HBF-III LEC 06 Gross Anatomy Perineum Notes 2025 (PDF)

The Perineum Dennis J. Goebel, Ph.D. Course Learning Objectives I. Describe the normal anatomy of the perineum. Session Learning Objectives Describe the normal anatomy of the male and female perineum. Describe the anatomy of the bones that form the skeleton. Describe the...

The Perineum Dennis J. Goebel, Ph.D. Course Learning Objectives I. Describe the normal anatomy of the perineum. Session Learning Objectives Describe the normal anatomy of the male and female perineum. Describe the anatomy of the bones that form the skeleton. Describe the anatomy of the muscles and facial coverings of the perineum. Describe the anatomy of the nerves that innervate structures. Describe the anatomy of arterial supply and venous drainage. Describe the anatomy of skin, joints, and fiscal tissues. Describe the anatomy of compartments, spaces, and transition areas. Describe the anatomy of glands and organs. Describe anatomical relationships of all structures. II. Relate the anatomy of each structure of the male and female perineum to its function(s). Relate the anatomy of bones to structural attachments functions. Relate the anatomy of muscles to actions on structures. Relate the anatomy of nerves to innervation of structures. Relate the anatomy of vessels to structures supplied or drained. Relate the anatomy of connective tissues to attachment functions. Relate the anatomy of compartments, spaces, & transition areas to connective functions. Relate the anatomy of glands and organs to visceral functions. III. Apply anatomical knowledge of the male and female perineum to evaluate clinically relevant problems. Apply anatomy to evaluate deficits of nerve lesions. Apply anatomy to evaluate effects of tissue damage/pathology. Apply anatomy to evaluate clinical approaches & procedures. Apply anatomy to evaluate radiological images. The Perineum Dennis J. Goebel, Ph.D. Session Outline I. The perineum A. Boundaries of the perineum B. Subdivisions of the perineum 1. Urogenital triangle 2. Anal triangle II. The urogenital triangle A. Compartmentalization of the urogenital (UG) triangle 1. Deep compartment (space or pouch) a. Suspension of UG-diaphragm b. Perineal membrane c. Boundaries of the deep compartment of the UG-diaphragm. d. Contents of the deep compartment of the UG-diaphragm. 2. Superficial compartment (pouch/space) of the UG triangle a. Deep perineal fascia b. Structures contained by the deep perineal fascia c. Components of the superficial compartment (space/pouch) III. Male external genitalia A. Scrotum and penis 1. The scrotum a. Function b. Innervation c. Blood supply 2. The penis a. Corpora cavernosum b. Corpus spongiosum c. Tunica albuginea d. The body of the penis 3. Innervation of the perineum a. The pudendal nerve pathway and branches b. Autonomic innervation of the erectile tissues 4. Blood supply 5. Venous return IV. Female external genitalia A. Components of the pudendum 1. Mons pubis 2. Labia majora 3. Labia minora 4. The clitoris 5. The Vestibular bulb 6. The greater vestibular glands 7. Innervation 8. Blood supply and venous return V. Anal triangle of the perineum A. Boundaries and contents of the anal triangle 1. The ischioanal fossa The Perineum Dennis J. Goebel, Ph.D. a. boundaries of the ischioanal fossa 2. Contents of the ischioanal fossa a. The pudendal canal b. Nerves and blood vessels c. Ischioanal fat pad 3. Anal canal VI. Clinical Relevance A. Pudendal nerve block B. Episiotomy C. Damage to the male urethra 1. Anterior urethral injuries (Straddle-type injury) 2. Posterior urethral injuries 3. Intercourse-related trauma to the corpora cavenosa/ distal penile urethra The Perineum Dennis J. Goebel, Ph.D. THE PERINEUM I. The Perineum is a diamond-shaped region, located just inferior to the pelvic diaphragm. It supports the attachments of the male and female external genitalia, and accommodates the terminal pathways for the urinary and gastrointestinal tracts. A. Boundaries of the perineum (Figure 1) 1. Anterior- pubic symphysis 2. Posterior- tip of the coccyx 3. Lateral- ischial tuberosities, Gray's, Figure 1: Fig. 5.32 Gray’s 5.32 ischiopubic rami and sacrotuberous ligaments 4. Superior- pelvic diaphragm B. Subdivisions: The perineum can be further subdivided into two triangular regions (the urogenital and anal triangles) by a line that traverses both ischial tuberosity’s (Figure 2). 