Perineum

toc =**Lecture Notes**=

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

=**Objectives**=


 * 1. Define the boundaries of the anatomical region known as the perineum.**


 * in front: the [|pubic arch] and the [|arcuate ligament] of the [|pubis]
 * behind: the tip of the [|coccyx]
 * on either side: the [|inferior rami of the pubis] and [|ischium], and the [|sacrotuberous ligament]

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.

**Anal Triangle**

 * A. Define the boundaries of the [|ischioanal fossa].**
 * || ANTERIOR * [|fascia of Colles] covering the [|Transversus perinei superficialis] * [|inferior fascia of the urogenital diaphragm] ||  ||
 * LATERAL * [|tuberosity of the ischium] * [|Obturator internus muscle] * [|obturator fascia] || SUPERIOR: * [|Levator ani] INFERIOR: * [|skin] || MEDIAL: * [|Levator ani] * [|Sphincter ani externus] * [|anal fascia] ||
 * || POSTERIOR * [|Gluteus maximus] * [|sacrotuberous ligament] ||  ||

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).

The pudendal nerve originates in the [|sacral plexus]; it derives its fibers from the ventral branches of the second, third, and fourth sacral nerves (S2, S3, S4). It passes between the [|piriformis] and [|coccygeus] muscles and leaves the pelvis through the lower part of the [|greater sciatic foramen]. It crosses the spine of the [|ischium], and reenters the [|pelvis] through the [|lesser sciatic foramen]. It accompanies the internal pudendal vessels upward and forward along the lateral wall of the [|ischiorectal fossa], being contained in a sheath of the [|obturator fascia] termed the [|pudendal canal]. The pudendal nerve gives off the [|inferior anal nerves]. It soon divides into two terminal branches: the [|perineal nerve], and the [|dorsal nerve of the penis] (males) or the dorsal nerve of the clitoris (in females).
 * B. Describe the course of the pudendal nerve and internal pudendal vessels through the gluteal region and anal triangle.**

The internal pudendal artery exits the [|pelvic cavity] through the [|greater sciatic foramen] to enter the [|gluteal region]. It then curves around the [|sacrospinous ligament] to enter the [|perineum] through the [|lesser sciatic foramen]. It travels through the [|pudendal canal] with the [|internal pudendal veins] and the [|pudendal nerve].

The pudendal canal is formed by the [|obturator fascia]. It encloses the following:
 * C. Define the location and contents of the pudendal canal.**
 * [|Internal pudendal artery]
 * [|Internal pudendal veins]
 * [|Pudendal nerve]

The inferior rectal nerve crosses the [|ischiorectal fossa], with the inferior rectal vessels, toward the [|anal canal] and the lower end of the [|rectum], and is distributed to the [|Sphincter ani externus] and to the integument around the anus. The inferior rectal artery arises from the [|internal pudendal artery] as it passes above the [|ischial tuberosity]. Piercing the wall of the [|pudendal canal], it divides into two or three branches which cross the [|ischioanal fossa], and are distributed to the muscles and integument of the [|anal] region, and send offshoots around the lower edge of the [|gluteus maximus] to the skin of the [|buttock].
 * D. Describe the course and distribution of the inferior rectal nerve and vessels.**

The //superficial//, constituting the main portion of the muscle, arises from a narrow tendinous band, the [|anococcygeal raphé], which stretches from the tip of the [|coccyx] to the posterior margin of the anus; it forms two flattened planes of muscular tissue, which encircle the anus and meet in front to be inserted into the [|central tendinous point of the perineum], joining with the [|Transversus perinæi superficialis], the [|Levator ani], and the [|Bulbocavernosus].
 * E. Describe the location and divisions of the external anal sphincter muscle.**

The //deeper// portion forms a complete sphincter to the [|anal canal]. Its fibers surround the canal, closely applied to the [|Sphincter ani internus], and in front blend with the other muscles at the central point of the [|perineum].

The **perineal body** is a fibrous point in the middle line of the [|perineum]. In females, it is between the [|vagina] and [|anus], and at this point, the following muscles converge and are attached:
 * F. Define the location and importance of the perineal body.**
 * [|External anal sphincter]
 * [|Bulbospongiosus]
 * [|Superficial transverse perineal muscle]
 * Anterior fibers of the [|levator ani]

External hemorrhoids are those that occur distal to the [|Pectinate line], and involve the external rectal plexus. Internal hemorrhoids are those that occur inside the [|rectum] and involve the internal rectal plexus of veins. As this area lacks pain receptors, internal hemorrhoids are usually not painful and most people are not aware that they have them.
 * G. Define the types of hemorrhoids and the vessels involved in each type.**

