Diagnosing Pyloric Stenosis on Imaging

The ultrasound criteria for diagnosing hypertrophic pyloric stenosis (HPS) typically dictate that:

• The single pyloric muscle thickness must measure 4 mm (or at least 3 mm) or greater, and

• the elongated pyloric canal length should measure 16 mm or greater.

On a plain abdominal radiograph, infants with HPS may occasionally show a "caterpillar sign," which represents prominent, hyperperistaltic waves of the stomach attempting to force contents through the obstructed pylorus.