A 4-week-old male infant presents with projectile non-bilious vomiting, olive-shaped palpable epigastric mass, visible peristalsis, and hypochloremic hypokalemic metabolic alkalosis. The most appropriate immediate investigation is:
- A Plain abdominal X-ray
- B Abdominal ultrasound showing pyloric muscle thickness >4 mm and length >16 mm ✓
- C Upper GI contrast study
- D Endoscopy
Correct answer: B. Abdominal ultrasound showing pyloric muscle thickness >4 mm and length >16 mm
Explanation
Hypertrophic pyloric stenosis (HPS) presents at 2–8 weeks of life in first-born males with the classic triad: projectile non-bilious vomiting, palpable pyloric 'olive' and metabolic alkalosis. Ultrasound is the investigation of choice: pyloric muscle thickness >4 mm and pyloric channel length >16 mm are diagnostic. Contrast studies are no longer recommended as first-line due to radiation. Treatment is Ramstedt's pyloromyotomy after metabolic correction.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.