Perineum

The perineum is a diamond-shaped region located at the inferior aspect of the trunk, between the thighs. It forms the outlet of the pelvis and contains structures of the urogenital and anal systems. The perineum includes muscles, fasciae, glands, vessels, and openings related to both the urinary and reproductive tracts, as well as the terminal part of the digestive system. It is divided into two distinct triangular regions: the urogenital triangle (anterior) and the anal triangle (posterior).

Structure

The perineum consists of surface skin, subcutaneous tissue, perineal muscles, fascia, and neurovascular components. It is bounded by skeletal landmarks and divided into two anatomical triangles by a line drawn between the ischial tuberosities.

Boundaries

• Anterior: Pubic symphysis
• Posterior: Tip of the coccyx
• Lateral: Ischial tuberosities
• Roof (superior boundary): Pelvic diaphragm (levator ani and coccygeus)
• Base (inferior boundary): Skin and fascia of the perineum

Divisions

• Urogenital triangle (anterior):
  • Males: Penis, scrotum, bulbourethral glands
  • Females: Vulva, vestibular glands
• Anal triangle (posterior):
  • Both sexes: Anal canal, external anal sphincter, ischioanal fossae

Perineal Fascia

• Superficial perineal fascia: Fatty layer (Camper’s) and membranous layer (Colles’ fascia)
• Deep perineal fascia (Gallaudet’s fascia): Invests the perineal muscles

Location

The perineum lies below the pelvic diaphragm and between the thighs. It is inferior to the levator ani muscle and is located between the external genitalia and the anus. It is most easily visualized in the lithotomy position or when the thighs are abducted.

Function

• Support of Pelvic Organs: Muscular and fascial layers of the perineum provide mechanical support to pelvic viscera
• Urinary and Reproductive Function: Contains external genitalia, urethral and vaginal openings, and associated glands (e.g., Bartholin's, bulbourethral)
• Defecation Control: External anal sphincter in the anal triangle controls passage of feces
• Sexual Function: Richly innervated area, involved in tactile sensation and arousal

Clinical Significance

• Episiotomy: Surgical incision in perineum to enlarge vaginal opening during childbirth
• Perineal Tears: Common during vaginal delivery; graded based on extent (1st to 4th degree)
• Perineal Hernias: Rare; can protrude through weakened pelvic floor
• Abscesses: Ischioanal abscesses may form in the anal triangle, requiring drainage