Pelvic Fascia and Perineopelvic Spaces
The steadily changing pressure and filling conditions in the pelvis require adaptability of those structures that support the viscera within the funnel-like frame of the pelvis. Part of this support derives from the anorectal musculature and the levatorani. But since these muscles are, to a great extent, involved in the sphincteric and emptying functions of the anorectal canal, their supporting tasks are assisted by the connective tissue structures of the pelvic fascia, which have substantial tensile strength. The anatomic relationships of the pelvic fascia and associated muscles are physiologically and surgically significant. The pelvic fasciae are divisible into a visceral and a parietal portion. The former lies entirely superior to the pelvic diaphragm, forming the fascial investments of the pelvic viscera, the perivascular sheaths, and the intervisceral and pelvovisceral ligaments, which are described below.
The parietal portion of the pelvic fascia may be divided into parts that lie either superior or inferior to the levatorani muscle. Superior to the levatorani, parietal pelvic fascia is a continuation of the parietal abdominal fascia. The iliopsoas fascia and the transversalis fascia of the abdomen are attached along the linea terminalis to the bony pelvis and then extend inferiorly into the pelvis over the inner surface of the obturator internus muscle as the obturator fascia. Anteriorly, the transversalis fascia is attached to the inner surface of the pubic bones and symphysis. The prevertebral fascia of the abdomen continues inferiorly into the pelvis as the presacral fascia.
The superior layer of the pelvic diaphragm arises from the arcus tendineus of the levator ani muscle, which is a thickening in the obturator fascia, running arc-wise and convex inferiorly from the posterior surface of the pubic ramus (1 or 2 cm in front of the obturator foramen) to a point just superior to the ischial spine. From this arcus, the superior fascia of the pelvic diaphragm spreads out to cover the superior (inner) surface of the levator ani and coccygeus muscles.
Anteriorly, this fascia spans the infrapubic interval in front of the transverse perineal ligament. The fascia descends just a few millimeters to form a small fossa, the bottom of which is pierced by the dorsal vein of the penis or clitoris, respectively. On each side of this small fossa, a thickening in the fascia extends posteriorly from each side of the lower end of the symphysis pubis to the prostate in the male and to the bladder in the female. These thickened parts are the medial puboprostatic ligaments (or anterior true ligaments of the prostate) in the male, to which correspond the medial pubovesical ligaments (pubourethral or anterior true ligaments) of the bladder, in the female. The lateral puboprostatic or pubovesical ligaments (or lateral true ligaments of prostate or bladder) lie just posterior to this and consist of lateral reflections from the fascia to the prostate or bladder, respectively.
The thickenings in the superior fascia of the pelvic diaphragm, which make up the medial puboprostatic or pubovesical ligaments, continue backward in a slight curve, concave downward, gradually diverging to the region of the ischial spine. This constitutes on each side the arcus tendineus of the pelvic fascia, which lies consider- ably more medially and below the arcus tendineus of the levator ani. The superior fascia of the pelvic diaphragm also continues medially and below its arcus tendineus. Anterior to the rectum, it spans the interval between the crura of the pubococcygeus muscles and, coursing around their free margins, fuses with the deep (superior) layer of the urogenital diaphragm. Here also it is reflected upon the prostate and bladder in the male and the vagina in the female as the visceral fascial sheaths of these respective organs.
Posteriorly, the superior fascia of the pelvic diaphragm surrounds the rectum as it passes through the pelvic diaphragm. It is reflected there as a sheath upon the rectum as the visceral (rectal) fascia, but it also blends with the longitudinal rectal musculature and contributes fibrous extensions to the formation of the fibromuscular, conjoined longitudinal muscle of the anal canal. The reflection takes place largely at the arcus tendineus of the pelvic fascia, but also more medially and more inferiorly in the region where the viscera begin to penetrate the pelvic diaphragm.
Inferior to the levatorani, the obturator fascia continues inferiorly on the medial walls of the pelvis below the arcus tendineus of the levatorani muscle. It covers the obturator internus muscle and is attached to the bony pelvis about the margins of that muscle. In its lower portion the fascia is split to form the more-or-less horizontal pudendal canal (Alcock canal), in which course the internal pudendal vessels and the pudendal nerve. Depending on when it leaves the pudendal nerve, the canal may also include the dorsal nerves of the penis. The inferior fascia of the pelvic diaphragm is a comparatively thin sheet that extends from the arcus tendineus of the levatorani muscle and covers the inferior surface of this and the coccygeus muscle. It continues around the lower rectum and the anal canal. It is reflected into the anterior recess of the ischioanal fossa.
