Perineum

Introduction

The perineum is a diamond-shaped anatomical region located between the pubic symphysis anteriorly and the coccyx posteriorly. It forms the floor of the pelvis and is divided into urogenital and anal triangles. The perineum plays a critical role in supporting pelvic organs, facilitating urinary and fecal continence, and in sexual function.

Anatomy of the Perineum

Boundaries

The perineum is bounded by bony and muscular landmarks that define its shape and functional divisions.

• Anterior: Pubic symphysis
• Posterior: Tip of the coccyx
• Lateral: Ischial tuberosities
• Division: The transverse line connecting the ischial tuberosities divides the perineum into:
  • Urogenital triangle: Anterior half containing external genital structures
  • Anal triangle: Posterior half containing the anal canal and surrounding structures

Layers of the Perineum

The perineum is composed of several layers, each with distinct anatomical structures.

• Skin and superficial fascia: Protective covering containing subcutaneous fat and connective tissue
• Superficial perineal pouch: Contains muscles, erectile tissues, and associated glands
• Deep perineal pouch: Houses deeper muscles, urethra, and parts of the external genitalia
• Perineal membrane: Fibrous sheet that provides support for urogenital structures
• Pelvic diaphragm: Forms the muscular floor of the pelvis, supporting pelvic organs

Muscles of the Perineum

The perineal muscles are categorized as superficial or deep based on their location and function.

• Superficial muscles:
  • Bulbospongiosus
  • Ischiocavernosus
  • Superficial transverse perineal
• Deep muscles:
  • Deep transverse perineal
  • External urethral sphincter
  • External anal sphincter

Nerve Supply

The perineum receives both sensory and motor innervation, essential for continence and sexual function.

• Pudendal nerve: Main nerve supplying perineal muscles and skin
• Other innervation: Autonomic fibers for vascular and glandular control

Blood Supply

Arterial and venous networks provide vascular support to the perineum.

• Arterial supply: Internal pudendal artery and its branches
• Venous drainage: Internal pudendal veins and associated venous plexuses

Lymphatic Drainage

Lymphatic channels drain the perineum to regional lymph nodes, with clinical relevance in infection and malignancy.

• Superficial lymph nodes drain skin and superficial structures
• Deep lymph nodes drain muscles, erectile tissues, and urogenital structures

Perineum in Males

Urogenital Triangle Structures

The urogenital triangle in males contains structures related to external genitalia and the anterior perineal muscles.

• Base of the penis: Includes the root and proximal shaft supported by perineal muscles
• Scrotum: Contains the testes and spermatic cords, covered by dartos and external fascia
• Associated muscles and fascia: Bulbospongiosus, ischiocavernosus, and superficial transverse perineal muscles

Anal Triangle Structures

The anal triangle in males surrounds the anal canal and plays a key role in continence.

• Anal canal: Terminal portion of the gastrointestinal tract, lined by mucosa
• External anal sphincter: Voluntary muscle controlling defecation
• Perianal skin and glands: Contains sweat and sebaceous glands, relevant in infections

Perineum in Females

Urogenital Triangle Structures

The female urogenital triangle contains external genitalia and supporting perineal muscles.

• Vulva: Includes labia majora, labia minora, and vestibule
• Clitoris: Erectile tissue with associated neurovascular structures
• Perineal body and muscles: Central fibromuscular point where perineal muscles converge

Anal Triangle Structures

The anal triangle in females is similar to males, encompassing structures involved in defecation and perianal support.

• Anal canal: Terminal segment of the rectum
• External anal sphincter: Maintains continence
• Perianal glands and skin: Includes sweat and sebaceous glands, susceptible to infection

Perineal Body

The perineal body is a central fibromuscular structure located at the junction of the urogenital and anal triangles. It serves as a key point of attachment for several perineal muscles and plays a critical role in maintaining pelvic floor integrity.

• Definition and location: Positioned between the vaginal orifice in females (or bulb of the penis in males) and the anus
• Muscles inserting into the perineal body:
  • Bulbospongiosus
  • External anal sphincter
  • Superficial and deep transverse perineal muscles
  • Levator ani fibers
• Clinical significance: Essential for pelvic floor support; injury can occur during childbirth, leading to incontinence or prolapse

Clinical Significance

Perineal Trauma

Trauma to the perineum commonly occurs during childbirth or surgical procedures and can range from minor lacerations to severe tears.

• Episiotomy: Surgical incision to enlarge the vaginal opening during delivery
• Perineal tears: Classified into four degrees based on depth and structures involved
• Management: Prompt repair of muscles and fascia to restore function and prevent complications

Infections and Abscesses

Infections in the perineal region can affect skin, glands, or deeper tissues, sometimes leading to serious complications.

• Perineal abscesses: Localized collections of pus requiring drainage
• Fournier’s gangrene: Rapidly progressive necrotizing infection of the perineum, requiring urgent intervention

Perineal Hernias

Weakness of the perineal muscles or connective tissue can result in herniation of pelvic contents through the perineal body, most commonly seen after pelvic surgery.

Pelvic Floor Dysfunction

• Urinary incontinence: Involuntary leakage due to weakened perineal support
• Fecal incontinence: Loss of control of bowel movements associated with sphincter or pelvic floor damage
• Role of perineal muscles: Strong perineal muscles contribute to continence and pelvic organ support

Perineal Surgery

Various surgical procedures involve the perineum, including urological, gynecological, and colorectal interventions. Knowledge of perineal anatomy is essential to avoid complications and preserve function.

Embryology

The perineum develops from the cloacal region of the embryo, which divides into urogenital and anorectal parts during early gestation. Proper formation is essential for normal anatomy and function of both the urogenital and anal triangles.

• Development of the urogenital triangle: Arises from the anterior cloacal membrane, giving rise to external genitalia and associated perineal structures
• Development of the anal triangle: Forms from the posterior cloacal membrane, differentiating into the anal canal and perianal skin
• Clinical correlations: Malformations such as imperforate anus, hypospadias, and perineal clefts result from disruptions in normal embryological development

References

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