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Bladder, prostate and urethra
Urinary Bladder
The urinary bladder is a reservoir. Its size, shape, position and relations all vary according to its content and the state of the neighbouring viscera. When the bladder is empty, it lies entirely in the lesser pelvis, but as it distends it expands superiorly into the abdominal cavity ( ). An empty bladder is somewhat tetrahedral and has a fundus, body, neck, apex and superior and inferolateral surfaces.
Relations
The fundus of the bladder is triangular and located posteroinferiorly. In females it is closely related to the anterior vaginal wall ( Fig. 73.1 ); in males it is related to the rectum, although it is separated from it superiorly by the rectovesical pouch and inferiorly by the seminal gland (vesicle) and ductus (vas) deferens on each side, and by the prostato-seminal fascia (Denonvilliers’ fascia) ( Fig. 73.2 ). The neck of the bladder, which is most fixed, lies most inferiorly, 3–4 cm behind the lower part of the pubic symphysis and just above the plane of the inferior aperture of the lesser pelvis. Essentially, the neck of the bladder is the internal urethral orifice, which lies in a constant position irrespective of the varying positions of the bladder and rectum. In males the neck rests on and is directly continuous with the base of the prostate; in females it is related to the pelvic fascia that surrounds the upper urethra. In both sexes the apex of the bladder, when not full, faces towards the upper part of the pubic symphysis. The median umbilical ligament (urachus) ascends behind the anterior abdominal wall from the apex of the bladder to the umbilicus, covered by peritoneum to form the median umbilical fold (see below).
The anterior aspect of the urinary bladder is separated from the transversalis fascia by adipose tissue in the potential retropubic space (of Retzius) (see Fig. 73.2D ). This adheres more to the bladder than to the anterior surface of the prostate, which aids reliable identification of the region of the neck of the bladder surgically. In males each inferolateral surface is related anteriorly to the pubis and puboprostatic ligaments. In females the relations are similar, except that the pubovesical ligaments replace the puboprostatic ligaments (see later for a fuller description). The inferolateral surfaces are not covered by peritoneum. The triangular superior surface is bounded by lateral borders from the apex to the ureteric entrances, and by a posterior border that joins them. In males the superior surface is completely covered by peritoneum, which extends slightly on to the fundus and continues posteriorly into the rectovesical pouch and anteriorly into the median umbilical fold; it is in contact with the sigmoid colon and the terminal part of the ileum. In females the superior surface is largely covered by peritoneum, which is reflected posteriorly on to the uterus at the level of the anatomical internal os of the uterus (the junction of the body and isthmus of the uterus) to form the vesico-uterine pouch. The posterior part of the superior surface, devoid of peritoneum, is separated from the supravaginal part of the cervix by fibroareolar tissue.
These relations are important in managing bladder trauma. Extraperitoneal injuries can often be managed conservatively because urine is contained, whereas intraperitoneal injuries usually require surgical repair since urine within the abdominal cavity can cause peritonitis, ileus and infection.
As the bladder fills it becomes ovoid (see ). Anteriorly, it displaces the parietal peritoneum from the suprapubic region of the anterior abdominal wall. Its inferolateral surfaces become anterior and rest against the abdominal wall without intervening peritoneum for a distance above the pubic symphysis that varies with the degree of distension, but is commonly 5–7 cm. If normal catheterization of the urinary bladder via the urethra is unsuccessful, the distended bladder can be punctured just above the pubic symphysis without traversing the peritoneum (suprapubic cystostomy) (see Fig. 73.2A ); surgical access to the bladder through the anterior abdominal wall is usually by this route. The summit of the full bladder points superiorly and anteriorly above the attachment of the median umbilical ligament, so that the peritoneum forms a supravesical fossa of varying depth between the summit and the anterior abdominal wall; this recess often contains coils of small intestine. The bladder is more cranially located at birth than in the adult because the lesser pelvis is shallow, and the internal urethral orifice is level with the upper border of the pubic symphysis. The bladder is then abdominal rather than pelvic and extends about two-thirds of the distance towards the umbilicus.
Urine samples can, therefore, be obtained in children by performing suprapubic needle puncture. A normogram of bladder volume index (BVI=length×width×depth of bladder), based on sonographic measurements in children, is shown in Fig. 73.3 . The bladder progressively descends with growth and reaches the adult position shortly after puberty.
Ligaments of the urinary bladder
The urinary bladder is anchored anteroinferiorly to the pubis, lateral pelvic side walls and rectum by condensations of pelvic fascia ( Fig. 73.4 ); although these condensations are not true anatomical ligaments, the term is applied in routine clinical use (see Ch. 71 for a further description of the visceral pelvic fascia).