The perineal fascia consists of a superficial subcutaneous and a deep membranous layer. The former is continuous with the subcutaneous fat (Camper fascia) of the abdominal wall; the latter is the superficial perineal fascia (Colles fascia), corresponding to the Scarpa fascia of the abdomen. The superficial layer varies considerably throughout the perineum. Over the anal triangle it forms the fatty layer of the deep part of the ischioanal fossa, whereas laterally over the ischial tuberosities, it is made up of fibrous fascicles that connect to the underlying bone and form, directly over the ischial tuberosities, fibrous bursal sacs. The main part of the superficial perineal fascia has a firm attachment to the pubic rami and to the posterior margin of the urogenital diaphragm. It spreads medially across the urogenital triangle, constituting the floor of the superficial perineal space, which lies between it and the inferior layer of the urogenital diaphragm and contains the superficial perineal musculature.
The visceral fascia invests, one by one, each of the pelvic organs, forming their fascial capsule (e.g., vesical fascia, prostatic fascia, vaginal-uterine fascia, rectal fascia). It also contains the ligaments that connect these viscera with each other and with the pelvic walls and floor, as well as the perivascular sheaths. The latter consist of the hypogastric sheath, which arises on each side from the parietal pelvic fascia over a roughly triangular area in the posterolateral angle of the pelvis and extends inferiorly to the spine of the ischium. This sheath contains the internal iliac vessels (and a variable number of their branches) and the ureter, as well as its accompanying nerves and lymphatics. Anteriorly, the sheath is continuous with the tendinous arch of the pelvic fascia, which extends anteriorly to the superolateral border of the bladder, where it splits into superior and inferior layers. These blend, respectively, with the superior and lateral aspects of the vesical fascia. Anteriorly, the arch carries the obliterated umbilical artery and superior vesical vessels to the urinary bladder as the lateral ligament of the bladder. Posteriorly, in the female, the hypogastric sheath fuses with the suspensory ligament of the ovary containing the ovarian vessels.
The uterosacral ligament extends inferiorly from the hypogastric sheath. Laterally, it blends with the superior fascia of the levatorani and medially with the inferolateral aspects of the bladder or prostatic fascial capsule. In a sense, it thus constitutes a reflection from the superior fascia of the levatorani to the vesical (visceral) fascia along the tendinous arch of the levatorani, its anterior portion containing the lateral true ligaments of the bladder or prostate. Posteriorly, the transversely placed transverse cervical (cardinal) ligament of the uterus extends from the uterosacral ligament, carrying the ureter, inferior vesical vessels, uterine vessels, and autonomic nerves.
The presacral fascia extends medially from the hypogastric sheath sitting anterior to the sacrum and anterior sacrococcygeal ligament, lying in a more or less vertical plane, in contrast to the superior and inferior wings, which unfold in a nearly horizontal plane. Upon reaching the sides of the rectum, the presacral fascia splits into two leaves that encircle the rectum as the rectal (visceral) fascia. This fascia carries the superior and middle rectal vessels, inferior hypogastric or pelvic nerve plexus, and many lymphatics.
The course of the pelvic muscles and the anorectal musculature, together with the superior and inferior fascia of the levator ani, give rise to a number of perineopelvic spaces, which require more than mere anatomic recognition because they have a fundamental importance for an adequate concept of infectious and malignant processes of the pelvis and perineum. As with the fasciae, these spaces are conveniently separated by the levator ani muscle. Superior to the levator ani, in the male, there are four main spaces: (1) the prevesical space (of Retzius), (2) the rectovesical space, (3) the bilateral pararectal spaces, and (4) the retrorectal space.
The prevesical space of Retzius is, in both sexes, a potentially large cavity surrounding the anterior and lateral walls of the bladder. The main cavity in front of the bladder contains two superimposed anteromedian recesses and two lateral compartments. The upper anteromedial recess lies posterior to the anterior abdominal wall (i.e., behind the most medial parts of the transversalis fascia) and is roofed by the peritoneal reflection from the dome of the bladder supported by the urachus and the umbilical prevesical fascia. Its lateral borders are demarcated by the obliterated umbilical arteries. The lower recess, continuous with the one above, lies posterior to the symphysis and pubic bones, anterior to the bladder, with a floor formed by the pubovesical ligaments in the female or the puboprostatic ligaments in the male. The lateral recesses of the prevesical space are bounded by a lateral wall formed by the obturator fascia and the superior fascia of the levatorani, and a median wall presented by the bladder and the lateral ligaments of the bladder. They contain the ureter and the main neurovascular supply to the bladder and, in the male, the prostate. The floor of the lateral recess is the superior fascia of the levatorani. Posteriorly, the lateral recess of the prevesical space extends to the hypogastric sheath in the region of the ischial spine. The roof is formed by the tendinous arch of pelvic fascia covered by the peritoneum, where these tissues are reflected from the lateral pelvic wall.
