Perineum

The perineum is the anatomical region located between the thighs, at the lower part of the pelvis, which contains structures related to the urinary and reproductive systems. It is shaped like a diamond and is divided into two triangles: the urogenital triangle and the anal triangle. The perineum supports the external genitalia and is involved in functions such as urination, defecation, and childbirth. It contains muscles, nerves, and blood vessels that are essential for these processes.

Location

The perineum is located at the inferior part of the pelvis, between the pubic symphysis (anteriorly) and the coccyx (posteriorly). It is bordered laterally by the ischial tuberosities. The perineum can be divided into two anatomical triangles: the urogenital triangle, which lies anteriorly and contains the external genitalia and urethra, and the anal triangle, which lies posteriorly and contains the anus. In females, the perineum lies between the vulva and the anus, while in males, it is located between the scrotum and the anus.

Structure and Anatomy

The perineum is an anatomical region located at the lower part of the pelvis and plays an important role in supporting various structures related to the urogenital and digestive systems. It is a diamond-shaped area divided into two triangular regions: the urogenital triangle and the anal triangle. The perineum contains important muscles, fasciae, and neurovascular structures that support the external genitalia, urinary, and anal functions. Below is a detailed description of its anatomy.

Boundaries of the Perineum

• Anterior Boundary:The anterior boundary of the perineum is formed by the pubic symphysis, the joint between the two pubic bones at the front of the pelvis.
• Posterior Boundary:The posterior boundary is formed by the coccyx (tailbone), located at the lower end of the vertebral column.
• Lateral Boundaries:The lateral boundaries of the perineum are the ischial tuberosities (bony prominences at the base of the pelvis). These are the points where the weight of the body is distributed when sitting.
• Roof:The superior limit or roof of the perineum is the pelvic diaphragm, a muscular sheet formed primarily by the levator ani and coccygeus muscles.
• Floor:The floor of the perineum is the skin and superficial fascia, which covers the underlying muscles and structures.

Subdivisions of the Perineum

The perineum is divided into two regions: the urogenital triangle (anterior) and the anal triangle (posterior). These regions are separated by an imaginary line drawn between the ischial tuberosities.

• Urogenital Triangle (Anterior):The urogenital triangle is located in the anterior part of the perineum and is responsible for housing structures related to the urinary and reproductive systems. It contains the external genitalia and the urogenital openings (urethra and vagina in females, urethra in males). This region is further divided into the superficial and deep perineal pouches.
• Boundaries:
  • • Anterior: Pubic symphysis.
    • Lateral: Ischiopubic rami.
    • Posterior: An imaginary line between the ischial tuberosities.
• Anal Triangle (Posterior):The anal triangle is located posteriorly and houses the anal canal and external anal sphincter. It is bordered by the coccyx, the ischial tuberosities, and the sacrotuberous ligaments. The anal triangle contains the ischioanal fossae, which are fat-filled spaces that support the expansion of the anal canal during defecation.
• Boundaries:
• • • Anterior: An imaginary line between the ischial tuberosities.
    • Lateral: Sacrotuberous ligaments.
    • Posterior: Coccyx.

Layers and Fasciae of the Perineum

The perineum contains several layers of fascia and muscles, which provide support to the pelvic structures and regulate functions like urination, defecation, and sexual activity. These layers are described below.

• Superficial Perineal Fascia:The superficial perineal fascia is composed of two layers:
  • Superficial layer (Camper’s fascia): This layer is fatty and continuous with the superficial fascia of the abdomen. In males, it is much thinner and blends into the scrotum.
  • Deep layer (Colles’ fascia): This membranous layer provides support and continues with Scarpa’s fascia of the anterior abdominal wall. It forms the boundary of the superficial perineal pouch.
• Deep Perineal Fascia (Gallaudet’s Fascia):The deep perineal fascia surrounds the muscles of the superficial perineal pouch, providing support. It helps separate the superficial structures from deeper tissues.
• Perineal Membrane:The perineal membrane is a strong fibrous layer that stretches between the two ischiopubic rami, covering the urogenital triangle. It serves as the inferior boundary of the deep perineal pouch and provides a platform for the attachment of several perineal muscles.
• Pelvic Diaphragm:The pelvic diaphragm forms the roof of the perineum and consists of the levator ani and coccygeus muscles. These muscles provide structural support to the pelvic organs and maintain continence.