In both sexes, stout bands of multilayered fibromuscular tissue, the puboprostatic (males only) and pubovesical ligaments, extend from the neck of the bladder to the inferior aspect of the pubis; they lie on each side of the median plane, leaving a midline urogenital hiatus through which numerous small veins pass. The puboprostatic and pubovesical ligaments have been variously and somewhat confusingly described in the literature. In the Terminologia Anatomica , both ligaments are listed as having medial and lateral components; the pubovesical ligament (presumably both medial and lateral parts) is also listed as synonymous with the medial puboprostatic ligament. Cadaveric dissection, histological and plastinated section studies (e.g. ) have identified the puboprostatic ligament as the anterior layer of the detrusor apron joined by decussated and un-decussated fibres of pubococcygeus; or part of the detrusor apron connecting the bladder to the pubic bone; or the merged fibres of the visceral endopelvic fascia. The pubovesical ligaments have been described as either an extension of the detrusor and its adventitia that is attached to the pubic bone and arcus tendineus fasciae pelvis, or the female equivalent of the medial puboprostatic ligaments, and either separate from the pubo-urethral ligaments or the superior extensions of the pubo-urethral ligaments.
The apex of the bladder is connected to the umbilicus by the remains of the urachus, which forms the median umbilical ligament ( ). The urachus is composed of longitudinal muscle fibres derived from detrusor and becomes more fibrous towards the umbilicus. It usually maintains a lumen lined with epithelium that persists into adult life but is only rarely complicated by a urachal cyst, sinus, fistula or adenocarcinoma.
The urachus could be critical for maintaining fetal life when atresia of the urethra results in complete obstruction to the flow of amniotic fluid. Anhydramnios noted at 17 weeks’ gestation has been reported to resolve by 21 weeks when the patent urachus acts as a fistula between the bladder and the amniotic cavity, preserving pulmonary and renal function ( ).
Other ligaments that have been described in relation to the fundus of the urinary bladder are the lateral, uterosacral and cardinal ligaments. The lateral ligament was described by : although never described in anatomical cadaveric dissection studies, it is recognized clinically as an important structure in the pararectal fossa at operation. It is a broad band of dense connective tissue, ranging in depth from 5 to 7 cm, and passing between the lateral wall of the pelvis and the fundus of the bladder at the point where the ureter terminates. It contains the middle anorectal artery and lymphatic vessels that pass from the distal rectum to the iliac nodes ( ). From the superior surface of the bladder, the peritoneum is carried off in a series of folds: the ‘false’ ligaments of the bladder. Anteriorly, there are three folds ( Fig. 73.5 ): the median umbilical fold over the median umbilical ligament (urachus), and two medial umbilical folds over the occluded parts of the umbilical arteries. The inferior epigastric vessels ( Fig. 73.6 ) are lateral to these folds on the anterior abdominal wall and when covered with peritoneum are termed lateral umbilical ligaments.
Urinary bladder interior
Mucosa of the bladder
Almost all of the bladder mucosa is attached only loosely to subjacent muscle ( Fig. 73.7 ); it folds when the bladder empties, and the folds are stretched flat as it fills. Over the trigone of the bladder, immediately above and behind the internal urethral orifice, it is adherent to the subjacent muscle layer and is always smooth. The anteroinferior angle of the trigone is formed by the internal urethral orifice, its posterolateral angles by the ureteric orifices. The superior boundary of the trigone is a slightly curved interureteric crest, which connects the two ureteric orifices and is produced by the continuation into the bladder wall of the ureteric internal longitudinal muscle. During cystoscopy, the interureteric crest appears as a pale band and is a guide to the ureteric orifices (see Fig. 73.7A, B ).
Trigone of the bladder
The smooth muscle of the trigone consists of two distinct layers, sometimes termed superficial trigone and deep trigone muscles. The latter is composed of muscle cells indistinguishable from those of detrusor, and is simply the posteroinferior portion of detrusor proper. The superficial trigone muscle represents a morphologically distinct component of the trigone, which, unlike detrusor, is composed of relatively small-diameter muscle bundles that are continuous proximally with those of the intramural ureters. It is relatively thin but is generally described as becoming thickened along its superior border to form the interureteric crest. Similar thickenings occur along the lateral edges of the superficial trigone. In both sexes, the superficial trigone muscle becomes continuous with the smooth muscle of the proximal urethra, and extends in the male along the urethral crest as far as the openings of the ejaculatory ducts.
Ureteric orifices and distal ureter
The slit-like ureteric orifices are placed at the posterolateral corners of the trigone of the bladder (see Figs 73.2B, 73.7A ). In empty bladders they are approximately 2.5 cm apart and 2.5 cm from the internal urethral orifice; these measurements can be doubled when the bladder is distended. The distal 1.5–2.0 cm of the ureter (intramural part) passes obliquely through the bladder wall before ending as the ureteric orifices. As the bladder fills and intravesical hydrostatic pressure increases, the distal ureter is compressed and acts like a flap valve preventing reflux of urine toward the kidney.
