Infantile Hypertrophic Pyloric Stenosis

Longitudinal scan of the stomach (as labeled) shows a thickened (5 mm) wall of the pylorus and elongation of the pyloric canal. Labe

Facts: Pyloric Stenosis

• Most common surgical etiology for young infant presenting emergently with nonbillous vomiting
• Incidence: 2 to 5 of every 1,000 infants
• Multifactorial etiology: genetic, biochemical and environmental association
• Hypertrophy of the pyloric muscle, leading to gastric outlet obstruction (vomiting, dehydration, poor weight gain and hypochloremic metabolic alkalosis)
• Average age of presentation = 3 weeks old (rare before 1 week, or after 3-4 months)

Imaging

• US is now the imaging modality of choice for diagnosis of this condition. It can directly show the pyloric muscle
• Elongation of the pyloric canal
• Persistent spasm of pyloric canal with little, if any, fluid passing into the duodenum
• Persistent thickening of the circular muscle in the canal
• Pyloric muscle thickness (one wall) greater than 4 mm, or pyloric length greater than 16 mm (cutoff values vary depending on the sensitivity, specificity needed to make the diagnosis)
• Imaging differential diagnosis is pylorospasm. In pylorospasm, there is usually no thickening of the pylorus (can be up to 2-3 mm) and when visualized in real time the pylorus can open
• If ultrasound is negative, UGI series or nuclear medicine to evaluate for reflux may be necessary.

References:

1. Swischuk LE. Imaging of the newborn, infant and young child, 5th edition.

2. Hernanz-Schulman M, Berch BR, Neblett WW. Imaging of infantile hypertrophic pyloric stenosis (IHPS). Evidence-based Imaging in Pediatrics 2010; 5:447-457.