Pyloric muscle in asymptomatic infants: sonographic evaluation and discrimination from idiopathic hypertrophic pyloric stenosis.

OBJECTIVE: To compare the morphological and functional US appearance of the pylorus in healthy infants with those suffering from idiopathic hypertrophic pyloric stenosis (IHPS) in order to determine the pathological limits and to find out the most discriminating morphometric parameter.

MATERIALS AND METHODS: The pylorus of 84 asymptomatic infants was prospectively evaluated with respect to morphology (pyloric length, pyloric diameter, muscle thickness and pyloric volume) and function (gastric peristalsis and emptying, pyloric opening and the fluid passage). Results were compared with 85 patients with proven IHPS.

RESULTS: In every normal infant we observed frequent pyloric opening with passage of gastric contents and quick gastric emptying. All infants with proven IHPS presented with a permanently closed pylorus and exaggerated, retrograde gastric peristalsis. For each of the four parameters, highly significant differences (P < 0.0001) were found between the control and IHPS groups. Pathological limits were 3 mm for muscle thickness (accuracy 100 %), 15 mm for pyloric length (accuracy 94 %), 11 mm for pyloric diameter (accuracy 92 %) and 12 ml for pyloric volume (accuracy 96 %).

CONCLUSIONS: Evaluation of pyloric function plays an important role in the diagnosis of IHPS. The morphometric parameters are highly accurate in differentiating IHPS from a normal pylorus, muscle thickness being the most discriminating parameter.