Tuesday, August 12, 2008


The rectum begins with the disappearance of the sigmoid mesentery opposite the third sacral vertebra. Peritoneum continues anteriorly over the upper two thirds of the rectum as the rectovesical pouch in males and as the rectouterine pouch (of Douglas) in females ( Fig. 2-23 ; see also Fig. 2-11 ). This peritoneal pouch extends inferiorly to the seminal vesicles or to the posterior fornix of the vagina. Inferior to this pouch, the anterior rectum is related to its fascial continuation (the rectogenital or Denonvilliers' fascia) down to the level of the striated urethral sphincter (see Figs. 2-3, 2-23, and 2-33 [3] [23] [33]). The rectum describes a gentle curve on the sacrum, coccyx, and levator plate (see Fig. 2-21 ) and receives innervation from the laterally placed pelvic autonomic plexus and blood supply from the superior (from inferior mesenteric), middle (from internal iliac), and inferior (from internal pudendal) rectal arteries.

Figure 2-23 Sagittal section through the prostatic and membranous urethra, demonstrating the midline relations of the pelvic structures. (From Hinman F Jr: Atlas of Urosurgical Anatomy. Philadelphia, WB Saunders, 1993, p 356.)

Figure 2-33 Median sagittal section of the female pelvis, showing the potential spaces between the pelvic organs. The posterior two thirds of the vagina lie nearly horizontal and rest with the uterine cervix on the rectum, which is in turn supported by the posterior portion of levator ani (the levator plate, not shown). RVS, rectovaginal space, the anterior wall is formed by the rectovaginal (Denonvilliers') fascia; SVSe, supravaginal septum, the fusion between the bladder and cervix; VCS, vesicocervical space; VVS, vesicovaginal space. (From Nichols DH, Randall CL: Vaginal Surgery, 3rd ed. Baltimore, Williams & Wilkins, 1989, p 34.)

The rectal wall is composed of an inner layer of circular smooth muscle and a virtually continuous sheet of outer longitudinal smooth muscle derived from the tenia of the colon. In its lowest part, the rectum dilates to form the rectal ampulla. At the most inferior portion of the ampulla, anterior fibers of the longitudinal muscle leave the rectum to join Denonvilliers' fascia and the posterior striated urethral sphincter in the apex of the perineal body ( Brooks et al, 2002 ). When approached from below, these fibers, the rectourethralis muscle, are 2 to 10 mm thick and must be divided to gain access to the prostate (see Fig. 2-36 ). The apices of the prostate and ampulla are in close proximity, and rectal injuries during radical prostatectomy commonly occur at this location. As the rectourethralis is given off, the rectum makes a right-angle turn posteroinferiorly to exit the pelvis at the anal canal (see Fig. 2-10 ). The anatomy of the anal canal is considered with the perineum.

Figure 2-36 Muscles and superficial fasciae of the male perineum. (From Hinman F Jr: Atlas of Urosurgical Anatomy. Philadelphia, WB Saunders, 1993, p 219.)

Pelvic Ureter

The ureter is divided into abdominal and pelvic portions by the common iliac artery. The structure of the ureter and its abdominal course are reviewed in Chapter 1 , Surgical Anatomy of the Retroperitoneum, Kidneys, and Ureters. Intraoperatively, the ureter is identified by its peristaltic waves and is readily found anterior to the bifurcation of the common iliac artery. At ureteroscopy, pulsations of this artery can be seen in the posterior ureteral wall. The ovarian vessels (infundibulopelvic ligament) cross the iliac vessels anterior and lateral to the ureter, and dissection of the ovarian vessels at the pelvic brim is a common cause of ureteral injury (see Fig. 2-13 ) ( Daly and Higgins, 1988 ). Pyeloureterography discloses a narrowing of the ureter at the iliac vessels, and ureteral calculi frequently become lodged at this location. Because the ureter and iliac vessels rest on the arcuate line, the ureter is subject to compression and obstruction by the gravid uterus and by masses within the true pelvis.

The ureters come within 5 cm of each other as they cross the iliac vessels. On entering the pelvis, they diverge widely along the pelvic side walls toward the ischial spines. The ureter travels on the anterior surface of the internal iliac vessels and is related laterally to the branches of the anterior trunk. Near the ischial spine, the ureter turns anteriorly and medially to reach the bladder. In males, the anteromedial surface of the ureter is covered by peritoneum, and the ureter is embedded in retroperitoneal connective tissue, which varies in thickness (see Fig. 2-13 ). As the ureter courses medially, it is crossed anteriorly by the vas deferens and runs with the inferior vesical arteries, veins, and nerves in the lateral vesical ligaments. Viewed from the peritoneal side, the ureter is just lateral and deep to the rectogenital fold. In females, the ureter first runs posterior to the ovary and then turns medially to run deep to the base of the broad ligament before entering a loose connective tissue tunnel through the substance of the cardinal ligament (see Fig. 2-13 ). As in the male, the ureter can be found slightly lateral and deep to the rectouterine folds of peritoneum. It is crossed anteriorly by the uterine artery and is therefore subject to injury during hysterectomy. As it passes in front of the vagina, it crosses 1.5 cm anterior and lateral to the uterine cervix. The ureter may be injured at this level during hysterectomy, resulting in a ureterovaginal fistula. The ureter courses 1 to 4 cm on the anterior vaginal wall to reach the bladder. Occasionally, a stone lodged in the distal ureter can be palpated through the anterior vaginal wall. The intramural ureter is discussed in the section on the bladder.

