This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal tract, Subject name: Pediatrics
Investigation of choice for neonatal hyperophic pyloric stenosis is _________ 
Select and explain. 
A. X-ray, B. CT scan, C. MRI, D. USG
D: USG
Answer: D: USG 
Explanation: The usual age of presentation is approximately 2 - 6 weeks of life. Approximately 95% of infantile hyperophic pyloric stenosis cases are diagnosed in those aged 3-12 weeks. In addition, premature infants have a delayed diagnosis secondary to low bih weight and atypical presentation. DIAGNOSIS : History and physical examination Abdominal USG: Pyloric muscle thickness >3-4mm pyloric length > 15-18mm in presence of functional gastric outlet obstruction Upper GI study when atypical presentation or negative USG Diagnostic: narrowed, elongated pyloric channel with pyloric mass effect on stomach and duodenum -- String/ Double tract / Beak / Pyloric teat sign Reference: GHAI Essential pediatrics, 8th edition