THE PENIS AND MALE PERINEUM

PELVIC STRUCTURES

The relationships of male pelvic structures are illustrated in these complementary sagittal views—a paramedian and a median section. In the lower median view, the complete course of the urethra from the bladder to the meatus at the end of the penis , its passage through the prostate gland and the urogenital diaphragm , is shown. In the upper paramedian view, part of the pelvic bones (os ilium and ischium) have been removed, but both rami of the left os pubis and part of the inferior ramus of the ischium are present. The soft parts are sectioned laterally from the midline. This view permits visualization of the course of the vas deferens as it originates in the scrotum and ascends to pass over the superior ramus of the pubis and ultimately to the posterior surface of the bladder, passing over the ureter on each side (“water under the bridge”). Note too that the bladder, as a hollow smooth muscular organ, has muscle fibers that run in all directions, like a ball of yarn, to enable uniform concentric contractions during micturition . The paramedian view also illustrates the fact that all male urogenital organs exist in the extraabdominal, retroperitoneal space and are covered by the peritoneum superiorly. Both views outline the attachments and course of the ischiocavernosus and bulbocavernosus muscles and demonstrate the suspensory and fundiform ligaments.

Anatomic details of external and internal organs will be discussed elsewhere (see pages 23 , 24 , 31 , 51 , 52 , 76 , and 77 ). However, well visualized here are the prostate gland below the bladder and paired seminal vesicles posterior to the bladder. The preperitoneal space of Retzius exists between the anterior surface of the prostate and bladder and the posterior surfaces of the symphysis and recti muscles. This retroperitoneally located potential space contains veins, areolar tissue, nerves, and lymphatics and is bounded below by the superior surface of the urogenital diaphragm. The posterior surfaces of the prostate and the seminal vesicles are separated from the anterior rectal wall by a definite, fibrous layer of fascia termed the rectovesical or Denonvilliers fascia that covers the entire posterior surface of the prostate from its apex , over the surface of the seminal vesicles superiorly to the rectovesical pouch . Denonvilliers fascia is an important surgical landmark for operations that involve removal of the prostate or reflection of the rectal wall from the surface of the prostate.

The fascial planes of the urogenital region have considerable clinical significance because of their important function in supporting anatomic structures, their identification as surgical landmarks, and because their layered arrangement forms several interfascial spaces that control the spread of exudates, malignancies, blood, or extravasated urine. In the plates that follow, these fascial layers will be shown in greater detail.

SUPERFICIAL FASCIAL LAYERS

The subcutaneous scrotal and perineal fasciae originate from the superficial fascia of the abdominal wall known as Scarpa fascia . This fascial layer is found deep to Camper fascia that backs the skin as a loose layer of fatty tissue. The abdominal Scarpa fascia is a true fascial layer that consists mainly of yellowy, elastic fibers that form a continuous membrane across the lower abdomen. In the upper abdomen, this fascia cannot be identified as a distinct membranous structure because it blends with the general superficial fascia of the upper abdomen. In the lower lateral abdominal region, Scarpa fascia is attached to the Poupart ligament , or to the fascia lata of the upper thigh just below this ligament. It passes over the external inguinal ring to continue inferiorly over the penis and scrotum into the perineum, where it fuses with the posterior inferior margin of the urogenital diaphragm . In the perineum, this fascia attaches laterally to the inferior rami of the pubis and the superior rami of the ischium and is called Colles fascia . As the fascia envelops the base of the penis, it is joined by additional fibers that extend from the dorsal penis to the symphysis, thus forming the fundiform ligament . Within the scrotum, this fascia is termed dartos fascia (dartos = flayed), as it is reinforced by smooth muscle fibers.

Thus, deep to the skin exists a continuous superficial fascial plane that begins in the lower abdomen and extends inferiorly to encompass the penis, scrotum, and anterior half of the perineum. Beneath it a potential space is formed in which fluids or exudates can accumulate and spread along well-defined planes. The points of fascial fixation, as described, lead to exudative, infectious, or extravasative processes taking on a characteristic “butterfly” shape of discoloration in this region. Although they can freely extend up the anterior abdominal wall to the clavicles, such processes do not normally extend beyond the inferior landmarks without penetrating this fascia.