1. The urogenital triangle (UG) is located anterior (ventral) to this transverse dashed line (defined by the ischial tuberosities, ischiopubic rami and pubic symphysis). It contains the urogenital diaphragm, external genitalia, and the terminal part of the urinary tract. 2. The anal triangle is located posterior (dorsal) to this transverse dashed line. This space is defined by the coccyx, sacrotuberous ligament and ischial tuberosities. Deep to the skin, this region contains the anal canal, the ischioanal fat pad and ischioanal fossa which will be describe later in these notes (Figures 1 & 2). Figure 2: Netter 358 The Perineum Dennis J. Goebel, Ph.D. II. The Urogenital triangle A. Compartmentalization- The UG-triangle is occupied by several distinct layers of fascia which, subdivides this region into a deep- and superficial-pouch/compartment. 1. The deep-pouch/compartment is comprised of a muscular diaphragm called the urogenital diaphragm, (designated UG diaphragm). It is attached laterally along the ischiopubic rami and bridges across the full extent of the UG-triangle. a. The deep compartment contains the deep transverse perineal muscle and associated muscle fibers that contribute to the urethra in the male and female. These muscles lie superiorly to a fibrous aponeurotic sheet called the perineal membrane. Together, they form the UG-diaphragm (See Figure 3). i. The perineal membrane (also known as the inferior perineal fascia) is located inferior to the deep transverse perineal muscle. It is made up of a tough aponeurotic sheet (tendinous sheet), which maintains the integrity of the UG diaphragm (See Figure 3 showing a female UG diaphragm). b Suspension of the UG diaphragm: In addition to the UG diaphragm being suspended laterally by the ischiopubic rami, it is also anchored at its posterior border (at midline) by a thickened centralized tendon called the perineal body. The perineal body is attached to the adjacent anal canal, which in turn, is suspended posteriorly by the anal coccygeal ligament to the coccyx at midline (See Figure 3 and Figure 4 on next page). Figure 3 (Gray’s 5.36) c. The boundaries of deep pouch of the UG diaphragm i. Anterior- The body of the pubis, (just lateral to the pubic symphysis). Note, there is an opening in the UG diaphragm that bridges the pubic symphysis. This opening is called the hiatus for deep dorsal vein. See Figures 4 & 5a. ii. Lateral- ischiopubic rami (IPR) up to the ischial tuberosities. The Perineum Dennis J. Goebel, Ph.D. iii. Posteriorly- a transverse line through ischial tuberosity’s extending to midline attachment called the perineal body (Figure 4). iv. Superiorly- Investing fascia (referred to as the superior perineal fascia) form from the fascia coverings from the levator ani and obturator internus muscles. v. Inferiorly- the perineal membrane. Figure 4: (N356a) d Contents of the Deep pouch (compartment) in the Male (M) see Figure 5a, and in the Female (F), see Figure 5b: on next page. i. Deep transverse perineal muscle (M & F) ii. Compressor urethrae and sphincter urethrovaginalis (F) iii. Membranous urethrae (M & F) iv. External urethral sphincter (also referred to as the sphincter urethrae muscle) (M & F) v. Bulbourethral glands (M) vi. Dorsal N. Penis/Clitoris (M/F) vii. Internal pudendal artery and veins (M & F) viii. Dorsal and Deep arteries of the penis/clitoris (M/F) The Perineum Dennis J. Goebel, Ph.D. Figure 5a: (N361b) Figure 5b: (N356b) 2. The superficial pouch (compartment) of the urogenital triangle of the male and female: For ease of discussion, the superficial compartment/ pouch in the perineum is defined by the space occupied inferior to the perineal membrane. See Figure 6. a. Contents of the superficial pouch: (See Figure 6) i. Erectile tissues (corpus cavenosum (M & F), corpus spongiosum (M) and vestibular bulb (F)). ii. Erectile tissue muscles (Ischiocavenosus and bulbospongiosus (M&F)) iii. Bulb of the penis (M) iv. Greater vestibular glands (F) The Perineum Dennis J. Goebel, Ph.D. 3. Fascia layers defining the perineum: a. Deep perineal fascia: The deep perineal