What is the preferred diagnostic test for suspected pyloric stenosis in a 4-week-old infant?

From the Guidelines

The preferred diagnostic test for suspected pyloric stenosis in a 4-week-old infant is an abdominal ultrasound. This non-invasive imaging study is considered the gold standard for diagnosis as it can directly visualize the thickened pyloric muscle and measure both the pyloric muscle thickness and channel length. Typically, findings consistent with pyloric stenosis include a pyloric muscle thickness greater than 3-4 mm and a pyloric channel length exceeding 15-18 mm. Ultrasound is preferred because it avoids radiation exposure, has high sensitivity and specificity, and can be performed quickly without sedation 1.

According to the international evidence-based guidelines on point of care ultrasound (POCUS) for critically ill neonates and children, POCUS may recognize hypertrophic pyloric stenosis, although a detailed assessment should be performed by a pediatric radiologist for a definitive diagnosis 1. The American College of Radiology also recommends starting with a thorough clinical evaluation, and if necessary, proceeding with imaging studies, with abdominal ultrasound being the preferred initial imaging test for suspected pyloric stenosis 1.

If ultrasound is unavailable or results are equivocal, an upper gastrointestinal (UGI) contrast study may be considered as an alternative, though it is less specific and involves radiation. Before proceeding with imaging, clinicians should ensure the infant is adequately hydrated and electrolyte abnormalities (particularly hypochloremic, hypokalemic metabolic alkalosis) are corrected, as these are common complications of the persistent vomiting associated with pyloric stenosis. Key points to consider in the diagnosis of pyloric stenosis include:

• Clinical evaluation, including history and physical examination
• Abdominal ultrasound as the preferred initial imaging test
• Correction of electrolyte abnormalities and hydration before imaging
• Consideration of alternative diagnoses, such as gastroesophageal reflux or other causes of vomiting in infants.

From the Research

Diagnostic Tests for Suspected Pyloric Stenosis

• The preferred diagnostic test for suspected pyloric stenosis in a 4-week-old infant is ultrasonography 2, 3, 4.
• Ultrasonography has been shown to be a simple and accurate method for diagnosing hypertrophic pyloric stenosis (HPS) 2.
• The use of ultrasonography as the initial imaging procedure is recommended due to its high sensitivity and specificity 3, 4.
• Studies have demonstrated that ultrasonography can accurately diagnose HPS, with a sensitivity of 98% and specificity of 100% 4.
• Other diagnostic tests, such as barium upper gastrointestinal series, may be used in cases where ultrasonography is negative and clinical symptoms persist 2, 5.

Advantages of Ultrasonography

• Ultrasonography is a non-invasive and painless procedure 6.
• It can be easily repeated in cases with an uncertain clinical diagnosis of HPS 4.
• Point-of-care ultrasound can be performed by emergency physicians to diagnose HPS, making it a valuable tool in emergency departments 6.

Clinical Diagnosis

• The clinical diagnosis of HPS relies on palpation of an olive-sized mass in the right upper quadrant of an infant with a history of projectile vomiting 6.
• However, studies have shown that clinicians may not always be able to detect the olive, highlighting the importance of ultrasonography in diagnosing HPS 6.