The superior rectum drains to the pararectal lymph nodes and the inferior rectum drains to the sacral nodes.
 * H. Describe the lymphatic drainage of the anal triangle.**

The fat of the ishiorectal fossa serves to support the anal canal.
 * I. Understand the importance of the fat in the ischiorectal fossa.**

**Urogenital Triangle.**
The superficial perineal pouch is a fully enclosed compartment:
 * A. Describe the fascial reflections in the urogenital triangle and the relationships each layr has to the major subdivisions of the urogenital triangle (superficial and deep pouches).**
 * its inferior border is the perineal [|fascia] ([|Fascia of Colles])
 * its superior border is the [|perineal membrane]

Deep perineal pouch is partially enclosed space in the [|perineum], located superiorly to the [|perineal membrane]. Unlike the [|superficial perineal pouch], the deep perineal pouch lacks a complete superior border, though it can be inferred as the inferior fascia of the pelvic diaphragm.


 * B. Define the relationships of the fascia of the urogenital triangle to that on the anterior abdominal wall.**

Superficial layer divided into Camper’s and Scarpa’s layers. In the male, most of the fat in fatty layer is lost in the UGT. Fat is picked up again in anal triangle. Literaly no fat in scrotal, penis, however still have a lot of fat in labia majorum in female. Size changes over time, increases with puberty in female. Camper’s still persists in female. Shaft of penis has loose CT. Just beneath the skin in the wall of scrotum, there is loose CT and skeletal muscle. This skeletal muscle is known as Dartos muscle. When they contract it pulls on the dermis and changes texture of skin of scrotum à orange peel appearance à decreases size of scrotal size. Regulate distance from body wall. Three degrees temperature difference between scrotum and body. Shaft of penis and scrotum lined by Dartos layer.

Scarpar’s layer exists in UGT as membranous layer. Very thin in wall of scrotum. Cannot be distinguished between dartos. Colles’ fascia, membranous layer of superficial fascia in shaft of penis and scrotum. As it ascends posterior scrotal fascia, labia majorum, it fuses with thick fibrous, elastic, SMC tissue in both sexes. This is called Perineal Body. Subcutaneous mass. Makes barrier UG and Anal triangles. If fluid accumulates in UGT it cannot go into AT. Scarpa’s becomes Colles’ in scrotum.


 * C. Be able to trace the possible routes of spread for fluids escaping into the potential space between the superficial and deep fascia of the urogenital triangle.**

Penis, Scrotum, lower abdominal wall.


 * D. Describe the contents of the superficial and deep pouches of the urogenital triangle.**

Superficial Deep
 * muscles
 * [|Ischiocavernosus] muscle
 * [|Bulbospongiosus] muscle
 * [|Superficial transverse perineal muscle]
 * other
 * [|Crura of penis] (males) / [|crura of clitoris] (females)
 * [|Bulb of penis] (males) / [|vestibular bulbs] (females)
 * [|Greater vestibular glands] (female)
 * [|Membranous portion of the urethra] (males) / proximal portion of [|urethra] (females)
 * [|External urethral sphincter] (and [|membranous urethra])
 * [|Deep transverse perineal muscle]
 * [|Bulbourethral gland] (males)


 * E. Describe the course of the pudendal nerve and internal pudendal vessels (and branches) through the superficial and deep pouches.**

The pudendal nerve originates in the sacral plexus; it derives its fibers from the ventral branches of the second, third, and fourth sacral nerves (S2, S3, S4). It passes between the piriformis and coccygeus muscles and leaves the pelvis through the lower part of the greater sciatic foramen. It crosses the spine of the ischium, and reenters the pelvis through the lesser sciatic foramen. It accompanies the internal pudendal vessels upward and forward along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal. The pudendal nerve gives off the inferior anal nerves. It soon divides into two terminal branches: the perineal nerve and the dorsal nerve of the penis/clitoris. The perineal nerve branches into deep and superficial branches but stays in the superficial pouch; it is a mixed nerve with both motor and sensory components. The dorsal nerve pierces the perineal membrane and enters the deep pouch and has sensory branches to penis.

The internal pudenal artery branches off the internal iliac artery and, like the pudenal nerve, exts the pelvis through the greater sciatic foramen, going around the sacropsinous ligament to enter the perineum through the lesser sciatic foramen and pudendal canal. the Internal pudendal artery gives off the inferior rectal artery to the anal canal before continuing 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 then pierces the perineal membrane and enters the deep pouch at the anal and UG triangle border.

The internal pudenal vein basically flows the internal pudenal artery. It receives the veins from the urethral bulb, and the perineal and inferior hemorrhoidal veins.


