Diagnostic Test for Pyloric Stenosis
Ultrasound is the diagnostic test of choice for pyloric stenosis and should be performed when clinical suspicion is high. 1, 2
Primary Recommendation
Ultrasound should be the first-line and definitive imaging modality for diagnosing infantile hypertrophic pyloric stenosis (IHPS). 2 The American College of Radiology specifically recommends ultrasound as the important tool for evaluating hypertrophic pyloric stenosis in infants. 1
When to Order Ultrasound
Order ultrasound when clinical suspicion remains high, even if no palpable "olive" mass is detected on physical examination. 3, 2 The absence of a palpable mass does not exclude pyloric stenosis. 3
The ultrasound should ideally be performed by a pediatric radiologist for definitive diagnosis. 1, 2
Diagnostic Ultrasound Criteria
The key sonographic measurements include:
Pyloric muscle thickness: The most discriminating criterion, with HPS showing thickness ≥2.0-5.0 mm (normal <2.0 mm). 4, 5
Pyloric canal length: The single most important discriminator, with HPS showing length ≥10.0 mm (normal <5.0 mm). 4 Traditional criteria using 16.0 mm are too conservative and delay diagnosis. 4
Pyloric diameter: Less useful as a discriminator, ranging 8.0-16.0 mm in HPS versus 6.0-11.0 mm in normal infants. 4
Role of Other Imaging Modalities
Upper GI series (X-ray with barium) should be reserved only for cases where ultrasound findings are equivocal or negative despite strong clinical suspicion. 1 This approach avoids unnecessary radiation exposure. 6
CT and endoscopy have no role in the diagnosis of pyloric stenosis in infants.
Performance Characteristics
Ultrasound demonstrates excellent diagnostic accuracy with 100% sensitivity and specificity when performed correctly. 7 Studies consistently show ultrasound as simple, accurate, and radiation-free for diagnosing HPS. 8, 7
Common Pitfall
The most important pitfall is using outdated diagnostic criteria (muscle thickness ≥3.0 mm, canal length ≥16.0 mm), which delays diagnosis and treatment. 4 Current evidence supports lower thresholds (muscle thickness ≥2.0 mm, canal length ≥10.0 mm) without risk of false positives. 4
Answer: B - Ultrasound