Ultrasound in the diagnosis of hypertrophic pyloric stenosis.

Abdominal B-scan ultrasound imaging was performed on 35 infants who presented with vomiting. A thick hypoechoic ring was visualized in 21 of the 23 patients found at surgery to have hypertrophic pyloric stenosis. The ring was shown to represent the hypertrophied circular muscle of the pylorus. Each side of the ring measured 4 mm or more in thickness in the positive studies. None of the patients without hypertrophic pyloric stenosis showed this finding, although thinner hypoechoic rings were often seen, representing parasagittal sections of distal antral muscle.