Ultrasonographic features of normalization of the pylorus after pyloromyotomy for hypertrophic pyloric stenosis

Purpose: The purpose of this study was to describe the time course, early p ostoperative changes, and morphologic features of normalization of the pylo rus after pyloromyotomy for hypertrophic pyloric stenosis. Methods: The subjects were 17 infants (9 boys, 8 girls) who underwent umbil ical incision Ramstedt pyloromyotomy. The pyloric muscle mass was measured immediately before the operation and then at intervals from 3 days to 6 mon ths after the operation using a 7.5-MHz ultrasound probe. Results: In longitudinal section, the dorsal part of the pyloric muscle thi ckened transiently and then thinned to normal values by 5 months after the operation. It was 5.1 +/- 0.8 mm (mean +/- SD) preoperatively, increased to 6.0 +/- 0.3 mm by day 3 after the operation (P < .05), and thinned to 2.8 <plus/minus> 0.2 mm by 5 months after the operation. Concomitantly, the len gth of the pylorus gradually decreased (from 20.1 +/- 2.9 mm preoperatively to 16.9 +/- 2.7 mm by 3 days postoperatively [P < .05] and to less than 15 mm, by 4 months). In transverse section, the muscle normalized as in the l ongitudinal section. At the site of the incision it was 4.3 <plus/minus> 0. 4 mm thick preoperatively, thickened to 4.6 +/- 0.4 mm by 3 days after the operation (P (.05), thinned to 2.1 +/- 0.9 mm by 7 days (P(.05), and then i ncreased slightly, but always was less than 3.0 mm. Morphologically, in tra nsverse section, the incised area looked like a wedge by 3 days after the o peration. Conclusions: After pyloromyotomy for hypertrophic pyloric stenosis, there i s an early transient increase in muscle thickness within the first few post operative days followed by a slow decrease that reaches normal thickness (< 3 mm) by 5 months. This decrease in thickness is accompanied by a gradual d ecrease in length to 75% of the preoperative value by 5 months. The morphol ogic features in this normalization are first a wedge (day 3), then a flat tire (days 7 and 14), and finally an elongated ring (5 months).