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FIGURE 116.13 Hypertrophic pyloric stenosis. Ultrasonography of the abdomen shows a
thickened pyloric muscle and elongated pyloric channel.

If the US study does not show a hypertrophic pylorus and the patient has
significant forceful emesis, an upper GI series may be considered in order to
eliminate gastroesophageal reflux, malrotation, and antral web as diagnostic
possibilities. In general, pyloric stenosis can be identified by the presence of a
“string sign” in the pyloric channel, seen best on oblique projections on the upper
GI series ( Fig. 116.14 ). For patients with an initially normal US but progressive
emesis, repeat US should be performed 24 to 48 hours later to remeasure the
pylorus.