In the scrotal midline, an inversion of the dartos fascia forms the scrotal septum , dividing the scrotal cavity into two halves. Anatomists differ as to whether a further inward extension of Colles fascia, termed the major leaf of Colles fascia, exists. It crosses the top of the scrotal cavity, thus forming a roof and separating it from the superficial urogenital pouch superiorly. Urine extravasation from the bulbar urethra would not normally gain access to the scrotal cavity without rupture or penetration of this major leaf of fascia. However, this fascia may contain rows of transverse slitlike openings in some individuals, which would allow urine access to the scrotal cavity.

As the major leaf of Colles fascia nears the upper scrotal cavity, it divides near the anterior margin of the scrotum, with a portion extending inward (see Plate 2-3 ). This so-called deep layer passes posteriorly, deep to the bulbospongiosus muscles , whereas the major leaf of Colles fascia in the perineal region is entirely superficial to the bulbospongiosus and ischiocavernosus muscles. The deep leaf of Colles fascia lying beneath the bulbospongiosus muscle, together with the superficial or major layer of fascia, forms a compartment for the bulbospongiosus muscle.

DEEP FASCIAL LAYERS

Beneath Colles fascia , within the urogenital triangle, is a potential space termed the superficial perineal compartment . Within this space, confined by the inferior fascia of the urogenital diaphragm on its deep aspect, lie the bulbospongiosus , ischiocavernosus, and superficial transverse perineal muscles. In addition, the bulb of the corpus cavernosum urethrae and the crura of the corpora cavernosa penis are found here. At the middle of the base of this triangle is the perineal body , a point of fusion between the muscles of the superficial perineal compartment and the adjacent anal triangle posteriorly.

The deep fascia ( Buck ) of the penis is a distinct structure lying beneath the superficial dartos or Colles fascia . Buck fascia is tenacious, dense, and whitish in appearance. It covers the penile corpora as a strong, fibrous, tubelike envelope and is adherent to the underlying tunica albuginea of the penis, which immediately covers the paired cavernous bodies (see Plate 2-2 ). Buck fascia is distinct from the tunica albuginea that covers the paired corporal cavernosa and the spongiosal bodies, though no demonstrable space exists between these adjacent fascial layers. Near the base of each crus, Buck fascia becomes less distinct as it merges with the tunica albuginea. At this point, it is continuous with the deep suspensory ligament of the penis, which is attached to the symphysis pubis (see Plate 2-1 ).

Buck fascia originates distally at the penile coronary sulcus and forms a transverse intercavernous septum , which separates the penis into two compartments: the paired corpora cavernosa dorsally and the single spongiosal body ventrally (see Plate 2-2 , cross section). In the perineum, this fascia forms three compartments by covering each crus. Buck fascia covers the paired penile dorsal arteries and nerves and the deep dorsal vein (see Plate 2-2 , cross section). In the perineum, Buck fascia lies beneath the reflected deep layer of Colles fascia that contains the bulbospongiosus and the ischiocavernosus muscles (see Plate 2-1 ).

Visualized in cross-sectional drawing on this page, a portion of Colles fascia ( crural septum ) spreads to cover the outer surfaces of the bulbospongiosus muscle and each ischiocavernosus muscle with the crura within. The cut margins of the crural septa, as they surround the ischiocavernosus muscles, are observed in the upper drawing. The deep layer of Colles fascia, shown extending posteriorly under the distal aspect of the bulbocavernosus muscle, is also illustrated. At this point, the deep layer of Colles fascia also turns backward around each penile crus and around the corpus spongiosum. This reflected layer blends with Buck fascia surrounding the crura.

Thus, in the urogenital triangle, four fascial layers cover the bulbous spongiosum and urethra. First is the perineal layer of Colles fascia external to the bulbospongiosus muscle. Beneath this is the deep extension of Colles fascia below the bulbospongiosus muscle, followed by Buck fascia and, finally, the tunica albuginea. Only three fascial layers cover each crus of the penis: Colles superficial fascia overlying the ischiocavernosus muscles and Buck fascia beneath this muscle, which blends with the deep reflected layer of Colles fascia over the tunica albuginea.

PENILE FASCIAE AND STRUCTURES

In this view, the distal end of the penis is shown intact to demonstrate the glans and the frenulum and the relationship to the foreskin or prepuce . In the sulcus between the corona of the glans and the internal surface of the foreskin are shown the openings of the preputial glands (Tyson glands) that excrete sebaceous material, a main constituent of smegma .

