Urogenital Triangle Anatomy

Urogenital Triangle

• The urogenital triangle is a division of the perineum.
• The perineum is a diamond-shaped space located at the inferior trunk and lies between the thighs.
• The perineum’s boundaries are the pubic symphysis (anterior), ischiopubic ramus (anterolateral), sacrotuberous ligament (posterolateral), and the coccyx and sacrum (posterior).
• A transverse line passing through the anterior ends of the ischial tuberosities divides the perineum into the urogenital triangle and the anal triangle.

Boundaries of Urogenital Triangle

• In front: Pubic symphysis and arcuate pubic ligament
• Behind: Imaginary transverse line
• Each side: Ischiopubic ramus

Urogenital Region Layers and Spaces

• Layers to know: layers, superficial and deep perineal pouches, urogenital diaphragm, and perineal body.
• There are two spaces in the urogenital triangle: the deep and superficial perineal pouches.
• The deep perineal pouch is located between the superior fascia of the urogenital diaphragm and perineal fascia and the inferior fascia of the urogenital diaphragm.
• The superficial perineal pouch is located between the perineal fascia, inferior fascia of the urogenital diaphragm, and the membranous layer of superficial fascia.
• From superficial to deep, the layers are the superficial fascia of perineum (Colles' fascia), superficial perineal space, inferior fascia of urogenital diaphragm (perineal membrane), deep perineal space, and the superior fascia of the urogenital diaphragm.

Superficial Perineal Pouch

• Definition: the space of the urogenital region below the perineal membrane.
• Above: Perineal membrane
• Below: Colles' fascia
• On each side: Inner surface of ischiopubic rami
• Behind: Closed by the union of the perineal membrane with Colle's fascia
• In front: Open and continuous with the spaces of the scrotum, penis, and anterior abdominal wall

Contents of the Superficial Perineal Pouch

• Muscles: superficial transverse perineal muscle, bulbospongiosus, crus penis (male), crus of clitoris (female) and ischiocavernosus
• Central part: bulb of penis (male), bulb of vestibule (female) and covering urethra (in both)
• Ducts of bulbourethral glands (male), greater vestibular glands (female)
• Branches of pudendal nerves and internal pudendal vessels

Contents of Superficial Perineal Pouch in Males

• Crura of the penis and (ischiocavernous)
• Bulbs of the penis and surrounding muscle (bulbospongiosus)
• Superficial transverse perineal muscles
• Branches of the internal pudendal artery
• Branches of the perineal branch of the pudendal nerves
• Posterior scrotal branches
• Transverse perineal branches
• Perineal branch of the posterior cutaneous nerve of thigh

Contents of Superficial Perineal Pouch in Females

• Root (crura) of the clitoris and muscle associated with it (ischiocavenous)
• Bulbs of the vestibule and surrounding muscle (bulbospongiosus)
• Superficial transverse perineal muscles
• Branches of the internal pudendal artery
• Branches of the perineal branch of the pudendal nerves
  • Posterior labial branches
  • Transverse perineal branches
  • Posterior labial branch
• Perineal branch of the posterior cutaneous nerve of thigh
• Greater vestibular glands

Deep Perineal Space/Pouch

• Boundaries
• Above: superior layer of urogenital diaphragm
• Below: inferior layer of urogenital diaphragm or perineal membrane
• In front: transverse ligament of the pubis
• Behind: fusion of both membranes

Contents of Deep Perineal Space/Pouch

• Membranous urethra (male), urethra and vagina (female)
• Deep transverse perineal muscle, sphincter urethrae
• Bulbourethral gland (male)
• Branches of internal pudendal vessels (artery of penis)
• Branches of pudendal nerve (dorsal nerve of penis)

Contents of the Deep Perineal Pouch in the Male

• The membranous part of the urethra
• The sphincter urethrae muscle
• The bulbourethral glands
• The deep transverse perineal muscles
• The internal pudendal vessels and their branches
• The dorsal nerves of the penis

Contents of Deep Perineal Pouch in Female

• Proximal part of urethra
• External urethral sphincter muscle
• Deep transverse perineal muscles
• Related vessels and nerves
• Deep artery of clitoris
• Dorsal artery of clitoris
• Artery to bulb of vestibule
• Urethral artery
• Dorsal nerve of clitoris

Deep Transverse Perineal Muscles

• The deep transverse perineal muscles lie posterior to the sphincter urethrae muscle.
• Each muscle arises from the ischial ramus and passes medially to be inserted into the perineal body.
• These muscles are clinically unimportant.

