27 The Perineum and Pelvis Structure List

THE PERINEUM

Learning Objectives

By the end of the course students will be able to:

1. Identify the skeletal and ligamentous boundaries of the perineum, and define the anal and urogenital triangles.
2. Describe the position and boundaries of the ischioanal fossa.
3. Describe the structure, contents, and course of the pudendal canal.
4. Trace the branching pattern of the internal pudendal vessels and the pudendal nerve.
5. Differentiate between the internal and external anal and urethral sphincters in structure and function.
6. Identify the components of the external genital organs and give the homologues in each of both sexes.
7. Describe structure and function of the erectile bodies.
8. Describe the nerve and blood supply to the external genital organs and the role that autonomic and voluntary motor fibers play in maintaining urinary and fecal continence
9. Describe the lymphatic drainage of the perineum.

Reference: Moore, Clinically Oriented Anatomy, chapter 3.

Particularly Relevant Blue Boxes in Moore:

●Disruption of the Perineal Body, p. 414

●Episiotomy, p. 414

●Rupture of the Urethra in males and Extravasation of Urine, p. 415.

●Hemorrhoids, p. 417.

●Urethral Catheterization, 425

●Administration of Pudendal and Ilioinguinal Nerve Blocks, p. 433

 

To access the Netter Presenter Database click here

To access the Primal Pictures software click here 

Check out the Primal Pictures model of the Pelvis and Perineum

 

THE PERINEUM 

OVERVIEW (Netter 356, 357, 358, 359, 360, 361)

The perineum is the region of the body inferior to the pelvic diaphragm and between the legs, thus the bony borders would be

The boundaries of the perineum are:

• anterior – pubic symphysis
• posterior – coccyx
• lateral – ischial tuberosities
• anterolateral – ischiopubic ramus
• posterolateral – sacrotuberous ligament

This diamond shaped area may be subdivided into an anterior UROGENITAL TRIANGLE and a posterior ANAL TRIANGLE. The anterior angle would be represented by the arcuate ligament.; the posterior angle would be the coccyx; the lateral angles would be the ischial tuberosities.

The view, as seen to the left (Netter 356), is the standard view of the perineum. Remember that the patient is lying on his/her back and you are looking directly into the area between the ischial tuberosities.  The pelvis is situated as though you were looking into the inferior pelvic outlet. With this view as it is drawn two-dimensionally, it is very difficult to appreciate the actual angles of the various regions.

SUMMARY OF THE TWO TRIANGLES OF THE PERINEUM

THE UROGENITAL TRIANGLE

The urogenital triangle may be divided into two spaces – the superficial perineal space (or pouch) and the deep peroneal space (or pouch)

A. Superficial perineal space (Netter 355, 356, 357, 358, 361)

♦Lies between the inferior fascia of the urogenital diaphragm (perineal membrane) and the membranous layer of the superficial perineal fascia (Colle’s fascia)

♦Contains the superficial transverse perineal muscle (Netter 356, 358) , the ischiocavernosus muscles and crus of the penis or clitoris, the bulbospongiosus muscle and the bulb of the penis or the vestibular bulbs, the central tendon of the perineum, the greater vestibular glands (in the female), branches of the internal pudendal vessels and the perineal nerve and its branches

Colle’s fascia:

♦Is the deep membranous layer of the superficial perineal fascia and forms the inferior boundary of the superficial perineal pouch

♦Is continuous with the dartos fascia of the scrotum, with the superficial fascia of the penis and with Scarpa’s fascia of the anterior abdominal wall.

The Perineal membrane:

♦is the inferior fascia of the urogenital diaphragm that forms the inferior boundary of the deep perineal pouch and the superior boundary of the superficial pouch

♦lies between the urogenital diaphragm and the external genitalia, is perforated by the urethra and is attached to the posterior margin of the urogenital diaphragm and the ischiopubic rami

The  Perineal Body:

♦is a fibromuscular mass located at the center of the perineum between the anal canal and the vagina (or the bulb of the penis)

♦serves as a site of attachment for the superficial and deep transverse perineal, bulbospongiosus, levator ani and external anal sphincter muscles

The greater vestibular (Bartholin’s glands):

♦lie in the superficial perineal space deep to the vestibular bulbs in the female

♦are homologous to the bulbourethral glands in the male

♦are compressed during coitus and secrete mucous that lubricates the vagina.