After removing the deep layer of Colles fascia and the overlying bulbospongiosus and ischiocavernosus muscles that cover the penile shaft and crura in Plate 2-3 , the true extent of Buck fascia is revealed. In addition to covering the corpus spongiosum and both crura, Buck fascia anchors the bulbous portion of the urethra (corpus spongiosum) and each crus firmly to the pubis, to the inferior rami of the ischium , and to the urogenital diaphragm . The removal of Colles fascia at its posterior insertion in the urogenital diaphragm exposes the superficial transverse perineal muscles and the inferior surface of the urogenital diaphragm . Removing the urogenital diaphragm exposes the deep transverse perineal muscle as shown in Plate 2-5 . The crural septum of Colles fascia, which extends between the bulbospongiosus and ischiocavernosus muscles, separates this portion of the perineum into three compartments. The perineal body is the focal point of attachment of the superficial transverse perineal muscles from each side and the anterior fibers of the external anal sphincter. Beneath the deep layer of the superficial fascia in the anal triangle , the greater part of the pelvic diaphragm , which includes the levator ani muscle as well as the ischiorectal fossa , is visible.

In the lower portion of Plate 2-4 , Buck fascia has been removed from the penis, demonstrating the corpus spongiosum , which contains the urethra and also forms the spongiosal glans penis that forms a “cap” over the joined bodies of the corpora cavernosa . To allow for this, the paired corpora terminate distally in a pointed fashion, about 1 to 2 cm from the actual end of the penis. In the treatment of prolonged erections due to ischemic priapism , the blood within the corporal bodies can be joined with that of the spongiosum to relieve this condition by surgically creating a hole between the spongiosal cap and the distal corporal bodies. The intercavernous septum of Buck fascia between the roof of the corpus spongiosum and the corpora cavernosa remains, as previously viewed in cross section in Plate 2-2 .

Beneath Buck fascia, each corporal crus of the penis is firmly fixed to the rami of the pubis and ischium . The cavernous spaces are surrounded by a thick, rigid fibrous capsule ( tunica albuginea ) consisting of both deep and superficial fibers. The latter course longitudinally and connect both corpora, but the deep fibers run in a circular manner and form a septum between the corpora after they become adjacent. Near the end of the penis, this septum becomes incomplete, allowing communication between the otherwise two distinct corpora cavernosa.

UROGENITAL DIAPHRAGM

In the upper figure, the penis, bulbous spongiosum, and both crura have been removed, exposing the inferior surface of the urogenital diaphragm . This surface of the diaphragm is penetrated by the membranous urethra and the ducts of Cowper (bulbourethral) glands that lie within the confines of the inferior and superior fascial layers. Nerves, arteries, and veins that supply both the corpus spongiosum and corpora cavernosa also penetrate the inferior fascial layer of the urogenital diaphragm. The deep dorsal vein of the penis, which drains the glans penis and corpora cavernosa, passes through an aperture above the transverse ligament of the pelvis. This ligament is formed by the fusion of the superior and inferior fascial layers of the urogenital diaphragm. The urethra, after passing through the urogenital diaphragm, pierces the dorsal surface of the corpus spongiosum and is contained within it.

In the middle figure, the inferior fascial layer of the urogenital diaphragm has been removed. Note that the intramembranous Cowper (bulbourethral) glands and the deep transverse perineal muscle are now exposed. This muscle lies between the inferior and superior fascial layers of the urogenital diaphragm. Anteriorly, the fibers of this muscle surround the membranous urethra and are termed the membranous urethral sphincter . Injury to this muscle or its nerve supply, for example at the time of radical prostatectomy for prostate cancer, can result in urinary incontinence.

The bulbospongiosus, ischiocavernosus, and transverse perineal muscles lie within the superficial perineal compartment (see Plate 2-3 ). The bulbospongiosus muscle envelops the posterior part (bulb) of the corpus spongiosum, and its anterior fibers encircle both the corpus spongiosum and the paired corpora cavernosa (see Plate 2-3 ). It takes origin from the perineal body in the perineum as well as from a median raphe in the midline. It acts to expel the last drops of urine from the urethra during micturition and to aid in the penile erection.