The pelvic ureter receives abundant blood supply from the common iliac artery and most branches of the internal iliac artery. The inferior vesical and uterine arteries usually supply the ureter with its largest pelvic branches. Blood supply to the pelvic ureter enters laterally; thus, the pelvic peritoneum should be incised only medial to the ureter. Intramural vessels of the ureter run within the adventitia and generally follow one of two patterns. In approximately 75% of specimens, longitudinal vessels run the length of the ureter and are formed by anastomoses of segmental ureteral vessels. In the remaining ureters, the vessels form a fine interconnecting mesh (plexiform) with less collateral flow ( Shafik, 1972 ). The pelvic ureter appears to have a high preponderance of plexiform vessels, which render it more susceptible to ischemia and less suitable for ureteroureterotomy ( Hinman, 1993 ). Lymphatic drainage of the pelvic ureter is to the external, internal, and common iliac nodes. Pathologic enlargement of the common and internal iliac nodes can encroach on and obstruct the ureter.

The pelvic ureter has rich adrenergic and cholinergic autonomic innervation derived from the pelvic plexus. The functional significance of this innervation is unclear, inasmuch as the ureter continues to contract peristaltically after denervation. Afferent neural fibers travel through the pelvic plexus and account for the visceral quality of referred pain from ureteral irritation or acute obstruction.

Bladder Anatomic Relationships

When filled, the bladder has a capacity of approximately 500 mL and assumes an ovoid shape. The empty bladder is tetrahedral and is described as having a superior surface with an apex at the urachus, two inferolateral surfaces, and a posteroinferior surface or base with the bladder neck at the lowest point (see Fig. 2-23 ).

The urachus anchors the bladder to the anterior abdominal wall (see Fig. 2-8 ). There is a relative paucity of bladder wall muscle at the point of attachment of the urachus, predisposing to formation of diverticula. The urachus is composed of longitudinal smooth muscle bundles derived from the bladder wall. Near the umbilicus, it becomes more fibrous and usually fuses with one of the obliterated umbilical arteries. 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 ( Begg, 1930 ). In rare instances, luminal continuity with the bladder serves as a bacterial reservoir or results in an umbilical urinary fistula.

The superior surface of the bladder is covered by peritoneum. Anteriorly, the peritoneum sweeps gently onto the anterior abdominal wall (see Fig. 2-13 ). 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 side wall by retropubic and perivesical fat and loose connective tissue. This potential space (of Retzius) may be entered anteriorly by dividing the transversalis fascia and provides access to the pelvic viscera as far posteriorly as the iliac vessels and ureters (see Fig. 2-11 ). The bladder base is related to the seminal vesicles, ampullae of the vas deferentia, and terminal ureter. The bladder neck, located at the internal urethral meatus, rests 3 to 4 cm behind the midpoint of the symphysis pubis. It is firmly fixed by the pelvic fasciae (see earlier discussion) and by its continuity with the prostate; its position changes little with varying conditions of the bladder and rectum.

In the female, the peritoneum on the superior surface of the bladder is reflected over the uterus to form the vesicouterine pouch and then continues posteriorly over the uterus as the rectouterine pouch (see Fig. 2-13 ). The vagina and uterus intervene between the bladder and the rectum, so that the base of the bladder and urethra rest on the anterior vaginal wall. Because the anterior vaginal wall is firmly attached laterally to the levator ani, contraction of the pelvic diaphragm (e.g., during increases in intra-abdominal pressure) elevates the bladder neck and draws it anteriorly. In many women with stress incontinence, the bladder neck drops below the pubic symphysis. In infants, the true pelvis is shallow and the bladder neck is level with the upper border of the symphysis. The bladder is a true intra-abdominal organ that can project above the umbilicus when full. By puberty, the bladder has migrated to the confines of the deepened true pelvis.


The internal surface of the bladder is lined with transitional epithelium, which appears smooth when the bladder is full but contracts into numerous folds when the bladder empties. This urothelium is usually six cells thick and rests on a thin basement membrane. Deep to this, the lamina propria forms a relatively thick layer of fibroelastic connective tissue that allows considerable distention. This layer is traversed by numerous blood vessels and contains smooth muscle fibers collected into a poorly defined muscularis mucosa. Beneath this layer lies the smooth muscle of the bladder wall. The relatively large muscle fibers form branching, interlacing bundles loosely arranged into inner longitudinal, middle circular, and outer longitudinal layers ( Fig. 2-24 ). However, in the upper aspect of the bladder, these layers are clearly not separable, and any one fiber can travel between each of the layers, change orientation, and branch into longitudinal and circular fibers. This meshwork of detrusor muscle is ideally suited for emptying the spherical bladder.

Figure 2-24 Dissection of the male bladder. 11, Posterior outer longitudinal detrusor, which forms the backing of the ureters (folded back); 11a, posterolateral portion of the outer longitudinal muscle forming a loop around the anterior bladder neck; 4′, 12, and 18, middle circular layer backing the trigone; 23 and 23a, lateral pedicle of the prostate. (From Uhlenhuth E: Problems in the Anatomy of the Pelvis. Philadelphia, JB Lippincott, 1953, p 187.)

Near the bladder neck, the detrusor muscle is clearly separable into the three layers described earlier. Here, the smooth muscle is morphologically and pharmacologically distinct from the remainder of the bladder, because the large-diameter muscle fascicles are replaced by much finer fibers. The structure of the bladder neck appears to differ between men and women. In men, radially oriented inner longitudinal fibers pass through the internal meatus to become continuous with the inner longitudinal layer of smooth muscle in the urethra.

The middle layer forms a circular preprostatic sphincter that is responsible for continence at the level of the bladder neck ( Fig. 2-25 ). The bladder wall posterior to the internal urethral meatus and the anterior fibromuscular stroma of the prostate form a continuous ringlike structure at the bladder neck ( Brooks et al, 1998 ). The fact that perfect continence can be maintained in men in whom the striated urethral sphincter is destroyed attests to the efficacy of this sphincter ( Waterhouse et al, 1973 ). This muscle is richly innervated by adrenergic fibers, which, when stimulated, produce closure of the bladder neck ( Uhlenhuth, 1953 ). Damage to the sympathetic nerves to the bladder, as a result of diabetes mellitus or retroperitoneal lymph node dissection for testis cancer, can cause retrograde ejaculation.