B. Deep perineal space (pouch)

♦lies between the superior and inferior fascia of the urogenital diaphragm

♦contains the deep transverse perineal muscle, the sphincter urethrae, the membranous part of the urethra, the bulbourethral glands (in the male) and branches of the internal pudendal vessels and pudendal nerve

Anal Triangle (Netter 373)

A. Ischiorectal (ischioanal) fossa) (Netter 370)

♦is the potential space on either side of the anus and rectum and is separated from the pelvis by the levator ani and its fascia

♦contains ischioanal fat which allows distention of the anal canal during defecation, the inferior rectal nerves and vessels, which are branches of the internal pudendal vessels and the pudendal the pudendal nerve

♦contains the pudendal (Alcock’s) canal on its lateral wall. This is ta fascial canal formed by a split in the obturator internus fascia and transmits the pudendal nerve and internal pudendal vessels

♦is occasionally the site of an abscess that can extend to other fossa

♦The walls of the ischiorectal fossa are as follows:

• medial – external anal sphincter
• lateral – obturator internus muscle
• superior – levator ani
• inferior – superficial fascia and skin

The Pelvic Diaphragm (Netter 339)

The pelvic diaphragm consists of of components – the levator ani and the coccygeus muscle

A. Levator Ani

1. Iliococcygeus: attaches to ischial spine, tendinous arch of levator ani and coccyx. This paired muscle contributes to the anococcygeal ligament.
2. Pubococcygeus: attaches to the inner surface of the pubic bone and obturator fascia; it passes back lateral to the anal canal to reach the coccyx. Like coccygeus, it is a bilateral structure.
3. Puborectalis: the fibers of this muscle run medial to those of pubococcygeus. They meet those from the other side, forming a muscular sling at the anorectal angle.

B. (Ischio) Coccygeus

It attaches to the spine t=of the ischium and is fused with the sacrospinous ligament

Ischiorectal (Ischioanal) Fossa (Netter 370) & Pelvic Diaphragm (Netter 355, 356)

These pictures represent the inferior surface of the pelvic diaphragm. In order to gain this perspective, it is necessary to remove the urogenital diaphragm totally, thus the inferior (superficial) fascia, the deep transverse perineus and sphincter urethrae muscles, and the deep (superior) fascia of the urogenital diaphragm have all been removed. It is also apparent that the total ischio-rectal fat pad, including the anterior recess portion have been removed.

It may be noted that in sequential order from anterior to posterior, one observes the urethra, vaginal opening, and anus with the perineal body situated between anus and vagina.

The pudendal nerve (Netter 389)

The pudendal nerve arises from cord segments S 2,3,4, the nerve passes through the greater sciatic foramen into the gluteal region and then through the lesser sciatic foramen to enter the ischiorectal fossa where it enters the pudendal (Alcock’s) canal in the lateral wall (splitting of fascia of the obturator internus. Within the deep perineal space (substance of U.G. diaphragm) the nerve gives off muscular branches (deep perineal branches.) to muscles of U.G. diaphragm and superficial pouch; the nerve then emerges to form the dorsal nerve of the penis onto the shaft. Within the ischiorectal fossa, inferior rectal banches cross medially to sphincter ani muscles; just prior to entering U.G. diaphragm, posterior scrotal nerves innervate posterior wall of scrotum.

A pudendal nerve block  (Netter 393a) is performed by injecting a local anesthetic near the pudendal nerve. It is accomplished by inserting a needle through the posterolateral vaginal wall, just beneath the pelvic diaphragm and toward the ischial spine, thus placing the needle around the pudendal nerve. A finger is placed on the ischial spine and the needle is inserted in the direction of the tip of the finger on the spine. Pudendal nerve blocks can be done subcutaneously through the buttock by inserting the needle on the medial side of the ischial tuberosity to deposit the anesthetic near the pudendal nerve.

Functional Considerations of Defecation:

Fecal continence involves the rectal sling, external anal sphincter and ischioanal fat Netter 370. When feces stored in the sigmoid colon suddenly move into the rectum, the rectal ampulla dilates and the urge to defecate is perceived. Defecation is prevented primarily by the puborectalis muscle (Netter 338)  (rectal sling) which moves the lower part of the rectum forward, effectively kinking the lumen. Additionally, when a peron is standing erect, the mass of ischioanal fat is compressed against the anal canal anteriorly and laterally by the location and tonic activity of the gluteus maximus muscle.

To prevent defecation when peritaltic waves occur, occasional voluntary contraction of the external anal sphincters (Netter 347) is required until the peristaltic waves subside. The anal sphincters relax, the internal under parasympathetic stimulation and the external, voluntarily.

Defecation. When the time and place is propitious, compression of the anal canal by the ischioanal fat is released by suitable anatomic positioning. The puborectalis muscle relaxes, allowing the rectum to straighten and descend slightly. The muscular movements of the terminal portion of the alimentary canal, assisted by gravity, evacuate the rectum. The Valsalva maneuver, which increases intra-abdominal pressure, facilitates expulsion of feces. After passage of the feces, the puborectalis muscle re-establishes the angle between the rectum and anus and the anal sphincters contract, thereby restoring anal continence

 

FEMALE Urogenital Triangle (Netter 354, 356)

In the female, the central region of the urogenital triangle remains divided into right and left sides surrounding the VESTIBULE (the common area for openings of urethra and vagina.) On either side of the vestibule, are the labia majora – folds of tissue with considerable fat in the subcutaneous region along with the bulbs of the vestibule (erectile tissue) and the greater vestibular (Bartholin’s) glands; also one finds the thin, labia minora. The clitoris (consisting of body and glans) is located in the anterior part of the vestibule and is covered partially by the prepuce of the clitoris – a flap-like fold of skin.

