Anatomical basis of the surgical approach to the membranous urethra.

The pars membranacea is the short segment of the urethra traversing the floor of the perineum. The main anatomical obstacles encountered in the approach to the membranous urethra are the perineal body posteriorly, and the deep dorsal vein of the penis and preprostatic venous plexus, anteriorly. These obstacles must be borne in mind when performing a surgical approach to the membranous urethra. The perineal body is the main obstacle to the perineal approach and can be avoided by incision of the sagittal raphes (anobulbar and rectourethral raphes) posterior to it and up to the apex of the prostate. When the trans-symphysial or transpubic approach is used, detachment of the suspensory ligament and roots of the penis allows exposure of the preprostatic venous plexus whose inferior part lies over the membranous urethra.