barium swallow is also diagnostic but exposes the infant to radiation and contrast aspiration risk. The double bubble sign is characteristic of duodenal atresia (bilious vomiting from birth). HPS typically causes hypochloremic, hypokalemic metabolic alkalosis.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.