Perineum+-+Lecture+Notes

=**Objectives**= toc

Perineum

=**Lecture Notes**=

[|Lecture 1] [|Lecture 2] [|Lecture 3]



**Lecture 1**
Female Pelvis is Wider, Lighter (muscle mass is thinner). The subpubic angle ~90 degrees. The ridge of bone circumferentially arranged by the hip bones is called the pelvic brim. It delineates the pelvis from peritoneum. Portion above pelvis above pelvic brim – false pelvis (greater pelvis). Contains abdominal organs (cecum, sigmoid colon). The true pelvis is below the pelvic brim. The pelvic inlet is the junction between false and true pelvis. Non-pregnant uterus is in the true pelvis but when pregnant, the uterus expands into the false pelvis to the abdominal cavity. Urinary bladder is also in the true pelvis and expands into the false pelvis as it fills.

Male Pelvis -- Not as wide. Subpubic angle ~60 degrees

Acetabulum (Small cup of vinegar) – where femur sits. 3 Bones of Hip: Red --> Pubis, Blue --> Ischium, which contains: ischial tuberosity (what you sit on), ischial spine (protuberance that separates the superior Greater Sciatic notch and the inferior Lesser Sciatic notch), arteries and nerves that leave the pelvis leave via greater/lesser sciatic foramen. Yellow --> Ilium which contains Obturator Foramen – closed over by muscle and fascia



Lateral View: Sacral-tuberous ligament and Sacral-spinous ligament, together with superior and inferior sciatic notches, creating the greater and lesser sciatic foramen, respectively. Function to let structures get through pelvis without going through pelvic floor.

Sacral spinous ligament and sacral tuberous ligament

Sacral spinous ligament and sacral tuberous ligament

Pelvic outlet forms a diamond: Inferior aspect of pubic symphysis, tip of coccyx, and ischial tuberosities.

Pelvic dimensions: important especially during childbirth. Superior edge of pubic symphysis to sacral promontory (superior tip of S1) --&gt; conjugate (obstetrical) dimension, ~11 cm. Inferior edge of pubic symphysis to sacral promotory --&gt; Diagonal conjugate, ~11 cm. ~11 cm diagonal conjugate is sufficient for vaginal delivery of pregnancy. Narrowest dimension in birth canal is the distance between ischial spines when non-pregnant. During childbirth, relaxin relaxes the joints of the pelvis, especially the pelvic symphysis, increases the distance between ischial spines. However, the conjugate (anterior-posterior) dimension is fixed and is the narrowest dimension of the birth canal during childbirth.

Pelvic floor, superior view. Pelvic diaphragm – muscles that close the pelvic outlet, not including the piriformis muscle and obturator internus muscle. Piriformis muscle goes through the greater sciatic foramen. Obturator internus covers the obturator foramen and goes to lesser schiatic foramen. Both are lower limb muscles. If you go through the pelvic diaphragm, you enter the perineum. Perineum is inferior to the pelvic diaphragm, below medial aspect of two thighs in anatomical position.

Diaphragm is highly concave with fibers that are almost vertical and form a sort of funnel.



Pelvic diaphragm are directed inferiorly towards the pelvic outlet, giving concavity to superior aspect.

The perineum when thighs are abducted in the lithotomy position, it forms a diamond shape and can be divided into a posterior anal triangle and anterior urogenital triangle. Dermatomes: L1 goes over the pelvic symphysis; the dominant dermatomes of anal triangle are S3-S5

Gluteus Maximus is not part of the anal triangle but part of the lower limb. Anal canal is the last few centimeters of the GI tract passing through pelvic floor. Anus is the opening. On either side of the anus are recessses that are packed full of fat on the posterior aspect of the pelvic diaphragm (ischioanal fat). The recesses on the left and right of pelvic diaphragm are called the ischioanal fossa. Fat compresses sides of anal canal to keep it closed but flexible enough to move aside during defecation. The last fat used when a person is in starvation. Abscesses common in ischioanal fossa. Fat does communicate right and left. Anococcygeal body – fibrous body where fat from ischioanal fossi can communicate between perineal body and anus. Perineal body – another fibrous body. Important in female during childbirth – episiotomy or incision into the perineal body to increase the aperture of the vaginal opening to avoid tearing during delivery.



