Sonographic diagnosis of infantile hypertrophic pyloric stenosis.

Twenty-five consecutive sonographic examinations performed at Flinders Medical Centre for possible infantile hypertrophic pyloric stenosis (IHPS) were analyzed retrospectively. The results and a pyloric muscle index calculated by a formula using length, diameter, muscle thickness, and body weight were compared with the clinical outcome (surgery or conservative management). In the children without IHPS, the calculated pyloric muscle index was less than 0.2, whereas in infants with proven pyloric stenosis, the index was greater than 0.2 (P < 0.001). This result suggested that the published index upper limit of > 0.4 to 0.46 was not valid in our institution. Pyloric length to muscle thickness ratio was also found to predict IHPS. A simplified index, including only length and muscle thickness, is proposed, whereby length (mm) plus 3.64 times thickness (mm), when greater than 25, implies IHPS.