Perineum

• Perineum


  The diamond-shaped shallow compartment bounded by the pelvic outlet
• Perineum


  • Separated from the pelvic cavity by the fascia covering the inferior aspect of the pelvic diaphragm
  • Levator ani
  • Coccygeus

  
• Boundaries of the perineum

  • Anterior: pubic symphysis
  • Anterolateral: ischiopubic rami
  • Lateral: ischial tuberosities
  • Posterolateral: sacrotuberous ligaments
  • Posterior: Inferior-most sacrum and coccyx

  
• Divisions of the perineum

  • Transverse line joining the anterior ends of the ischial tuberosities
  • Divides the perineum into anal triangle posteriorly and urogenital triangle anteriorly
  • Urogenital triangle further divided by perineal membrane into superficial and deep pouches
  • Perineal body- central tendon at the midpoint of this line

  
• Perineal body


  • Lies deep to the skin with little subcutaneous tissue
  • Posterior to the vestibule of the vagina/bulb of the penis
  • Anterior to the anus and anal canal
  • Site of attachment for: Bulbospongiosus, External anal sphincter, Superficial and deep transverse muscles, External urethral sphincter, Levator ani

  
• Fasciae and Pouches of the Urogenital Triangle


  • Superficial (subcutaneous tissue): Superficial fatty layer, deep membranous layer (Colles fascia)
  • Deep (Gallaudet/investing): only present in urogenital triangle

  
• Superficial fatty layer


  • Continuous posteriorly with ischio-anal fat pad in the anal region in both sexes
  • In females: Makes up substance of labia majora and mons pubis, Continuous anteriorly and superiorly with abdominal Camper fascia
  • In males: Diminished in the urogenital triangle, Replaced by dartos muscle in the penis and scrotum, Continuous between the penis/scrotum and thighs with Camper fascia

  
• Deep membranous layer


  • Does not extend into the anal triangle
  • Attachments: Posterior: Posterior margin of perineal membrane, Perineal body; Lateral: Fascia lata of superomedial thigh; Anterior: In males- dartos fascia of scrotum and penis, In females- continuous with Scarpa fascia of abdomen after passing superiorly to fatty layer of labia majora

  
• Deep perineal fascia


  AKA Gallaudet fascia/investing fascia
• Deep perineal fascia


  • Invests: Ischiocavernosus, Bulbospongiosus, Superficial transverse perineal muscles
  • Attached laterally to ischiopubic rami
  • Continuous with deep fascia covering external oblique muscle
  • In males: Fused anteriorly to suspensory ligament of penis
  • In females: Fused anteriorly to suspensory ligament of the clitoris

  
• Superficial Perineal Pouch


  Potential space
• Boundaries of Superficial Perineal Pouch

  • Floor: perineal (Colle's) fascia
  • Roof: perineal membrane
  • Laterally: ischiopubic rami and obturator internus

  
• Contents of Superficial Perineal Pouch

  • In males: Root (bulb and crura) of penis, Ischiocavernosus and bulbospongiosus, Proximal part of spongy urethra, Superficial transverse perineal muscles, Deep perineal br. of internal pudendal vessels, Pudendal nerves
  • In females: Clitoris and ischiocavernosus, Bulbs of vestibule and bulbospongiosus, Greater vestibular glands, Superficial transverse perineal muscles, Deep perineal br. of internal pudendal vessels, Pudendal nerves

  
• Deep Perineal Pouch


  Potential space
• Boundaries of Deep Perineal Pouch

  • Inferior- perineal membrane
  • Superior- inferior fascia of pelvic diaphragm
  • Lateral- inferior portion of obturator fascia

  
• Contents of Deep Perineal Pouch

  • In both sexes: Part of external urethral sphincter, Anterior extensions of ischio-anal fat pads
  • In males: Intermediate part of urethra, Deep transverse perineal muscles, Bulbourethral glands, Dorsal neurovascular structures of the penis
  • In females: Proximal part of urethra, Vaginal hiatus, Muscles: Deep transverse perineal muscles, Sphincter urethrovaginalis, Compressor urethrae, External urethral sphincter, Dorsal neurovasculature to clitoris

  
• Layers and contents of the perineum

  • Superficial (subcutaneous tissue): Superficial fatty layer, deep membranous layer (Colles fascia)
  • Deep (Gallaudet/investing): only present in urogenital triangle
  • Superficial Perineal Pouch
  • Deep Perineal Pouch

  
• Ischio-anal Fossae


  Large fascia-lined wedge-shaped spaces on each side of the anal canal

  
• Ischio-anal Fossae


  • Apex superiorly where levator ani arises from the obturator fascia
  • Wide base inferiorly at the skin of the anal region
  • Boundaries: Lateral- Ischium, Inferior part of obturator internus; Medial- External anal sphincter, Medial part of levator ani; Posterior- Sacrotuberous ligament, Gluteus maximus; Anterior- Bodies of the pubic bones