Ischioanal fossae on either side are pyramidal with the base at the skin and apex deep where the fibers of the pelvic diaphragm take origin at obturator internus. Fibers of pelvic diaphragm muscles are taking origin at the fascia of obturator internus. The obturator internus makes up lateral wall of the ischioanal fossa and the pelvic diaphragm makes up the medial wall. Fascia of obturator internus splits and forms a tunnel called the pundendal canal on either side containing the internal pudendal vessels (artery and vein) from internal iliac vessels inside the pelvis and pudendal nerve from the sacral plexus (S2-S4). This neurovascular bundle supplies the perineum. The pudendal nerve leave the pelvis through the greater sciatic foramen and re-enter through the lesser sciatic foramen to keep from piercing the pelvic diaphragm. External anal sphincter is on either sides of the anal canal. This is a voluntary sphincter to regulate its action. The smooth muscle internal sphincter is a thickened portion of the GI tract. The internal sphincter is always contracted by the sympathetic canal, keeping the anal canal close. As the rectum fills with feces, it distends, causing the parasympathetic system to relax the internal sphincter. The external anal sphincter can still control defecation up to a point.

Internal pudendal vessels and pudendal nerve are on the lateral wall of the peritoneum. The first branch of these vessels is the Inferior rectal artery, vein and nerve, distributing to the anal triangle. Inferior rectal nerve supplies sensory to skin and motor component to external anal sphincter.



Anal canal is divided to an upper portion and the lower portion. The upper portion has longitudinal ridges called anal columns, circumferentially. These are formed by blood vessels in the submucosa. These blood vessels are the terminal arteries of the superior rectal artery. Venous blood goes into the inferior mesenteric vein to splenic vein to the portal vein (portal drainage). Lower portion of anal columns are connected by mucosal folds called anal valves, collecting mucuous. During defecation, the valves are pressed up against wall of anal canal, squeezing mucous out to help lubricate the anal canal for passing feces. Internal venous plexus are where the veins of the anal columns dumps to. There venous-venous and arteriole-venous anastomoses at the anal canal – why blood from tear in anal canal is bright red. Junction between the anal column and the smooth lower portion of the anal canal is the pectinate line and is the junction between the endoderm and ectoderm. Nerve supply, blood supply, and lymphatics is different. Ectoderm: Somatic innervation – pain, temperature, pressure; Blood from inferior rectal artery and vein; Lymphatics – drain to inguinal nodes. Endoderm: Autonomic innervation – sensitive to distension; Arteries – inferior mesenteric artery; Lymphatics – drains to internal iliac lymph nodes. Anal Fissure – tear in lining of the anal canal; usually in lower part of anal canal – very painful because of somatic innervation. Anal fissures are often caused by foreign objects placed into anal canal or not drinking enough water – feces are hard



**Lecture 2**
Path of the pudendal nerve, which runs with the internal pudendal artery and vein

Hemorrhoids are varicosities. Chronic intra-abdominal pressure increases impede blood flow in veins in abdominal pelvic cavity. In women, a common cause is pregnancy. Other causes include abdominal tumor, or cirrhosis of the liver from drug/alcohol abuse, blocking portal vein blood flow. Venous drainage related to superior rectal vessels, and forms the anal columns in the lumen of the anal canal. These superior rectal veins around the anal columns, when under pressure, will protrude into the lumen of the anal canal. If they protrude enough, defecation can cause abrasion and cause bleeding. These are internal hemorrhoids. Sometimes they can prolapse through the anus, but are still internal hemorrhoids.

External hemorrhoids are varicosities on the external or superficial venous plexus from the inferior rectal vein. Internal hemorrhoids are submucosal while external hemorrhoids are subcutaneous. Internal hemorrhoids in general drain into the IVC; external hemorrhoids in general drain to the portal vein. However there is a rich anastomoses. Internal hemorrhoids used to be treated aggressively; nowadays, treated only if they prolapsed. Development of internal hemorrhoids can lead to development of external hemorrhoid or vice versa because of the anastomoses and continued presence of whatever is blocking the venous drainage. Internal hemorrhoids are associated with the upper portion of the anal canal and are not painful. They may bleed or itch, but are not painful, even if they protrude.

