Ultrasound diagnosis of hypertrophic pyloric stenosis.

Thirty infants presenting with vomiting were examined sonographically. In 18 of these patients, a hypoechoic mass medial to the gallbladder and anterior to the right kidney was demonstrated. The mass measured more than 1 cm in diameter in all cases, with an average of 1.7 cm, and was interpreted as representing the hypertrophied muscle mass in pyloric stenosis. Sixteen of these infants had subsequent confirmation of this diagnosis by upper gastrointestinal tract examination and surgery. In two infants, both of whom had a small-diameter mass, the upper gastrointestinal tract study showed an atypical appearing pyloric canal; these two infants were thought to have atypical hypertrophic pyloric stenosis. Of importance technically is operator experience and patience and the use of different patient positions and even real-time imaging for completeness. Potential pitfalls include the fluid-filled duodenal bulb and gastric antrum, which cause a false positive diagnosis, and obscuration of a lesion by overlying bowel gas, which leads to a false negative diagnosis.