  
• Contents of Ischio-anal Fossae

  • Fatty tissue
  • Internal pudendal vessels
  • Pudendal nerve
  • Inferior rectal nerves and vessels
  • Posterior scrotal nerve and vessels
  • Perineal branch of S4
  • Perforating cutaneous (cluneal) nerves
  • Lymphatics

  
• Pudendal Canal


  Horizontal passageway within the obturator fascia which lines the medial aspect of obturator internus and the lateral wall of the ischio-anal fossae

  
• Contents of Pudendal Canal

  • Internal pudendal artery and vein
  • Pudendal nerve
  • Nerve to obturator internus

  
• Anal Canal


  Terminal part of the large intestine

  
• Anal Canal


  • Extent: Superior aspect of pelvic diaphragm to anus
  • Course: Begins as the rectal ampulla narrows proximal to the puborectalis of levator ani, Descends posteroinferiorly between the anococcygeal ligament and perineal body

  
• Internal anal sphincter


  Involuntary sphincter

  
• Internal anal sphincter


  • Surrounds the superior 2/3 of the anal canal
  • Contraction: Stimulated by sympathetic fibres from the superior rectal and hypogastric plexuses, Inhibited by parasympathetic fibres from the pelvic splanchnic nerves

  
• External anal sphincter


  Voluntary sphincter
• External anal sphincter


  • Broad band on each side of the inferior 2/3 of the anal canal
  • Attachments: Anterior- perineal body, Posterior- coccyx, Superior- blends with puborectalis

  
• Internal structure of anal canal

  • Anal columns
  • Anorectal junction
  • Anal valves and sinuses
  • Pectinate (dentate) line

  
• Arterial supply of anal canal

  • Superior rectal a. (anal canal superior to pectinate line)
  • Inferior rectal aa. (anal canal inferior to pectinate line, surrounding muscles and peri-anal skin)
  • Middle rectal aa. (forms anastomoses with the superior and inferior rectal aa.)

  
• Venous drainage of anal canal

  • Superior to pectinate line- to superior rectal v.
  • Inferior to pectinate line- to inferior rectal vv.
  • Middle rectal vv. (drain muscularis externa of the ampulla, anastomose with superior and inferior rectal vv.)

  
• Lymph drainage of anal canal

  • Superior to pectinate line: Internal iliac nodes, common iliac and lumbar nodes
  • Inferior to pectinate line: Superficial inguinal nodes

  
• Innervation of anal canal

  • Superior to pectinate line: Inferior hypogastric plexus
  • Inferior to pectinate line: Inferior anal nerves from pudendal nerve

  
• Distal male urethra


  Urethra subdivided into 4 parts: Intramural (preprostatic), Prostatic, Intermediate, Spongy

  
• Intermediate part of urethra

  • Begins at the apex of the prostate, Traverses the deep perineal pouch where it is surrounded by the external urethral sphincter, Penetrates the perineal membrane, Ends as the urethra enters the bulb of the penis

  
• Spongy part of urethra

  • Begins at the distal end of the intermediate part and ends at the external urethral orifice, Dilated in the bulb of the penis (intrabulbar fossa) & in the glans of the penis (navicular fossa), On each side, the ducts of the bulbourethral glands open into the proximal spongy urethra

  
• Arterial supply, venous drainage, lymph drainage, innervation of distal male urethra

  • Arterial supply: Dorsal artery of the penis
  • Venous drainage: Dorsal vein of the penis
  • Lymph drainage: Intermediate part- internal iliac nodes, Spongy urethra- deep inguinal nodes
  • Innervation: Intermediate part- prostatic nerve plexus from inferior hypogastric plexus (autonomic), Spongy urethra- dorsal nerve of the penis from pudendal nerve (somatic)

  
• Scrotum


  Cutaneous fibromuscular sac

  
• Scrotum


  • 2 layers: Heavily pigmented skin, Dartos fascia (fat-free layer containing smooth muscle fibres (dartos muscle))
  • Divided internally by a continuation of the dartos fascia (Septum of the scrotum)
  • Scrotal raphe- indication of bilateral embryonic formation of the scrotum

  
• Arterial supply, venous drainage, lymph drainage, innervation of scrotum

  • Arterial supply: Posterior scrotal branches from perineal a. of internal pudendal a., Anterior scrotal branches from deep external pudendal a. of femoral a., Cremasteric a. from inferior epigastric a.
  • Venous drainage: Accompany aa. to external pudendal vv.
  • Lymph drainage: Superficial inguinal nodes
  • Innervation: Genital br. of genitofemoral n. to anterolateral surface, Anterior scrotal nn. of ilioinguinal n. to anterior surface, Posterior scrotal nn. of pudendal n. to posterior surface, Perineal br. of post. cutaneous n. of thigh to posteroinferior surface