Lack of the complete circular rhabdosphincter and a distinct circular smooth muscle layer around the proximal urethra in elderly Japanese women: an anatomical study.

Histological observations of semiserial sections obtained from the cadavers of 30 elderly Japanese women (aged 61-93 years) found that the urethral rhabdosphincter (URS) usually occurred as a ventrally localized structure instead of exhibiting the normal completely circular configuration. The superoinferior length, thickness and muscle fiber density of the URS area showed significant interindividual variation. A thick fascicle, extending posterolaterally from the URS and radiating to the lateral vaginal wall and other perineal tissues, was usually observed. A circular smooth muscle layer, which immediately surrounded the longitudinal smooth muscle layer, was consistently present in the proximal urethral but not in the bladder neck. These findings suggest that voluntary sphincteric action is weak or incomplete in elderly Japanese women. We therefore hypothesize that upward retraction of the midurethra by the URS, compression of the distal urethra by its posterolateral extensions, and tonus provided by the outer circular smooth muscle layer all contribute to maintaining continence in these women.