The paired, fusiform-shaped ischiocavernosus muscles arise from the inner surfaces of the ischial tuberosities and ischiopubic rami . They cover and insert into the crura of the penis. They act to produce an erection by compressing the crura.

The superficial transverse perineal muscles are slender slips that arise from the inner, anterior part of the ischial tuberosity and run transversely and insert into the central perineal body. Here, they blend with the superficial external anal sphincter (see Plate 2-4 ). The perineal branch of the pudendal nerve supplies all of these perineal muscles.

The lowest figure shows the relevant anatomic landmarks used to divide the perineum into two topographic regions: the urogenital triangle anteriorly and the anal triangle posteriorly. The bases of each triangle are shared and extend between the bony ischial tuberosities , roughly paralleling the course of the transverse perineal muscles. The apex of the urogenital triangle is the pubic symphysis anteriorly and that of the anal triangle is the tip of the coccyx posteriorly. Surgical procedures that traverse these anatomic regions, especially the anal triangle, are commonly performed in urology to remove the cancerous prostate (radical perineal prostatectomy).

BLOOD SUPPLY OF PELVIS

The internal iliac (hypogastric) arteries supply the greater part of the pelvic wall and pelvic organs. Subject to variations, these arteries each divide into two major branches. The anterior branch gives off the following arteries: obturator, inferior gluteal, umbilical, superior vesical, middle vesical, inferior vesical, and internal pudendal, which supplies the external genitalia.

The blood supply of the bladder is derived from three arteries that enter it on each side and anastomose freely. The superior vesical artery, supplying the bladder dome, arises from the umbilical artery. The middle vesical artery, supplying the bladder fundus and seminal vesicles, may originate from either the internal iliac artery or a branch of the superior vesical artery. The inferior vesical artery, which usually arises as a major division of the middle hemorrhoidal artery, supplies the inferior portion of the bladder, the seminal vesicles, and the prostate. The arterial blood supply to the vas deferens (deferential artery) may rise from the superior vesical artery or from the inferior vesical artery.

The internal pudendal artery, which along with the gluteal artery stems from the internal iliac, or hypogastric, artery, supplies the external genitalia. The vessel courses downward and anteriorly to reach the lower portion of the greater sciatic foramen where, at the lower border of the piriformis muscle, it leaves the pelvis. In this region, the internal pudendal artery is adjacent to the ischial spine under the cover of the gluteus maximus muscle. The artery then passes through the sciatic foramen and enters the perineum, where it finally divides into the perineal artery and the deep (cavernous) and dorsal arteries of the penis. It is the internal pudendal–perineal segment of the artery that may be injured and result in vascular erectile dysfunction associated with long-term bicycle use. After the artery enters the perineum, it courses upward and anteriorly along the lateral wall of the ischiorectal fossa (Alcock canal), where it gives off the inferior rectal artery.

The prostatic blood supply is surgically relevant as “nerve-sparing” radical prostatectomy procedures attempt to identify and avoid cavernous nerves associated with these vessels to protect erectile function. The blood supply of the prostate comes from the inferior vesical artery (branch of internal iliac artery). The middle hemorrhoidal and internal pudendal arteries also send small branches to the apical prostate. Within the prostate, two groups of arteries are reliably observed. The internal or urethral groups supply approximately one third of the prostatic mass and the urethra as far as the verumontanum. These vessels penetrate the prostatic capsule at the prostaticovesical junction and give off branches that enter and supply the lateral prostatic lobes (illustrated in a case of hyperplasia). Inside the gland they proceed in a perpendicular manner and reach the urethral lumen at the vesical orifice (neck) at a location of 7 to 11 o'clock on the left and 1 to 5 o'clock on the right of the orifice, as viewed cystoscopically. After the arteries pass these locations, they turn distally and course parallel to the urethral surface beneath the mucosa, supplying the prostatic urethra and also branching to the prostatic tissue.

The external or capsular arterial group supplies approximately two thirds of the prostate. These vessels course along the posterolateral surface of the prostate, where they are identified during prostatectomy surgery and give off branches both ventrally and dorsally to supply the outer surface of the gland. Many branches enter the prostatic capsule and anastomose to a moderate extent with vessels of the urethral group. At the apex of the prostate, the capsular arterial group penetrates inward to supply the urethra and that portion of the prostate in the region of the verumontanum.

