Anatomy of The Bladder



Anatomy of The Bladder


CLINTON W. COLLINS

ADAM P. KLAUSNER



GENERAL DESCRIPTION

The bladder is a hollow, muscular retroperitoneal organ with a capacity of 400 to 500 mL in the normal adult. The bladder is a pelvic organ when empty, lying behind the pubic symphysis. However, when distended, it can be palpated above the pubic symphysis and can protrude well into the abdomen during an episode of severe urinary retention.


PERITONEAL RELATIONSHIPS

The peritoneum covers the superior and a portion of the posterior bladder. In females, the peritoneum continues posteriorly onto the surface of the uterus and rectum, establishing the vesicouterine and rectouterine pouches, respectively (Fig. 17.1) (1). In the male, the peritoneum continues along the surface of the rectum, establishing the rectovesical pouch of Douglas. The two leaves of the peritoneum embryologically coalesce to form the anterior and posterior layers of Denonvilliers fascia (rectovesical fascia), a critical landmark in the performance of a radical retropubic prostatectomy (Fig. 17.2) (2).






FIGURE 17.1 Sagittal view of female pouches.


PERITONEAL FOLDS

As seen from a typical laparoscopic approach to the abdominal cavity, the anterior surface of the peritoneum has three characteristic deflections, also called folds. The midline fold is called the median umbilical ligament and the paired paramedian folds are called the medial umbilical ligaments. Fortunately, the anatomy itself is less confusing than the terminology. In relation to the bladder, the median umbilical fold is the most important of these structures as it contains the urachal ligament. Attaching to the bladder anteriorly at its dome, this ligamentous structure, containing fatty and vascular tissue, tethers the bladder to the umbilicus. This structure, which represents the obliterated urachus, contains paraumbilical veins and must be ligated when divided during surgical exposure of the bladder. The bladder muscle, also called the detrusor, is attenuated where the urachal ligament attaches, predisposing this area to the formation of diverticula. Retropubic and perivesical fat is present anteroinferior and lateral to the bladder.






FIGURE 17.2 Lateral view of the male pelvis showing the peritoneal reflection and the pouch of Douglas.



LIGAMENTOUS ATTACHMENTS

In the pelvis, the bladder is supported anatomically by two types of ligaments: fibroareolar (true) ligaments and peritoneal folds. True ligaments provide support for the bladder laterally via the lateral ligament of the bladder and posteriorly via the vesicovenous plexus. The lateral ligament derives from the transversalis (endopelvic) fascia as it courses over the levators and attaches the bladder to the tendinous arch of the endopelvic fascia. This ligament contains the inferior vesical and vesicodeferential arteries in the lateral extensions as well as the pudendal plexuses of nerves and vessels. In addition, in males, this ligament contains the vasa deferentia. The posterior ligaments provide posterolateral support to the bladder. These ligaments are connective tissue condensations in which the vesical venous plexus drains into the internal iliac veins. Peritoneal folds also connect the bladder to the pelvic sidewalls and consist of the median, medial, and lateral umbilical folds as well as the sacrogenital folds. The median umbilical fold and medial umbilical folds originate at the bladder and terminate at the umbilicus. They contain the urachus and the obliterated umbilical arteries, respectively. The lateral umbilical folds attach the bladder to the pelvic sidewalls and contain the inferior epigastric arteries. The sacrogenital folds connect the bladder to the sacrum (Fig. 17.3) (3).

The bladder is also fixed to the symphysis pubis by the pubovesical ligaments in females and the puboprostatic ligaments in males. The dorsal vein of the clitoris or penis passes between these paired ligaments. These ligaments represent an important surgical landmark as they form the anteromedial portion of the retropubic space, also called the space of Retzius. The space of Retzius is bound anteriorly by the transversalis fascia, inferiorly by the puboprostatic (pubovesical) ligaments, and infralaterally by the lateral ligaments of the bladder (Fig. 17.4).






FIGURE 17.3 Axial view of the female pelvis illustrating the ligamentous supports of the bladder.






FIGURE 17.4 Lateral view of a portion of the male pelvis showing the space of Retzius. The space of Retzius is bound anteriorly by the transversalis fascia, inferiorly by the puboprostatic (pubovesical) ligaments, and infralaterally by the lateral ligaments of the bladder.


