Changes in the anal sphincter with age. An endosonographic study.

Purpose: To describe the changes in the endosonographic appearance of the anal sphincter muscles with age.
Material and Methods: Fifty subjects (age range 22-85 years) with no history of anorectal disease or surgery were studied with anal endosonography. The thickness of the internal and external anal sphincter was registered and correlated to age. For the internal sphincter, which is often asymmetric, the maximum and minimum thicknesses were measured at any part of the circumference (except anteriorly for anatomic reasons) and also in the lateral positions.
Results: A significant positive correlation with age was found for all maximum, minimum, and average internal sphincter thicknesses. Moreover, the echogenicity of the internal sphincter changed with age as the sphincter muscle became more echogenic. There was no significant correlation between external sphincter thickness and age.
Conclusion: Knowledge of the normal variation of the internal sphincter thickness with age is important since endosonography may be used to identify patients with hypertrophy of the internal sphincter. Currently, we consider maximal thicknesses above 4 mm to be abnormal in patients under 50 years of age, whereas in patients aged at least 50 years thicknesses of 5 mm or more are considered abnormal.