Venous blood from the prostate drains through the puboprostatic and vesicoprostatic (pudendal) plexus into the vesical and hypogastric veins. This plexus spreads between the lower part of the os pubis, the ventral surface of the bladder and the prostate, and receives major contributions from the deep dorsal vein of the penis and numerous prostatic veins to form the retropubic plexus of Santorini over the prostatic capsule. Control of this venous plexus is critical to reduce blood loss during radical prostatectomy procedures.

BLOOD SUPPLY OF PERINEUM

The internal pudendal artery, after emerging from the Alcock canal, gives off several branches. One, the perineal artery, passes beneath the Colles fascia in the perineum to course forward anteriorly, either under or over the superficial transverse perineal muscle. This vessel supplies the superficial structures of the urogenital diaphragm and sends a small branch, usually transversely, across the perineum (transverse perineal artery) that anastomoses with the artery from the opposite side. The perineal artery then continues anteriorly underneath the pubic arch and supplies both the ischiocavernosus and bulbospongiosus muscles. It also sends branches to the posterior scrotal surface.

The deep terminal branch of the internal pudendal artery pierces the inferior layers of the urogenital diaphragm and continues forward in the cleft between the ischiocavernosus and bulbospongiosus muscles, where it divides into the dorsal artery and the cavernous artery of the penis. As it courses between the inferior and superior layers of the fasciae of the urogenital diaphragm, it supplies the bulbous portion of the urethra and the corpus spongiosum. Distal to the bulbar urethra, a small branch passes downward through the inferior fascial layer of the urogenital diaphragm and enters the corpus spongiosum, where it continues to the glans penis (urethral artery).

The deep or cavernous artery of the penis pierces the inferior layer of the urogenital diaphragm, enters the crus penis obliquely on each side, and continues distally in the center of the corpus cavernosum of the penis. The blood flow within this artery is commonly measured by ultrasound in the evaluation of arterial erectile dysfunction. The dorsal artery of the penis pierces the inferior fascia of the urogenital diaphragm, just below the transverse ligament of the pelvis (see Plate 2-5 ), after which it traverses the suspensory ligament of the penis and courses forward on the dorsum of the penis beneath Buck fascia, where it terminates in the prepuce and glans penis. The paired dorsal arteries of the penis are situated between a single deep dorsal vein and paired dorsal nerves. The dorsal artery sends branches downward through the tunica albuginea of the penis into the corpus cavernosum, where they anastomose with the ramifications of the cavernous artery.

In general, the arteries supplying the internal and external genitalia are accompanied by similarly named veins. The dorsal veins of the penis, however, pursue a different course. The subcutaneous dorsal (median and lateral) veins, which receive tributaries from preputial veins, pass proximal to the symphysis pubis, where they terminate in the superficial external pudendal veins that drain into the femoral veins. The single deep dorsal vein of the penis originates in the sulcus behind the glans penis and drains the glans and the corpus spongiosum. It courses posteriorly in a sulcus between the right and left corpora and passes between both of the two layers of the suspensory ligament at the penile base (see Plate 2-6 ). It then passes through an aperture between the arcuate ligament of the pubis and the anterior border of the transverse pelvic ligament (see Plate 2-5 ). The deep dorsal vein then divides into branches that join the prostatic venous plexus. This plexus of thin-walled veins, with similar veins from the bladder and rectum, communicate freely with one another and with adjacent venous tributaries. Ultimately, they empty into the internal iliac veins.

BLOOD SUPPLY OF TESTIS

The internal spermatic artery originates from the abdominal aorta just below the renal artery. Embryologically, the testicles lie opposite the second lumbar vertebra and keep the blood supply that is acquired during the first weeks of life as they descend into the scrotum. The internal spermatic artery joins the spermatic cord above the internal inguinal ring and lies adjacent to the testicular veins (pampiniform plexus) to the testis mediastinum. Inferior to the scrotal pampiniform plexus, the spermatic artery is highly coiled and branches before entering the testis. Extensive interconnections, especially between the internal spermatic and deferential arteries, allow maintenance of testis viability even after division of the internal spermatic artery. A single artery enters the testis in 56% of cases; two branches enter in 31% of cases and three or more branches in 13% of testes. In men with a single testicular artery, its interruption can result in testicular atrophy. The testicular arteries penetrate the testis tunica albuginea and travel inferiorly along its posterior surface and penetrate into the parenchyma. Individual arteries to the seminiferous tubules, termed centrifugal arteries, travel within the septa between tubules. Centrifugal artery branches give rise to arterioles that become individual intertubular and peritubular capillaries.