Contents of the Urogenital Triangle

• External Genitalia:
• • Males: The urogenital triangle contains the penis, scrotum, and urethra. The penis is composed of erectile tissues (the corpora cavernosa and corpus spongiosum) that allow for erection. The scrotum houses the testes and associated structures.
  • Females: In females, the urogenital triangle contains the vulva, which includes the labia majora, labia minora, clitoris, and the openings of the urethra and vagina.
• Muscles:The urogenital triangle contains important muscles that support the external genitalia and aid in the control of urination and sexual function. These muscles include:
  • Bulbospongiosus Muscle: Surrounds the bulb of the penis in males and the vestibular bulbs in females, aiding in erection and the expulsion of fluids.
  • Ischiocavernosus Muscle: Covers the crura of the penis (in males) or clitoris (in females) and helps maintain erection by compressing the erectile tissues.
  • Superficial Transverse Perineal Muscle: This small muscle helps stabilize the perineal body and supports the pelvic floor.
• Neurovascular Structures:The urogenital triangle is supplied by the internal pudendal artery and the pudendal nerve, which provide blood flow and innervation to the external genitalia and perineal muscles.

Contents of the Anal Triangle

• Anal Canal and External Anal Sphincter:The anal triangle houses the anal canal, which terminates at the anus. The external anal sphincter surrounds the anal canal and provides voluntary control over defecation.
• Ischioanal Fossae:These fat-filled spaces lie on either side of the anal canal and allow for the expansion of the anal canal during defecation. The ischioanal fossae are bordered by the levator ani medially and the obturator internus laterally.
• Neurovascular Structures:The anal triangle is supplied by branches of the internal pudendal artery and innervated by the inferior rectal nerves, which are branches of the pudendal nerve. These structures provide sensory and motor control to the anus and surrounding structures.

Perineal Body

The perineal body is a central fibromuscular mass located at the junction of the urogenital and anal triangles. It serves as a point of attachment for several muscles of the perineum and pelvic floor, including the bulbospongiosus, external anal sphincter, levator ani, and superficial transverse perineal muscles. The perineal body provides stability to the perineum and plays a critical role in maintaining the integrity of the pelvic floor.

Perineal Muscles

The perineum contains several important muscles, which support the urogenital and anal structures. These muscles are divided between the urogenital triangle and the anal triangle:

• Urogenital Triangle Muscles:
  • Bulbospongiosus Muscle: Compresses the bulb of the penis or vestibular bulbs and helps with the expulsion of fluids and sexual function.
  • Ischiocavernosus Muscle: Compresses the crura of the penis or clitoris to maintain erection.
  • Superficial and Deep Transverse Perineal Muscles: Provide stability to the perineum and support the perineal body.
• Anal Triangle Muscles:
• • External Anal Sphincter: Controls the voluntary closure of the anal canal and plays a critical role in maintaining continence.
  • Levator Ani Muscle: Forms part of the pelvic diaphragm, providing structural support to the pelvic organs and maintaining continence.

Neurovascular Supply of the Perineum

The perineum receives its blood supply and innervation from several important neurovascular structures:

• Pudendal Nerve:The pudendal nerve provides motor and sensory innervation to the perineal muscles and external genitalia. It is the primary nerve of the perineum and gives rise to branches such as the inferior rectal nerve (for the anal canal) and the perineal nerve (for the urogenital structures).
• Internal Pudendal Artery:The internal pudendal artery supplies blood to the external genitalia, perineal muscles, and anal canal. It runs through the perineum, providing oxygenated blood to the perineal tissues.
• Veins:Venous drainage of the perineum occurs through the internal pudendal vein, which drains blood from the perineal structures and returns it to the systemic circulation.

Function

The perineum plays a vital role in supporting several key bodily functions, including sexual function, urinary control, defecation, and maintaining the integrity of the pelvic floor. Its muscles, neurovascular structures, and connective tissues work together to facilitate these functions, providing structural support and allowing voluntary control of essential processes. Below is a detailed explanation of the perineum’s functions.

Support of the Pelvic Floor and Organs

The perineum forms the lower boundary of the pelvic floor and provides essential support for the pelvic organs, including the bladder, rectum, and, in females, the uterus and vagina.

• Structural Support: The muscles and connective tissues of the perineum, such as the levator ani and perineal body, work in conjunction to hold the pelvic organs in place. This prevents pelvic organ prolapse, a condition where the pelvic organs descend into or beyond the perineal area due to weakened support structures.
• Pelvic Stability: The perineal body, a fibromuscular mass located at the junction of the urogenital and anal triangles, serves as an attachment point for several pelvic muscles. It helps maintain the integrity of the pelvic floor and resists the increased pressure that occurs during activities like coughing, lifting, or childbirth.

Sexual Function

The perineum plays a critical role in sexual function through the muscles, erectile tissues, and neurovascular structures it contains. These structures work together to support sexual arousal, orgasm, and ejaculation.