Camper’s and Scarpa’s fascia from anterior abdominal wall extend down to UG triangle. Camper’s layer in the male just deep to skin on penis does not have any fat and is replaced by loose CT or smooth muscle (in scrotum). The smooth muscle is known as the dartos muscle. This muscle regulates the size of the scrotal sac and is temperature sensitive. High temperature --> dartos muscle relaxes to expand the scrotal sac, vice versa. Buck’s fascia is deep fascia of the penis or clitoris and necessary for erection. In the female, the camper’s layer retains its fat to make the labia majora and called the labial fat. It is the equivalent of the male dartos layer. Scarpa’s layer also extends down to the peritoneum. It looses its distinction in the shaft of the penis/clitorus, labia majora, and wall of scrotum. Colles fascia is membranous layer just deep to the skin posteriorly approaching the border of the UG and anal triangle and in the same plane as the Scarpa’s layer. Colles fascia forms a partition in the perineum isolates the UG triangle from anal triangle. Dartos/Colles fascia defines a pouch that subdivides the UG triangle and makes the superficial pouch. Its inferior limit (floor) is the dartos/colles fascia. The roof is called the perineal membrane, extends from side to side, filling in the ischiopubic rami. There is a fascia reflection from the perineal membrane that faces the pelvis superior to it and creates another little pouch called the deep pouch. Superficial pouch + Deep pouch --> UG triangle

Scrotum removed, revealing the cut edge of Colles fascia. Penis and clitoris belongs in the superficial pouch. Pair of muscles lateral in the superficial pouch are the left and right ischiocavernosis muscle. Slightly more inferiorly is a pair of fused muscles called the bulbospongiosus muscle and is usually refered to is one muscle. Even more inferiorly and attaches to the ischial tuberosity is the superficial transverse perineal muscle. Both the ischiocavernosis muscles or bulbospongiosus muscle do not extend to the shaft of the penis.

Erectile tissue is a rich venous sinusoid. During erection, blood is trapped. Deep to the ischiocavernosus muscles or bulbospongiosus muscle are the erectile tissue of the left and right crus of the penis. The erectile shaft continues out towards the shaft of the penis and changes its name to the corpus cavernosum. There are 2 corpus cavernosum. Muscles of the superficial perineal pouch are contracted to help propel the last bit of urine. It is involuntarily contracted during ejaculaton. Ischiocavernosus muscle acts like a sleeve and restrict the diameter of the penis during erection that allows the penis to be engorged with blood. Medially, there is another erectile tissue called the bulb of the penis. The root of the penis is composed of 2 crus and a bulb. When the bulb reaches the shaft of the penis, it continues on as the corpus spongiosum. Urethra pierces the peritoneal membrane, enters the bulb and through the corpus spongiosum and exits the external urethral orifice.

Corpus spongiosum expands at the distal tip into the glans. Running the length of the bulb and corpus spongiosum is the urethra. Corpus cavernosum ends bluntly but remain separate and don’t fuse into one. At the top, the corpus cavernosum forms a cap. Corpus cavernosum has more erectile tissue than the corpus spongiosum. Most of the rigidity of penis during erection is due to the crura and the corpus cavernosum. Between the bulb and the crus, is the perineal membrane, extending across the ischiopubic rami.

Remove the erectile tissue and you reveal the perineal membrane, the deepest extent of the superficial pouch. The male urethra can be seen piercing the peritoneal membrane.

