Objectives: To clarify the topographical relationship between the urethral rhabdosphincter and the rectourethralis muscle as these structures lying dorsally to membranous urethra are important factors to post-prostatectomy urinary continence.
Methods: Pelvic floor specimens including prostate, bulbus penis, and anorectum, obtained from 15 male cadavers (ages at death 66 to 80 years), were examined with standard histologic and immunohistochemical techniques using semiserial sagittal and transverse sections.
Results: The rectourethralis muscle was defined. It was found to be located at the interface between the levator ani muscle and rectum. It was not possible to histologically identify the fibromuscular node known as the perineal body. The urethral rhabdosphincter was found to be inserted into the rectourethralis muscle, which is composed of the smooth muscle fibers. Abundant nerves passed between the rectourethralis muscle and the levator ani, or through the rectourethralis muscle. The urethral rhabdosphincter was closely attached to the apical or ventral portion of the rectourethralis muscle. Morphologically, the membranous urethra was fixed to the rectourethralis muscle through the urethral rhabdosphincter.
Conclusions: The rectourethralis muscle influences the stabilization of membranous urethra. The posterior stitches for the reconstruction of the dorsal musculofascial plate might injure the nerve fibers running along and through the rectourethralis muscle.