• Erectile Function in Males:The ischiocavernosus muscle and bulbospongiosus muscle are responsible for compressing the corpora cavernosa and corpus spongiosum, respectively, aiding in the maintenance of penile erection by restricting venous outflow and promoting blood engorgement during sexual arousal.
• Clitoral Erection in Females:The ischiocavernosus muscle in females covers the crura of the clitoris, assisting in maintaining clitoral erection by compressing the erectile tissues. This promotes sexual arousal and enhances sensitivity during sexual activity.
• Expulsion of Fluids:The bulbospongiosus muscle assists in the expulsion of semen during ejaculation in males. In females, it compresses the greater vestibular (Bartholin’s) glands, helping to secrete lubricating fluids into the vaginal vestibule during sexual arousal.
• Sensory Feedback:The perineum contains rich sensory innervation from the pudendal nerve, contributing to sexual sensation and arousal in both males and females.

Urinary Continence and Urethral Control

The perineum contains muscles that contribute to the control of the urethra, aiding in the voluntary control of urination.

• External Urethral Sphincter Control:The deep perineal pouch contains the external urethral sphincter, which is responsible for maintaining urinary continence by preventing involuntary leakage of urine. The muscles of the superficial perineal pouch, such as the bulbospongiosus, assist in emptying the urethra completely after urination, particularly in males.
• Support of Urogenital Structures:The muscles and fascia of the perineum help stabilize the external genitalia and the urethra, ensuring that these structures remain in proper alignment for effective control of urination.

Defecation and Anal Continence

The perineum is essential for maintaining control over defecation and supporting the functions of the anal canal. The muscles and neurovascular structures within the anal triangle contribute to both the voluntary and involuntary control of the anal sphincters.

• External Anal Sphincter Control:The external anal sphincter, located in the anal triangle of the perineum, provides voluntary control over the release of feces. It allows individuals to retain or expel stool by contracting or relaxing the muscle at will.
• Support for Defecation:The ischioanal fossae, fat-filled spaces located within the anal triangle, allow for the expansion of the anal canal during defecation, facilitating the passage of feces through the anal opening. The muscles of the perineum, including the levator ani, contribute to the force needed to expel stool.

Protection of Neurovascular Structures

The perineum contains important neurovascular structures that supply the external genitalia and perineal muscles. These structures, such as the pudendal nerve and the internal pudendal artery, provide both sensory and motor innervation and are critical for maintaining the function of the perineum.

• Sensory Innervation:The pudendal nerve provides sensory innervation to the skin of the perineum, external genitalia, and anus. This allows for sensation during sexual activity, urination, and defecation, contributing to bodily awareness and voluntary control.
• Blood Supply:The internal pudendal artery supplies blood to the perineal muscles, external genitalia, and the anal canal. This ensures proper blood flow to these structures, supporting their function and tissue health.

Facilitation of Childbirth (Females)

In females, the perineum plays a critical role during childbirth. The perineum provides support for the birth canal and helps accommodate the stretching required for the passage of the baby.

• Stretching and Support During Delivery:During childbirth, the muscles and connective tissue of the perineum stretch to allow for the delivery of the baby. The perineal body acts as a key structure in maintaining pelvic floor integrity during this process.
• Postpartum Recovery:After childbirth, the muscles and connective tissue of the perineum play a role in the recovery and restoration of pelvic floor function. Proper rehabilitation of these structures is essential for preventing postpartum complications such as pelvic organ prolapse and urinary incontinence.

Coordination with the Pelvic Diaphragm

The perineum works closely with the pelvic diaphragm (formed by the levator ani and coccygeus muscles) to maintain the integrity and function of the pelvic floor. Together, they provide support to the pelvic organs and regulate bodily functions such as urination and defecation.

• Pelvic Organ Support:The levator ani muscles, in coordination with the perineal muscles, provide support to the pelvic organs, ensuring that they remain in their proper anatomical position and function correctly.
• Prevention of Organ Prolapse:By working with the pelvic diaphragm, the perineum helps prevent the descent of pelvic organs (such as the bladder, uterus, or rectum) into or beyond the perineal area, a condition known as pelvic organ prolapse.

Clinical Significance

The perineum is vital for multiple functions, including sexual health, urinary continence, defecation, and childbirth. It can be affected by various medical conditions and traumas:

• Childbirth Injuries: In females, the perineum is often injured during childbirth, leading to tears or episiotomies (surgical cuts to prevent tearing). Damage to the perineal muscles and the perineal body can result in pelvic floor dysfunction, contributing to pelvic organ prolapse, urinary incontinence, or sexual dysfunction. Proper repair and postpartum care are essential for recovery.
• Perineal Trauma and Surgeries: In both males and females, perineal injuries from accidents, surgeries, or procedures like prostatectomy can damage the pudendal nerve and perineal muscles, affecting sexual function, urinary control, or anal continence.
• Infections and Abscesses: Perineal abscesses or infections can occur in the ischioanal fossae, leading to severe pain, swelling, and potential complications if untreated.
• Cancer: The perineum can be affected by cancers such as anal cancer or vulvar cancer, requiring surgical and oncological management.