The relationships of the vestibular bulb and corpora cavernosa to the female urethra: A microanatomic study - Part 2

This study evaluated the female urethra and showed that the crural and bulbal cavernous structures constituted a significant portion of the urethral wall. Five embalmed cadavers and two fresh cadavers underwent excision and section of the urethra from the point where the proximal urethra joins the bladder to a point 3-5 mm above where the distal urethra terminates at its external meatus. Serial cuts were made, each 2-3 mm in length. The last segment was 1 cm in length (distal segment). The latter were numbered 1 through 8, section 1 being the most proximal and section 8 the most distal. The individual sections were stained with hematoxylin and eosin, Masson's trichrome (connective tissue, muscle), and Verhoeff's elastic (elastic tissue, muscle, connective tissue). The stained slides were studied and photomicrographed. The proximal urethra demonstrated prominent cavernous tissue at levels 3 and 4, derived principally from the vestibular bulb but also from the corpora cavernosa clitoris. These structures were incorporated into the anterior and anterolateral walls of the urethra. Overlying these structures was striated muscle derived from the levator ani muscles. The cavernous structures were most prominent in the first 15 mm of urethra. At levels 5 and 6, this had given way largely to skeletal muscle, which, again, constituted the major component of the anterior and lateral urethral walls. Thus, at 15-22 mm, skeletal muscle replaced the cavernous structures. Interestingly, no skeletal muscle nor cavernous tissue was seen on the posturethral wall. The circular and longitudinal smooth muscle of the urethra was seen throughout all sections and did not change from level to level. Little elastic tissue was identified in the submucosal or involuntary muscle components of the urethra. Extensive amounts of elastic tissue were seen in the anterior vaginal wall and within the cavernous fibrous tissue. This study demonstrated for the First time, to the authors' best knowledge, that vascular cavernous tissues constitute a significant portion of the proximal female urethra. Additionally, skeletal muscle arising from the levator ani is present in the anterior and lateral walls of the first 22 mm of the human female urethra.