Hypertrophic pyloric stenosis (ultrasound measurements mnemonic)

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Hypertrophic pyloric stenosis can be characterized on ultrasound by the measurements of the hypertrophic muscle. Although the criteria can vary from publication to publication, an easy way to keep in mind the values is using a mnemonic which relies upon remembering the first digits of the number "pi", also represented by the Greek letter "π":

π = 3.1415

  • pyloric muscle thickness, i.e. diame­ter of a single muscular wall on a transverse image >3 mm (most accurate )
  • pyloric transverse diameter ≥14 mm
  • length, i.e. longitudinal measurement >15 mm

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