Ultrasound of the Abdomen is the Most Appropriate Imaging Study
For this 4-week-old infant with classic hypertrophic pyloric stenosis (HPS) presentation—forceful non-bilious vomiting, visible peristaltic waves, palpable epigastric mass ("olive"), and eager feeding—ultrasound of the abdomen is the definitive initial imaging study of choice. 1
Why Ultrasound is Superior
The American College of Radiology explicitly designates ultrasound abdomen as "usually appropriate" for infants older than 2 weeks and up to 3 months with new onset nonbilious vomiting when HPS is suspected. 1
Ultrasound is superior to upper GI series as the initial imaging test when HPS is strongly considered based on clinical presentation. 1, 2
The clinical scenario described—age 4 weeks, progressive forceful non-bilious vomiting after every feeding, visible peristaltic waves, palpable firm mid-upper abdominal mass, and eager feeding—represents the pathognomonic presentation of HPS. 2, 3
Why Other Modalities Are Inappropriate
Plain Radiography (X-ray)
- Abdominal radiographs are not indicated for suspected HPS; they are reserved for neonates with vomiting in the first 2 days of life to evaluate for bowel obstruction patterns. 1
CT Scan
- CT is not recommended for suspected HPS due to unnecessary radiation exposure and lower sensitivity compared to ultrasound for this specific condition. 2
MRI
- MRI is impractical in infants due to longer acquisition times, potential need for sedation, limited availability, and no diagnostic advantage over ultrasound for HPS. 2
Upper GI Series (Fluoroscopy)
- While upper GI series can diagnose obstructive causes of vomiting, it is explicitly "less ideal than ultrasound as an initial imaging test if HPS is a strong consideration." 1, 2
- Upper GI series exposes the infant to ionizing radiation unnecessarily when ultrasound provides superior diagnostic accuracy for HPS. 4
Clinical Advantages of Ultrasound
Ultrasound provides real-time evaluation without sedation, intravenous contrast, or ionizing radiation. 5
Ultrasound has been validated as accurate, reliable, and rapid for evaluating upper gastrointestinal disease in children, with excellent correlation to surgical outcomes for pyloric stenosis. 4
The modality allows direct visualization and measurement of the hypertrophied pyloric muscle, which is the pathologic finding in HPS. 5, 6
Critical Management Considerations
Once HPS is confirmed by ultrasound, meticulous preoperative fluid and electrolyte resuscitation is essential before proceeding to pyloromyotomy. 7, 6
Patients with chloride ≤97 mmol/L should receive two 20 ml/kg saline boluses; those with chloride <85 mmol/L require three boluses before rechecking electrolytes. 8
Delayed diagnosis worsens metabolic derangements (hypochloremic, hypokalemic metabolic alkalosis), but after successful pyloromyotomy, outcomes are excellent with essentially zero mortality. 7, 6