Figure 2-25 Structure of the male bladder neck and trigone. A, Anterior view reveals that the trigone narrows below the ureteral orifices and then widens at the bladder neck to become continuous with the anterior fibromuscular stroma of the prostate. B, Lateral projection shows that the trigone and anterior fibromuscular stroma are in continuity. The trigone thickens near the bladder neck as it meets the anterior fibromuscular stroma. C, Oblique view shows this structure at the bladder neck, where it forms the internal urethral sphincter. (From Brooks JD, Chao W-M, Kerr J: Male pelvic anatomy reconstructed from the Visible Human data set. J Urol 1998;159:868-872.)

The outer longitudinal fibers are thickest posteriorly at the bladder base. In the midline, they insert into the apex of the trigone and intermix with the smooth muscle of the prostate to provide a strong trigonal backing. Laterally, the fibers from this posterior sheet pass anteriorly and fuse to form a loop around the bladder neck (see Fig. 2-24 ). This loop is thought to participate in continence at the bladder neck. On the lateral and anterior surfaces of the bladder, the longitudinal fibers are not as well developed. Some anterior fibers course forward to join the puboprostatic ligaments in men and the pubourethral ligaments in women. These fibers contribute smooth muscle to these supports and are speculated to contribute to bladder neck opening during micturition ( DeLancey, 1989 ).

At the female bladder neck, the inner longitudinal fibers converge radially to pass downward as the inner longitudinal layer of the urethra, as described earlier. The middle circular layer does not appear to be as robust as that of the male, and several authors have denied its existence altogether (Gosling, 1979, 1985 [22] [23]; Williams et al, 1989 ). Whereas several other investigators have noted an anterior loop of external longitudinal muscle (see Fig. 2-32 ), the authors just cited deny the existence of this structure as well. They maintain instead that the external fibers pass obliquely and longitudinally down the urethra to participate in forming the inner longitudinal layer of smooth muscle. Regardless, the female bladder neck differs strikingly from the male in possessing little adrenergic innervation. In addition, its sphincteric function is limited; in 50% of continent women, urine enters the proximal urethra during a cough ( Versi et al, 1986 ).

Figure 2-32 Female bladder and striated urethral sphincter. a, Diagram of striated urethral sphincter showing disposition of the muscle fibers. 1, The proximal third of the sphincter encircles the urethra entirely. 2, The middle bundles surround the urethra in front and pass off the lateral sides to blend with the vaginal wall (compressor urethrae). 3, The distal portion surrounds the urethra and vagina together and has been called the urethrovaginal sphincter. The bulbocavernosus also acts as a sphincter around the vaginal vestibule. b, Urethral sphincter in its entirety. The relationship of the pelvic viscera is shown. Interlacing detrusor fibers are also demonstrated. c, Posterolateral outer longitudinal detrusor muscle looping anterior to the bladder neck. Inner longitudinal smooth muscle fibers run the length of the urethra, deep to the striated sphincter. d, Cross section of the urethra, showing thick, highly vascularized lamina propria and folded mucosa, which act as a urethral seal. Longitudinal smooth muscle surrounds the lamina propria. (From the Brödel Archives, Johns Hopkins School of Medicine, Baltimore.)

Ureterovesical Junction and the Trigone

As the ureter approaches the bladder, its spirally oriented mural smooth muscle fibers become longitudinal. Two to 3 cm from the bladder, a fibromuscular sheath (of Waldeyer) extends longitudinally over the ureter and follows it to the trigone ( Tanagho, 1992 ). The ureter pierces the bladder wall obliquely, travels 1.5 to 2 cm, and terminates at the ureteral orifice ( Fig. 2-26 ). As it passes through a hiatus in the detrusor (intramural ureter), it is compressed and narrows considerably. This is a common site in which ureteral stones become impacted. The intravesical portion of the ureter lies immediately beneath the bladder urothelium and therefore is quite pliant; it is backed by a strong plate of detrusor muscle. With bladder filling, this arrangement is thought to result in passive occlusion of the ureter, like a flap valve. Indeed, reflux does not occur in fresh cadavers when the bladder is filled ( Thomson et al, 1994 ). Vesicoureteral reflux is thought to result from insufficient submucosal ureteral length and poor detrusor backing. Chronic increases in intravesical pressure resulting from bladder outlet obstruction can cause herniation of the bladder mucosa through the weakest point of the hiatus above the ureter and produce a “Hutch diverticulum” and reflux ( Hutch et al, 1961 ).

Figure 2-26 Normal ureterovesical junction and trigone. A, Section of the bladder wall perpendicular to the ureteral hiatus shows the oblique passage of the ureter through the detrusor and also shows the submucosal ureter with its detrusor backing. Waldeyer's sheath surrounds the prevesical ureter and extends inward to become the deep trigone. B, Waldeyer's sheath continues in the bladder as the deep trigone, which is fixed at the bladder neck. Smooth muscle of the ureter forms the superficial trigone and is anchored at the verumontanum. (From Tanagho EA, Pugh RC: The anatomy and function of the ureterovesical junction. Br J Urol 1963;35:151-165.)

The triangle of smooth urothelium between the two ureteral orifices and the internal urethral meatus is referred to as the trigone of the bladder (see Fig. 2-26 ). The fine longitudinal smooth muscle fibers from the vesical side of the ureters pass to either side of their respective orifices to join the lateral and posterior ureteral wall fibers and fan out over the base of the bladder. Fibers from each ureter meet to form a triangular sheet of muscle that extends from the two ureteral orifices to the internal urethral meatus. The edges of this muscular sheet are thickened between the ureteral orifices (the interureteric crest or Mercier's bar) and between the ureters and the internal urethral meatus (Bell's muscle).

