In relation to the etiology of the chronic constipation with simple megarectum, much attention have been paid to the distended rectosigmoid. In this study, the anorectal manometry was performed on the chronically constipated patients with and without megarectum, and it was found that the most of the constipated patients with simple megarectum showed an extremely high resting pressure of the anal canal. The authors propose "high anal pressure syndrome (HAPS)" for such constipated patients with simple megarectum. As to the surgical treatment, 6 patients with simple megarectum had a posterior internal sphincterotomy and the postoperative results were excellent or good in our series. In conclusion, we suppose that the etiology of chronic constipation with simple megarectum is mainly due to the hypertonic sphincter activity, and the internal sphincterotomy should be the first choice of operation for such constipated patients with megarectum.