fascia is derived from the deep investing fascial layer of the anterior abdominal muscles and gives rise to: i. Gallaudet’s fascia (the investing fascia of the erectile tissue muscles (ischiocavenosus and bulbospongiosus m.) in both male (Figures 6 & 7) and female (See Figure 24 of these notes). This fascia has firm attachment to the posterior border of the perineal membrane, and laterally to the ischiopubic rami. ii. Deep penile fascia of the penis (also known as Buck’ fascia) and the deep clitoral fascia in the female. These fascia’s invest the erectile tissues that make up the penis and clitoris, and will be described later in these notes. Figure 7: (N361c) b. Superficial perineal fascia: is a membranous layer that is continuous with Scarpa’s fascia (the membranous layer of the subcutaneous fascia that covers the anterior abdominal wall). It attaches to the free edge of the UG diaphragm and to the inferior margins of the ischiopubic rami. See Figures 8 & 9. i. In the male, the superficial perineal fascia consists of Colle’s fascia posterior to the scrotum, and Dartos fascia (which contains smooth muscle fibers). Dartos fascia covers the scrotum and forms the superficial penile fascia, which surrounds the body of the penis. Both layers lack adipose tissue. See Figures 8 & 9. ii. Due to the continuity of Scarpa’s fascia with Colle’s (M & F) and Dartos (M) fascia in the perineum, an infection, fluid accumulation or hemorrhage resulting from a laceration of the anterior abdominal wall between Scarpa’s’ and the deep The Perineum Dennis J. Goebel, Ph.D. investing fascia of the abdominal muscles, can result in fluid accumulation in the perineum. Here, the fluid would reside in between the superficial perineal fascia (Colles’ fascia) in the female, and (Dartos fascia) in the male (M) and the deep perineal fascia (Gallaudet’s (M &F) and the deep penile fascia (Bucks fascia ,(M)). See Figures 8 and 9. a. It is important to note that the in the male perineum, both Colle’s and Dartos layers of the scrotum are bound posteriorly to the free border of the UG diagram, and laterally along the ischiopubic rami (indicated by the dashed lines in Figure 9 below). Therefore, fluid accumulation in the superficial pouch will be restricted from gaining access to the ischial anal fossa and inferiorly into the region of the thighs. See dashed lines in Figure 9 (on the next page) highlighting the inferior boundary of Scarpa’s and the superficial perineal fascia (Colle’s and Dartos fascia’s) in the male. i. Same is true in the female, except that the superficial perineal fascia consists only of Colle’s fascia (e.g., lacks a Dartos layer). The Perineum Dennis J. Goebel, Ph.D. Figure 9 III. Male External Genitalia A. Consists of the scrotum and penis 1. The scrotum is a double sac, separated by a septum, which house the testicles. It consists of two layers, an outer layer of skin containing hair follicles and glands (sweat and sebaceous) overlying a thickened fascial layer (defined as the superficial perineal fascia) that contains smooth muscle fibers (in the male this is called the Dartos layer: Figure 10). The Perineum Dennis J. Goebel, Ph.D. Figure 10: (N365a) a. Function: The scrotum regulates testicular temperature by contracting, in response to the cooling of the testicles, or relaxing in response to an elevation of temperature. b. Innervation: Sensory innervation to the scrotum is provided by: (Details to follow in Section 3 of these notes.) i. Anterior scrotal N. (branch of ilio-inguinal N.) ii. Genital branch of genitofemoral N. iii. Posterior scrotal (branch of pudendal N.) iv. Perineal branch of posterior femoral cutaneous N. c. Blood supply is provided by: (Details to follow in Section 4 of these notes) i. Posterior scrotal A., a branch of the internal pudendal A. ii. Anterior scrotal A., a branch of the external pudendal A. iii. Testicular A. which provides a very small contribution to the scrotum. 