 * F. Describe the autonomic components responsible for erection of the penis/clitoris and for ejaculation.**

Corpus cavernosum has more erectile tissue than the corpus spongiosum and most of the rigidity of penis during an erection is due to the crura and the corpus cavernosum. Erectile tissue is a rich venous sinusoid that fills with blood during erection. 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, causing them to uncoil and dump arteriole blood into the erectile tissue. The tough Buck’s fascia restricts the deep dorsal vein, preventing blood from escaping from the erectile tissue. Additionally, the ischiocavernosus muscles also acts to restrict the diameter of the penis during erection to help trap blood. Muscles of the superficial perineal pouch are contracted to help propel the last bit of urine. They are involuntarily contracted during ejaculation.


 * G. Describe the arrangement of the erectile bodies for the penis/clitoris.**

In the male, the bulbospongiosus muscle is a pair of fused muscles found medially in the superficial pouch. Laterally on both sides of the bulbospongiosus muscle are the left and right ischiocavernosis muscles. Neither the ischiocavernosis muscles or bulbospongiosus muscles extend to the shaft of the penis. Inferior to these muscles and on either side are the superficial transverse perineal muscles. Deep to the ischiocavernosus muscles and bulbospongiosus muscle is the erectile tissue: the left and right crus of the penis and the bulb of the penis in the middle. These three bodies anchor the penis. The left and right crus continue to the shaft of the penis, changing its name to the corpus cavernosum. The bulb of the penis also continues to the shaft of the penis and changes its name to the corpus spongiosum. The 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.

The shaft of the cliteris is formed by the continuation the erectile tissue of the two crura, which become the corpus cavernosum. The ischiocavernosus muscle ends at the clitoris. The bulbospongiosus muscles in the female remain separated around the vestibule. The erectile body at posterior edge, deep to the bulbospongiosus muscles on either side, is the bulb of the vestibule.


 * I. Define the blood and nerve supply to the penis/clitoris.**

Internal pudendal artery enters the deep pouch at the anal and UG triangle border to supply urethra, muscle, and glands. As it approaches the pubic symphysis, it splits into its two terminal branches: deep artery of the penis/clitoris and dorsal artery of the penis/clitoris. The deep artery of the penis/clitoris goes back through the perineal membrane to the crura in the superficial pouch. The dorsal artery goes to supply the dorsal aspect of the penis/clitoris.

Deep fascia of the penis is Buck’s fascia around the erectile fascia. The superficial fascia between Buck’s fascia and the skin is the dartos fascia. Big vein on the dorsal side of the penis 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, the 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.


 * J. Define the position and importance of the muscles in the superficial and deep pouches.**

__Superficial Pouch__ In the male, the bulbospongiosus muscle is a pair of fused muscles found medially in the superficial pouch; they remain separated in the female because of the position of the vestibule. Laterally on both sides of the bulbospongiosus muscle are the left and right ischiocavernosis muscles. either the ischiocavernosis muscles or bulbospongiosus muscles extend to the shaft of the penis. Inferior to these muscles and on either side are the superficial transverse perineal muscles. Muscles of the superficial perineal pouch are contracted to help propel the last bit of urine. They are involuntarily contracted during ejaculation. They crura of the penis and bulb of the penis are erectile tissue that anchor the penis. They continue on to the shaft the penis as the corpus cavernosum and corpus spongiosum, respectively. The female has equivalent structures, the crura of the clitoris and vestibular bulbs, respectively. The female also has the ducts of the greater vestibular glands that open inferior and on either side of the vaginal opening.

__Deep Pouch__ The male urethra can be seen piercing the peritoneal membrane. The deep transverse perineal muscles inferiorly and deep to the superficial transverse perineal muscles and perineal membrane. The other muscles of the deep pouch are called the external urethral sphincter and collectively act on the urethra as a 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 neutralize the acidity of the male urethra and vagina.


 * K. Be able to define the following:**

__Vulva__ The external [|genital organs] of the female consisting of the //[|labia majora]// and //[|labia minora]//, [|clitoris], opening of the [|urethra] ([|meatus]), and the opening of the [|vagina].

__Vestibule__ The [|vestibule] is a part of the [|vulva] between the [|labia minora] containing the [|urethral opening] and the [|vaginal opening].

__Prepuse__ The [|prepuse] is a retractable piece of skin which covers the [|glans].

__Hymen__ The [|hymen] (is a fold of [|mucous membrane] which surrounds or partially covers the external [|vaginal] opening.

__Episiotomy__ An [|episiotomy] is a [|surgical] incision through the [|perineum] made to enlarge the [|vagina] and assist childbirth.

__Circumcision__ [|Circumcision] is a [|surgical] procedure which consists in cutting some or all of the [|prepuce] from the [|penis]. When performed to [|clitoral prepuce] in some cultures, it is referred to as [|female genital mutilation] and often includes at least the partial removal of the clitoris.