Ultrasound diagnosis of evolving pyloric stenosis.

Two infants with recurrent episodes of vomiting had upper gastrointestinal barium studies that did not show radiographic features of pyloric stenosis. However, follow-up abdominal sonograms done 1-2 weeks later documented hypertrophic pyloric stenosis, which led to surgery. This entity is not congenital, but an evolving acquired lesion. Therefore, ultrasound is an excellent modality to evaluate and monitor patients clinically suspected of developing hypertrophic pyloric stenosis despite their initially negative imaging studies.