What is the most appropriate diagnostic imaging modality for a 1-month-old boy presenting with forceful, nonbilious vomiting, a palpable 'olive' in the abdominal right upper quadrant, and symptoms suggestive of pyloric stenosis?

Ultrasound Abdomen is the Most Appropriate Diagnostic Imaging for Pyloric Stenosis

Ultrasound abdomen is the most appropriate initial imaging modality for a 1-month-old boy presenting with forceful, nonbilious vomiting and a palpable "olive" in the right upper quadrant, which are classic signs of hypertrophic pyloric stenosis (HPS). 1

Clinical Presentation and Diagnosis

• The clinical presentation of a 1-month-old with forceful, nonbilious vomiting, constant hunger, and a palpable "olive" in the right upper quadrant is highly suggestive of hypertrophic pyloric stenosis 2, 3
• HPS typically presents between 3-6 weeks of life with projectile, nonbilious vomiting and is more common in firstborn males 4, 3
• The palpable "olive" represents the hypertrophied pyloric muscle, which is a pathognomonic physical finding when present 3

Imaging Recommendations

• According to the American College of Radiology Appropriateness Criteria, ultrasound abdomen is the "usually appropriate" initial imaging study for infants older than 2 weeks and up to 3 months with new onset nonbilious vomiting when HPS is suspected 1
• Ultrasound is preferred over upper GI series as the initial imaging test when HPS is strongly suspected based on clinical presentation 1
• Ultrasound has excellent diagnostic accuracy for HPS, allowing direct visualization of the thickened pyloric muscle and measurement of pyloric dimensions 3

Rationale for Ultrasound Over Other Modalities

• CT abdomen: Not recommended as initial imaging for suspected HPS due to unnecessary radiation exposure and lower sensitivity compared to ultrasound for this specific condition 1
• MRI abdomen: While radiation-free, MRI is less practical in infants due to longer acquisition times, potential need for sedation, and limited availability compared to ultrasound 1
• Upper GI series: Though excellent for diagnosing obstructive causes of vomiting, it is "less ideal than ultrasound as an initial imaging test if HPS is a strong consideration" 1

Management Considerations

• Once HPS is confirmed, patients require correction of fluid and electrolyte abnormalities before surgical intervention 5
• Chloride levels are particularly important to monitor, as hypochloremic metabolic alkalosis is common in HPS and requires correction before anesthesia 5
• Pyloromyotomy remains the standard surgical treatment for HPS with excellent outcomes 2, 6

Common Pitfalls to Avoid

• Failing to recognize the classic clinical presentation of HPS can lead to delayed diagnosis and worsening metabolic derangements 7, 3
• Relying solely on clinical examination without confirmatory imaging may lead to missed diagnosis, as the pyloric "olive" may not be palpable in up to 50% of cases 3
• Inadequate fluid resuscitation before surgical intervention can lead to increased anesthetic risks 5