The muscle of trigone forms three distinct layers: (1) a superficial layer, derived from the longitudinal muscle of the ureter, which extends down the urethra to insert at the verumontanum; (2) a deep layer, which continues from Waldeyer's sheath and inserts at the bladder neck; and (3) a detrusor layer, formed by the outer longitudinal and middle circular smooth muscle layers of the bladder wall. Through its continuity with the ureter, the superficial trigonal muscle anchors the ureter to the bladder. During ureteral reimplantation, this muscle is tented up and divided to gain access to the space between Waldeyer's sheath and the ureter. In this space, only loose fibrous and muscular connections are found. This anatomic arrangement helps prevent reflux during bladder filling by fixing and applying tension to the ureteral orifice. As the bladder fills, its lateral wall telescopes outward on the ureter, thereby increasing intravesical ureteral length ( Hutch et al, 1961 ).

The urothelium overlying the muscular trigone is usually only three cells thick and adheres strongly to the underlying muscle by a dense lamina propria. During filling and emptying of the bladder, this mucosal surface remains smooth.

Bladder Circulation

In addition to the vesical branches, the bladder may be supplied by any adjacent artery arising from the internal iliac artery. For convenience, surgeons refer to the vesical blood supply as the lateral and posterior pedicles, which, when the bladder is approached from the rectovesical space, are lateral and posteromedial to the ureters, respectively. These pedicles are the lateral and posterior vesical ligaments in the male and part of cardinal and uterosacral ligaments in the female (see Fig. 2-13 ). The veins of the bladder coalesce into the vesicle plexus and drain into the internal iliac vein. Lymphatics from the lamina propria and muscularis drain to channels on the bladder surface, which run with the superficial vessels within the thin visceral fascia. Small paravesical lymph nodes can be found along the superficial channels. The bulk of the lymphatic drainage passes to the external iliac lymph nodes (see Fig. 2-18 ). Some anterior and lateral drainage may go through the obturator and internal iliac nodes, whereas portions of the bladder base and trigone may drain into the internal and common iliac groups.

Bladder Innervation

Autonomic efferent fibers from the anterior portion of the pelvic plexus (the vesical plexus) pass up the lateral and posterior ligaments to innervate the bladder. The bladder wall is richly supplied with parasympathetic cholinergic nerve endings and has abundant postganglionic cell bodies. Sparse sympathetic innervation of the bladder has been proposed to mediate detrusor relaxation but probably lacks functional significance. A separate nonadrenergic, noncholinergic (NANC) component of the autonomic nervous system participates in activating the detrusor, although the neurotransmitter has not been identified ( Burnett, 1995 ). As mentioned, the male bladder neck receives abundant sympathetic innervation and expresses α-adrenergic receptors. The female bladder neck has little adrenergic innervation. Nitric oxide synthase–containing neurons have been identified in the detrusor, particularly at the bladder neck, where they may facilitate relaxation during micturition. The trigonal muscle is innervated by adrenergic and nitric oxide synthase–containing neurons. Like the bladder neck, it relaxes during micturition. Afferent innervation from the bladder travels with both sympathetic (via the hypogastric nerves) and parasympathetic nerves to reach cell bodies in the dorsal root ganglia located at thoracolumbar and sacral levels. As a consequence, presacral neurectomy (division of the hypogastric nerves) is ineffective in relieving bladder pain.

Prostate Anatomic Relationships

The normal prostate weighs 18 g; measures 3 cm in length, 4 cm in width, and 2 cm in depth; and is traversed by the prostatic urethra (see Fig. 2-23 ). Although ovoid, the prostate is referred to as having anterior, posterior, and lateral surfaces, with a narrowed apex inferiorly and a broad base superiorly that is contiguous with the base of the bladder. It is enclosed by a capsule composed of collagen, elastin, and abundant smooth muscle. Posteriorly and laterally, this capsule has an average thickness of 0.5 mm, although it may be partially transgressed by normal glands. Microscopic bands of smooth muscle extend from the posterior surface of the capsule to fuse with Denonvilliers' fascia. Loose areolar tissue defines a thin plane between Denonvilliers' fascia and the rectum. On the anterior and anterolateral surfaces of the prostate, the capsule blends with the visceral continuation of endopelvic fascia. Toward the apex, the puboprostatic ligaments extend anteriorly to fix the prostate to the pubic bone (see Fig. 2-40 ). The superficial branch of the dorsal vein lies outside this fascia in the retropubic fat and pierces it to drain into the dorsal vein complex.

Laterally, the prostate is cradled by the pubococcygeal portion of levator ani and is directly related to its overlying endopelvic fascia (see Figs. 2-8 and 2-10 [8] [10]). Below the juncture of the parietal and visceral endopelvic fascia (arcus tendineus fascia pelvis), the pelvic fascia and prostate capsule separate and the space between them is filled by fatty areolar tissue and the lateral divisions of the dorsal vein complex. During a radical retropubic prostatectomy, the endopelvic fascia should be divided lateral to the arcus tendineus fascia pelvis to avoid injury to the venous complex. In the process, the endopelvic fascia overlying the levator ani is actually peeled off the muscle and displaced medially with the prostate. Although this is truly a parietal endopelvic fascia, it is commonly referred to as the “lateral prostatic fascia” ( Myers, 1994 ). As mentioned earlier, the cavernosal nerves run posterolateral to the prostate in the substance of the parietal pelvic fascia (lateral prostatic fascia). Thus, to preserve these nerves, this fascia must be incised lateral to the prostate and anterior to the neurovascular bundle ( Walsh et al, 1983 ).

The apex of the prostate is continuous with the striated urethral sphincter (see Fig. 2-30 ). Histologically, normal prostatic glands can be found to extend into the striated muscle with no intervening fibromuscular stroma or “capsule.” At the base of the prostate, outer longitudinal fibers of the detrusor fuse and blend with the fibromuscular tissue of the capsule. As mentioned, the middle circular and inner longitudinal muscles extend down the prostatic urethra as a preprostatic sphincter. As with the apex, no true capsule separates the prostate from the bladder. In surgically resected prostate carcinomas, this peculiar anatomic arrangement can make interpretation of these margins difficult and has led some pathologists to propose that the prostate does not possess a true capsule ( Epstein, 1989 ).