Internal urethral orifice
The internal urethral orifice is sited at the apex of the trigone of the bladder, the lowest part of this organ, and is usually somewhat crescentic in section. There is often an elevation immediately behind it in adult males (particularly past middle age), which is caused by the prostate.
Neck of the bladder
The smooth muscle of the neck of the bladder is histologically, histochemically and pharmacologically distinct from detrusor proper, so the neck of the bladder should be considered as a separate functional unit. Males and females have quite different arrangements of smooth muscle in this region, and will be described separately.
Females
In females the neck of the bladder consists of morphologically distinct smooth muscle (see Fig. 73.7C ). The large-diameter fasciculi characteristic of detrusor are replaced by small-diameter fasciculi that extend obliquely or longitudinally into the urethral wall. In the normal female the neck of the bladder sits above the pelvic diaphragm, supported predominantly by the pubovesical ligaments (see Fig. 73.4A ), the endopelvic fascia of the pelvic diaphragm and levator ani. These structures support the urethra at rest; with elevated intra-abdominal pressure, the pelvic diaphragm contracts, increasing urethral closure pressure to maintain continence. This anatomical arrangement commonly alters after parturition and with increasing age, such that the neck of the bladder lies beneath the pelvic diaphragm, particularly when intra-abdominal pressure rises. This means that the mechanism described above fails to maintain continence and females can experience stress incontinence ( ).
Males
In males the neck of the bladder is completely surrounded by a circular collar of smooth muscle with its own distinct adrenergic innervation, which extends distally to surround the intramural part of the urethra. These smooth muscle bundles are distinct from those that run in continuity from the neck of the bladder down to the prostatic urethra, and from the smooth muscle within the prostate. The bundles that form the internal urethral (preprostatic) sphincter are small compared with the muscle bundles of detrusor, and are separated by a relatively large connective tissue component rich in elastic fibres.
The neck of the bladder is sometimes called the proximal or internal urethral sphincter mechanism, to distinguish it from the distal or external urethral sphincter. The internal urethral sphincter contributes to urinary continence and, in the face of distal sphincteric incompetence, can at times maintain continence independently. Unlike detrusor and the rest of the urethral smooth muscle (in males and females), the internal urethral sphincter is richly supplied with sympathetic noradrenergic nerves and is almost totally devoid of parasympathetic cholinergic nerves (see below).
Urinary bladder outflow obstruction
The muscle of the bladder hypertrophies in progressive chronic obstruction to micturition, e.g. as a result of prostatic enlargement or urethral stricture, or in children with congenital bladder outflow obstruction, e.g. posterior urethral valves. The muscle fasciculi increase in size and, because they interlace in all directions, a thick-walled ‘trabeculated bladder’ is produced (see Fig. 73.7D ). Mucosa between the fascicles forms ‘diverticula’ owing to the increased intravesical pressure required to pass urine through the obstruction. When outflow is obstructed, emptying may not be complete; some urine can remain and lead to infection and stone formation within the bladder. Back-pressure from a chronically distended bladder can gradually dilate the ureters, renal pelves and even the renal collecting ducts bilaterally and can result in progressive renal impairment.
Vascular supply and lymphatic drainage
Arteries
The bladder is supplied principally by the superior and inferior vesical arteries (see Figure 75.3, Figure 72.20C ), derived from the anterior division of the internal iliac artery and supplemented by the obturator and inferior gluteal arteries. In females, additional branches are derived from the uterine and vaginal arteries.
Superior vesical artery
The superior vesical artery arises from the patent part of the umbilical artery. It supplies many branches to the fundus of the bladder. The artery to the ductus deferens often originates from one of these branches and accompanies the ductus deferens to the testis, where it anastomoses with the testicular artery. Other branches of the superior vesical artery supply the ureter.
Inferior vesical artery
The inferior vesical artery often arises with the middle anorectal artery from the internal iliac artery. It supplies the fundus of the bladder, prostate, seminal glands and distal ureter, and sometimes provides the artery to the ductus deferens. Branches to the prostate communicate across the midline.
Veins
The veins that drain the bladder form a complicated plexus on its inferolateral surfaces and pass backwards in the lateral ligaments of the bladder to end in the internal iliac veins (see Fig. 75.3 ).
Lymphatic drainage
Lymphatics that drain the bladder begin in mucosal, intermuscular and adventitial plexuses (see Fig. 75.3 ). There are three sets of collecting vessels; most end in the external iliac nodes. Vessels from the trigone emerge on the exterior of the bladder to run superolaterally. Vessels from the superior surface of the bladder converge to the posterolateral angle and pass superolaterally to the external iliac nodes (some might drain to the internal or common iliac nodes). Vessels from the inferolateral surface of the bladder ascend to join those from the superior surface or run to the lymph nodes in the obturator fossa. Minute nodules of lymphoid tissue can occur along the lymph vessels of the bladder.
