Significance of the thickness of the anal sphincters with age and its relevance in faecal incontinence.
Ultrasonographic studies in healthy volunteers showed that the external anal sphincter (EAS) and internal anal sphincter (IAS) thicknesses were inversely related at rest. The functional importance of the two sphincters in continence control was demonstrated in the relationship between the sum of the thicknesses of the two sphincters and the anal canal resting pressure. The aims of the present study were to assess the morphometric appearance of the anal sphincters by endosonography in faecally incontinent patients and to contrast this with that of older healthy subjects. Twenty-eight female patients with neurogenic faecal incontinence (FI) were studied. An older group of 7 healthy women, aged 41-75 years, and a young group of 11 nulliparous healthy women, aged 20-23 years, served as control groups. Anal endosonography was performed with a radial rotating endoprobe, with the subject in the left lateral position. Conventional anal manometry was performed in all subjects. The EAS in the FI group was thicker than the EAS in the old (p < 0.04) but did not differ from the EAS in the young. The IAS thickness in the FI group did not differ from that in the older group. In both these groups the IAS was thicker than in the young women (p < 0.01). The anal pressures in the FI group were reduced compared with the normal groups (p < 0.04). There was a direct relationship between the two sphincters in FI (p < 0.001). The increased thickness of the IAS in the FI group does not seem to compensate for function and results in a failure of the sphincter mechanism to maintain continence, whereas in healthy elderly subjects the increased IAS thickness appears to be compensatory and important for continence control.