Bladder: Position, Relations, Gross
Structure
The urinary
bladder is an expandable reservoir that receives urine from the ureters. When
empty, the bladder lies entirely within the lesser pelvis and resembles a
flattened, four-sided pyramid with rounded edges. The apex, which corresponds to
the tip of the pyramid, is directed anteriorly. Opposite the apex is the base
(fundus), the expansive posterior surface. Between the apex and fundus is the
body of the bladder, which has a single superior surface, as well as two convex
inferolateral surfaces separated by a rounded inferior edge. The bladder’s most
inferior and most fixed aspect is known as the neck. It is located just proximal
to the outlet, also known as the internal urethral orifice.
The bladder wall consists of a loose, outer connective tissue layer,
known as the vesical fascia; a three-layered muscularis propria of smooth
muscle, known as the detrusor; and an internal mucosa. The ureters enter the
bladder on its posteroinferior surface and then take an oblique course through
its wall before terminating at the ureteric orifices. The two ureteric orifices,
combined with the internal urethral orifice, bound an internal triangular region
known as the trigone.
Anatomic Relations
Anterior. The anterior portion of the bladder rests on the
pubic symphysis and adjacent bodies of the pubic bones; when empty, the bladder
rarely extends beyond their superior margin. Between the pubic bones/ symphysis
and the bladder is the retropubic (prevesical) space (of Retzius), which
contains a matrix of loose areolar tissue encasing the anterior portions of the
vesical and prostatic venous plexuses. This space facilitates extraperitoneal
access to the bladder and prostate via suprapubic abdominal incision.
As the bladder fills with urine, the body expands, causing its
anterosuperior aspect to ascend into the extraperitoneal space superior to the
pubic crest. The base and neck of the bladder, in contrast, remain relatively
constant in both shape and position.
The apex of the empty bladder sends a solid, slender projection known as the median umbilical
ligament superiorly along the midline
of the abdominal wall, toward the umbilicus. This ligament represents a vestige
of the urachus (see Plate 2-33) and rarely possesses a residual allantoic
lumen. If a lumen is present, it infrequently may communicate with that of the
bladder, but a urachus that is patent from bladder to the umbilicus is very
rare.
Superior. The peritoneum covering the anterosuperior aspect
of the bladder reflects onto the abdominal wall to form the paired supravesical
fossae of the peritoneal cavity.
These fossae are divided by the median umbilical ligament and bounded laterally
by the obliterated umbilical arteries, which form the medial umbilical
ligaments. The level of the supravesical fossae (and consequently, the superior
extent of the retropubic space) changes with bladder emptying and filling.
Lateral. The walls of the bladder are covered by peritoneum
to the level of the umbilical artery/medial umbilical ligament. The reflection
of the peritoneum from the lateral walls of the bladder onto the lateral pelvic walls forms the shallow paravesical fossae of the peritoneal
cavity. These fossae extend posteriorly to the vasa deferentia in males. In
females, they extend to the anterior aspect of the broad ligament, which
conveys the round ligaments of the uterus. Inferior to the para- vesical
fossae, the loose areolar tissue of the retropubic space continues laterally.
Posterior. In the male, the two seminal glands (vesicles)
and ampullae of the vasa deferentia lie between the base of the bladder and the
rectum on each side of the midline. These structures are separated from the
rectum by the rectoprostatic (rectovesical) fascia cor septum (also known as
Denonvilliers fascia). This fascia is continuous with the tough envelopes of
the ampullae of the vasa deferentia and seminal glands (vesicles), and it
continues posterior to the prostate until it reaches the perineal body.
In the female, the urethra and bladder are separated from the vagina and
cervix by the vesicovaginal fascia, which normally contains a small amount of
areolar tissue. The vesicovaginal fascia, as well as the rectovaginal fascia
(or septum, located posterior to the vagina), together are homologous to the
male rectoprostatic (rectovesical) fascia.