HISTOLOGIC STRUCTURE

The lumen of the bladder is lined by transitional epithelium, also called urothelium. This unique epithelium is characterized by its outer layer of umbrella cells, which are sealed closely together and communicate via tight junctions. The term transitional denotes the ability of these outer cells to undergo significant transitions in shape depending on the state of bladder filling. Thus, the cells are puffy and cuboidal when the bladder is empty and become flat and elongated when the bladder is distended (4). Beneath these umbrella cells, the transitional epithelium contains additional layers of cells (usually about seven) and a distinct layer of basal cells. Deep to the transitional epithelium lies the lamina propria, composed of fibroelastic connective tissue through which vessels course. Wisps of smooth muscle also course within the lamina propria, and this portion of the lamina propria is sometimes referred to as the muscularis mucosa (Fig. 17.5).

The distinction between the muscularis mucosa and muscularis propria or true muscular layer of the bladder that lies deep to the lamina propria is critical in the staging and prognosis of urothelial cancer. Cancer that is confined to the urothelium or lamina propria, even when surrounded by wisps of muscularis mucosa, is considered superficial disease and is mainly treated via local resection or with intravesical immuno- or chemotherapeutic agents. However, cancer that penetrates into the muscularis
propria, characterized histologically by large, distinct detrusor smooth muscle bundles (Fig. 17.6), is considered invasive cancer and is treated more aggressively, usually requiring surgical removal of the entire bladder or bladder-preserving chemoradiation. Within the muscularis propria, detrusor smooth muscle bundles course in inner longitudinal, middle circular, and outer longitudinal orientations. In addition, interstitial cells surround and percolate within the muscle bundles and may be important in maintenance or modulation of bladder muscle tone (5). These muscle layers are less distinct in the upper aspect of the bladder. However, they become quite prominent at the bladder neck, although composed of finer fibers. In males, the middle layer of circular detrusor smooth muscle forms a preprostatic layer that has robust expression of alpha receptors (mainly alpha 1a) and contributes to continence at the bladder neck. Furthermore, the success in treatment of benign prostatic hyperplasia with alpha blockers stems, in part, from a pharmacologic reduction in tone in the smooth muscle surrounding the prostate and bladder neck (6). In females, the bladder neck differs dramatically, with a less distinct middle layer of smooth muscle (1,7).






FIGURE 17.5 Microscopic image of normal bladder. Note wisps of smooth muscle (arrow) within the lamina propria (asterisk).






FIGURE 17.6 Confocal immunohistochemical imaging showing detrusor bundle. Detrusor bundle is stained purple with phalloidin, which binds actin in detrusor smooth muscle cells. Nuclei within detrusor smooth muscle bundles and nuclei within interstitial cells are stained blue with DAPI, which binds strongly to DNA.


URETERAL VESICAL JUNCTION AND TRIGONE

The spiral fibers of the ureter become more longitudinally oriented near the bladder and are encased in the fibromuscular Waldeyer sheath from a distance just proximal to its entrance
into the bladder wall through its course to the trigone (1,8). Obliquely, the ureters enter the bladder posteroinferiorly and course approximately 2 cm toward the ureteral orifice, narrowing as the intramural ureter is compressed by the detrusor of the bladder surrounding it. The ureter lies just beneath the bladder mucosa with a muscular layer backing (1).






FIGURE 17.7 Anterior view of the bladder of a male opened and demonstrating intravesical anatomy. Note the trigone continues into the prostatic urethra.

A distinct landmark is formed at a triangle located between the ureteral orifices and the bladder neck, referred to as the bladder trigone. Layers of ureteral and bladder smooth muscle coalesce here as a raised ridge of tissue between the two orifices referred to as the interureteric ridge. This ridge is helpful in identifying the ureteral orifices endoscopically (Fig. 17.7). The trigone is composed of three distinct layers: (a) a superficial layer derived from the longitudinal layer of ureteral smooth muscle; (b) a deep layer that is continuous from Waldeyer sheath, inserting at the bladder neck (Fig. 17.8); and (c) the detrusor layer, derived from the outer longitudinal and middle circular layers of smooth muscle (1). The unique anatomic structure of the intramural ureter and trigone contributes to the intrinsic antireflux mechanism, which prevents vesicoureteral reflux during bladder filling and voiding.






FIGURE 17.8 Lateral view of ureter as it enters the bladder via the intramural tunnel. Note Waldeyer sheath extends from the bladder to encase the distal ureter just proximal to the bladder and fuses to the ureteral musculature. Waldeyer sheath is a continuation of the deep trigone and connects by a few fibers to the detrusor muscle at the ureteral hiatus.

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Apr 24, 2020 | Posted by in UROLOGY | Comments Off on Anatomy of The Bladder
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