2. The penis: is composed of three cylinders of specialized erectile tissue (corpora cavernosa (paired) and a single mid-line tube called the corpus spongiosum), Proximal ends of both are firmly anchored to the UG-diaphragm. These erectile tissues are each invested by muscles and two layers of perineal fascia in the UG- triangle; and converge to form the pendulous part of the penis, defined as the body of the penis (Figure 11). a. Corpora cavernosum (CC) are paired cylinders of erectile tissue, with their proximal ends (called crus) fused to inferior surface of the perineal membrane of The Perineum Dennis J. Goebel, Ph.D. the urogenital diaphragm, and to the medial surface of the ischiopubic rami (Figure 11). The distal ends of the CC form 2/3's of the penile body, and terminate with blunted ends that are capped by the glans of the penis (terminal part of the corpus spongiosum: see section 2.b. below). In the UG triangle, the crus of the corpus cavernosa are directly invested by deep penile fascia (aka, Buck's fascia: See Figure 12, on next page), followed by the covering by the rt & left ischiocavenosus muscles (See Figure 12), and then invested by a second layer of the deep perineal fascia (called Gallaudet’s fascia (See Figure 12). Both Buck’s and Gallaudet’s fascia are derived from the deep investing fascia of the abdominal muscles. Note that the deep perineal fascia (Gallaudet’s) blends with the deep penile fascia (Buck’s) on the body of the penis (See Figure 12). Figure 11a: (N360b) Figure 11b: (N360a) b. The corpus spongiosum (CS) is a single midline cylinder of erectile tissue that contains the penile urethra. At its proximal end, it is firmly attached to the perineal membrane, and is regionally defined as the penile bulb. The penile urethra receives mucus secretions from the paired bulbo-urethral glands (Cowper’s glands, shown in Figure 14) that empty into the penile bulb (Figure 11a), which defines the transition from the membranous urethra (located within the UG diaphragm) to the penile urethra (See Figure 14). As the corpus spongiosum continues ventrally, it attaches in between the two corpora cavernosum on their inferior surface to collectively form the body of the penis. The corpus spongiosum is also invested by the deep penile fascia (Buck’s fascia), from the penile bulb to the margin of corona of the glans of the penis. Note that the glans of the penis is not covered by Buck’s fascia, or by the The Perineum Dennis J. Goebel, Ph.D. superficial penile fascia (Dartos fascia). Figure 12: (N375a, 5th Edition) c. Tunica albuginea: Each of the erectile tissues (corpora cavernosum and spongiosum) has a thickened fibrous outer capsule called the tunica albuginea (see Figure 13). Figure 13: N359b The Perineum Dennis J. Goebel, Ph.D. d. The body of the penis is a pendulous structure that is attached to the inferior surface of the pubic symphysis by the suspensory ligament of the penis (best illustrated in Figure 20). This ligament is derived from the investing fascial layer of the abdominal muscles. The body of the penis terminates as the glans of the penis (See Figure 14). At the tip of the glans the penile urethra terminates as external urethral meatus. Just deep to this opening is an expanse in the penile urethra called the navicular fossa, which is designed to disrupt the linear flow of urine to produce a concentrated stream upon urination (See Figure 14). Figure 14: (N363) The Perineum Dennis J. Goebel, Ph.D. 3. Innervation of the perineum is provided mostly by the pudendal N. a. The pudendal N. i. Pathway of the pudendal N.: The pudendal N. has its origin from the sacral plexus and is derived from ventral rami of sacral nerves S2-4. The rt &L pudendal nerves exit out of the pelvis into the gluteal region via the greater sciatic foramen and enter the perineum, though the lesser sciatic foramen, by passing posterior to the sacral spine & sacrospinous ligament, and anterior to the sacrotuberous ligament (See Figure 15). Note that the pudendal nerve enters the perineum in the region of the ischioanal fossa of the anal triangle (Figure 15). Figure 15: (N389b) ii. Proximal branches of the Pudendal N. The branching pattern of the pudendal nerve in the male and female are identical, however, naming of their respected branches related to the penis/clitoris within the perineum are gender specific. a. Inferior Rectal N: Upon entering the perineum, the right and left pudendal N’s. give off 2-3 branches in the anal triangle, that traverse the ischioanal fat pad (in a lateral to medial direction) in