Removing the perineal membrane exposes the deep pouch. Deep transverse perineal muscle inferiorly. Only thing separating the superficial and deep transverse perineal muscles is the perineal membrane. Deep pouch muscles act on the urethra as a sphincter and are called the external urethral sphincter to stop/prevent flow of urine. Bulbururethral (Cowper’s) gland in the deep pouch are accessory reproductive glands. These glands have ducts that go through the perineal membrane and enter the urethra in the superficial pouch. It secretes an alkaline secretion prior to the bulk of the ejaculate to neutralizes the acidity of the male urethra and vagina. Internal pudenal artery enters the deep pouch to supply urethra, muscle, and glands. As it appoaches the pubic symphysis, it splits into its two terminal branches: deep artery of the penis and dorsal artery of the penis. The deep artery of the penis goes back through the perineal membrane to the crus in the superficial pouch. The dorsal artery goes to supply the dorsal aspect of the penis. Dorsal surface of the penis faces anterior when flacid. Male is in anatomical position when erect. Know the inferior rectal artery, dorsal artery, and internal perineal artery

Internal pudendal artery gives off the inferior rectal artery to the anal canal and continues to the border of the anal and UG triangle. As it approaches the border, it gives off a branch called the perineal artery which distributes to structures of the superficial pouch – muscles, skin, posterior aspect of scrotum. Internal pudendal artery enters the deep pouch at the anal and UG triangle border.

Internal perineal nerve gives off the inferior rectal nerve and the perineal and dorsal nerve. Pertineal nerve goes to the superficial pouch is a mixed nerve. Dorsal nerve to the penis goes to the deep pouch and has sensory branches to penis.



Deep fascia of the penis is Buck’s fascia around the erectile fascia. The fascia between Buck’s fascia and the skin is the dartos fascia. Big vein on the dorsal side is the superficial dorsal vein in the subcutaneous tissue, draining skin of penis. Deep to Bucks’ fascia is the deep dorsal vein. Flanking the deep dorsal vein is a pair of dorsal arteries (terminal branch of the internal pudendal artery). Lateral to the dorsal arteries on each side are the dorsal nerves. Urethra is on the ventral side. Corona of the glans of the penis has the highest concentration of nerve endings. Arrangement of deep dorsal arteries and veins essential to deriving the erection of the penis/clitoris. Sympathetic nervous system keeps arteries in the flaccid penis coiled and doesn’t let a lot of blood into the erectile tissue. During arousal, the parasympathetic nervous system relaxes smooth muscles in the arteries that uncoil the arteries and dumps arteriole blood into the erectile tissue. The tough Buck’s fascia restricts the deep dorsal vein, preventing blood from escaping from the erectile tissue.

Foreskin: double layer of skin called prepace. Smegma is a substance that is secreted between the glans and foreskin. Balonitis: inflammation of the glans, most common in boys who are still wearing diapers. Priapism: pathologically erect penis; erection that lasts more than 4 hours is not a sexual response but a neurological response; compromises the blood supply in the area. Phimosis: foreskin is a tight collar around the skin and cannot be retracted, resulting in discomfort. Paraphimosis: foreskin is retracted but is unable to return over the glans, forming a tight collar around the shaft and the glans, compromising the blood supply of the glans. Deep pouch is about the thickness of a cracker. Calles fascia comes up the dorsal side of the scrotum through the perineum and to the perineal body. Tears in the urethra can result in urine leaking out into the superficial fascia. Urine can accumulate into the shaft of the penis or the scrotum or even the anterior abdominal wall (deep to Scarpa’s fascia). However, colles fascia blocks the UG triangle from the anal triangle so fluid cannot go posteriorly to the anal triangle. In females, the urethra ends right away so it won’t leak into the superficial pouch.



**Lecture 3**
Deep fascia of the penis is Buck’s fascia around the erectile fascia. The fascia between Buck’s fascia and the skin is the dartos fascia. Big vein on the dorsal side is the superficial dorsal vein in the subcutaneous tissue, draining skin of penis. Deep to Bucks’ fascia is the deep dorsal vein. Flanking the deep dorsal vein is a pair of dorsal arteries (terminal branch of the internal pudendal artery). Lateral to the dorsal arteries on each side are the dorsal nerves. The deep arteries and dorsal arteries do not have paired veins. Superficial vein of the penis dumps into the veins of the thigh. Dorsal vein of the penis will pass through the perineal membrane and dump into a venous plexus in the pelvis on the other side of the pubic symphysis. Urethra is on the ventral side. Corona of the glans of the penis has the highest concentration of nerve endings. Arrangement of deep dorsal arteries and veins essential to deriving the erection of the penis/clitoris. Sympathetic nervous system keeps arteries in the flaccid penis coiled and doesn’t let a lot of blood into the erectile tissue. During arousal, the parasympathetic nervous system relaxes smooth muscles in the arteries that uncoil the arteries and dumps arteriole blood into the erectile tissue. The tough Buck’s fascia restricts the deep dorsal vein, preventing blood from escaping from the erectile tissue.

