TITLE:
The Perineal Membrane: Its Composite Fibers and Nerve Content, and Relationship to the Levator Ani and Deep Transverse Perineal Muscles
AUTHORS:
Tetsuji Kurokawa, Nobuyuki Hinata, Hiromasa Sasaki, Gen Murakami, Masato Fujisawa, Shin-Ichi Abe, Yoshio Yosida
KEYWORDS:
Vagina, Levator Ani Muscle, Perineal Membrane, Smooth Muscles, Elastic Fibers, Nerves
JOURNAL NAME:
Open Journal of Obstetrics and Gynecology,
Vol.4 No.7,
May
30,
2014
ABSTRACT:
The perineal membrane (PM) is a
thick, elastic fiber-rich, smooth muscle-poor membrane extending along the
vestibule and lower vaginal wall and embedding the urethrovaginal sphincter and
compressor urethrae muscles. To provide a better understanding of the
topographical relationship between the PM and the levator ani muscle, we
examined histological sections from 15 female cadavers. The composite fibers of
the PM were usually continuous with that of a fascia covering the inferior or
lateral surface of the levator ani (fascia diaphragmatis pelvis inferior)
rather than the endopelvic fascia covering the superior or medial surface of
the latter muscle. However, this fascial connection was sometimes interrupted
by a venous plexus. The deep transverse perineal muscle was consistently
adjacent to the posterolateral aspect of the PM, but whether it extended
superficially or deeply to the PM depended on size of the muscle. In contrast
to the endopelvic fascia embedding abundant middle-sized nerves (cavernous and
sphincter nerves; 0.05 - 0.1 mm in thickness), the PM contained very thin
nerves: many in 10 cadavers but few in 5 cadavers. Most of the nerves seemed to
be sensory on the basis of immunohistochemistry. The levator ani muscle was
considered likely to provide traction force to the PM, but active elevation
appeared to be difficult because of the highly elastic nature of the PM and the
interrupting venous plexus. Loss of nerves in the PM might be one of a number
of factors that can accelerate pelvic organ prolapse.