Handa 9781496386441 Full Sample Chap 1

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CHAPTER 1  Surgical Anatomy of the Female Pelvis

muscle in the woman and are continuous with the exter- nal urethral sphincter muscle. They act to compress the distal urethra. Posteriorly, intermingled within the mem- brane are skeletal muscle fibers of the transverse vaginal muscle and some smooth muscle fibers. Parts of the dorsal and deep nerve and vessels of the clitoris are also found within this membrane and were described previously. The primary function of the perineal membrane is related to its attachment to the vagina and perineal body. By attach- ing these structures to the bony pelvic outlet, the perineal membrane supports the perineal part of the pelvic floor against gravity and the effects of increases in intra-abdom- inal pressure. The anterior part of pubococcygeus and puborectalis portions of the levator ani muscles lie just at the upper margin of the perineal membrane contacting its cranial surface. Contraction of these muscles elevates the medial margin of the perineal membrane (along with the vagina), while relaxation allows for its caudal movement. The amount of downward descent that is permitted by the connections of the perineal membrane to the midline structures can be assessed during an examination under anesthesia by placing a finger in the rectum, hooking it forward, and gently pulling the perineal body downward. If the perineal membrane has been torn during parturi- tion, then an abnormal amount of descent is detectable, and the pelvic floor sags and the introitus gapes. Perineal Body Within the area bounded by the lower vagina, perineal skin, and anus is a mass of fibromuscular tissue called the perineal body (see FIG. 1.14 ). The term central point (tendon) of the perineum has been applied to this structure and is descriptive, suggesting its role as a cen- tral point into which many muscles insert.

The perineal body is attached to the inferior pubic rami and ischial tuberosities through the perineal membrane and superficial transverse perineal muscles. Anterolaterally, it receives the insertion of the bulbo- spongiosus muscles. On its lateral margins, the upper portions of the perineal body are connected with some fibers of the pelvic diaphragm, the puboperinealis por- tion of the pubococcygeus muscle. Posteriorly, the perineal body is indirectly attached to the coccyx by the external anal sphincter. These connections anchor the perineal body and its surrounding structures to the In the posterior triangle of the pelvis, the ischioanal fossa lies between the obturator muscle and medial layer of fascia at the perineal walls and the levator ani muscles and its inferior layer of fascia (see FIG. 1.14 ). It has an anterior recess that lies above the perineal membrane. It is bounded superomedially by the leva- tor ani muscles and laterally by the obturator internus muscle. The main portion of the fossa is lateral to the levator ani and external anal sphincter, and it has a posterior portion that extends above the gluteus maxi- mus. Traversing this fossa is the pudendal neurovas- cular trunk. The pudendal canal with neurovascular bundle lies on its lateral wall. Anal Sphincters The external sphincter lies in the posterior triangle of the perineum ( FIG. 1.19 ). It is a single mass of muscle that has traditionally been divided into a subcutane- ous, superficial, and deep portion. The subcutaneous part lies attached to the perianal skin and forms an bony pelvis and help to keep it in place. Posterior Triangle: Ischioanal Fossa

I

Circular m.

Anorectal wall

Longitudinal m.

Coccyx Coccygeus m. Iliococcygeus m. Anococcygeal raphe Retrosphincteric space Puborectalis m.

Rectovaginal septum

Posterior vaginal wall

FIGURE 1.19  Schematic view of anorectal region. The external sphincter muscle is cut in the ante- rior midsagittal plane and reflected posteriorly. Note the relationship of anterior muscle bundle to perineal body and interdigitations with the transverse perineal muscle. Note origin and posi- tion of internal anal sphincter relative to external anal sphincter muscle. The origin of the anterior muscle bundle is clarified, and the remaining anterolateral portions of the external sphincters are interdigitated into the transverse perinei.

Perineal body

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Internal anal sphincter m.

External anal sphincter m. (cut)

Deep

Superficial Subcutaneus

Transverse perineal m.

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