Perineum

The perineum is divided into two compartments: superficial and deep. These are separated by a fibrous connective tissue layer called the perineal membrane. The borders of the perineum are the ischiopubic rami, ischial tuberosities, sacrotuberous ligaments, and coccyx. A line connecting the ischial tuberosities divides the perineum into the urogenital triangle anteriorly and the anal triangle posteriorly.

The perineal body marks the point of convergence of the bulbospongiosus muscles, superficial and deep transverse perinei, perineal membrane, external anal sphincter, posterior vaginal muscularis, and the insertion of the pub-orectalis and pubococcygeus muscles. The bulbospongio-sus originates on the inferior surface of the superior pubic rami and the crura of the clitoris. It inserts on the perineal body, where its fibers blend with the superficial transverse perinei, and external anal sphincter. It is innervated by the pudendal nerve. The superficial transverse perinei are bilateral muscles that extend from the medial ischial tuberosities to insert on the perineal body. Some fibers blend with the bulbospongiosus and the external anal sphincter. It is innervated by the pudendal nerve. The ischiocavernosus originate from the medial ischial tuberosities and ischiopubic rami. They insert on the infe-

Pudendal Artery

Innervation of the Ilioinguinal Nerve

Innervation of the Pudendal Nerve

Pudendal Artery

Pudendal Nerve and Branches

- Clitoral

- Perineal

- Inferior Rectal

External Anal Sphincter

Innervation of the Ilioinguinal Nerve

Innervation of the Pudendal Nerve

Pudendal Nerve and Branches

- Clitoral

- Perineal

- Inferior Rectal

External Anal Sphincter

Figure 4-2.6. Perineal anatomy with Martius flap inset. The distribution of the pudendal and ilioinguinal innervation is shown.The inset shows the dual vascular supply to the labial fat pad used during a Martius flap procedure. (Reprinted with the permission of The Cleveland Clinic Foundation.)

rior aspect of the pubic angle and are innervated by the pudendal nerve.

The deep perineal compartment is composed of the deep transverse perineal muscles, portions of the external urethral sphincter muscles (compressor urethrae and urethrovaginal sphincter), portions of the anal sphincter, and the vaginal musculofascial attachments.

The neurovascular anatomy of the perineum is illustrated in Figure 4-2.6. The motor and sensory innervation of the perineum is via the pudendal nerve. The pudendal nerve originates from S2-S4 and exits the pelvis through the greater sciatic foramen, hooks around the ischial spine, then reenters the pelvis through the lesser sciatic foramen. It then travels along the medial surface of the obturator internus, through the ischiorectal fossa in a thickening of fascia called Alcock's canal. It emerges posterior and medial to the ischial tuberosity where it pierces the perineal membrane and divides into three branches to supply the perineum: clitoral, perineal, and inferior rectal (inferior hemorrhoidal). Damage to the pudendal nerve (i.e., birth trauma) can result in denervation of the periurethral muscles involved in reflex contraction during increased intraabdominal pressure resulting in stress urinary incontinence.

The blood supply to the perineum is from the pudendal artery, which travels with the pudendal nerve to exit the pelvis. Similar to the nerve, there are three main branches with rich collateral anastomosis: clitoral, perineal, and inferior rectal. It is this rich collateral anastomosis that allows a Martius flap to be utilized by pelvic surgeons. A Martius flap receives its rich blood supply anteriorly and posteriorly from branches of the external and internal pudendal arteries, respectively (Figure 4-2.6, inset). Details of the anus, urethral sphincter, and external anal sphincter, and their continence mechanisms are discussed in Chapters 4-1 and 4-3.

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