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.