In males, the rectoprostatic (rectovesical) fascia is located inferior to
the rectovesical pouch, the inferior-most extent of the peritoneal cavity. In
the fetus, this pouch is a deeper excavation, which dips posterior to the
prostate as far as the pelvic floor. In females, the rectovaginal fascia is
directly inferior to a similar space, termed the recto-uterine pouch
(cul-de-sac of Douglas). In the male, the peritoneum extends from the bladder
around each side of the rectum toward the sacrum as a pair of sickle-shaped
shelves called the sacrogenital (vesicosacral) folds, bounding the pararectal
fossae. In the female, the sacrogenital (uterosacral) folds arise from the dorsolateral
walls of the uterine cervix (see
Plate 1-6). At the base of the bladder, these folds contain the terminal
portions of the ureters and, in the male, the ductus deferens.
Inferior. Except for a variable layer of endopelvic fascia,
the neck of the bladder rests directly on the pelvic floor muscles (e.g.,
levator ani) in females, whereas in males the prostate gland is interposed
between them. In the male, the internal urethral orifice lies about 1 or 2 cm
superior to, and 2 cm posterior to, the subpubic angle. In the female, the
position of the urethral orifice is
slightly more inferior. In the newborn, the bladder is more abdominal than
pelvic in position, and the urethral orifice may be situated as far superiorly
as the pubic crest.
Ligamentous Attachments
The inferior, subperitoneal aspect of the bladder is connected to the
pubis by two ligaments originating in the prostatic fascia in males and vesical
fascia in females.
The first of these
ligaments is known as the medial puboprostatic ligament in males and the medial
pubovesical ligament in females. This ligament lies close to the pelvic floor
and flanks the deep dorsal vein of the penis (or clitoris) as it pierces up the
pelvic floor to enter the prostatic (or vesical) venous plexus. Other ligaments
flanking this vein include the inferior (arcuate) pubic ligament anteriorly,
which forms the inferior margin of the pubic symphysis, and the transverse perineal
ligament posteriorly, which is an anterior thickening of the perineal membrane.
The second ligament is known as the lateral puboprostatic ligament in
males and the lateral pubovesical ligament in females. This ligament is formed
by a lateral extension of the prostatic (or, in females, vesical) fascia over
the inferior group of vesical arteries, pudendal veins (draining the vesical
plexus), and autonomic nerves. The terminal part of the ureter and (in males)
vas deferens contribute adventitia to this ligament. At its lateral edge, this
ligament joins the superior fascia of the pelvic diaphragm, which invests the
levatorani. This linear area of attachment is known as the tendinous arch of
the pelvic fascia.
Bladder Structure
The detrusor muscle, which contracts under parasympathetic stimulation,
consists of three layers of muscle. Unlike in the gastrointestinal tract,
however, these muscle layers are not clearly distinct in all areas.
The outer muscle layer consists of predominantly longitudinal fibers,
which are especially numerous in the midline region and near the neck. The thin
middle muscle layer encircles the fundus and body. In males, additional
circular fibers create the internal urethral sphincter in the inferior neck,
which contracts during sympathetically stimulated ejaculation to prevent reflux
of semen into the bladder.
The innermost layer of the detrusor contains additional longitudinal
fibers. In the region of the trigone, this
layer is intimately attached to the mucosa and forms the trigonal muscle.
Around the ureteric orifices, the muscular coat of each ureter also fans
out into the bladder. Some of these muscle fibers cross the midline to unite
with strands from the opposite side, raising an interureteric crest.
The sides of the trigone are outlined by yet another group of submucosal
fibers, known as Bell muscle, which connect the ureteral muscles with the wall
of the urethra. Tension across these bands, especially when combined with pressure from the
neighboring middle lobe of the prostate (in males), leads to a small elevation
above the bladder neck known as the uvula.
The innermost layer of the bladder is the mucosa. When the bladder is
empty, the mucosa is corrugated by numerous folds. As the bladder distends,
however, the folds are obliterated. The mucosa of the trigone is anatomically
distinct, however, because it is firmly attached to the muscularis, consequenly
appearing smooth even when the
bladder is empty.