Innervation
The nerves supplying the bladder arise from the inferior hypogastric plexus, a mesh of autonomic nerves and ganglia lying on the lateral aspects of the rectum, internal genitalia and fundus of the bladder ( Fig. 73.8 ). They consist of both sympathetic and parasympathetic components. For further reading, see .
Efferent fibres
Parasympathetic fibres arise from the second to the fourth sacral segments of the spinal cord and enter the inferior hypogastric plexus on the posterolateral aspects of the rectum as the pelvic splanchnic nerves. The sympathetic fibres are derived from neuronal cell bodies in the lower three thoracic and upper two lumbar segments of the spinal cord and form the coeliac and mesenteric plexuses in the abdomen; from here, the superior hypogastric plexus descends into the pelvis as fairly discrete nerve bundles within the extraperitoneal connective tissue posterior to the ureter on each side. The anterior part of the inferior hypogastric plexus is known as the vesical plexus. Small groups of autonomic neurones occur within the plexus and throughout all regions of the bladder wall. These multipolar intramural neurones are rich in acetylcholinesterase (AChE) and occur in ganglia containing up to 20 neuronal cell bodies. Most of the preganglionic nerve terminals correspond morphologically to presumptive cholinergic fibres. Noradrenergic terminals also relay on cell bodies in the inferior hypogastric plexus; it is not known whether similar nerves synapse on intramural bladder ganglia.
The urinary bladder is profusely supplied with nerves, which form a dense plexus among detrusor muscle cells. Most of these nerves contain AChE and are abundant throughout the muscle layer of the bladder. Axonal varicosities adjacent to detrusor muscle cells possess features that are considered to typify cholinergic nerve terminals, and contain clusters of small (50 nm diameter) agranular vesicles, occasional large (80–160 nm diameter) granulated vesicles and small mitochondria. Terminal regions approach to within 20 nm of the surface of the muscle cells and can be partially surrounded by Schwann cell cytoplasm; more often they are naked nerve endings.
Detrusor possesses a sparse but definite supply of sympathetic noradrenergic nerves that generally accompany the vascular supply and only rarely extend among the myocytes. Non-adrenergic, non-cholinergic nerves have been identified, and a number of other neurotransmitters or neuromodulators have been detected in intramural ganglia, including the peptide somatostatin. The superficial trigone muscle is associated with more noradrenergic (sympathetic) fibres than cholinergic (parasympathetic) nerves, a difference that supports the view that the superficial trigone muscle should be regarded as ‘ureteric’ rather than ‘vesical’ in origin. However, it should be emphasized that this muscle forms a very minor part of the total muscle mass of the neck of the bladder and proximal urethra in either sex and is probably of little significance in the physiological mechanisms that control these regions.
The smooth muscle of the neck of the bladder in males is predominantly orientated obliquely or circularly. It is sparsely supplied with cholinergic (parasympathetic) nerves but possesses a rich noradrenergic (sympathetic) innervation. There is a similar distribution of autonomic nerves in the smooth muscle of the prostate, seminal glands and ducti deferentia. Stimulation of sympathetic nerves causes contraction of smooth muscle in the wall of the genital tract, resulting in seminal emission. Concomitant sympathetic stimulation of the proximal urethral smooth muscle causes sphincteric closure of the internal urethral sphincter, preventing reflux of ejaculate into the bladder.
The neck of the bladder is disrupted in the vast majority of men undergoing transurethral resection of the prostate and this can result in retrograde ejaculation. Similarly, an ejaculation can result when the sympathetic fibres are disrupted during retroperitoneal lymph node dissection surgery. Although this genital function of the neck of the bladder of the male is well established, it is not known whether the smooth muscle of this region contributes actively to the maintenance of urinary continence. In contrast, in females the smooth muscle of the neck of the bladder contains relatively few noradrenergic nerves but is richly supplied with cholinergic fibres. The sparse supply of sympathetic nerves presumably relates to the absence of a functioning ‘genital’ portion of the wall of the female urethra.
The lamina propria of the fundus and inferolateral walls of the bladder is virtually devoid of autonomic nerve fibres, apart from some noradrenergic and occasional cholinergic perivascular nerves. However, the density of nerves unrelated to blood vessels increases closer to the internal urethral orifice. At the neck of the bladder and trigone a nerve plexus of cholinesterase-positive axons extends throughout the lamina propria, independent of blood vessels. Some of the larger diameter axons are myelinated and others lie adjacent to the basal urothelial cells. In the absence of any obvious effector target sites, the subepithelial nerve plexuses of the bladder and the ureter are assumed to subserve a sensory function.
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