Bladder Anatomy

The bladder is an extraperitoneal muscular urine reservoir that lies behind the pubic symphysis in the pelvis. A normal bladder functions through a complex coordination of musculoskeletal, neurologic, and psychological functions that allow filling and emptying of the bladder contents. The prime effector of continence is the synergic relaxation of detrusor muscles and contraction of the bladder neck and pelvic floor muscles. This occurs during bladder filling and urine storage. See the image below.

The normal adult bladder accommodates 300-600 mL of urine. A central nervous system response is usually triggered when the volume reaches 400 mL and is perceived as the sensation of bladder fullness and the need to void. However, urination can be prevented by cortical suppression of the peripheral nervous system or by voluntary contraction of the external urethral sphincter. ^[1]

The adult bladder is located in the anterior pelvis and is enveloped by extraperitoneal fat and connective tissue. It is separated from the pubic symphysis by an anterior prevesical space known as the space of Retzius or retropubic space. The dome of the bladder is covered by peritoneum, and the bladder neck is fixed to neighboring structures by reflections of the pelvic fascia and by true ligaments of the pelvis.

The body of the bladder receives inferior support from the pelvic diaphragm in females or prostate in males and lateral support from the obturator internus and levator ani muscles. At its apex, the medial umbilical ligament, or the urachal remnant, courses along the anterior abdominal wall to the umbilicus. ^{[2, 3]} See the image below.

Bladder neck

The bladder neck serves as the internal sphincter in women. At the bladder neck, the muscular bladder wall is more organized and 3 relatively distinct layers become apparent. The inner longitudinal muscle layer fuses with the inner longitudinal layer of the urethra. The middle circumferential muscle layer is most prominent in the proximity of the bladder neck, and it fuses with the deep trigonal muscle layer. The outer longitudinal muscle layer contributes some anterior fibers to what become the pubovesical muscles, which terminate on the posterior surface of the pubic bone. Posteriorly, the outer longitudinal fibers interdigitate with deep trigonal fibers and the detrusor muscle. See the image below.

It is thought that the differing groups of muscle fibers aid in bladder neck opening during micturition and bladder neck closure during bladder filling and urine storage phases. In addition to these muscle layers, the pubourethral ligament serves to support the bladder neck and urethra via attaching these structures to the dorsal aspect of the pubis. In males, the bladder neck is contiguous with the prostate and both serve together as the internal urethral sphincter. The prostate is attached to the pubis by puboprostatic ligaments.

Trigone

The trigone is a triangular portion of the bladder floor bordered (ventrally) by the internal urethral opening or bladder neck and (dorsolaterally) by the orifices of the right ureter and left ureter. The ureters, which transport urine from the kidneys to the bladder and insert into the trigone, approach the bladder as they course inferiorly from their posterolateral locations. The superior or dorsal border of the trigone is a raised area termed the interureteric ridge, which courses from one ureteral meatus to the other. The intravesical ureteral orifices are roughly 2-3 cm apart. The intramural ureters are each about 1.5 cm in length.

Vascular supply

The arterial blood supply of the bladder arrives primarily via the internal iliac (hypogastric) arteries. These branch into the umbilical artery, which supplies several superior vesicle branches, and inferior vesical arteries, which come as direct internal iliac branches in males or from the vaginal arteries in females. The arterial supply of the bladder is also derived in part from the obturator artery and inferior gluteal artery. In females, this is via the uterine artery and vaginal artery. The venous return of the bladder is a rich network of vessels that generally parallels the arteries in both anatomic course and name. The vast majority of venous return from the bladder drains into the internal iliac vein.

Lymphatic drainage

The lymphatic drainage of the bladder is into the obturator, external iliac, internal iliac (hypogastric), and common iliac lymph nodes. As with any region of the body, prior surgery may alter the lymphatic outflow of the region. The internal iliac lymph nodes are usually the primary site of lymphadenopathy related to bladder pathology.

Bladder in relation to nearby structures

In males, the seminal vesicles, ductus deferens, ureters, and rectum border the inferoposterior aspect of the bladder and prostate. Anterior to the bladder is the space of Retzius or retropubic space, which is composed of fibroadipose tissue and the prevesical fascia. The dome and posterior surface of the bladder are covered by parietal peritoneum, which reflects superiorly to the seminal vesicles and is continuous with the anterior rectal peritoneum.

In females, the posterior peritoneal reflection is continuous with the uterus and vagina and is referred to as the anterior cul-de-sac or vesicouterine pouch. The inferoposterior aspect of the bladder thus rests on the anterior vaginal wall, through which the urethra courses. As a result of positioning adjacent to the reproductive organs and behind the bony pubis, the bladder neck and urethra are at risk for both direct and hypoxic injury during childbirth. ^{[4, 5]} See the image below.

Bladder

The bladder wall is most organized at the bladder neck, where 3 relatively distinct layers are observed. The inner longitudinal muscular layer fuses with the inner longitudinal layer of the urethra. The middle circumferential muscular layer is most prominent in the proximity of the bladder neck, and it fuses with the deep trigonal muscle layer. The outer longitudinal muscular layer contributes some anterior fibers to the pubovesical muscles that terminate on the posterior pubis. Posteriorly, the outer longitudinal muscle fibers interdigitate with the deep trigonal muscle fibers and the detrusor muscle itself.

Trigone

Deep to the mucosa, there are 2 muscular layers in the trigone. The superficial layer connects to the longitudinal urethral musculature. The deep muscle layer fuses with the detrusor fibers. It also joins the Waldeyer sheaths or fibromuscular coverings of the intramural ureters. Here, the muscle fibers are longitudinal in orientation.

Urothelium or bladder mucosa

The bladder mucosa is transitional epithelium and is loosely connected to the muscular bladder wall by the lamina propria that serves as a connective-tissue layer. The bladder submucosa or lamina propria is rich in microvasculature and overlies the detrusor muscle. At the trigone, the epithelium is more densely adherent to the underlying muscle. A layer of fatty connective tissue covers most of the anterior and lateral bladder in the retropubic space and can be viewed cystoscopically in the case of a bladder perforation. The peritoneum covers the bladder posteriorly and separates it from the anterior cul-de-sac or vesicouterine pouch and abdominal cavity contents. A glycosaminoglycan layer coats the luminal surface of the bladder mucosa.

The clinical need for autologous tissue to replace or augment the urinary bladder is significant. Basic science work has led to the successful growth of urothelial and smooth muscle bladder grafts in the laboratory that have been implanted in clinical trials. ^[6] However, the viability and use of these tissues is often limited by a lacking lamina propria and the vascularity this provides. ^[7]  This makes the development of a true 3-layered replacement for bladder tissue containing not only urothelium and smooth muscle but also a robust lamina propria a necessary challenge. ^[8] Nonetheless, many techniques that may facilitate this are under investigation.