Part 17: Perineum

Question 1

What are the boundaries of the perineum?

Answer 1

Diamond shape
Symphysis pubis anterior, coccyx posterior. Sacrotuberous ligaments posterior lateral border. Ischiopubic rami anterior lateral border

Question 2

What is the dividing line between urogenital and anal region of perineum?

Answer 2

Line between ischial tuberosity

Question 3

What is the nervous supply of the perineum?

Answer 3

Anal region: inferior rectal nerve (S3,4), perineal branch of S4, twigs of coccygeal plexus
Urogenital region: Ilioinguinal nerve (L1) to anterior scrotum/labium majus. Skin of penis from dorsal nerve (S2). Posterior 2/3 scrotum/labia majus from perineal branches of pudendal nerve (S3)

Question 4

How long is the anal canal? How many muscle layers does it have?

Answer 4

4cm. 
Has two muscle layers.
Both circular.
Internal (visceral sphincter)
External (skeletal) sphincter

Question 5

Where is the junction between the anal canal and the rectum?

Answer 5

Pelvic floor - puborectalis angles the gut forward at this junction

Question 6

Describe the internal anal sphincter

Answer 6

Circular muscle - continuation of inner circular muscle layer of bowel wall. Visceral control. Does occupy whole length of anal canal but stops slightly short

Question 7

What is the conjoint longitudinal coat?

Answer 7

Longitudinal layer of bowel wall muscle forms thin fibroelastic sheet between internal and external sphincters

Question 8

Describe the external sphincter

Answer 8

Said to have 3 parts (deep, superficial and subcutaneous) but are rather continuous.
Deep - continuation of puborectalis (anorectal ring)
Superficial/middle: Ellipitical, attached to coccyx and perineal body in front.
Subcutaneous: Circular ring, cuffing around internal sphincter

Question 9

What is the intersphincteric groove?

Answer 9

The palpable gap between end of internal sphincter and external sphincter

Question 10

What is the mucous membrane of the anal canal?

Answer 10

Upper 1/3 has 12 longitudinal ridges - anal columns which join together.
Top part is typical columnar epithelium.
Zone of variable epithelium (columnar and squamous) just above pectinate line. Below intersphincteric groove is histology typical of skin with stratified squamous keratinizing epithelium with hair follicles, sebaceous glands.

Question 11

What are the anal sinuses?

Answer 11

Openings of up to 10 mucous secreting anal glands. Found in anal valves (lower end of anal columns). Glands are different to ordinary mucosa in that they submucosal, some may even penetrate internal sphincter. Infection results in anal abscess and fistulae.

Question 12

What is the epithelium of pecten?

Answer 12

Stratified squamous epithelium but non-keratinizing, no hair follicles or sebaceous cysts

Question 13

What is the blood supply of the anal canal?

Answer 13

Superior rectal artery, middle rectal artery and median sacral artery with lower end being supplied by inferior rectal artery.

Question 14

What is the venous drainage of anal canal?

Answer 14

Corresponds with arterial supply - hence creates portal-systemic anastomosis with inferior rectal draining to systemic and superior rectal vein to portal system. Although they are rectal arteries this anastomosis actually takes place in anal canal

Question 15

What is the lymph drainage of anal canal

Answer 15

Upper canal to internal iliac nodes, lower end to superficial inguinal group

Question 16

What is the ischioanal fossa? What are it’s boundaries?

Answer 16

Wedge shaped space filled with fat lateral to anal canal.
Base: Skin of anal region of perineum
Medial: Canal and levator ani
Lateral: Ischial tuberosity
Anterior: Perineal body
Posterior: sacrotuberous ligament

Question 17

Each fossa has a anterior and posterior recess. Where do these extend?

Answer 17

Anterior: above urogenital diaphragm to posterior side of pubis
Posterior: Lower border of glut maximus to underlying sacrotuberous ligament

Question 18

What is the role of the ischioanal fat pad?

Answer 18

Within the ischioanal fossa - allows for dilation in defecation, child birth

Question 19

What is the pudendal canal?

Answer 19

Connective tissue sheath in lower lateral wall of ischioanal fossa containing pudendal nerve and internal pudendal vessels conducting from lesser sciatic notch to deep perineal pouch. Overlies obturator internus and lies on medial side of ischial tuberosity.

Question 20

Where do inferior rectal branches of vessels and nerve arise?

Answer 20

Proximal end of pudendal canal, run across transversely across fossa towards anus. Slightly convex arch to path.

Question 21

What is the perineal body/tendon?

Answer 21

Elongated midline fibromuscular mass to which number of muscles gain attachment. Lies in front of anal canal, behind posterior body of perineal membrane to which it is attached.
Muscles attached to it are:
Internal + external anal sphincters
Levator ani
Bulbospongiosus
Superficial and deep transverse perinei

Question 22

What is the anococcygeal ligament

Answer 22

Fibromuscular mass between raphe and skin, seperates 2 ischioanal fossa