Bladder and urethra

Internal surface

The urothelium of the bladder body and its associated basement membrane is folded and loosely attached to the subjacent detrusor muscle by the lamina propria. Bladder filling leads to an unfolding and flattening of the urothelium, a decrease in the coiled tortuosity of bladder wall collagen and a rearrangement of muscle bundles within the detrusor layer. Bladder outlet obstruction leads to a trabeculated appearance in which the muscle fasciculi hypertrophy and the mucosa between them bulges out to form sacculations and diverticula.

The trigone is the triangular area at the base of the bladder, demarcated internally by two slit-like ureteric orifices and the internal urethral meatus at its apex. The mucosa lining the trigone is smooth and is firmly attached to the underlying smooth muscle layer. In males, the elevation caused by the median lobe of the prostate (the vesical crest) means that the internal urethral orifice is not circular ( Fig. 70.3 ). The ureters terminate by passing obliquely through the bladder wall for approximately 1.5 cm, forming the intramural ureters. The ureteric orifices are 2–3 cm apart in the empty bladder, connected by an interureteric bar of muscle formed by the continuation of the internal longitudinal muscle of the ureter. This ridge forms the superior boundary of the trigone and is easily identifiable endoscopically as a raised fold of bladder mucosa.

A duplex collecting system is a common congenital renal tract abnormality; it can be either partial or complete, and unilateral or bilateral. Embryologically, duplication occurs when two separate ureteric buds arise from a single mesonephric duct. The Weigert–Meyer rule describes the inverse relationship of the duplex ureteric orifices, in which the opening of the ureter associated with the upper moiety is caudal to that of the lower moiety ( Ch. 69 ). Ectopic ureters, single or duplex, do not enter the trigone of the bladder ( Fig. 70.4 ). In males, an ectopic ureter always enters the urogenital system above the external sphincter or pelvic floor, whereas in females the site of entry can be anywhere from the bladder neck to the perineum, and the ureter may empty into the vagina, uterus or rectum. A ureterocele is a cystic dilation of the distal end of the ureter that either is located within the bladder (intravesical) or spans the bladder neck and urethra (extravesical).

Vascular supply, lymphatic drainage and innervation

The arterial blood supply of the bladder is derived mainly from the anterior divisions of the internal iliac arteries. The superior vesical artery arises from the patent proximal part of the umbilical artery and gives off several branches that supply the bladder body and ureter. The inferior vesical artery supplies the base of the bladder and distal ureter, as well as the seminal vesicles and prostate in males. It is a direct branch from the internal iliac artery in males or from the vaginal artery (a branch of the uterine artery) in females. An extensive anastomosis develops between the superior and inferior vesical arteries, supplemented by branches from the obturator and inferior gluteal arteries.

The veins draining the bladder form a complex plexus on its inferolateral surfaces, passing backwards in the posterior ligaments of the bladder to form tributaries that drain into the internal iliac veins.

The urinary bladder is drained by mucosal, intermuscular and serosal lymphatic plexuses via one of three groups of lymphatic channels, most of which end in the external iliac lymph nodes. Vessels from the trigone emerge on the outer aspect of the bladder and run superolaterally. Vessels from the superior surface of the bladder converge towards the posterolateral angle and pass superolaterally to the external iliac lymph nodes, but some may drain into internal or common iliac groups. Vessels from the inferolateral surfaces ascend to join those of the superior surface or drain to lymph nodes in the obturator fossa. Lymphatic trunks leading from the pelvic lymph nodes drain into more proximal common iliac lymph nodes and then to the aortocaval groups.

The bladder is innervated by sympathetic and parasympathetic fibres via the vesical plexus. Briefly, preganglionic sympathetic fibres converge on the superior hypogastric plexus lying in the midline at the level of the bifurcation of the aorta and above the sacral promontory. Along their course, the majority of these neurones synapse with their postganglionic sympathetic counterparts. They descend via their respective hypogastric nerve to the right and left inferior hypogastric (pelvic) plexuses, where they are joined by preganglionic parasympathetic fibres travelling via the pelvic splanchnic nerves. The inferior hypogastric (pelvic) plexus is a meshwork of efferent autonomic and visceral afferent fibres and ganglia lying lateral to the rectum: on each side, the inferior hypogastric (pelvic) plexus innervates the bladder, prostate/uterus and vagina, and rectum via the vesical, prostatic/uterovaginal and rectal plexuses, respectively ( Fig. 70.5 ).

The parasympathetic fibres arising from S2–4 sacral segments convey motor fibres to the detrusor muscle and cause bladder contraction, with the largest contribution afforded by the S3 segment. This makes the S3 foramen the preferred position for electrode lead placement in sacral nerve stimulation, as used to treat lower urinary tract dysfunction (see Fig. 71.3 ). Throughout bladder filling, the parasympathetic innervation of the detrusor is inhibited and the smooth and striated parts of the urethral sphincter are activated, preventing involuntary bladder emptying (the ‘guarding reflex’). The sympathetic fibres arising from thoracolumbar spinal segments T11–L2 provide excitatory innervation to the smooth muscle of the bladder neck and urethra, and cause relaxation of the detrusor muscle. Visceral afferent fibres transmitting sensory information from the bladder are carried predominantly by the parasympathetic nerves and consist primarily of small myelinated (Aδ) and unmyelinated (C) fibres that respond to chemical and mechanical stimuli. Normal sensations of bladder filling appear to be dependent on the integrity of the Aδ afferents; micturition is initiated by a supraspinal reflex pathway that passes through a centre in the brainstem and is triggered by these afferents. The more numerous C fibres are ‘silent’ under normal circumstances, but may be activated under pathological conditions and are of particular importance in bladder pain syndrome.

