TBL23 - Perineum

Question 1

What is the perineum?

Answer 1

The perineum is a shallow, subcutaneous compartment immediately inferior to the pelvic diaphragm between the superomedial thighs

Question 2

When the lower limbs are abducted, what shape does the perineum take and where does it extend from and to?

Answer 2

When the lower limbs are abducted, the perineum is diamond-shaped extending from the pubic symphysis to the tip of the coccyx and between the ischial tuberosities

Question 3

What does an imaginary line between the ischial tuberosities form in the perineum? What is the central point of the perineum called? What occupies the anterior urogenital (UG) triangle? What occupies the posterior anal triangle?

Answer 3

1) An imaginary line between the tuberosities forms the anterior urogenital (UG) triangle and posterior anal triangle
2) The central point of the perineum is the perineal body
3) The genitalia and urethra occupy the UG triangle
4) The anal canal and anus reside in the anal triangle

Question 4

What does the urogenital hiatus allow to exit the pelvic cavity? What is the perineal membrane and where does it span?

Answer 4

1) The urogenital hiatus enables the urethra, and in females the vagina, to exit the pelvic cavity
2) The perineal membrane is a fascial sheet that spans across the urogenital hiatus and stretches between the ischiopubic rami to cover the UG triangle

Question 5

What does the perineal membrane separate the UG triangle into? Where does the urethra traverse into and where is this in relation to the perineal membrane? After perforating the perineal membrane, where does the uretha enter?

Answer 5

1) The perineal membrane separates the UG triangle into deep and superficial pouches
2) Thus, the urethra traverses the urogenital hiatus into the deep pouch, which is superior to the perineal membrane
3) After perforating the perineal membrane, the urethra enters the superficial pouch that is inferior to the perineal membrane

Question 6

What covers both perineal triangles? Like the fascia of the anterolateral abdominal wall below the umbilicus, what does the perineal fascia consist of?

Answer 6

1) Skin and subcutaneous fascia cover both perineal triangles
2) Like the fascia of the anterolateral abdominal wall below the umbilicus, the perineal fascia consists of a superficial fatty layer representing the continuation of Camper’s fascia and a deep fibrous layer called Colles fascia, a continuation of Scarpa’s fascia

Question 7

In males, what is the Scarpa’s fascia continuous with on the penis and scrotum? What does the dartos (smooth) muscle join? Posterior to the scrotum, what is the dartos fascia continuous with? Where does the Colles fascia extend to?

Answer 7

1) In males, Scarpa’s fascia is continuous with the dartos fascia on the penis and scrotum
2) The dartos (smooth) muscle joins the dartos fascia on the scrotum
3) Posterior to the scrotum, the dartos fascia is continuous with Colles fascia
4) Colles fascia extends to the posterior margin of the perineal membrane

Question 8

Notice the presence of contents of the deep and superficial pouches in both sexes. What separates the two pouches?

Answer 8

The perineal membrane stretches between the ischiopubic rami to separate the pouches

Question 9

What is the deep pouch between? What resides in the deep pouch?

Answer 9

1) The deep pouch is the shallow space between the pelvic diaphragm and the perineal membrane
2) The voluntary external urethral sphincter and compressor urethrae, a slip of skeletal muscle from the pubococcygeus in females, reside in the deep pouch

Question 10

What is the deep transverse perineal muscle and where does it reside?

Answer 10

The deep transverse perineal muscle, a slip of involuntary smooth muscle from the muscularis externa of the superior portion of the anal canal, resides in the deep pouch of both sexes

Question 11

In the superficial pouch, what is the perineal membrane a foundation for and what are the associated erectile tissues covered by?

Answer 11

In the superficial pouch, the perineal membrane is a foundation for the bulb and crura of the penis, the body of the clitoris, and the associated erectile tissues, which are covered by thin sheets of skeletal muscle

Question 12

What is the superficial transverse perineal muscle? What are the structures of the superficial pouch covered by?