The prostate is composed of approximately 70% glandular elements and 30% fibromuscular stroma. The stroma is continuous with capsule and is composed of collagen and abundant smooth muscle. It encircles and invests the glands of the prostate and contracts during ejaculation to express prostatic secretions into the urethra.

The urethra runs the length of the prostate and is usually closest to its anterior surface. It is lined by transitional epithelium, which may extend into the prostatic ducts. The urothelium is surrounded by an inner longitudinal and an outer circular layer of smooth muscle. A urethral crest projects inward from the posterior midline, runs the length of the prostatic urethra, and disappears at the striated sphincter ( Fig. 2-27 ). To either side of this crest, a groove is formed (prostatic sinuses) into which all glandular elements drain ( McNeal, 1972 ). At its midpoint, the urethra turns approximately 35 degrees anteriorly, but this angulation can vary from 0 to 90 degrees (see Figs. 2-23, 2-25, and 2-28 [23] [25] [28]). This angle divides the prostatic urethra into proximal (preprostatic) and distal (prostatic) segments that are functionally and anatomically discrete (McNeal, 1972, 1988 [35] [36]). In the proximal segment, the circular smooth muscle is thickened to form the involuntary internal urethral (preprostatic) sphincter described earlier. Small periurethral glands, lacking periglandular smooth muscle, extend between the fibers of the longitudinal smooth muscle to be enclosed by the preprostatic sphincter. Although these glands constitute less than 1% of the secretory elements of the prostate, they can contribute significantly to prostatic volume in older men as one of the sites of origin of benign prostatic hyperplasia.

Figure 2-27 Posterior wall of the male urethra. (From Anson BJ, McVay CB: Surgical Anatomy, 6th ed. Philadelphia, WB Saunders, 1984, p 833.)

Figure 2-28 Zonal anatomy of the prostate as described by J. E. McNeal (Am J Surg Pathol 1988;12:619-633). The transition zone surrounds the urethra proximal to the ejaculatory ducts. The central zone surrounds the ejaculatory ducts and projects under the bladder base. The peripheral zone constitutes the bulk of the apical, posterior, and lateral aspects of the prostate. The anterior fibromuscular stroma extends from the bladder neck to the striated urethral sphincter.

Beyond to the urethral angle, all major glandular elements of the prostate open into the prostatic urethra. The urethral crest widens and protrudes from the posterior wall as the verumontanum (see Fig. 2-27 ). The small slitlike orifice of the prostatic utricle is found at the apex of the verumontanum and may be visualized cystoscopically. The utricle is a 6-mm müllerian remnant in the form of a small sac that projects upward and backward into the substance of the prostate. In males with ambiguous genitalia, it may form a large diverticulum that protrudes from the posterior side of the prostate. To either side of the utricular orifice, the two small openings of the ejaculatory ducts may be found. The ejaculatory ducts form at the juncture of the vas deferens and seminal vesicles and enter the prostate base where it fuses with the bladder. They course nearly 2 cm through the prostate in line with the distal prostatic urethra and are surrounded by circular smooth muscle ( Fig. 2-28 ; see also Figs. 2-23 and 2-25 [23] [25]).

In general, the glands of the prostate are tubuloalveolar with relatively simple branching and are lined with simple cuboidal or columnar epithelium. Scattered neuroendocrine cells, of unknown function, are found between the secretory cells. Beneath the epithelial cells, flattened basal cells line each acinus and are believed to be stem cells for the secretory epithelium. Each acinus is surrounded by a thin layer of stromal smooth muscle and connective tissue.

The glandular elements of the prostate have been divided into discrete zones, distinguished by the location of their ducts in the urethra, by their differing pathologic lesions, and, in some cases, by their embryologic origin (see Fig. 2-28 ). These zones can be demonstrated clearly with transrectal ultrasonography. At the angle dividing the preprostatic and prostatic urethra, the ducts of the transition zone arise and pass beneath the preprostatic sphincter to travel on its lateral and posterior sides. Normally, the transition zone accounts for 5% to 10% of the glandular tissue of the prostate. A discrete fibromuscular band of tissue separates the transition zone from the remaining glandular compartments and may be visualized at transrectal ultrasonography of the prostate. The transition zone commonly gives rise to benign prostatic hypertrophy, which expands to compress the fibromuscular band into a surgical capsule seen at enucleation of an adenoma. It is estimated that 20% of adenocarcinomas of the prostate originate in this zone.

The ducts of the central zone arise circumferentially around the openings of the ejaculatory ducts. This zone constitutes 25% of the glandular tissue of the prostate and expands in a cone shape around the ejaculatory ducts to the base of the bladder. The glands are structurally and immunohistochemically distinct from the remaining prostatic glands (which branch directly from the urogenital sinus), which has led to the suggestion that they are of wolffian origin ( McNeal, 1988 ). In keeping with this suggestion, only 1% to 5% of adenocarcinomas arise in the central zone, although it may be infiltrated by cancers from adjacent zones.

The peripheral zone makes up the bulk of the prostatic glandular tissue (70%) and covers the posterior and lateral aspects of the gland. Its ducts drain into the prostatic sinus along the entire length of the (postsphincteric) prostatic urethra. Seventy percent of prostatic cancers arise in this zone, and it is the zone most commonly affected by chronic prostatitis.

Up to one third of the prostatic mass may be attributed to the nonglandular anterior fibromuscular stroma. This region normally extends from the bladder neck to the striated sphincter, although considerable portions of it may be replaced by glandular tissue in adenomatous enlargement of the prostate. It is directly continuous with the prostatic capsule, anterior visceral fascia, and anterior portion of the preprostatic sphincter and is composed of elastin, collagen, and smooth and striated muscle. It is rarely invaded by carcinoma.

Clinically, the prostate is often spoken of as having two lateral lobes, separated by a central sulcus that is palpable on rectal examination, and a middle lobe, which may project into the bladder in older men. These lobes do not correspond to histologically defined structures in the normal prostate but are usually related to pathologic enlargement of the transition zone laterally and the periurethral glands centrally.