The deferential artery (artery of the vas deferens) originates from either the inferior or superior vesical artery (see Plate 2-6 ) and supplies the vas deferens and the cauda of the epididymis. Near the testis, the internal spermatic artery and the deferential artery anastomose. A third artery, the external spermatic artery (cremasteric artery), arises from the inferior epigastric artery from within the internal inguinal ring, where it enters the spermatic cord. This artery forms a network over the tunica vaginalis and usually anastomoses at the testicular mediastinum with the internal spermatic and deferential arteries. The external spermatic artery also forms anastomotic patterns that supply the scrotal wall.

The veins of the spermatic cord emerge from the testis mediastinum to form the extensive pampiniform plexus. These veins gradually coalesce and, in 60% of cases, form a single trunk within the inguinal canal. The pampiniform plexus consists of three groups of freely anastomosing veins: (1) the internal spermatic vein group that emerges from the testicle and accompanies the spermatic artery to enter the vena cava; (2) the deferential group that accompanies the vas deferens to veins within the pelvis; and (3) the external spermatic (cremasteric) group that follows a course along the posterior spermatic cord. The latter group empties into branches of the superficial and deep inferior epigastric veins and into the superficial external and deep pudendal veins. These groups of veins afford routes of collateral circulation for blood return from the testicles.

The right internal spermatic vein enters the inferior vena cava obliquely below the right renal vein, whereas the left internal spermatic vein terminates in the left renal vein at a right angle, apparently without natural valve formation. These differences in drainage patterns likely explain the fact that 95% per cent of varicoceles occur on the left side, where natural resistance to increased abdominal pressure on retrograde flow through these veins is lower.

With varicocele formation, blood flow in the internal spermatic vein is reversed. With varicocelectomy, all veins except the deferential veins are ligated to reverse this process and improve pain or testis function. The deferential vein affords a sufficient avenue for blood return. When performed in the retroperitoneum (Palomo or laparoscopic), varicocele recurrence rates after surgery are higher than when performed inguinally or subinguinally because of more complete ligation of all suspicious contributing veins observed more distally. Because of the increased number of pampiniform plexus veins subinguinally and the potential lack of a sufficiently collateralized arterial supply, varicocelectomy at this anatomic level is performed microscopically.

LYMPHATIC DRAINAGE OF PELVIS AND GENITALIA

The scrotal skin contains a rich network of lymphatics that join the lymphatics of the penile skin and the prepuce. These channels, turning outward, terminate in the superficial inguinal nodes located in the subcutaneous tissue beneath the superficial fascia, inferior to Poupart ligament and above the great saphenous vein. Penile and scrotal skin diseases can also progress to the deep inguinal lymph nodes beneath the fascia lata of the thigh, within the femoral triangle on the medial side of the femoral canal. Some lymphatics from the penile skin may also enter the subinguinal nodes that are deep inguinal lymph nodes located below the junction of the saphenous and femoral veins. Cloquet or Rosenmüller nodes in this nodal group are located in the external crural canal. Because of the communication between these nodes, it is important to inspect and remove all superficial and deep inguinal lymph nodes in penile cancer cases.

The lymphatics of the glans penis drain toward the frenulum. They then circle the corona, and the vessels from both sides unite on the dorsum to accompany the deep dorsal vein beneath Buck fascia. These lymph channels may pass through the inguinal and femoral canals without traversing nodes until they reach external iliac nodes that surround the external iliac artery and the anterior surface of the corresponding vein. Glans penis lymphatics may also terminate in the deep inguinal lymph nodes and the presymphyseal node located anterior to the symphysis pubis.

The lymphatic channels of the penile urethra, passing around the lateral surfaces of the corpora, accompany those of the glans penis outlined above or may pierce the rectus muscle to course directly to the external iliac nodes. The bulbous and membranous urethra drain through channels that accompany the internal pudendal artery and terminate in the internal iliac or hypogastric (obturator) nodes that are associated with the branches of the internal iliac (hypogastric) arteries or in the external iliac nodes.

