Bladder

Embryology

• The terminal part of the hindgut ends in the cloaca§
• The cloaca is divided by the urorectal septum into the:§
  • Dorsal (inferior) portion
    • Develops into the rectum and anal canal
  • Ventral (superior) portion (also known as urogenital sinus)
    • Develops into:
      • Common: bladder
      • Males: transitional and peripheral zone of prostate, prostate and penile urethra, and bulbourethral glands
      • Females: distal 1/3 of vagina and urethra and lower urogenital tracts

Relationships

• In the infant, the bladder is an intra-abdominal organ and may project above the umbilicus.
• Urachus
  • Anchors the bladder to the anterior abdominal wall
  • Urachal vessels run longitudinally, and the ends of the urachus must be ligated when it is divided.
  • An epithelium-lined lumen usually persists throughout life and uncommonly gives rise to aggressive urachal adenocarcinomas
• The superior surface of the bladder is covered by the peritoneum.
• Anteriorly the peritoneum sweeps onto the anterior abdominal wall.
  • With distention, the bladder rises out of the true pelvis and separates the peritoneum from the anterior abdominal wall. It is therefore possible to perform a suprapubic cystostomy without risking entry into the peritoneal cavity.
• Posteriorly, the peritoneum passes to the level of the seminal vesicles and meets the peritoneum on the anterior rectum to form the rectovesical space
• Anteroinferiorly and laterally, the bladder is cushioned from the pelvic sidewall by retropubic and perivesical fat and loose connective tissue.
• The potential space (of Retzius) may be entered anteriorly by dividing the transversalis fascia, and it provides access to the pelvic viscera as far posteriorly as the iliac vessels and ureters
• Insert figure

Histology

• Main histologic layers (3):
  • Superficial to deep:
    1. Urothelium
       • Lacks bloods vessels or lymphatics, low opportunity for metastasis
       • Normal bladder urothelium is multilayered and < 7 cells thick and rests on a thin basement membrane.
    2. Lamina propria (suburothelial loose connective tissue)
       • Rich blood vessels or lymphatics, high opportunity for metastasis
       • Contains smooth muscle fibers collected into a poorly defined muscularis mucosae (different than muscularis propria)
         • Muscularis mucosa is not present in 70% of specimens
         • Invasion of muscularis mucosa is considered pT1
    3. Detrusor or muscularis propria
       • The relatively large muscle fibers form branching, interlacing bundles are loosely arranged into inner longitudinal, middle circular, and outer longitudinal layers
       • Absent in diverticula

Structure

• When filled, the bladder has a capacity of ≈500 mL.
• In contrast to the male, the female bladder neck has:
  • Little adrenergic innervation
  • 2 layers of smooth muscle, an inner longitudinal and an outer circular, external to the urethra that constitute the involuntary urethral sphincter
    • The inner longitudinal fibers converge radially to pass downward to the external meatus as the inner longitudinal layer of the urethra
    • The middle circular layer does not appear to be as robust as that of the male.

Ureterovesical junction and the trigone

• The ureter pierces the bladder wall obliquely, travels 1.5-2 cm, and terminates at the ureteral orifice
• Vesicoureteral reflux is thought to result from (2):
  1. Insufficient submucosal ureteral length
  2. Poor detrusor backing
• Bladder filling is thought to result in passive occlusion of the ureter, like a flap valve.
• A hutch diverticulum is herniation of bladder wall at the weakest point of detrusor hiatus, above ureter
• The triangle of smooth urothelium between the two ureteric orifices and the internal urethral meatus is referred to as the trigone of the bladder
• Smooth muscle of the ureter forms the interureteric ridge (Mercier bar)
• The urothelium overlying the muscular trigone is usually only 3 cells thick
• Bladder neck is 3-4cm behind midpoint of pubic symphysis
• Layers of trigone muscle (3):
  1. Superficial layer, derived from the longitudinal muscle of the ureter.
  2. Deep layer, derived from Waldeyer sheath on the ureter and inserts at the bladder neck.
  3. Detrusor layer.

Vasculature

• Arterial Supply
  • Superior and inferior vesical arteries, which come from the anterior branch of the internal iliac.
    • In addition to the vesical branches, the bladder may be supplied by any adjacent artery arising from the internal iliac artery.
  • The bladder, when approached from the rectovesical space, has a lateral pedicle that is lateral to the ureter and a posterior pedicle that is posteromedial to the ureter. For convenience, surgeons refer to the vesical blood supply as the lateral and posterior pedicles.

• Venous drainage
  • Veins of the bladder coalesce into the vesical plexus and drain into the internal iliac vein.

Lymphatic drainage

• The bulk of the lymphatic drainage passes to the external iliac lymph nodes.
• Some anterior and lateral drainage may go through the obturator and internal iliac nodes
• Portions of the bladder base and trigone may drain into the internal and common iliac groups.
• Limits of dissection for standard lymphadenectomy during radical cystectomy:
  • Superior: ureter/bifurcation of the common iliac artery
  • Inferior: circumflex iliac vein and Cloquet’s node/Cooper ligament at the femoral canal
  • Lateral: genitofemoral nerve
  • Medial: bladder and internal iliac artery
  • Posterior: obturator nerve/fossa

Innervation

• Efferent
  • The bladder wall is richly supplied with parasympathetic cholinergic nerve endings.
  • Sparse sympathetic innervation of the bladder has been proposed to mediate detrusor relaxation but probably lacks functional significance
  • Nitric oxide synthase–containing neurons have been identified in the detrusor, particularly at the bladder neck, where they facilitate relaxation during micturition.
  • In males, the internal sphincter is richly innervated by adrenergic fibers, which act on α1-adrenergic receptors, and when stimulated, produce closure of the bladder neck.
    • The internal sphincter is responsible for continence at the level of the bladder neck.
      • Perfect continence can be maintained in men in whom the striated urethral sphincter is destroyed, demonstrating the efficacy of this sphincter.
      • Damage to the sympathetic nerves leading to the bladder, as a result of diabetes mellitus or retroperitoneal lymph node dissection for testis cancer, can cause retrograde ejaculation.
  • The female bladder neck has little adrenergic innervation.
  • The trigonal muscle is innervated by adrenergic and nitric oxide synthase–containing neurons. Like the bladder neck, it relaxes during micturition.
• Afferent
  • Both sympathetic (via the hypogastric nerves) and parasympathetic nerves travel via the lateral and posterior pedicles to reach cell bodies in the dorsal root ganglia located at thoracolumbar and sacral levels, respectively.
    • In females, the parasympathetics travel via the cardial ligament. As a consequence, presacral neurectomy (division of the hypogastric nerves) is ineffective in relieving bladder pain.

Questions

1. What is the arterial blood supply to the bladdery?

Answers

1. What is the arterial blood supply to the bladdery?
   • Superior and inferior vesical arteries, which are derived from the anterior branch of the internal iliac artery

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 21