Perineal anatomy

Question 1

Borders of the superficial perineal pouch

Answer 1

Inferior: perineal fascia
Superior: perineal membrane
Lateral: ischiopubic rami

Question 2

Contents of superficial perineal pouch in males

Answer 2

• Root of penis and associated muscles
• Proximal part of spongy urethra
• Superficial transverse perineal muscles
• Pudendal nerves
• Deep branches of pudendal vessels

Question 3

Contents of superficial perineal pouch in females

Answer 3

• Clitoris and associated muscles
• Bulb of vestibule and muscle
• Greater vestibular glands
• Superficial transverse perineal muscles

Question 4

Boundaries of deep perineal pouch

Answer 4

Inferior: perineal membrane
Superior: super diaphragmatic fascia

Question 5

Contents of deep perineal pouch

Answer 5

Urogenital diaphragm - triangular shaped muscle that contains external urethral sphincters

Question 6

Layers of the abdomen in the perineum, scrotum and penis

Answer 6

Question 7

Epithelium of the urethra

Answer 7

Proximal 2/3: transitional epithelium

Distal 1/3: stratified squamous epithelium

Question 8

Male vs female urethra

Answer 8

Female:

• Shorter (about 4cm)
• Exits between clitoris and vagina
• Only 1 sphincter (innervated by pudendal nerve)

Male:

• Longer (about 20cm)
• 2 sphincters (internal and external)
• 4 narrowings: bladder neck, superior to navicula fossa, membranous urethra, external urethral orifice

Question 9

Rupture of urethra above urogenital diaphragm

Answer 9

Urine accumulates in rectovesical space (trapped by levator ani)

Question 10

Rupture of urethra below the urogenital diaphragm (perineal membrane)

Answer 10

No rupture of Buck’s fascia = accumulation of urine in Buck’s fascia

Rupture of Buck’s fascia = accumulation of urine in Colles’ and Scarpa’s fascia

Question 11

Sections of the male urethra

Answer 11

• Pre-prostatic urethra:
  
  • Contains internal urethral orifice and sphincter
• Prostatic urethra:
  
  • Through the prostate
  • Ejaculatory duct joins here
• Membranous urethra:
  
  • Narrowest part
  • Site of external urethral orifice
  • At level of urogenital diaphragm
• Spongy urethra:
  
  • In corpus spongiosum
  • Curves at infrapubic angle and prepubic angle
• Navicular fossa:
  
  • Widest part of the urethra, just before external urethral orifice

Question 12

What is the anorectal junction?

Answer 12

The point at which the anal canal joins with the rectum - at the level of puborectalis

Question 13

Detail the two anal sphincters

Answer 13

• Internal anal sphincter
  
  • Involuntary, sympathetic innervation
  • Covers superior 2/3 of anal canal
• External anal sphincter
  
  • Voluntary, innervated by inferior rectal nerve
  • Blends with puborectalis posteriorly

Question 14

Detail the structure of the anal canal

Answer 14

• Superior 2/3 of canal is mucous membrane arranged into anal columns (longitudinal ridges) - contain terminal branches of superior rectal artery and vein
• Inferior 1/3 contains anal valves (mark the pectinate line)
  
  • Note that superior anal valves are called anal sinuses - these secrete mucous when compressed
• Laterally surrounded by ischioanal fossa

Question 15

What is marked by the pectinate line?

Answer 15

The junction between superior anal canal (derived from endoderm) and the inferior anal canal (derived from ectoderm)

Question 16

Compare neurovasculature and lymphatic drainage above and below the pectinate line

Answer 16

Arterial supply:

• Above:
  
  • Superior rectal artery (from IMA)
• Below:
  
  • Middle rectal artery (from internal iliac)
  • Inferior rectal artery (from internal pudendal)

Venous drainage:

• Above:
  
  • Internal haemorrhoidal plexus (prone to varices from portal HPT)
• Below:
  
  • External haemorrhoidal plexus

Nervous supply:

• Above:
  
  • Inferior hypogastric plexus (sensitive to only stretch)
• Below:
  
  • Inferior anal nerve (sensitive to touch, pain and temperature)

Lymph supply:

• Above:
  
  • Internal iliac -> common iliac -> lumbar lymph nodes
• Below:
  
  • Superior inguinal lymph nodes

Question 17

Ischioanal fossa

Answer 17

Between skin of anal region and pelvic diaphragm

Contains fat and loose connective tissue - means infections spread easily through the fossa

Question 18

Pudendal canal

Answer 18

Horizontal passage through the fascia of obturator internus

Carries pudendal artery and nerve:

• After canal, artery and nerve split into:
  
  • Perineal artery and nerve:
    
    • Artery mainly supplies the superficial perineal pouch
    • Nerve innervates bulbospongiosus, ischiocavernosus, levator ani and external urethral sphincter
  • Dorsal artery and nerve of clitoris/penis:
    
    • Runs into deep perineal pouch
    • Especially sensitive at the distal end

Question 19

Nerves of the perineum

Answer 19

• Primary innervation comes from the pudendal nerve (S2, S3, S4) - motor and sensory
• Small amount of innervation from genital branch of genitofemoral nerve:
  
  • Males: goes to scrotal skin
  • Females: goes to skin of mons pubis and labia majora

NOTE: pudendal nerve blocks administered near the ischial spine