Anatomy of the perineum Flashcards
What are the different degrees of perineal tears?
- It depends on how deep the tear is
1) First degree: involves the superficial muscles only
2) Second degree: It extends to the deeper muscles of the perineum, but the anal sphincter is still intact
3) Third-degree tear: Involves superficial, deep, and the anal sphincter
4) Fourth-degree tear: When the tear gets more deep affecting the rectum
What is meant by episiotomy?
A cut incision through the area between the vaginal opening and the anus to facilitate childbirth
What happens if the perineal body was injured (during vaginal delivery or episiotomy)?
The pelvic organs (urinary bladder, ureters, etc) will prolapse
Where will the urine go in case of trauma to the pelvic region?
- If the urethra ruptures as it gets crushed against the symphysis pubis the urine content would go to colle’s fascia (the membranous layer of the superficial fascia of the perineum around the superficial perineal space and it is continuous with the Scarpa’s fascia)
What is the perineum?
It is a diamond shape region at the medial aspect of the upper thigh (superomedial to the thigh)
What are the boundaries of the perineum?
1) Anteriorly: Pubic symphysis
2) Anterolaterally: Ischiopubic rami
3) Laterally: Ischial tuberosities (body structure we sit on)
4) Posteriorly: Tip of the coccyx
5) Posterolaterally: Sacrotuberous ligaments (extends from the sacrum to the ischial tuberosities)
What are the divisions of the perineum?
The diamond-shaped perineum is divided into two triangles:
- Urogenital triangle (anteriorly)
- Anal triangle (Posterior)
- Formed by an imaginary line that passes through the ischial tuberosity on either side
What are the important spaces/pouches that is deep into the colle’s fascia?
1) Superficial perineal pouch
2) Deep perineal pouch
What are the urogenital structures of a female perineum?
- Posterior
- Vaginal opening
- Urethral opening
- Clitoris formed of two main parts:
- Glans clitoris
- Prepuce of clitoris (skin-like flap)
- Mons pubis (fatty pad “merging of the labia”)
- Labium minus/minora (inner flaps/folds)
- Most anterior
What are the urogenital structures of the male perineum?
- Once we remove the scrotum we will see the root of the penis which consists of erectile tissues (not muscles):
- The bulb of the penis (located centrally)
- Crus of the penis (lateral to the bulb of the penis one on each side)
What are the fascias that are found in the urogenital triangle?
- Most superficial
- Superficial fascia/Colle’s fascia
- Perineal membrane
- Inferior pelvic fascia
- Deepest structure
When dissecting the urogenital triangle describe the structures we pass through
- Skin
- Superficial fatty layer and the deep membranous layer (colle’s fascia AKA superficial perineal fascia)
- Superficial perineal pouch
- Deep fascia of the perineum (encloses the muscles in the superficial perineal pouch, must be removed to access the muscles in the superficial perineal pouch)
- Perineal membrane (aka the inferior fascia of the urogenital diaphragm, it separates the superficial and deep perineal pouches)
- Deep perineal pouch
- Superior layer of the urogenital diaphragm (aka inferior pelvic fascia)
- Levator ani
- Superior layer of the pelvic diaphragm (aka superior pelvic fascia)
What are the layers of the superficial fascia?
- Fatty layer
- Deep membranous layer/Colle’s fascia/Superficial perineal fascia where;
- Anteriorly it is continuous with the fascia of the Scarpa of the anterior abdominal wall, fascia of the penis, dartos of the scrotum
- Deep perineal fascia
What are the layers of the deep fascia of the urogenital triangle?
1) Perineal membrane (AKA inferior fascia of the urogenital diaphragm)
2) Inferior pelvic fascia (superior fascia of the urogenital diaphragm/inferior fascia of the pelvic diaphragm/endopelvic fascia
What are the boundaries of the superficial perineal pouch?
1) Floor: Colle’s fascia/perineal fascia
2) Roof: Perineal membrane
3) Laterally: Pubic arch
4) Posteriorly: Fused with the perineal membrane
5) Anteriorly: Open (anterior abdominal wall, scrotum, penis), it is limited by the pubic symphysis
What is the fascia that colle’s fascia is continuous with?
Colle’s fascia is continuous with Scarps’s fascia in the abdomen and it extends downwards to be continuous with the fascia of the penis and further inferior with the dartos fascia of the scrotum
What are the structures we see when we remove the colle’s fascia?