route to the levator ani, and anal sphincter muscles (Figure 15 above & Figure 16 on the next page). These branches provide motor and sensory innervation to the muscles and mucosae of this region. Note, the inferior pudendal N’s are the only branches of the pudendal nerve that are “exposed” to the ischial anal fossa. The Perineum Dennis J. Goebel, Ph.D. b. Distal branches of the pudendal N. After giving off the inferior rectal N.s, the pudendal nerve, and accompanying internal pudendal artery and vein, run along the lateral perineum wall, on the surface of the obturator internus muscle. Both artery and nerve are invested by the obturator internus fascia, until they reach the posterior border of the UG diaphragm. This region is defined as the pudendal canal (See Figure 16). c. At the posterior boundary of the UG diaphragm, the right and left pudendal nerves split to give rise to the perineal N, and to the dorsal nerve of the penis (male), or dorsal nerve of the clitoris (female). i. Each perineal nerve splits to give rise to a superficial perineal N. (sensory) and to a deep perineal N. (which provides motor to the following erectile tissue muscles: Superficial transverse perineal muscle and the muscles located in the deep compartment, e.g. external urethra sphincter m. and deep transversus perineal muscle). The superficial perineal branch terminates in the male as the posterior scrotal nerve (See Figure 16: below and Figure 17: on next page); and in the female, the posterior labial nerve (See Figure 25a later in these notes) and provides sensory to these regions. Figure 16: (N389a) The Perineum Dennis J. Goebel, Ph.D. d. The dorsal nerves (Rt & L) (of the penis or clitoris) enter the deep compartment (DC) of the UG diaphragm on its superior surface (piercing the superior perineal fascia), and run along the ischiopubic rami border almost up to the anterior border of the UG-diaphragm (See Figure 16 on the previous page and Figure 17 below). These nerves exit the UG- diaphragm by piercing the perineal membrane, and then run along the crus of the corpus cavernosum to the dorsal body of the penis in the male (see Figure 16), and on the crus of the clitoris in the female: (See Figure 25 of these notes). In both the male and female, the rt & left dorsal nerves travel on the dorsal surface of the erectile tissues of the penis/clitoris. The nerves are then invested by the deep penile fascia of the penis (Buck's fascia) in the male; and in the female, by the deep clitoral fascia. These nerves provide sensory to the body & glans of the penis/clitoris. See Figure 17 (male) and Figure 26 (female). Innervation of the perineum Pudendal N. (Motor/sensory) Cavernous N. (Parasympathetics from pelvic splanchnics (S2,3,4) and sympathetics from inferior hypogastric plexus) Dorsal N. Penis (Clitoris). Inf. Rectal N. (motor/sensory) DC Perineal N. PM (IFPF) Deep Perineal N. DS-SC (motor) Deep penile fascia Superficial Perineal N. (sensory) Deep perineal fascia SS-SC Post. Scrotal (labial) N. (sensory) Superficial perineal fascia Figure FigureDJG 17:3 (DJG3) b. Autonomic input to the erectile tissues: Autonomic input to the erectile tissues of the penis (and clitoris in female) is supplied by the pelvic splanchnic nerves (preganglionic parasympathetic fibers derived from the ventral rami of S2, S3, and S4) and sympathetic innervation from the sacral splanchnic nerves (L1- L2). Both utilize the inferior hypogastric plexus (located in the pelvis) to reach their targets. These nerves converge to form cavernous nerves. The cavernous nerves pierce the pelvic and UG diaphragms to innervate the erectile tissues in both male and female (See, Figure 17). The Perineum Dennis J. Goebel, Ph.D. Blood supply: The branching pattern of the male and female internal pudendal arteries are identical, however as is the case with the nerves above, the naming of terminal branches are gender specific. (See Figure 18 a & b and Figure 19). The arterial supply to the deep structures of the perineum is provided by the internal pudendal artery, which is a branch of the internal iliac artery located in the pelvis. The internal pudendal artery follows the same pathway as the pudendal nerve in leaving the pelvis and entering the perineum. Once