Superficial fascia of the female UG triangle is equivalent to the darthos fascia of the male. All of the female external genitalia is known as the vulva. The mons pubis is included in the vulva. Extending from the mons pubis are the labia majora. Labia majora are created because of deposition of fat dependent on hormonal influence (sexual maturity will make the labia majora more prominent until menopause when it regresses). Anterior commissure and posterior commissure are where labia majora meet at the anterior and posterior ends. Posterior commissure may regress after first vaginal delivery. Labia minora are medial to the labia majora and contain no fat and mostly CT and skin. Labia minora unite anteriorly and posteriorly. Anteriorly, the labia minora forms a prepuce, reflecting over the clitoris and forming a hood. There is variation of how much the prepuce covers the clitoris. Labia minora help direct the flow of urine. Space bound by two labia minora is known as the vestibule. Anteriorly, the glans of the clitoris project into the vestibule. Posteriorly, is the external urethral orifice. Posterior to that is the vaginal orifice. Posterior and laterally to either side are the two openings of the duct of the vestibule gland. These glands secrete mucous to maintain lubrication in the area of the vestibule and are homologs of the male prostate gland. Skene’s glands have ducts emptying along the length of the urethra and lateral to the urethral orifice. The vaginal orifice is fairly irregular. It is a rather smooth contour in a virginal female but sexual activity, tampoon use, and sport activities results in irregular contour. Hymen is the thin fold that projects into the vaginal orifice. Small tags give irregular contours to vaginal orifice and are remnants of the hymen. Developmentally, the hymen was a complete separation of the vagina and the outside. By birth, the hymen should become perforate.

Skene’s glands have ducts along the urethra and in the vestibule adjacent to the urethral orifice. Part of the female orgasm myth. Anterior wall of the vagina has a high number of sensory nerve endings just before the pubic symphysis wall. This point is usually refered to as the “G” spot.

Presence of urethra and vagina keep the erectile bodies separate from the midline. Flanking the wall of the vestibule is the bulbospongiosis muscle. Deep to the bulbospongiosis muscle is the bulb of the vestible on each side. Behind the ischiocavernosus muscle are the paired crus of the vestibule. Female also has superficial transverse perineal muscle. Episiotomy: cut through the perineal body to prevent tearing during vaginal delivery. Perineal nerve goes into superficial pouch, takes care of muscles, and skin. The bulbs of the vestuble extends anteriorly and stop. They do not continue to the shaft of the clitoris. Perineal membrane forms roof of the superficial pouch.

Shaft of the cliteris is formed by the contination of the two crura. When it gets there it becomes the corpus cavernosum. Erectile body at posterior edge is greater vestibular gland, duct empties into the vestibule and is deep to the bulbospongiosus muscle. Contraction of the bulbospongiosus muscle contracts the vestibular glands and erectile tissue. Ischiocavernosum muscle serves as a sleeve like in the male, to trap blood. Cliteris is organ of sexual pleasure only. In the deep pouch, there is absence of bulbourethral gland. 2 muscles: deep transverse perineal muscle, and the sphinter urethrus.

Nerves in the female are the same as male.

Female arteries also same as male: Inferior rectal, Perineal and Dorsal artery from the internal perineal artery.

Laterally are the left and right crus coated by the ischiocavernosus muscle. Peritoneal membrane just behind the bulbospongiosus muscle. Bulb of the vestibule are 2 bodies of erectile tissue. Superficial and deep transverse perineal muscles, external anal sphincter, bulbouspongiosus muscle inserts into the peritoneal body. Episiotomy should not disrupt too much of these muscles.

Male only has one body of erectile tissue where the urethra enters.