Vascular Supply

Most commonly, the arterial supply to the prostate arises from the inferior vesical artery. As it approaches the gland, the artery (often several) divides into two main branches ( Fig. 2-29 ). The urethral arteries penetrate the prostatovesical junction posterolaterally and travel inward, perpendicular to the urethra. They approach the bladder neck in the 1- to 5-o'clock and 7- to 11-o'clock positions, with the largest branches located posteriorly. They then turn caudally, parallel to the urethra, to supply it, the periurethral glands, and the transition zone. Thus, in benign prostatic hypertrophy, these arteries provide the principal blood supply of the adenoma ( Flocks, 1937 ). When these glands are resected or enucleated, the most significant bleeding is commonly encountered at the bladder neck, particularly at the 4- and 8-o'clock positions.

Figure 2-29 Arterial supply of the prostate. (Adapted from Flocks RH: The arterial distribution within the prostate gland: Its role in transurethral prostatic resection. J Urol 1937;37:524-548.)

The capsular artery is the second main branch of the prostatic artery. This artery gives off a few small branches that pass anteriorly to ramify on the prostatic capsule. The bulk of this artery runs posterolateral to the prostate with the cavernous nerves (neurovascular bundles) and ends at the pelvic diaphragm. The capsular branches pierce the prostate at right angles and follow the reticular bands of stroma to supply the glandular tissues. Venous drainage of the prostate is abundant through the periprostatic plexus (see Fig. 2-17 ).

Lymphatic drainage is primarily to the obturator and internal iliac nodes (see Fig. 2-18 ). A small portion of drainage may initially pass through the presacral group, or less commonly, the external iliac nodes.

Nerve Supply

Sympathetic and parasympathetic innervation from the pelvic plexus travels to the prostate through the cavernous nerves. Nerves follow branches of the capsular artery to ramify in the glandular and stromal elements. Parasympathetic nerves end at the acini and promote secretion; sympathetic fibers cause contraction of the smooth muscle of the capsule and stroma. α-Adrenergic blockade diminishes prostate stromal and preprostatic sphincter tone and improves urinary flow rates in men affected with benign prostatic hypertrophy; this emphasizes that this disease affects both the stroma and the epithelium. Peptidergic and nitric oxide synthase–containing neurons also have been found in the prostate and may affect smooth muscle relaxation ( Burnett, 1995 ). Afferent neurons from the prostate travel through the pelvic plexuses to pelvic and thoracolumbar spinal centers. A prostatic block may be achieved by instilling local anesthetic into the pelvic plexuses.

Membranous Urethra

In its course from the apex of the prostate to the perineal membrane, the membranous urethra spans on average 2 to 2.5 cm (range, 1.2 to 5 cm) ( Myers, 1991 ). It is surrounded by the striated (external) urethral sphincter, which is often incorrectly depicted as a flat sheet of muscle sandwiched between two layers of fascia. The striated sphincter is actually signet ring–shaped, broad at its base and narrowing as it passes through the urogenital hiatus of the levator ani to meet the apex of the prostate ( Fig. 2-30 ; see also Figs. 2-10 and 2-23 [10] [23]). In utero, this muscle forms a vertically oriented tube that extends from the perineal membrane to the bladder neck ( Oelrich, 1980 ). As the prostate grows, posterior and lateral portions of this muscle atrophy, although transverse fibers persist on the entire anterior prostate through adulthood. At the apex of the prostate, circular fibers surround the urethra, and they thin posteriorly to insert into a fibrous raphe. Distally, the fibers do not meet posteriorly; rather, they acquire an ω shape as they fan out laterally over the perineal membrane. Throughout its length, the posterior portion of the striated sphincter inserts into the perineal body. When the sphincter contracts, the walls of the urethra are pulled posteriorly toward the perineal body ( Strasser et al, 1998 ). In contrast to the levator ani, the sphincter consists only of fine, type I (slow-twitch) fibers, rich in acid-stable myosin adenosine triphosphatase, which appear designed for tonic contraction. The myofibrils are surrounded by abundant connective tissue that blends with adjacent supporting structures.

The striated sphincter is related anteriorly to the dorsal vein complex (which may invade its anterior portion with age) and laterally to the levator ani. Connective tissue from deep within the lateral and anterior walls inserts into the puboprostatic ligaments posteriorly and into the suspensory ligament of the penis anteriorly to form a sling of fibrous tissue that suspends the urethra from the pubis ( Steiner, 1994 ). A similar suspensory mechanism is found in the female urethra (see later discussion and Fig. 2-34 ). Two bulbourethral glands lie superior to the perineal membrane and are invested in the broad base of sphincter muscle. During sexual excitement, these glands secrete clear mucus into the bulbous urethra.

Figure 2-34 Urethral suspensory mechanism. The pubourethral ligament (P.U.L.) is composed of an anterior portion (suspensory ligament of the clitoris), a posterior portion (pubourethral ligament of endopelvic fascia), and an intermediate portion that bridges the other two. U.G.D., urogenital diaphragm; V, vagina; U, urethra. (From Milley PS, Nichols DH: The relationship between the pubo-urethral ligaments and the urogenital diaphragm in the human female. Anat Rec 1971;170:281-283.)

The striated sphincter corresponds to the location of peak urethral closing pressure and is responsible for continence after prostatectomy. Components involved in generating this closing pressure are (1) the pseudostratified columnar epithelium, which contracts into radial folds as it meets to occlude the lumen; (2) the submucosa, which is rich with blood vessels and soft connective tissue and contributes to urethral sealing ( Raz et al, 1972 ); (3) the longitudinal and circular urethral smooth muscle (intrinsic component of the external sphincter); (4) the striated sphincter; and (5) the pubourethral component of the levator ani.