The rich lymphatic network of the prostate, as well as the prostatic urethra, ends in the external iliac lymph nodes. Some lymphatics may accompany the inferior vesical artery to terminate in the internal iliac or hypogastric (obturator) nodes. These two nodal groups are most commonly surgically resected when regional spread of prostate cancer is suspected. Still others may cross the lateral surface of the rectum to terminate in the presacral and lateral sacral nodes within the concavity of the sacrum, near the upper sacral foramina and the middle and lateral sacral arteries. On the basis of this wide variation in lymphatic drainage of prostate cancer, lymph node dissection is performed for diagnostic but not therapeutic reasons.

The lymphatic vessels of the epididymis join those of the vas deferens and terminate in external iliac nodes. Nodal metastases from testicular tumors in these nodes indicate probable involvement of the epididymis, because the lymphatic drainage of the testis follows the internal spermatic vein through the inguinal canal to the retroperitoneal space.

Depending on the side, testicular lymphatics, after angulating sharply toward the midline on crossing the ureter, terminate in defined groups of retroperitoneal nodes located along the vena cava and aorta from the bifurcation to the level of the renal artery. The lymphatics from the right testis drain mainly to the right paracaval nodes, including precaval, postcaval, lateral caval, and interaortocaval retroperitoneal lymph nodes. The lymphatics from the left testis drain mainly to the left paraaortic nodes, including the preaortic, lateral aortic, and postaortic lymph nodes. Lymphatic collaterals between the two testis sides exist, and contralateral metastases can occur when the ipsilateral nodes become obstructed.

INNERVATION OF GENITALIA I

Genitourinary organs receive a blend of autonomic and somatic nervous innervation. Autonomic nerves provide afferent and efferent innervation to organs, blood vessels, and smooth muscle and are characterized by the presence of peripheral synapses. Somatic nerves supply afferent and efferent innervation to skeletal muscle. Although these two nerve types leave the spinal cord within shared nerves, their course and function diverge widely.

The autonomic system is further divided into sympathetic and parasympathetic fibers. Sympathetic preganglionic fibers are found in the thoracic and lumbar spine, and parasympathetic preganglionic fibers originate in the cranial and sacral spinal cord. The pelvic organs receive a blend of these two autonomic nerve types through several pelvic ganglia. This autonomic innervation is demonstrated diagrammatically here, with a complete description of the anatomic and functional connections found elsewhere in this Collection.

The parasympathetic fibers leave the spinal cord with the anterior spinal nerve roots from the sacral cord segments S2 through S4. After passing through the sacral foramen, they (nervi erigentes) enter the pelvic nerve plexus (inferior hypogastric) and follow blood vessels to visceral organs, including the descending and sigmoid colon, rectum, bladder, penis, and external genitalia (see table ).

The sympathetic fibers are derived from the thoracolumbar spinal cord segments (T10-L2). They descend through the preaortic plexus and abdominal chains to the presacral area and form a distinct midline nerve plexus usually located below the aortic bifurcation called the superior hypogastric plexus. Below this point, various ramifications of these nerves form the inferior hypogastric nerve plexus and branches from these two plexuses pass on to the pelvic organs. These adrenergic nerves terminate as postganglionic fibers and innervate the bladder neck, prostate, vasa deferentia, and seminal vesicles. They are primarily responsible for seminal emission (see table ). Resection of this plexus or division of the abdominal sympathetic chain generally results in smooth muscle paralysis in these organs that is clinically manifest as either retrograde ejaculation or complete anejaculation, depending on the degree of injury.

The nerve supply of the penis is derived from the somatic pudendal nerve (S2-S4) and from the pelvic autonomic plexus. The pudendal nerve traverses the pelvis adjacent to the internal pudendal artery (see Plate 2-6 ) and is distributed to the same organs as the vessel supplies. The perineal branch supplies somatic motor function to the bulbospongiosus and ischiocavernosus muscles and also to the muscles of the urogenital diaphragm, including the sphincter urethrae (external sphincter). These muscles are important for somatic nervous system control of expulsion of the ejaculate that occurs with ejaculation. Sensory branches of this nerve are distributed to the skin of the penis (dorsal nerve of the penis), perineum, and posterior scrotum (see Plate 2-11 ).

