TITLE:
Supportive tissues of the vagina with special reference to a fibrous skeleton in the perineum: A review
AUTHORS:
Hiromasa Sasaki, Nobuyuki Hinata, Tetsuji Kurokawa, Gen Murakami
KEYWORDS:
Vagina; Levator Ani Muscle; Perineal Membrane; Smooth Muscles; Elastic Fibers; Nerves; Pelvic Floor Anatomy
JOURNAL NAME:
Open Journal of Obstetrics and Gynecology,
Vol.4 No.3,
February
24,
2014
ABSTRACT:
With
the aid of immunohistochemistry, the present review attempts to demonstrate the
composite fibers and nerve topographical anatomy in the vaginal supportive
tissues. Along the tendinous arch of the pelvic fasciae, distal parts of the
pelvic plexus extend antero-inferiorly and issue nerves to the internal anal
sphincter as well as the cavernous tissues. At the attachment of the levator
ani muscle to the rectum, smooth muscles in the endopelvic fascia lining the
levator ani merge with the longitudinal smooth muscle layer of the rectum to
provide the conjoint longitudinal muscle coat or the longitudinal anal muscle
(LAM: smooth muscle). However, at the rectovaginal interface, the longitudinal
smooth muscle layer of the rectum continues to the LAM without any contribution
of the endopelvic fascia. The bilateral masses of the perineal smooth muscles
(PSMs) are connected by the perineal body, and the PSMs receive 1) the longitudinal
anal muscle, 2) the internal and external anal sphincters and, 3) the perineal
membrane lining the vestibular wall. Tensile stress from the levator ani seems
to be transferred to the PSMs via the LAM. Because of their irregularly arrayed
muscle fibers, instead of a synchronized contraction in response to nerve
impulses, the PSMs are likely to act as a barrier, septum or protector against
mechanical stress because, even without innervation, such smooth muscle fibers
resist (not absorb) pressure, in accordance with Bayliss’ rule. The external
anal sphincter, a strong striated muscle, inserts into the PSMs and seems to play a dynamic role in supporting the rectovaginal interface
to maintain the antero-posterior length of the urogenital hiatus. However, we
do not think that smooth muscles play an active traction role without
cooperation from striated muscle. The fibrous skeleton composed of smooth
muscle in the female perineum is explained in terms of a “catamaran” model.