Gross dissection and retrograde axonal tracing techniques have confirmed that the striated sphincter is supplied by the pudendal nerve ( Tanagho et al, 1982 ). However, urologists have long been puzzled as to why pudendal nerve sectioning does not ablate sphincter activity. Lawson (1974) and Zvara and colleagues (1994) identified a second source of somatic innervation to the sphincter: a branch of the sacral plexus that runs on the pelvic surface of the levator ani (see Fig. 2-20 ). Injury to this nerve at radical prostatectomy may contribute to postoperative urinary incontinence ( Hollabaugh et al, 1997 ). Autonomic innervation to the intrinsic smooth muscle of the membranous urethra is likely given by the cavernous nerves as they pass nearby, although dividing these nerves does not appear to affect urinary continence significantly ( Steiner et al, 1991 ). Afferent fibers from the striated sphincter have not been defined but are sure to have interesting and important functional roles, because this muscle lacks proprioceptive muscle spindles ( Gosling et al, 1981 ).

Vas Deferens and Seminal Vesicle

As it arises from the tail of the epididymis, the vas (ductus) deferens is somewhat tortuous for 2 to 3 cm (see Fig. 2-43 ). It runs posterior to the vessels of the cord and through the inguinal canal and emerges in the pelvis lateral to the inferior epigastric vessels (see Fig. 2-7 ). At the internal ring, it diverges from the testicular vessels and passes medial to all structures of the pelvic side wall to reach the base of the prostate posteriorly (see Figs. 2-7, 2-13, and 2-15 [7] [13] [15]). The terminal vas is dilated and tortuous (ampulla) and is capable of storing spermatozoa. The vas has a thick wall of outer longitudinal and inner circular smooth muscle and is lined by pseudostratified columnar epithelium with nonmotile stereocilia.

Figure 2-43 Testis and epididymis. A, One to three seminiferous tubules fill each compartment and drain into the rete testis in the mediastinum. Twelve to 20 efferent ductules become convoluted in the head of the epididymis and drain into a single coiled duct of the epididymis. The vas is convoluted in its first portion. B, Cross section of the testis, showing the mediastinum and septations continuous with the tunica albuginea. The parietal and visceral tunica vaginalis are confluent where the vessels and nerves enter the posterior aspect of the testis.

The seminal vesicle is a lateral outpouching of the vas, approximately 5 cm long, with a capacity of 3 to 4 mL (see Figs. 2-8 and 2-28 [8] [28]). Despite its name, it does not store sperm but contributes the largest portion of fluid to the ejaculate. The seminal vesicle comprises a single coiled tube with several outpouchings that is lined by columnar epithelium with goblet cells. The tube is encased in a thin layer of smooth muscle and is held in its coiled configuration by a loose adventitia.

The seminal vesicle and ampulla of the vas lie posterior to the bladder. The ureter enters the bladder medial to the tip of the seminal vesicle. As they join to form the ejaculatory duct, their smooth muscle coats fuse with the prostatic capsule at its base. Denonvilliers' fascia or, occasionally, the rectovesical pouch of peritoneum separates these structures from the rectum (see Fig. 2-23 ). Unless involved by a pathologic process, these structures are not palpable on rectal examination.

The blood supply for both structures comes from the vesiculodeferential artery, a branch of the superior vesical artery. This artery supplies the vas throughout its length and then passes onto the anterior surface of the seminal vesicle near its tip. Additional arterial supply may come from the inferior vesical artery. The pelvic vas and seminal vesicle drain into the pelvic venous plexus. Lymphatic drainage passes to the external and internal iliac nodes (see Fig. 2-18 ). Innervation arises from the pelvic plexus, with major excitatory efferents contributed by the (sympathetic) hypogastric nerves ( Kolbeck and Steers, 1993 ).

Female Pelvic Viscera

The uterus measures 8 × 6 × 4 cm in a normal woman and is composed largely of dense smooth muscle ( Fig. 2-31 ). It has a narrowed neck, the cervix, that opens through the anterior vaginal wall and a broad corpus that is capped by the rounded fundus. As discussed earlier, it lies in front of the rectum and over the dome of bladder; its impression may be appreciated cystoscopically (Figs. 2-32 and 2-33 [32] [33]). The fallopian tubes extend laterally from the junction of the corpus and fundus and are draped by leaves of peritoneum called the broad ligaments (see Figs. 2-13 and 2-31 [13] [31]). As they extend to the pelvic side walls, the fallopian tubes angle up and backward to open posteromedially. The tubes are divided into four segments: uterine, isthmus, ampulla, and infundibulum, which is crowned by the fimbriae. The ovary rests posterior to the elbow of the tube and is supported by its own peritoneal fold, the mesovarium. The ureter may be found directly posterior to the ovary, covered by pelvic peritoneum. The infundibulopelvic ligament, mentioned earlier, suspends the ovary and lateral fallopian tube from the pelvic side wall and transmits the ovarian vessels to both structures. The round ligament of the ovary passes medially through the broad ligament to fix the ovary to the lateral wall of the uterus. Beneath its point of attachment, the round ligament of the uterus passes laterally, in the leaves of the broad ligament, to exit through to inguinal canal and attach to the labial fat pad (see Figs. 2-13 and 2-31 [13] [31]).

The uterine artery crosses in front of the ureter and runs in the broad and cardinal ligaments to supply the proximal vagina, uterus, and medial two thirds of the fallopian tube (see Fig. 2-31 ). It is joined by a rich plexus of uterine veins that freely connect with the ovarian veins. Nerves from the pelvic plexus travel to the female pelvic viscera through the cardinal and uterosacral ligaments in the company of the vessels; thus, after hysterectomy, the bladder may become neurogenic.

The vagina extends inward from the vestibule at a 45-degree angle and then turns horizontal over the levator plate (see Fig. 2-33 ). It is lined by rugate nonkeratinized squamous epithelium backed by a thick, well-vascularized lamina propria. It is surrounded by a smooth muscle coat of inner circular and stronger external longitudinal layers. In cross section, the vagina is H shaped ( Fig. 2-34 ) as a result of firm attachments of its anterior wall to the levator ani at the arcus tendineus fascia pelvis and of its posterior wall to the rectovaginal septum. The anterior vaginal wall is pierced by the cervix proximally. The shallow fossae around the cervix are referred to as the anterior, lateral, and posterior fornices. Because the apex of the vagina is covered with the peritoneum of the rectouterine pouch, the peritoneal cavity may be accessed through the posterior fornix (see Fig. 2-33 ).