Nerves emanating from the pelvic autonomic plexuses also distribute to the penis and through the cavernous nerve innervate the smooth muscle of the paired cavernous spaces and the central cavernous artery and arterioles within the penis. Thus, through the parasympathetic nervous system, they control cavernous vascular filling and erections (see table ).

Somatic nerves to the pelvic organs are derived from the lumbosacral plexus containing input from T12 to S4. They are demonstrated on the left side of the diagram. The iliohypogastric and ilioinguinal nerves are both derived from L1 and supply multiple motor branches to the abdominal wall muscles and sensory innervation to the skin of the lower abdomen and genitalia. The lateral femoral cutaneous nerve and the genitofemoral nerve are derived from L1-L3 and provide sensory input to the skin of the upper thigh and lateral genitalia. The genital branch of the genitofemoral nerve supplies the cremaster and dartos layers of the scrotum and is responsible for the cremasteric reflex that can be compromised with swelling of the spermatic cord as a consequence of testis torsion.

INNERVATION OF GENITALIA II AND OF PERINEUM

The nerves supplying the anterior scrotal wall are the ilioinguinal and the external spermatic branch of the genitofemoral branch of the lumbar nerves. The superficial perineal branches of the internal pudendal nerve, along with branches from the posterior cutaneous nerves of the thigh, innervate the posterior scrotal wall. The unstriated muscle in the dartos fascia is innervated by fine autonomic fibers that arise from the hypogastric plexus and reach the scrotum along with the blood vessels. Because of this complex innervation from various sources, the entire scrotum is difficult to anesthetize with local anesthesia, unlike the spermatic cord and testicles.

The nerves supplying the spermatic cord, epididymis, vas deferens, and testis track along the internal spermatic artery or the vas deferens to reach these organs (see Plate 2-10 ). Three nerves converge in the spermatic cord and innervate these organs: First, the superior spermatic nerve that penetrates to the interior of the testicle and supplies it and associated structures. It accompanies the internal spermatic artery, originating from the tenth thoracic cord level, and passes through the preaortic and renal plexuses. Second, the middle spermatic nerve takes origin from the superior hypogastric plexus and joins the vas deferens at the internal inguinal ring and supplies mainly the vas deferens and epididymis. Third, the inferior spermatic nerve, derived from the inferior hypogastric nerve plexus and also coursing with the vas deferens, also supplies the vas deferens and epididymis.

In the lower figure, note that perineal nerve and dorsal nerve of the penis, both derived from the pudendal nerve ( upper figure ), course medial to the ischial tuberosity on each side of the perineum. Coursing parallel to these nerves are the perineal artery and the artery of the penis, both derived from the internal pudendal artery (see Plate 2-7 ). Recent research indicates that the pressure on the male perineum when sitting on a standard bicycle saddle is sevenfold higher than that observed sitting in a chair. It is thought that this increased pressure compresses either the perineal and dorsal nerves or the perineal and dorsal arteries, leading to perineal numbness and erectile dysfunction.

A spinal cord reflex termed the “bulbocavernosus reflex” (more appropriately, the bulbospongiosus reflex) refers to anal sphincter contraction in response to squeezing the glans penis. This reflex is mediated through the dorsal nerve of the penis (afferent) via the pudendal nerve to the inferior hemorrhoidal nerves (efferent) and tests the integrity of spinal cord levels S2-S4. In cases of spinal cord injury, the absence of this reflex documents continuation of spinal shock or spinal injury at the level of the reflex arc itself (cauda equina injury). Likewise, the return of the bulbospongiosus reflex signals the termination of spinal shock.

“Referred pain” to and from the scrotal region is of considerable clinical interest. In general, stimulation of the testis, epididymis, and tunica vaginalis can cause pain locally and also pain that projects to the lower abdomen, above the internal inguinal ring. Scrotal pain is likely perceived by the genital (external spermatic) branch of the genitofemoral nerve. Pain in the testis proper is referred to its point of origin in the retroperitoneum by referral through the superior spermatic nerve. Pain associated with renal stones may be perceived as arising from the testicle because both the testicle and kidney, including the renal pelvis, receive autonomic fibers from the same preaortic autonomic plexus near the renal arteries. Another source of this pain is radiating pain due to irritation of the genitofemoral nerve often adjacent to the upper ureter.