in the perineum, the internal pudendal artery gives off an inferior rectal branch in the ischioanal fossa, and then proceeds within the pudendal canal to the free border of the UG diaphragm. Here, the pudendal artery gives rise to a perineal branch, (which supplies structures within the superficial compartment), and a deep artery of the penis/clitoris upon piercing the deep compartment of the UG diaphragm. Once in the deep compartment of the UG diaphragm, the Rt & L internal pudendal arteries branch, and give off a deep artery of the penis/clitoris, which supplies the corpus cavenosum, and a dorsal artery of the penis/clitoris. See Blood supply to the male in Figure 19. Figure 18a: (N383a) Figure 18b: (N383b) Figure 19: (DJG4)  The Perineum Dennis J. Goebel, Ph.D. 5. Venous return: The naming of the branches of the internal pudendal veins mirror their arteries, and most follow the return path alongside their arterial counterparts into the internal pudendal vein. The exception to this is the venous return from the erectile tissues by the deep dorsal vein of the penis/clitoris. a. In the male, the deep dorsal vein passes from the perineum into the pelvis through the hiatus for the deep dorsal vein (located between the inferior surface of the pubic symphysis and the UG-diaphragm) and empties into the prostatic plexus located in the floor of the pelvis (See Figure 20). b. In the female the deep dorsal vein of the clitoris follows the same path, and empties into the inferior vesical plexus (See Figure 21 on next page). 6. As a side note, the skin of the penis and the clitoris, are supplied by the Rt or L external pudendal artery and vein (a branch of the femoral artery and vein). Venous return from these veins empty into the systemic (Caval) venous system (via. external pudendal veins). Figure 20 The Perineum Dennis J. Goebel, Ph.D. Figure 21 IV. Female External Genitalia A. Component of the pudendum: Consists of the mons pubis, labia majora, labia minora, clitoris, vestibule, bulbs of the vestibule, crura of the clitoris, vestibular gland, vaginal and urethral orifice (see Figure 22 on next page), and is collectively named, the vulva or pudendum. 1. The mons pubis: is a rounded fatty elevation located anterior to the pubic symphysis. It consists of an underlying fatty layer of subcutaneous connective tissue and is covered with course pubic hair beginning at the onset of puberty. Posterior to the mons pubis are the Labia majora (majus) and Labia minora (minus). 2. Labia majora (majus), which are two symmetrical folds of skin, provide protection for the vaginal and urethral orifices. These folds are lined with subcutaneous fat, covered with pubic hair and flank the pudendal cleft (a slit between the labia majora, which opens to the vestibule of the vaginal). The labia majora meet anteriorly to form the anterior labial commissure (See Figure 22). 3. Labia minora (minus) are paired hairless folds of skin (with little subcutaneous fat) that flank the vestibule of the vagina. Unlike the labia majora, the two folds of labia minora join anteriorly at the base of the clitoris as the anterior frenulum and posteriorly, as the posterior frenulum of the labia minor (See Figure 22 on next page). The Perineum Dennis J. Goebel, Ph.D. Figure 22 4. The clitoris (Figure 23) is formed by the joining of the paired corpus cavernosa. As in the male, each corpus cavernosum forms a crus (paired), which firmly attach to the perineal membrane and ischiopubic rami. The corpus cavernosa are invested by a deep clitoral fascia, which is much thinner than its male counterpart (Buck’s fascia). The crus of the clitoris is covered by a Rt & L ischiocavenosus muscle and invested by the deep perineal fascia (Also called Gallaudet’s fascia). a. The body of the clitoris is derived mostly from the corpus cavernosum, however, there remains some controversy as to whether the vestibular bulb contributes to the body and the glans of the clitoris. The body and glans of the clitoris is covered anteriorly by a wrap of skin called the prepuce (Figure 22). Figure 23  The Perineum Dennis J. Goebel, Ph.D. Figure 24: (N356a) 5. Vestibular bulb is the male equivalent of the corpora spongiosum, however unlike the male; they are paired in the female (Figure 22 on previous page). They are located lateral to the vaginal/urethra orifice at the base of the labia minora, are firmly attached to perineal membrane, and invested by a thin layer of deep clitoral fascia. Each is covered by a bulbospongiosus muscle and then invested by the deep perineal fascia (also known as Gallaudet’s fascia). See Figure 24. 