The external component originates from the arcus tendineus, extending from the pubic bone to the ischial spine. It gives rise to fibers of differing directions, including the pubococcygeus, the iliococcygeus, and the coccygeus.
Figure 5.26 The fascial components of the pelvic diaphragm.
The internal component originates from the pubic bone above and medial to the origin of the pubococcygeus and is smaller but thicker and stronger (47). Its fibers run in a sagittal direction and are divided into the following two portions: 1.
Pubovaginalis fibers run in a perpendicular direction to the urethra, crossing the lateral vaginal wall at the junction of its lower one-third and upper two-thirds to insert into the perineal body. The intervening anterior interlevator space is covered by the urogenital diaphragm.
2.
Puborectalis superior fibers sling around the rectum to the symphysis pubis; its inferior fibers insert into the lateral rectal wall between the internal and external sphincter.
The pelvic diaphragm is covered superiorly by fascia, which includes a parietal and a visceral component and is a continuation of the transversalis fascia (Fig. 5.26). The parietal fascia has areas of thickening (ligaments, septae) that provide reinforcement and fixation for the pelvic ﬂoor. The visceral (endopelvic) fascia extends medially to invest the pelvic viscera, resulting in a fascial covering to the bladder, vagina, uterus, and rectum. It becomes attenuated where the peritoneal covering is well defined and continues laterally with the pelvic cellular tissue and neurovascular pedicles.
Musculofascial elements (the hypogastric sheath) extend along the vessels originating from the internal iliac artery. Following these vessels to their respective organs, the hypogastric sheath extends perivascular investments that contribute to the formation of the endopelvic fascia so critical for the support of the pelvic organs.
Thus, the parietal fascia anchors the visceral fascia, which defines the relationship of the various viscera and provides them with significant fixation (uterosacral and cardinal ligaments), septation (vesicovaginal and rectovaginal), and definition of pelvic spaces (prevesical, vesicovaginal, rectovaginal, paravesical, pararectal, and retrorectal).
For its support, the pelvic ﬂoor relies on the complementary role of the pelvic diaphragm and its fascia resting on the perineal fibromuscular complex. It is composed of the perineal
Figure 5.27 The double-layered muscular support of the pelvic diaphragm.
membrane (urogenital diaphragm) anteriorly and the perineal body joined to the anococcygeal raphe by the external anal sphincter posteriorly. This double-layered arrangement, when intact, provides optimal support for the pelvic organs and counterbalances the forces pushing them downward with gravity and with any increase in intra-abdominal pressure (Fig. 5.27). Dynamic imaging techniques, such as MRI, CT, and ultrasonography, increasingly are used to provide additional information in the evaluation of pelvic ﬂoor problems by visualizing anatomic landmarks during different functional phases.
Endopelvic Fascia Controversy exists surrounding the use of the term “fascia” as it applies to the pelvis. Histologic studies reveal that the linings of the levator ani, piriformis, and obturator internus are genuine examples of pelvic fascia. One example in which the term “fascia” is incorrectly used is in reference to the tissue that is plicated in an anterior colporrhaphy. Histologically, it is the muscular lining of the vagina that is plicated. There are no discrete capsules of fascia that separate the bladder and vagina from each other.