The retrovesical compartment in the male, divisible into three subspaces, lies between the bladder and the prostate, covered by the vesical and prostatic fasciae anteriorly, and the rectal fascia covering the rectum posteriorly. Its roof is formed by the rectovesical recess or pouch of the peritoneum, which comes into existence by the continuity of the peritoneal reflection from the rectum to the bladder. Its floor is the posterior part of the urogenital diaphragm. The rectoprostatic (Denonvilliers) fascia, originating from the undersurface of the rectovesical peritoneal pouch and extending inferiorly in a coronal plane, divides into two leaves, an anterior leaf, blending with the prostatic fascia or capsule, and a posterior leaf, attaching below to the urogenital diaphragm medially and to the hypogastric sheath laterally. Thus the retrovesical compartment can become subdivided into the retrovesical space and retroprostatic space anteriorly and the prerectal space posteriorly. The inferior aspect of the hypogastric sheath marks the lateral boundary of the two anterior spaces and also the separation from the lateral recess of the space of Retzius. Inferiorly, the prerectal space terminates where the rectal fascia attaches itself to the urogenital diaphragm or its thin superior fascia. The retroprostatic space (Proust space) terminates inferiorly in the same region but varies, depending on the very inferior limit of the rectoprostatic fascia and its attachments to the prostatic capsule.
In the female, as in the male, the area between the bladder and the rectum is divided into three spaces. The dominant dividing structure, however, is not the recto- prostatic fascia but the much more substantial vagina, cervix, and uterus. Anterior to these structures, two spaces come into existence, the vesicocervical space supe- riorly and the vesicovaginal space inferiorly. They are separated by a fascial septum, the supravaginal septum or vesicocervical ligament, which forms the floor of the vesicocervical space and the roof of the vesicovaginal space. The vesicocervical space is roofed by the utero- vesical fold of the peritoneum and extends inferiorly to the point where the urethra and vagina are in apposition superior to the urogenital diaphragm. In the floor of this space, the medial and lateral pubovesical ligaments surround the urethra. Laterally, the vesicovaginal space is limited by the strong fascial connections between the bladder and the cervix.
In the female, the rectovaginal space is farther from the anterior compartments because the substantial mass of the cervix, uterus, and vagina provide more separation than in the male. Whether or not the small area between the rectum and the genital organs can be divided into a retrovaginal and a prerectal space is a controversial question of no practical significance. Of more practical importance is the fact that the rectovaginal space is roofed by a deep peritoneal fold that forms the recto- uterine pouch (of Douglas). The boundaries of this space are, anteriorly, the vaginal fascia and, posteriorly, the rectal fascia. Laterally, the space extends to the fusion of the vaginal and rectal fascial collars, which, in this region, form the wings of the vagina. The space terminates inferiorly at the line of fusion between the posterior vaginal wall and the anal canal. In this region numerous fascial and muscular elements fuse, terminating inferiorly at the perineal body, also called the “central point of the perineum.”
The pararectal space extends on each side from the rectoprostatic fascia (male) or the cardinal ligament (female) to the presacral fascia. It lies on the supraanal fascia covering the superior surface of the pubococcygeus muscle, alongside the inferolateral parts of the rectum or its fascial enclosure. Its roof is made up, in both sexes, of the peritoneum reflected from the lateral aspects of the rectum to the pelvic walls, forming the floor of the pararectal peritoneal fossa.
The presacral space, similar in both sexes, constitutes the interval between the parietal pelvic fascia, covering the sacrum as well as the piriformis, coccygeus, and pubococcygeus muscles, and the presacral fascia, which envelops the rectum as the rectal fascia. Where the posterior rectal wall lies almost horizontally, the ventral lining of the presacral space is produced by the rectal fascial collar. Superiorly, the space becomes continuous with the prevertebral-retroperitoneal areolar tissue. A strong lateral barrier for this space is provided by the attachment of the hypogastric sheath to the parietal fascia, a fact that explains why retrorectal abscesses are more apt to rupture into the rectum than to penetrate into the space superior to the levatorani.