Within the vestibule, the urethal opening is anterior to the vaginal opening. Minute openings for the ducts of the greater vestibular glands may be noted in the postero-lateral walls of the vestibule.

The anal opening may be noted at the inferior of the diagram (located within the anal triangle).

FEMALE PERINEUM (Netter 355)

Moore, Fig. 3.52. Successive dissections (A- E) of the female urogenital triangle.

Note:

In the five diagrams of the female perineum shown in Moore Fig 3.52, it is necessary to cut out areas along the dotted lines to expose the structures which lie at sequentially deeper levels. Thus, in this picture, it is essential to cut carefully along the two triangles (regions of ischio-rectal fat pads) which lie anterior to the superficial transverse perineal muscle. In addition, it is necessary to remove the area posterior to the superficial transverse perineus, in order to see deeper structures.

MALE Urogenital Triangle (Netter 358, 359 , 360) Muscles of the superficial perineal space in the male. The superficial perineal fascia has been removed The urethral surface of the penis. The muscles in the superficial perineal space have been removed to show the crura and the penile bulb.

Muscles of Superficial Pouch (Netter 359).

In the male, the crus of the corpus cavernosum is covered by the ischiocavernosus muscle. The bulb of the penis (centrally located) is covered by the two bulbospongiosus muscles which meet in a ventral mid-line raphe. The superficial transverse perineus muscle runs from the ischial tuberosity to the central tendon of the perineum.

The functions of the ischiocavernosus and bulbospongiosus muscles are to help create and maintain an erection (contraction of muscles puts pressure on veins which are returning blood from corpora cavernosae and corpus spongiosum) and to expel semen during ejaculation and final droplets of urine following urination.

Erectile Bodies of Penis (Netter 360)

The urethra passes throughout the length of the shaft within the substance of the corpus spongiosum.

Netter 361 shows a drawing of a dissection of the deep perineal space of a male. The crura of the root of the penis have been removed. Note that the urethra is bound to the dorsum of the bulb of the penis. Examine the septum in the bulb indicating its bilateral origin. Netter 383: Observe the artery to the bulb (here double); the artery to the crus called the deep artery; and the dorsal artery which ends in the glans penis. Note the deep dorsal vein, originally double. which ends in the prostatic plexus.

The urethra in the male (Netter 362, 363) may be subdivided into three sections: 1) prostatic, passing directly through the substance of the prostate gland, which is immediately inferior to the bladder, 2) membranous part, passing through the U.G. diaphragm, and 3) the spongy part, passing through the corpus spongiosum. Within the glans penis, the urethra dilates to form the fossa navicularis. The narrowest part of the urethra is located usually at the opening on the glans penis.The bulb of the penis is attached firmly to the perineal membrane, the crura are attached laterally to the inferior pubic rami. The shaft of the penis in the flaccid state assumes a sharp angle due to the suspensory ligament, which holds the base of the shaft against the pubic symphysis. Thus, the corpus cavernosum lies anterior and the corpus spongiosum lies posterior; however, upon erection (or in quadripeds) the corpus cavernosus assumes a dorsal orientation and the corpus spongiosum becomes ventral (this is true “anatomical position”. This position of the penis accounts for the names “dorsal” for the nerve, arteries, and veins which run along the superficial surface of the corpus cavernosum on the dorsum of the penis.

Examine the diagram of the pudendal nerve in Netter Plate 389. Note the five regions in which it runs and the three divisions into which It divides. Observe the pudendal canal for the pudendal nerve and the internal pudendal vessels. Observe the thickened inferior portion of the fascia of the obturator internus muscle. In the ischiorectal fossa it it splits to form the fibrous pudendal canal Observe that the dorsal nerve of the penis runs through the deep perineal space or pouch to reach the penis

 Frontal Section of the Male Urogenital (UG) Diaphragm

In Netter 348 (bottom) image, you can appreciate the relationships of the different structures in the UG triangle from superficial to deep and medial to lateral.

First identify the hip bone and notice that it has been cut at the obturator foramen which is covered by the obturator membrane. Then identify the UG diaphragm itself.

Starting from inferior and working your way upward identify:

• Colles’ fascia – continuation of Scarpa’s fascia of abdomen
• structures in the superficial perineal space:
  • ischiocavernosus muscles
  • crura of the penis
  • bulbospongiosus
  • bulb of penis
  • perineal membrane
• UG diaphragm
• inferior fascia
• deep perineal space
• muscle in the space
• urethra
• Cowper’s gland
• superior fascia
• anterior extension of icshiorectal fossa
• obturator internus muscle
• levator ani muscle
• prostate – a pelvic structure above the UG diaphragm
• prostatic urethra
• membranous urethra – that part within the deep perineal space

Netter 374  Schematic drawings of midline sections showing the urogenital diaphragm and the perineal spaces (pouches). Understand that the superficial perineal fascia (Colles fascia) is a continuation of the deep or membranous layer (Scarpa’s fascia) of the superficial fascia of the abdomen.