[Anatomical measurements of the internal anal sphincter--the relative site of the dentate line in the internal anal sphincter].

Not only the length and the width of the internal anal sphincter but also the relative site of the dentate line in the internal anal sphincter were investigated in 62 resected specimens obtained by abdominoperineal resection of the rectum for malignancy. Mean length and width of the internal sphincter were 25.8 +/- 4.1mm (mean +/- standard deviation) and 4.0 +/- 1.1mm, respectively. The length of the internal sphincter from its distal end to the level of the dentate line was 11.3 +/- 3.1mm, which corresponded to 44% of the total length of the internal sphincter. The individual difference in the site of the dentate line in the internal sphincter was objectively demonstrated. It seems to be therefore important to modulate the extent of sphincterotomy in order to minimize postoperative anal dysfunction on the surgery for fissure or fistula-in-ano, in which sphincterotomy is widely practiced up to the level of the dentate line.