In the spaces inferior to the levatorani, the submucous space, encircling the sphincteric portion of the rectum and extending from the anorectal muscle ring to the dentate line, is the highest or most cranial. Its practical significance is explained by its contents: the terminal anastomotic network of the internal rectal venous plexus and a rich lymphatic plexus, both embedded in a supportive fibroelastic connective tissue.
A potential but not truly anatomic space, with somewhat ill-defined borders, lies within the conjoined longitudinal muscle between the internal and external anal sphincters. This intermuscular space surrounds the entire circumference of the anal canal, from the junction of the external sphincter with the levatorani to the intra muscular groove. Abscesses in this intermuscular space may develop as a result of infection of the perianal glands expanding within it. Both the submucous and intermuscular spaces are not interfascial but, rather, intravisceral.
The perianal space is located between the skin and the transverse septum of the ischioanal fossa. Its boundaries, projected to the surface, correspond to the anal triangle. Anteriorly, the space extends to the posterior border of the superficial transverse perineal muscle and laterally as far as the ischial tuberosities. Medially, the perianal space is confined by the anoderm superiorly as far as the latter’s firm attachment to the internal anal sphincter. Numerous fibrous extensions from the conjoined longitudinal muscle, which pass through the subcutaneous external anal sphincter, transverse the perianal space. It is important to note that, circumanally, the perianal space reaches to the inferior end of the internal sphincter, within the subcutaneous external anal sphincter. The space contains the external rectal venous plexus and superficial perianal lymphatics. Posteriorly, extending as far as the coccyx, the perianal space changes its name and becomes the superficial post- anal space, which extends from the anal canal to the subcutaneous tissue inferior to the extensions of the superficial external anal sphincter, known as the anococcygeal ligament, as it attaches to the posterior surface of the coccyx. It is noteworthy that the perianal space of each side communicates with its counterpart of the opposite side via this superficial postanal space inferior to the anococcygeal ligament in just the same fashion as the ischioanal fossae of each side communicate superior to this ligament via the deep postanal space. Posteriorly, the relationships to the extensions of the conjoined longitudinal muscle and the fibers of the corrugator cutis ani confine abscesses and fistulas complicating anal fissures to the superficial tissues.
The largest and most important of the spaces inferior to the levatorani muscle are the paired ischioanal fossae (average 6 to 8 cm anteroposteriorly, 2 to 4 cm wide, 6 to 8 cm deep). Each of these is irregularly wedgeshaped, with the apex at the pubic angle and the base at the gluteus maximus muscle. The superomedial wall is formed by the circumanal and infraanal fasciae covering the superficial and deep portions of the external anal sphincter and the superimposed puborectalis and pubococcygeus portions of the levatorani muscle. The attachments of this muscle and the infraanal fascia to the urogenital diaphragm mark the medial wall of the anterior extension (Waldeyer space), which extends anteriorly into the space above the urogenital diaphragm. At the most cranial point of the ischioanal fossa, the inner wall joins the outer wall, which is formed by the obturator fascia, overlying the obturator internus muscle, and farther inferiorly by the ischial tuberosity. The infraanal fascia covering the iliococcygeus muscle is the roof of the ischioanal fossa. The coccyx, sacrospinous ligament, sacrotuberous ligament, and overlapping gluteus maximus muscle constitute the base or posterior wall of the fossa. These structures thus confine the posterior extension of the ischioanal fossa, which has, posteriorly to the anal canal, no medial walls. The fossae of each side communicate with each other by what is known as the deep postanal space, which lies superior to the anococcygeal ligament or posterior extension of the external anal sphincter and inferior to the levatorani muscle.
This deep postanal space is also known as the posterior communicating space, because through it communicate the right and left ischioanal fossae. The deep postanal space is thus the usual pathway for purulent infections to spread from one ischioanal fossa to the other, resulting in the semicircular or “horseshoe” posterior anal fistula. The floor of the ischioanal space posterior to the urogenital diaphragm is the transverse septum of the ischioanal fossa. In the anterior recess the floor is formed by the urogenital diaphragm. The ischioanal space is filled with adipose tissue in a matrix of thin collagenous fibrils. The inferior rectal vessels and nerves cross each space obliquely from its posterolateral angle en route from the pudendal vessels and nerves in the obturator canal to the anal canal.
The superficial and deep compartments of the urogenital diaphragm occupy the space within the pubic arch and contain the urogenital musculature that is in close functional relationship to the pelvic diaphragm and the anorectal sphincters.