Anatomy of the Perineum

Perineum

• Located below the pelvic floor, overlies the pelvic outlet
• Divided into two triangles: urogenital triangle and anal triangle

Urogenital Triangle

• Lies between the sides of the pubic arch
• Protected by the urogenital diaphragm
• Contents:
  • Anal canal
  • Ischio-anal fossa
  • Urogenital pouches (superficial and deep)

Anal Triangle

• Lies behind the urogenital triangle
• Contents:
  • The ano-coccygeal body, located in the anal triangle, is a part of the pelvic region. It forms the floor of the anal canal and is part of the anorectal junction, which is the connection between the anus and the rectum.
  • Anal canal
  • Ischio-anal fossa

Ischio-anal Fossa

• Wedge-shaped fossa

• Base: downwards, formed by the skin

• Edge: upwards, at the tendinous arch

• Medial boundary: formed by external anal sphincter and levator ani

• Lateral boundary: formed by obturator internus, fascia, and ischial tuberosity

• Anterior boundary: formed by urogenital triangle

• Posterior boundary: formed by sacro-tuberous ligament, covered by gluteus maximus

• Contents:

• Pudendal canal containing pudendal nerve, internal pudendal vessels

• Inferior rectal nerve and vessels

• Perineal branch innervates external anal sphincter, playing a crucial role in regulating bowel movements and maintaining continence.

• The urogenital pouches are two sac-like structures that contain the urethra and vagina in males and females, respectively. They are separated by the scrotum in males and the labia in females.

• Superficial pouch: covered only by skin and superficial fascia

• Deep pouch: covered by deep fascia, stretched between the sides of the pubic arch

• Contents of deep pouch:

  • Urethra surrounded by external urethral sphincter (in female)
  • Vagina surrounded by deep transverse perineal muscles (in female)
  • Nerves and vessels (dorsal nerve clitoris and vessels of clitoris) (in female)
  • Membranous urethra surrounded by external urethral sphincter and bulbourethral glands (in male)
  • Deep transverse perineal muscles (in male)
  • Nerves and vessels (dorsal nerve penis and penis vessels) (in male)

Perineal Membrane

• Thickened inferior fascia of urogenital diaphragm
• Separates the two perineal pouches
• Pierced by:
  • Vagina and urethra (in female)
  • Clitoris artery, vessels of the bulb, deep vessels of clitoris, dorsal vessels of clitoris, dorsal nerve of clitoris (in female)
  • Membranous urethra, bulbourethral ducts, bulb vessels, urethral vessels, deep vessels of penis, dorsal vessels of penis, dorsal nerve of penis (in male)

Superficial Perineal Pouch

• Position: below the perineal membrane, between the perineal membrane and membranous layer of superficial fascia
• Opened anteriorly and continuous with the anterior abdominal wall
• Closed posteriorly
• Contents:
  • Root of penis or clitoris
  • Superficial perineal muscles (bulbospongiosus, ischiocavernosus, superficial transverse perineal)
  • Branches of pudendal nerve and internal pudendal vessels
  • Part of urethra
  • Testis or vagina and greater vestibular gland

Perineal Body

• Fibromuscular mass in the center of the perineum
• Receives the following muscles:
  • Levators ani
  • External anal sphincter
  • Bulbospongiosus
  • Transverse perineal muscles

Pudendal Nerve

• Origin: inside the pelvis, from sacral plexus (S2,3,4)
• Leaves the pelvis through the greater sciatic foramen
• Enters the perineum through the lesser sciatic foramen
• Passes in the pudendal canal and ends at the lower end of the canal
• Branches:
  • Inferior rectal nerve
  • Dorsal nerve of penis or clitoris
  • Perineal nerve, which gives muscular and posterior scrotal nerves

Blood Supply and Drainage

• Internal iliac artery and vein
• Internal pudendal artery and vein
• Artery of penis or clitoris
• Deep dorsal vein of penis or clitoris
• Superficial dorsal vein of penis