Answer 12

1) The superficial transverse perineal muscle is a slip of smooth muscle from the muscularis externa of the anal canal
2) The structures of the superficial pouch are covered by dartos fascia in males and Colles fascia in both sexes

Question 13

Where is the anal triangle in relation to the UG triangle? In both sexes, where does the fatty layer of perineal fascia extend into, what are these structures filled with and what do they surround?

Answer 13

1) The anal triangle is posterior to the UG triangle
2) In both sexes, the fatty layer of perineal fascia extends posteriorly into the ischioanal fossae, which are filled with white fat and surround the anal canal

Question 14

Where does the perineal body lie?

Answer 14

The perineal body lies at the site of convergence of the voluntary external anal sphincter with the transverse perineal muscles and the bulbospongiosus muscle

Question 15

Do the perineal membrane and Colles fascia extend into the anal triangle? Is the anal triangle separated into superficial and deep pouches?

Answer 15

1) The perineal membrane and Colles fascia do not extend into the anal triangle
2) Thus, the triangle is not separated into superficial and deep pouches

Question 16

What clinical consequences can occur if the perineal body is damaged during childbirth?

Answer 16

1) Stretching or tearing the attachments of perineal muscles from the perineal body can occur during childbirth, removing support from the pelvic floor
2) As a result, prolapse of pelvic viscera, including prolapse of the bladder (through the urethra) and prolapse of the uterus and/or vagina (through the vaginal orifice) may occur

Question 17

Why is a mediolateral episiotomy preferable to a median episiotomy?

Answer 17

1) The perineal body is the major structure incised during a median episiotomy. When further tearing does occur, it is directed toward the anus, and sphincter damage or anovaginal fistulae are potential sequelae. Recent studies indicate median episiotomies are associated with an increased incidence of severe lacerations, associated in turn with an increased incidence of long-term incontinence, pelvic prolapse, and anovaginal fistulae
2) Mediolateral episiotomies appear to result in a lower incidence of severe laceration and are less likely to be associated with damage to the anal sphincters and canal. (Note: The clinical use of the term mediolateral is technically inappropriate here; it actually refers to an incision that is initially a median incision that then turns laterally as it proceeds posteriorly, circumventing the perineal body and directing further tearing away from the anus)

Question 18

What does the obturator fascia cover and what does it form? What does this structure provide a passageway for and where?

Answer 18

1) Obturator fascia, which covers the medial surface of the obturator internus muscle, forms the pudendal canal
2) The pudendal canal provides a horizontal passageway in the perineum for the internal pudendal artery and pudendal nerve (S2-S4)

Question 19

What do branches of the anterior division of the internal iliac artery supply? What are the internal pudendal artery and inferior gluteal arteries branches of and what does the internal pudendal artery supply?

Answer 19

1) The anterior division of the internal iliac artery has aforementioned branches that supply the pelvic viscera
2) The internal pudendal artery, which supplies the perineum, and the inferior gluteal arteries are branches of the anterior division of the internal iliac artery

Question 20

What is the superior gluteal artery a branch of? What do branches of the posterior division of the internal iliac artery supply?

Answer 20

1) The superior gluteal artery is a branch of the posterior division of the internal iliac artery
2) Branches (ignore names) of the posterior division also supply the posterior abdominal wall

Question 21

Where do the internal pudendal artery and pudendal nerve emerge from? Where do they travel and descend?

Answer 21

1) The internal pudendal artery and pudendal nerve emerge from the greater sciatic foramen into the gluteal region
2) They immediately hook around the sacrospinous ligament to traverse the lesser sciatic foramen into the perineum where they descend to the pudendal canal

Question 22

What does the pudendal nerve provide to the perineum? Where does the inferior rectal nerve course and what does it innervate?

Answer 22

1) The pudendal nerve provides somatic motor and sensory fibers to the perineum
2) The inferior rectal nerve (branch of pudendal nerve but ignore other branches) courses through the white fat of the ischioanal fossae to innervate the external anal sphincter and anus