- Perineal membrane (inferior layer of the urogenital diaphragm)
- Deep into it we find the inferior pelvic fascia/endopelvic fascia (superior layer of the urogenital diaphragm)
- The space between colle’s fascia (most ant and the perineal membrane “the middle layer” is the superficial perineal pouch/space)
- The space between the perineal membrane (middle layer) and the inferior pelvic fascia (last layer) is the deep perineal pouch/space
- FYI the perineal membrane separates the two spaces
- To access the muscles that are in the superficial perineal pouch we have to remove the fatty layer the membranous layer (colle’s fascia) then the deep fascia of the perineum which covers the muscle
Why does urine accumulate at the superficial perineal pouch in case of urethral rupture?
The splitting of the deep membranous layers folds after attaching to Holden’s line on the sides forms a pocket that goes to the Ant.abd.wall, and thus a urethral rupture will result in urine accumulation at the superficial perineal pouch only and it won’t escape to the thigh due to holden line
What are the attachments of the perineal membrane?
- Laterally: Periosteum of the ischiopubic rami
- Apex/anteriorly: Arcuate pubic ligament “inferior pubic ligament” (between the pubic symphysis), it is thickened to form the perineal ligament
- Posteriorly: It continues with the inferior pelvic fascia, colle’s fascia and it is attached to the perineal body
What are the boundaries of the deep perineal pouch?
- Found between the perineal membrane inferiorly and inferior pelvic fascia superiorly
- Floor: Perineal membrane
- Roof: Pelvic fascia
- Laterally: Pubic arch
- Posteriorly: Fused with the perineal membrane to the pelvic fascia
- Anteriorly: Fused with the perineal membrane to the pelvic fascia
What are the contents of the superficial pouch in males?
1) Root of the penis (bulb & the 2 cruras)
2) 3 muscles:
- Bulbospongiosus (covers the bulb which is located centrally, it is located in the middle)
- Ischiocavernosus (covers the Crus and it is the closest to the ischiopubic ramus)
- Superficial transversus perineal
- FYI: These muscles are in both females and males and they run over the erectile tissue (bulb + crus)
3) Vessels and nerves:
- 2-Scrotal nerves
- 2 Scrotal vessels
What is the perineal body?
A fibromuscular point where multiple muscles insert including:
1) Anal sphincter
2) Levator ani
3) Superficial transverse perineal muscle
4) Bulbospongiosus muscle
5) Deep transverse perineal muscle
- If the perineal body is torn, all of these muscles can be affected
What is the nerve supply of the perineal muscles?
- Mainly by the pudendal nerve and its branches
- The pudendal nerve passes through the pudendal canal
- As the pudendal nerve enters the perineal region it gives off three main branches:
1) Dorsal nerve of the penis/clitoris (first branch and it moves anteriorly)
2) Inferior rectal nerve (second branch and it moves posteriorly)
3) Perineal nerve (3rd branch and it supplies the perineal muscles)
- A muscular branch of the perineal nerve enters the deep perineal pouch where it supplies the deep perineal muscles and then it pierces the perineal membrane to supply the muscles of the superficial perineal pouch
The perineal nerve is found in the deep or superficial perineal pouch?
Deep, its posterior scrotal/labial branch is a content of the superficial perineal pouch
What are the branches of the perineal nerve?
- Muscular (AKA deep perineal nerve), goes to the deep perineal pouch
- Posterior crotal (AKA superficial perineal nerve), goes to the superficial perineal pouch
Sumarrize the nerve supply of the perineum
- Pudendal nerve (enters through the pudendal canal)
2a. Inferior rectal nerve
2b. Dorsal nerve of the penis/clitoris
2c. Perineal nerve
2c.1) Muscular
2c.2) Posterior scrotal/labial nerve
Summarize the blood supply of the perineum
1) Inferior pudendal artery
1a) Inferior rectal artery
1b) Dorsal artery of the penis/clitoris
1c) Perineal artery
1c.1) Muscular artery
1c.2) Posterior scrotal/labial artery
What are the contents of the superficial perineal pouch in females?