6. Greater vestibular glands are located within the base of the labia minora, posterior to the vestibular bulbs, and just lateral to the vaginal opening. These glands provide mucus lubrication to the vaginal opening upon sexual stimulation. Both glands give off a short duct that opens just lateral to the vaginal opening. Note, the external urethra orifice is located just anterior to the vaginal orifice and is also contained by the labia minora (Figure 24). 7. Innervation of the female perineum parallels that of the male, and is supplied by the right and left pudendal nerves (see Figure 25 on next page). Each branches into the inferior rectal, perineal N. and dorsal N. of the clitoris. The perineal N. gives rise to the superficial perineal N. (which is mostly sensory and terminates as the posterior labial N.) and the deep perineal N. provides motor fibers to the erectile tissue muscles and the muscles in the deep compartment. The dorsal N of the The Perineum Dennis J. Goebel, Ph.D. clitoris enters the deep compartment and travels along the ischiopubic ramus. It then pierces the perineal membrane and then travels on the superior surface of the curs of the clitoris, with each branch then reflecting onto their respective sides of the dorsal surface of the body of the clitoris. Both rt and left nerves terminate on the glans of the clitoris. See Figure 25. 8. Blood supply and venous return of the clitoris parallels that of the male, with the internal pudendal artery providing the perineal and the dorsal- and deep-arteries of the clitoris (See Figure 26). a. Venous return of the clitoris is from the deep dorsal vein, which passes through hiatus of the deep dorsal vein (ventral to the UG diaphragm), and enters the floor of the pelvis. The deep dorsal vein of the clitoris drains into the vesical plexus surrounding the bladder (See Figure 21 on page 17 of my notes). Figure 25: (N391) Figure 26: (N382a) The Perineum Dennis J. Goebel, Ph.D. V. The Anal Triangle A. The anal triangle is defined as the region that is posterior (dorsal) to the transverse line between the ischial tuberosities, flanked laterally by the sacrotuberous ligaments, and posteriorly by the tip of the coccyx (Figure 27). The anal triangle contains the ischioanal fossa, anal canal, the external anal sphincter, ischioanal fat pad and the pudendal canal (which allows passage of the internal pudendal artery/vein and pudendal nerve (S2-4) to structures associated with the perineum. Figure 27: (N257) 1. The ischioanal fossa is occupied by the ischioanal fat pad, a fibrous/elastic fat mass that maintains the shape of the region surrounding the anal canal (in the ischial anal fossa). It extends into the anterior recess (superior to the UG diaphragm) and occupies the space within the ischioanal fossa that approximates the pelvic diaphragm. With the ischioanal fat pad removed, the pelvic diaphragm can be observed (see Figures 25 and 26). a. Boundaries of the ischioanal fossa i. The roof of the ischioanal fossa is formed by the levator ani (pelvic diaphragm), which encircles the anal canal (See Figures 24, 25 & 26). ii. The walls are defined by the coccyx, sacrotuberous ligament, the obturator internus muscle and the ischiopubic rami. iii. The ischioanal fossa has direct communication with the anterior recesses (paired), a space that is bounded: a. Inferiorly: by the UG diaphragm, b. Medially::by the levator ani/pelvic diaphragm, The Perineum Dennis J. Goebel, Ph.D. c. Laterally: by the obturator internus muscle/fascia, the medial surface of the ischiopubic rami and anteriorly by the body of the pubis (See Figure 28). Figure 28: (DJG9) 2. Contents of the ischioanal fossa (IAF): a. The pudendal canal: Accommodates the passage (between the surface of the obturator internus muscle and its fascia) of the internal pudendal artery & Vein and the pudendal N (S2-S4) from their entrance into