Immediately in front of the cervix, the base of the bladder rests on the vaginal wall. Smooth muscle fibers tether the posterior bladder wall and base to the uterine cervix and vagina (see Fig. 2-33 ). Division of these fibers yields posterior access to the vesicovaginal space. This space extends distally to the proximal third of the urethra (where the urethra and vagina fuse) and is limited to each side by the lateral ligaments of the bladder. It may be accessed transvaginally through incision of the anterior vaginal wall in front of the cervix. Incision of the anterior vaginal wall to either side of the urethra leads into the retropubic space (see Fig. 2-12 ). The tough leaves of visceral endopelvic fascia are felt medially and should be included in all transvaginal urethral suspension procedures ( Mostwin, 1991 ).

The vagina is separated from the rectum by the rectovaginal septum (see Fig. 2-33 ), and rectoceles result from a loss of integrity of this septum. Deep to this septum lies a second potential space, the rectovaginal space. The bowel may herniate into this space to form an enterocele. On its lateral surfaces, the vagina is related to the levator ani. Near the vestibule, fibers of the levator ani blend and fuse with the vaginal muscularis. The vaginal vessels and nerves lie on the anterolateral surface of the vagina deep to arcus tendineus fascia pelvis.

Female Urethra

On average, the female urethra traverses 4 cm from the bladder neck to the vaginal vestibule. Its lining changes gradually from transitional to nonkeratinized stratified squamous epithelium. Many small mucous glands open into the urethra and can give rise to urethral diverticula. Distally, these glands group together on either side of the urethra (Skene's glands) and empty through two small ducts to either side of the external urethral meatus. A thick, richly vascular submucosa supports the urethral epithelium and glands (see Fig. 2-32 ). Together, the mucosa and submucosa form a cushion that contributes significantly to urethral closure pressure ( Raz et al, 1972 ). These layers are estrogen dependent; at menopause they may atrophy, resulting in stress incontinence. A relatively thick layer of inner longitudinal smooth muscle continues from the bladder to the external meatus to insert into periurethral fatty and fibrous tissue. In contrast to the male proximal urethra, no circular smooth muscle sphincter can be identified. A rather thin layer of circular smooth muscle envelops the longitudinal fibers throughout the length of the urethra. It is thought that the longitudinal smooth muscle of the urethra contracts coordinately with the detrusor during micturition to shorten and widen the urethra ( Gosling, 1979 ).

The striated urethral sphincter invests the distal two thirds of the female urethra ( Oelrich, 1983 ). It is composed exclusively of delicate type I (slow-twitch) fibers surrounded by abundant collagen. Proximally, it forms a complete ring around the urethra that corresponds to the zone of highest urethral closure pressure (see Fig. 2-32 ). Farther down the urethra, the fibers do not meet posteriorly but continue off the lateral sides of the urethra onto the anterior and lateral walls of the vagina. Contraction of these fibers (the compressor urethrae) closes the urethra against the fixed anterior vaginal wall. Near the vestibule, the fibers completely surround the urethra and vagina to form a urethrovaginal sphincter. Contraction of this muscle group, along with bulbospongiosus, tightens the urogenital hiatus.

The suspensory ligament of the clitoris (anterior urethral ligament) and the pubourethral ligaments (posterior urethral ligaments) form a sling that suspends the urethra beneath the pubis (see Figs. 2-12 and 2-34 [12] [34]) ( Zacharin, 1963 ). The striated urethral sphincter receives dual somatic innervation, like that in the male, from the pudendal and pelvic somatic nerves ( Borirakchanyavat et al, 1997 ). Little sympathetic innervation is found in the female urethra. Parasympathetic cholinergic fibers are found throughout the smooth muscle. Somatic and autonomic nerves to the urethra travel on the lateral walls of the vagina near the urethra. During transvaginal incontinence surgery, the anterior vaginal wall should be incised laterally to avoid these nerves and prevent type III urinary incontinence ( Ball et al, 1997 ).

Female Pelvic Support

The pelvic muscles and fasciae cooperate to prevent prolapse of the urogenital organs through the hiatus. Three functional supportive elements are recognized: (1) the pubovisceral and perineal muscles, which form a sphincter around the urogenital hiatus (see Fig. 2-32 ); (2) the levator plate, which acts as a horizontal shelf beneath the bladder, uterine cervix, posterior vagina, and rectum (see Fig. 2-33 ); and (3) the cardinal and uterosacral ligaments, which anchor the pelvic viscera over the levator plate ( Zacharin, 1985 ; Mostwin, 1991 ; DeLancey, 1993 ). The pelvic muscles contract tonically to counteract gravitational forces. In response to stress, the levator ani contracts, closing the urogenital hiatus and increasing the anteroposterior length of the levator plate. Increased intra-abdominal pressure forces the pelvic viscera downward against a fixed levator plate, closing the vagina like a flap valve.

Pelvic and perineal muscles play the greatest role in pelvic support. Damage to the perineal body during parturition destroys the urogenital sphincter, enlarges the urogenital hiatus, and erodes the levator plate. Aging and birth trauma partially denervate and weaken the levator ani ( Snooks et al, 1985 ). With loss of muscular support, intra-abdominal forces impinge directly on the pelvic fasciae; over time, these either tear or stretch. Procedures to correct pelvic prolapse or urinary incontinence that rely solely on these fasciae may be successful initially but do not fare well over time ( Trockman et al, 1995 ). Repair of a single pelvic defect—a cystocele for instance—may unmask another (e.g., enterocele, rectocele); therefore, successful repair of pelvic prolapse must address all components of anatomic support ( Zacharin, 1985 ; DeLancey, 1993 ).

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