Endosonography of the Anal Canal

PURPOSE: The aim of this study was to determine the endosonographic anatomy in children to define normal age-related differences in sphincter morphology and measurements. METHODS: One hundred ten consecutive children (76 males and 34 females; mean age, 3.94 years; range, 1.10-15.09) with endoanal ultrasonography were studied. The thickness of the anal canal of the internal and external anal sphincter of each child was registered and correlated with the age. RESULTS: At the high level, the puborectalis muscles were clearly visualized, with a median thickness of 4.73 mm, and the internal anal sphincters were observed, with a mean thickness of 1.21 mm. At the mid level, both the internal and external anal sphincters were visualized, as well. The mean internal anal sphincter thickness was 1.23 mm and the median thickness of the external anal sphincter was 4.47 mm. At the lower level, the median external anal sphincter thickness was 5.39 mm. There was no significant correlation between the thickness of the internal and external sphincters and sex. The puborectalis and the external anal sphincter thickness showed a highly significant positive correlation with age. There was no significant correlation between the internal sphincter thickness and age. CONCLUSIONS: The endosonographic morphology of children is similar to that of adults, although the structures in children less than 5 years of age are difficult to differentiate. We detected a significant increase in the thickness of the external anal sphincter as patients grow older, but not in the internal anal sphincter.