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 bulb al cavernous structures constituted a significant portion of the urethral w all. Five embalmed cadavers and two fresh cadavers underwent excision and s ection of the urethra from the point where the proximal urethra joins the b ladder to a point 3-5 mm above where the distal urethra terminates at its e xternal meatus. Serial cuts were made, each 2-3 mm in length. The last segm ent 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 in dividual sections were stained with hematoxylin and eosin, Masson's trichro me (connective tissue, muscle), and Verhoeff's elastic (elastic tissue, mus cle, connective tissue). The stained slides were studied and photomicrograp hed. The proximal urethra demonstrated prominent cavernous tissue at levels 3 and 4, derived principally from the vestibular bulb but also from the co rpora cavernosa clitoris. These structures were incorporated into the anter ior and anterolateral walls of the urethra. Overlying these structures was striated muscle derived from the levator ani muscles. The cavernous structu res were most prominent in the first 15 mm of urethra. At levels 5 and 6, t his 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 s keletal 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 ur ethra. Extensive amounts of elastic tissue were seen in the anterior vagina l wall and within the cavernous fibrous tissue. This study demonstrated for the First time, to the authors' best knowledge, that vascular cavernous ti ssues constitute a significant portion of the proximal female urethra. Addi tionally, skeletal muscle arising from the levator ani is present in the an terior and lateral walls of the first 22 mm of the human female urethra.