Penile and Scrotal Anatomy

Penile and Scrotal Anatomy





The penis is composed of the corpus spongiosum, the paired corpora cavernosa, and the glans penis (Fig. 64.1). Each of the three corporal bodies is attached to the pelvis. First, the paired crura of the corpora cavernosa are firmly adherent to the inferior edge of the pubic arch. These dense fibrous chambers extend distally until the level of the pubic symphysis, where the two crura join at the penile hilum to form the dorsal aspect of the pendulous portion of the penis.

The corpus spongiosum begins proximally as the dilated bulb and then tapers to join the ventral side of the corpora cavernosa at the hilum, completing the pendulous portion of the penis. Proximally, the bulb is adherent to the central tendon, securing it to the perineal body. The bulb can be accessed through a perineal incision as in artificial urinary sphincters, male slings, and bulbar urethroplasties (Fig. 64.2). Distally, the spongiosum dilates into the glans penis, which covers the tips of the corpora cavernosa completing the glans portion of the penis. The most proximal part dilates circumferentially forming the corona of the glans. Each of the three chambers has its own blood supply and can be dissected from the other for complex epispadias repair (Fig. 64.3).

FIGURE 64.1 Anatomy of the three corporal bodies comprising the penis.

FIGURE 64.2 Perineal dissection showing the bulbar urethra, note the dissected and split bulbocavernosus (bulbospongiosus) muscle.

The outer layer of each corpora is called the tunica albuginea. The tunica of the cavernosa is a dense two-layered fibrous structure. The paired cavernosa share a common outer longitudinal sheath and an inner circular sheath that is only shared at the medial surface. The shared medial surface is called the septum (Fig. 64.4). The tunica is the layer inflicted by scar and plaque in Peyronie disease (Fig. 64.5), believed to occur between the two layers, commonly at the septal
insertion (1). Conversely, the tunica of the spongiosum is only composed of a circular layer and is thus much thinner than that of the corpora cavernosa.

FIGURE 64.3 Complete penile disassembly during a complex epispadius repair. This highlights the completely separate blood supply of (a) each corpora, (b) skin, and (c) corpora spongiosum (including urethra and glans cap). (Photo courtesy of Dr. Miro Djordjevic.)

FIGURE 64.4 Penile amputation showing the corpora cavernosa, septum, and erectile tissue. The cavernosal arteries, dorsal artery, and dorsal vein have been clipped during repair. The urethra (not seen) has been repaired.

FIGURE 64.5 Degloved penis showing left lateral curvature due to Peyronie plaque in the tunica albuginea. Note normal superficial dorsal vein anatomy and the subtle appearance of the penile dorsal nerves.

FIGURE 64.6 Diagram of sagittal section showing the fascial planes of the male external genitalia, perineum, and lower abdomen. (From Hohenfellner M, Santucci RA. Emergencies in Urology. Heidelberg, Germany: Springer, 2007. © Copyright, 2007 Dr. Markus Hohenfellner, with permission.)

Buck fascia covers the two cavernosal bodies and then splits ventrally to encircle the spongiosum. In the perineum, Buck fascia fuses with the tunical layer. Covering the crural fascia is the ischiocavernosus muscle. This muscle compresses the erectile bodies, potentiating an erection. The fascia of the bulb of the spongiosum is covered by the bulbocavernosus muscle. When contracted, this muscle will also potentiate an erection but further acts to express semen and urine. Distally, Buck fascia fuses with the corona of the glans. This margin can be accessed to insert malleable prosthesis for erectile dysfunction. Fibers from the pubic symphysis fuse with the dorsal aspect of Buck fascia forming the suspensory ligament.

Buck fascia is covered by a loose connective tissue called dartos fascia. Dartos fascia is in communication with Colles fascia of the perineum, Scarpa fascia of the abdomen, and the dartos layer of the scrotum (Fig. 64.6). Thus, injury deep to Buck fascia, as in penile fractures, will result in a hematoma
confined to the penis (Fig. 64.7), whereas injury to the tunica and Buck fascia will have the potential to spread into the perineum, laterally to the fascia lata, and cephalad over the abdominal wall (Fig. 64.8). The dartos layer allows the skin to move freely over the shaft of the penis.

FIGURE 64.7 Penile hematoma consistent with penile fracture deep to Buck fascia.

FIGURE 64.8 Pelvic fracture consistent with injury to Buck fascia confined deep to the dartos, Colles, and Scarpa fascia.

FIGURE 64.9 Cavernosospongiosal shunt highlighting the different venous drainage of the corpora cavernosa and the corpora spongiosum of the penis. (From Hohenfellner M, Santucci RA. Emergencies in Urology. Heidelberg, Germany: Springer, 2007. © Copyright, 2007 Dr. Markus Hohenfellner, with permission.)

The skin of the penis is thin, devoid of fat and hair, and highly elastic. The only glands are those that produce smegma at the coronal margin. At this margin, the penile skin folds over itself covering the glans and forming the foreskin or prepuce. The inner surface of the prepuce is thinner than the outer surface. The skin thickness distinction is important when performing a circumcision because one wants to leave a margin of the inner, thin layer intact to secure to the outer thicker layer. The frenulum of the prepuce is located ventrally and medially, extending from the corona to the urethral meatus of the glans. The frenulum is the most distal component of the median raphe, which extends from the urethral meatus down the shaft of the penis, over the medial scrotum and to the perineum. The median raphe serves as a good entry point to the underlying structures. The skin of the glans is tightly adherent to the underlying tunica of the spongiosum and clinically indistinguishable. This layer can be divided to gain access to the tip of the cavernosa as may be necessary when performing a cavernoglandular shunt for priapism (2). Correction of priapism may also require a perineal approach, so the proximal bulb may be anastomosed to the cavernosum allowing the blood to flow out of the cavernosa into the spongiosum (Fig. 64.9).

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Apr 24, 2020 | Posted by in UROLOGY | Comments Off on Penile and Scrotal Anatomy

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