Perineal Anatomy

The perineum is the diamond-shaped region forming the inferior outlet of the pelvis, between the thighs and below the pelvic floor. A line between the ischial tuberosities divides it into an anterior urogenital triangle, which transmits the urethra and, in the female, the vagina, and a posterior anal triangle containing the anal canal and the ischioanal fossae.

Definition

The perineum is the region of the trunk between the thighs, below the pelvic diaphragm, bounded by the pubic symphysis, ischiopubic rami, ischial tuberosities, sacrotuberous ligaments, and coccyx, and divided by the interischial line into a urogenital triangle anteriorly and an anal triangle posteriorly.

Scope

This topic covers the boundaries and triangles of the perineum, the perineal body, the superficial and deep perineal pouches and the perineal membrane, the muscles of the urogenital and anal regions, the external genitalia and erectile bodies, the ischioanal fossae, and the pudendal neurovascular supply. It is a reference description of structure and relations, not clinical guidance.

Core questions

• How is the perineum bounded and divided into its two triangles?
• What is the perineal body and why is it important?
• How are the superficial and deep perineal pouches and the perineal membrane arranged?
• What are the contents of the anal triangle and the ischioanal fossae?
• How does the pudendal nerve supply the perineum?

Key concepts

• Urogenital and anal triangles
• Perineal body (central tendon of the perineum)
• Perineal membrane and the deep and superficial pouches
• Superficial perineal muscles and erectile bodies
• External anal sphincter and ischioanal fossae
• Pudendal nerve and internal pudendal vessels

Mechanisms

The interischial line divides the perineum into the urogenital triangle, where the perineal membrane and the deep and superficial pouches house the erectile bodies, their muscles, and the urethral (and in the female vaginal) openings, and the anal triangle, containing the anal canal, external sphincter, and the fat-filled ischioanal fossae. The perineal body is a fibromuscular node anterior to the anal canal into which several perineal and pelvic-floor muscles converge, anchoring the perineum and contributing to support and continence (woodman-2002). The levator ani above forms the pelvic floor with which the perineal structures interact (guo-2007). The pudendal nerve, with the internal pudendal vessels, enters through the pudendal canal and supplies the perineal muscles, skin, and the external anal and urethral sphincters, while branches also reach the levator ani (loukas-2015, standring-2020, moore-2018).

Clinical relevance

Perineal anatomy underlies childbirth-related injury and repair, the planes of perineal and anorectal surgery, the spread of infection within the ischioanal fossae, and the targets of pudendal nerve block. The perineal body is a key structure in obstetric repair. The entry describes structure and relationships for orientation and is not a basis for diagnosis or treatment.

Evidence & guidelines

Description follows consensus reference anatomy (standring-2020, moore-2018) with focused work on the perineal body (woodman-2002), the levator ani (guo-2007), and the nerve supply to the pelvic floor (loukas-2015). As descriptive anatomy it is not guideline-governed.

History

The triangular organisation of the perineum, the perineal pouches, and the perineal membrane were established in classical dissection anatomy and elaborated in standard texts. Later work clarified the composition and role of the perineal body in obstetric injury (woodman-2002) and mapped the nerve supply to the pelvic floor and perineal musculature (loukas-2015).

Seminal works

• standring-2020
• moore-2018
• woodman-2002

Frequently asked questions

What is the perineal body?

It is a fibromuscular mass in the median plane between the urogenital and anal triangles, anterior to the anal canal, into which several perineal and pelvic-floor muscles attach; it serves as a central anchoring point for perineal support.

What are the two triangles of the perineum?

A line between the ischial tuberosities divides the perineum into an anterior urogenital triangle, which contains the external genitalia and the urethral (and in females the vaginal) opening, and a posterior anal triangle, which contains the anal canal and the ischioanal fossae.