the ischial anal fossa to structures associated with the UG triangle (Figure 29). Figure 29: N389a The Perineum Dennis J. Goebel, Ph.D. b. Inferior rectal Art, vein & Nerves: (Discussed above) c. Ischioanal fat pad 3. The Anal Canal will be discussed in detail in a future lecture; however, its relationship with the ischioanal fossa, needs some discussion here. The anal canal is anchored at midline by the anococcygeal ligament (posterior to the canal) and the perineal body anteriorly to it (See Figure 27 on page 21 of these notes). VI. Clinical Relevance A. Pudendal nerve block(s) for surgical procedures involving structures within the perineum: Knowing the anatomy of the perineum with respect to the location of pudendal canal and the ischial spine, are essential to direct administration of anesthesia to the perineum. B. Episiotomy: During the process of birthing, it may be necessary to surgically enlarge the birth canal to accommodate the delivery of the baby. To prevent damage to the pubococcygeus muscle of the levator ani, a controlled incision is made (either by a median incision from the posterior opening of the vagina to the external anal sphincter, or by a medial/lateral incision from the posterior wall of the vagina towards the ischiopubic rami). C. Damage to the male urethra. Clinically, damage to the male urethra is classified as being either an anterior urethral injury (damage within the bulbar or penile urethra of the corpus spongiosum) or a posterior urethral injury (involving damage to the prostatic or membranous urethra within the pelvis). 1. Anterior Urethral Injuries: Damage to the bulbar (penile) urethra usually results from a direct blunt trauma (e.g. slipping off the pedals of a bike and hitting “the bar” or the “stem of the handle bars”) to the perineum region (referred to as a Straddle- type injury). In most cases straddle-type injury does not result in pelvic fractures however, the corpus spongiosum containing the bulbar and penile urethra are particularly vulnerable to tearing by the direct force of the impacting object. Urine leakage and hematoma formation from the ruptured corpus spongiosum (and its investing fascia, e.g. Bucks) can then escape into the superficial perineal compartment, where it is retained by the superficial perineal fascia (e.g. Colle’s and Dartos layer of the scrotum and the superficial penile fascia). 2. Posterior Urethral injuries: Most commonly are caused by pelvic fractures resulting from a decelerating impact e.g., car accident (high speed head-on crash, or falling from heights). In most cases, the shearing force from the impact to the pelvis results in the dissociation (tearing) of the membranous urethra from the prostatic urethra. Urine and blood leakage will be contained above the UG diagram within the endopelvic fascia surrounding the prostate gland in the pelvis. Note that the endopelvic fascia is continuous with transversalis fascia of the abdominal wall, thus allowing the accumulating urine and blood from the rupture urethra to flow within the plane of transversalis fascia, and be contained by the parietal peritoneum of the body wall. The Perineum Dennis J. Goebel, Ph.D. 3. Intercourse-related trauma to the male corpora cavernosa and distal penile urethra: The copra cavernosa is particularly vulnerable to damage (rupture) by blunt trauma when the penis is erect. Usually this results from the penis being bent and compressed against the female pubis during intense intercourse. In 20% of these cases, the penile urethra and corpus spongiosum are also damaged. Tearing of the deep penile fascia (Bucks) usually occurs allowing the blood from the erectile tissues to gain access into the superficial compartment of the perineum. Hematomas are retained by the superficial perineal fascia (Colle’s and Dartos fascia of the scrotum), as well as by the superficial penile fascia. If bleeding is extensive, hematomas can make their way up the anterior abdominal wall being contained by Scarp’s fascia. Sources for figures in the notes: Drake, Vogl and Mitchell, Gray's Anatomy for Students, 3rd Ed., Churchill & Livingstone, Philadelphia, © 2015. Netter, Atlas of Human anatomy, 6th Ed., Saunders, Philadelphia, © 2014. The Perineum Dennis J. Goebel, Ph.D.