1) Root of the clitoris, formed of:
- Bulb of the vestibule
- Crus (2 crura)
2) 3-muscles
- Bulbospongiosus (covers the bulb)
- Ischiocavernosus (covers the crus)
- Superficial transversus perineal
3) Vessels and nerves:
- 2 Labial nerves
- 2 Labial vessels
4) Gland: The superficial vestibular
Compare the vascularity of the female erectile tissue with the males
The female erectile tissue is highly vascular (the bulb is very vascular) which makes it susceptible to disruption of vessels due to trauma for example which will result in vulvar hematoma in the labia majora
What is the difference between the nerve and vascular innervation of the female and male perineum?
The nerves are the same in both males and females, but in females, the posterior labial nerves and arteries are involved.
What are the contents of the deep perineal pouch in males and females
1) Urethra of both
2) Bulbourethral/Cowper glands (males), its ducts open into the urethra
3) Vaginal opening (females)
4) Muscles:
- Deep transverse perineal (both)
- Sphincter urethrovaginalis (touches the urethra and encircles the vagin) and compressor urethra (located anteriorly, in front of the urethra, and they assist in compressing the urethra) (females)
- FYI: Only the DTP makes up the urogenital diaphragm in males. For females, the 3 muscles that we’ve just discussed make up the UGD.
5) Dorsal nerve of the penis/clitoris
6) Deep branches of the internal pudendal vessels and the perineal nerve
In summary, what is the perineal body?
- A fibro-muscular tissue attached to the midline between the anal and urogenital triangles, its dimmanod in shape between (pubic symphysis “ant”, the two ischial tuberosities “lat”, and the coccyx “post”)
- Subdivided into triangles (the anterior triangle is the urogenital region and the posterior triangle is the anal region)
- It serves as a central point of attachment for:
- External anal sphincter muscle (inferior “its anterior part”)
- Bulbospongiosus muscle (from the ant aspect)
- Superficial transverse perineal muscle (from the sides)
- Deep transverse perineal muscle (comes from the deep perineal pouch)
- Levator ani (puborectalis/pubovaginalis) muscles (inferiorly)
- These muscles support the pelvic floor
- The perineal body is larger in females
- The perineal body is very important for the support of the pelvic viscera
What is the clinical significance of the perineal body?
- Childbirth can lead to damage (stretching/tearing) of the perineal body which might lead to prolapse of the pelvic viscera
- Episitomy (planned surgical incision during delivery, which is made from the frenulum and extends posterolaterally to avoid the anal sphincter) can avoid this
Very important in females, as during vaginal delivery, a small incision (episiotomy) is sometimes made, so it is crucial to be careful not to injure these structures
What are the orifices in the perineum?
- Urogenital region:
- Urethral orifice
- Vaginal orifice
- Anal region
- Anal orifice
When do we see colle’s fascia?
Once we remove the skin and the fatty layer of the superficial fascia, the membranous layer we see after that is the colle’s fascia (superficial), the membranous part continuous with colle’s and covers the anal region is the inferior pelvic fascia
- Once we remove colle’s fascia we see the deep fascia of the perineum which covers the muscles (superficial perineal muscles “bulbospongiosus, ischiocavernosus, and the superficial transverse perineal muscles”)
- Below the muscles is the perineal membrane/inferior fascia of the UG diaphragm (roof of the superficial pouch)
- When we remove the perineal membrane/inferior fascia of the urogenital diaphragm we will see the deep perineal pouch which includes muscles (deep transverse perinei in both sexes and the sphincter urethrovaginalis and compressor urethra in females)
- When we go deeper into the deep pouch we will see the inferior pelvic fascia covering the urogenital triangle
- When we remove the inferior pelvic fascia we will reach the pelvic diaphragm
What is the function of the bulbospongiosus?
- Males:
- helps in maintaining an erection, expel urine and semen from the urethra
- Females:
- Helps to reduce the vaginal vestibule
- The pudendal nerve innervates all muscles
Describe the deep transverse perinei muscle
- Transversely arranged fibers that extend between the ischiopubic rami
- It inserts into the perineal body
- In females, the anterior fibers insert into the lateral wall of the vagina, supporting the pelvic viscera
- It is supplied by the perineal branch of the pudendal nerve
What forms the pelvic diaphragm?
1) Levator ani which is formed of:
- Pubococcygeus
- Puborectalis
- Iliococcygeis
2) Coccygeus (ischiococcygeus)