Sphincter Urethrae Muscle

• The sphincter urethrae muscle surrounds the urethra in the deep perineal pouch.
• It arises from the pubic arch on the two sides and passes medially to encircle the urethra.
• The perineal branch of the pudendal nerve supplies the sphincter.
• The muscle compresses the membranous part of the urethra and relaxes during micturition.
• It is the means by which micturition can be voluntarily stopped.

Internal Pudendal Artery

• The internal pudenal artery on each side enters the deep perineal pouch and passes forward, giving rise to:
• The artery to the bulb of the penis
• The arteries to the crura of the penis
• The dorsal artery of the penis, which supplies the skin and fascia of the penis
• The duct bulbourethral glands are two small glands that lie beneath the sphincter urethrae muscle.
• Their ducts pierce the perineal membrane and enter the penile portion of the urethra.
• The secretion is poured into the urethra as a result of stimulation.

Male Urogenital Muscles

• Bulbospongiosus: fascia of bulb of penis and corpus spongiosum and cavernosum; perineal body; perineal branch of pudendal nerve
• Ischiocavernosus: ischial tuberosity; fascia covering crus penis; perineal branch of pudendal nerve
• Sphincter urethrae: pubic arch; surrounds urethra; perineal branch of pudendal nerve
• Superficial transverse perineal muscle: Ischial tuberosity; perineal body; perineal branch of pudendal nerve
• Deep transverse perineal muscle: ischial ramus; perineal body; perineal branch of pudendal nerve

Female Urogenital Muscles

• Bulbospongiosus: fascia of corpus cavernosum; perineal body; perineal branch of pudendal nerve
• Ischiocavernosus: ischial tuberosity; fascia covering crus penis; perineal branch of pudendal nerve
• Sphincter urethrae: pubic arch; surrounds urethra; perineal branch of pudendal nerve
• Superficial transverse perineal muscle: Ischial tuberosity; perineal body; perineal branch of pudendal nerve
• Deep transverse perineal muscle: ischial ramus; perineal body; perineal branch of pudendal nerve

Urogenital Diaphragm

• Formed by sphincter of urethra, deep transverse perineal muscle, superior and inferior fascia of urogenital diaphragm.
• The urogenital diaphragm is pierced by urethra in both male and female and by also by vagina behind the urethra in female.
• Function:
  • It provides support to prostate gland or the urinary bladder.
  • Sphincter urethrae exert voluntary control to micturition.
  • It also constricts the vagina in female.

Perineal Central Tendon (Perineal Body)

• Wedge-shape fibromuscular mass
• In female, between anal canal and lower end of vagina
• In male, between anal canal and root of penis
• It is larger in the female than in the male and support to the posterior wall of the vagina
• It is composed convergence of:
  • bulbospongiosus
  • superfical transverse perinea
  • deep transverse perinea
  • sphincter urethrae and
  • superficial part of external anal sphincter
  • deep part of external anal sphincter and
  • levator ani

Perineal Membrane

• Also called as inferior fascia of urogenital diaphragm
• Situated between superfical and deep perineal pouch
• Attachments
• Sides: Ischiopubic Ramus
• Anteriorly: Has free margin behind pubis transverse ligament of pubis
• Posteriorly: Fuses with the transversus profundus muscle

Perineal Membrane in Males

• In Males is pierced by:
  • Urethra
  • Duct of bulbourethral gland
  • Artery & nerve to bulb of penis
  • Dorsal & deep artery of penis
  • Urethral artery
  • Post. scrotal nerve & vessels
  • Branches of perineal nerve to superficial muscles

Perineal Membrane in Females

• In Females is pierced by:
  • Urethra+ vagina
  • Artery & nerve to bulb of vestibule
  • Dorsal & deep artery of clitoris
  • Urethral artery
  • Posterior labial nerve & vessels
  • Branches of perineal nerve to superficial muscles

Pelvic Diaphragm

• The pelvic diaphragm is a muscular partition formed by the levator ani and coccygi, with which may be included the parietal pelvic fascia on their upper and lower aspects.
• It separates the pelvic cavity above from the perineal region below.

Clinical Correlations

• Damage to perineal body: prolapse of uterus
• Episiotomy: Median or Mediolateral
• Pudendal nerve block: done before episiotomy
• Deep extravasation comes from instrumentation or pelvic fracture or RTA; superficial comes from straddle-type injuries