Microstructure

Bladder wall thickness ranges between 1.8 and 4.7 mm and tends to be greater in males than females; a small increase in thickness occurs in both genders with ageing. Histologically, the bladder wall is composed of four layers: urothelium, lamina propria, muscularis propria and adventitia or serosa. The urothelium is a transitional epithelium that forms the watertight interface between the bladder lumen and the underlying bladder wall. The lamina propria lies beneath the basement membrane of the urothelium and there is mounting evidence for its importance in bladder function. The lamina propria is composed of an extracellular matrix that contains numerous cell types, including fibroblasts, adipocytes, smooth muscle (muscularis mucosae) and interstitial cells, a rich vascular network, lymphatic channels, elastic fibres, and a variety of afferent and efferent nerve endings. The term mucosa is used to describe the combination of urothelium, its associated basement membrane and the lamina propria.

The muscularis propria consists of detrusor smooth muscle that is orientated in three layers: an inner and outer longitudinal layer with an intermediate circular layer. These layers are clearly distinct near the bladder neck, but are less easily discernible elsewhere as the longitudinal and circumferential layers mix freely without definite orientation. The detrusor muscle is better developed in males, as it needs to generate a greater pressure to overcome the outflow resistance related to the prostate and longer urethra. The serosa is the outermost layer that covers the superior urinary bladder, and beneath it there is a variable amount of vascularized adipose tissue. The other surfaces of the bladder are covered by a layer of connective tissue known as adventitia, which loosely connects the bladder to the surrounding tissues of the pelvis.

Open bladder surgery

A transperitoneal, retropubic (extraperitoneal) or combined approach can be used to expose the peritoneal and/or extraperitoneal surfaces of the bladder. To improve access and visibility, the patient should be positioned with the mid-table hinge at the level of the umbilicus and the table broken; the patient is placed in the slight head-down position. In women, placing the legs in stirrups in an abducted position (Lloyd-Davies position) allows access to the perineum and manipulation of the vaginal vault using a povidone–iodine-soaked swab on a Rampley sponge forceps placed in the vagina.

Radical cystectomy in the male includes the en bloc removal of the bladder, distal ureters, prostate, membranous urethra, seminal vesicles and distal vas deferens. A simultaneous total urethrectomy is rarely performed because of the increased morbidity and the low risk of subsequent urethral recurrence. An interval urethrectomy may be considered, based on adverse histological findings, but most patients undergo urethroscopic surveillance. In the female, radical cystectomy includes removal of the bladder, adjacent anterior vagina, urethra, uterus, Fallopian tubes, ovaries and distal round ligaments. Modified genital organ-sparing techniques can be considered in younger women to preserve sexual and reproductive function. Pelvic lymphadenectomy is routinely performed because the pelvic lymph nodes are the primary landing site for metastases, which tend to occur in an orderly progression. Urinary diversion with either an ileal conduit or construction of a continent reservoir is required.

The bladder pedicles can be separated into diverging lateral and posterior components for vascular control and division. During erectile-sparing surgery, it is important to preserve the posterior part because contributions from the inferior hypogastric plexus to the bladder and neurovascular bundles run inferomedial to the ureter within this pedicle towards the posterolateral edge of the seminal vesicles.

The optimal extent of lymph node dissection has yet to be established, but removal of at least ten lymph nodes in radical cystectomy for cancer is associated with improved overall survival in retrospective series. The surgical boundaries for standard lymphadenectomy in bladder cancer patients involve removal of nodal tissue cranially up to the common iliac bifurcation, medially to the ureter, laterally to the genitofemoral nerve, distally to the circumflex iliac vein and lymph node of Cloquet, and posteriorly to the internal iliac vessels ( Fig. 70.6 ). This should include the internal iliac, presacral, obturator fossa and external iliac groups of lymph nodes. During pelvic lymph node dissection, caution should be exercised in the obturator fossa to avoid injury to the obturator nerve. The genitofemoral nerve can also be damaged as it runs over the psoas muscle lateral to the external iliac vessels; care must be taken to try to preserve both its genital and femoral branches.

During ureteric reimplantation, a psoas hitch to the tendon of psoas minor or psoas major fascia helps minimize tension at the uretero-neocystotomy anastomosis. Absorbable sutures are placed parallel to the external iliac vessels to avoid injury to the genitofemoral and femoral nerves. This can be combined with a Boari flap, in which an anterior bladder wall flap is used to compensate for a greater loss of distal ureteric length. The posteriorly based convex flap must be kept sufficiently broad to maintain adequate vascularization. The flap is tubularized and closed in continuity with bladder closure. Ligation and division of the contralateral superior vesical artery (identifiable as it crosses the ureter) may be required to increase bladder mobility.

Tips and Anatomical Hazards

• During pelvic lymphadenectomy, dissection lateral to the genitofemoral nerve is associated with an increased risk of lower limb lymphoedema.

• Open cystotomy is facilitated by prior placement of stay sutures because it aids retraction and defines the edges of the opening.

• Absorbable sutures must be used in lower urinary tract surgery because non-absorbable material becomes encrusted when exposed to urine, leading to stone formation and possibly becoming a nidus for infection.

• A pelvic drain is advisable following reconstructive surgery to help identify and manage urine leaks.

• Patients who have had prior lower abdominal surgery may have bowel interposed between the abdominal wall and the bladder, making supra-pubic catherization hazardous.

• The position of the right ureter is much more variable and often takes a lateral course over the external iliac vessels.

• Excessive proximal dissection and mobilization of the ureters during cystectomy can result in ischaemic strictures related to devascularization.