Perineal body

The perineal body is a small but critical fibromuscular structure located in the midline of the perineum, between the urogenital and anal triangles. Despite its modest size, it plays a central role in maintaining the structural integrity of the pelvic floor. It acts as a convergence point for multiple muscles, provides stability to the perineum, supports the pelvic viscera, and helps maintain continence. Its function is especially crucial in females, where it provides a mechanical connection between the vagina, rectum, and external genitalia. Damage to the perineal body, especially during childbirth, can result in pelvic floor dysfunction, incontinence, or prolapse.

Structure

The perineal body is composed of dense fibrous connective tissue interspersed with smooth muscle and skeletal muscle fibers. It acts as a central tendon of the perineum and serves as a point of interdigitation for muscles of the pelvic floor, perineum, and anal sphincter complex. It varies in shape and size based on sex and parity, and is often more prominent in females.

Muscles Attaching to the Perineal Body

A total of 8 muscles (some sources count 10, depending on subdivisions) attach directly to the perineal body:

• External anal sphincter

• Bulbospongiosus

• Superficial transverse perineal muscle

• Deep transverse perineal muscle

• Levator ani (particularly pubococcygeus fibers)

• Portions of the longitudinal smooth muscle of the rectum

• Perineal portion of the external urethral sphincter (deep perineal muscle)

• Fibers from the vaginal wall or perineal membrane

Location

The perineal body is located in the midline of the perineum at the junction of the urogenital and anal triangles. In females, it lies between the posterior vaginal wall and the anterior wall of the anal canal. In males, it lies between the bulb of the penis and the anal canal. It is palpable during physical or surgical examination and serves as a landmark for perineal and pelvic floor surgeries.

Landmark Relation Anterior Posterior wall of vagina (female), bulb of penis (male) Posterior External anal sphincter and anal canal Lateral Perineal muscles and fascia of the urogenital triangle

Function

• Pelvic Floor Support: Acts as a central anchor point for muscles maintaining the pelvic floor’s tone and structure

• Vaginal and Rectal Stability: Provides posterior support to the vaginal wall and anterior support to the anal canal

• Continence Mechanism: Indirectly contributes to both urinary and fecal continence through structural stabilization

• Resistance to Intra-abdominal Pressure: Helps resist forces generated during coughing, sneezing, lifting, and childbirth

• Coordination of Perineal Muscles: Serves as a relay point for force transfer and coordinated contraction of pelvic musculature

Histology

The perineal body consists of densely packed collagen and elastin fibers with embedded skeletal and smooth muscle elements. It is encased in fibrous connective tissue and contains an irregular array of fibroblasts, myofibroblasts, and vascular channels. The proportion of muscle to connective tissue may vary depending on sex, age, and history of childbirth or trauma.

Development

Embryologically, the perineal body forms during the division of the cloaca by the urorectal septum. As the septum grows caudally, it separates the cloacal membrane into the urogenital membrane and the anal membrane. The point where the urorectal septum reaches the cloacal membrane becomes the perineal body. Thus, it originates from mesodermal tissues and acts as a developmental boundary between urogenital and anorectal structures.

Sex Differences

Feature Female Male Size Larger, more fibrous Smaller and more compact Anterior Relation Posterior wall of the vagina Bulb of penis Clinical Relevance Frequently involved in obstetric trauma Less commonly injured

Clinical Significance

• Obstetric Trauma: The perineal body is commonly torn during childbirth, especially in cases of large fetal head, rapid delivery, or episiotomy

• Perineal Tears: Classified into degrees; third- and fourth-degree tears involve the perineal body and external anal sphincter

• Episiotomy: A surgical incision of the perineum performed to prevent uncontrolled tearing may involve or avoid the perineal body depending on the type (midline vs mediolateral)

• Pelvic Organ Prolapse: Damage or weakening of the perineal body reduces posterior vaginal wall support, predisposing to rectocele and vaginal vault prolapse

• Incontinence: Loss of structural integrity affects the efficiency of the anal and urethral sphincter mechanisms

• Perineal Body Reconstruction: Surgical reinforcement during pelvic floor repair helps restore anatomical and functional support

• Midline Pelvic Surgeries: Acts as a landmark and anchoring site in procedures like posterior colporrhaphy and perineorrhaphy

Imaging and Examination

• Palpable Landmark: During bimanual pelvic or rectal examination, the perineal body can be felt as a firm central structure between vagina and anus

• Ultrasound: Perineal or transperineal ultrasound can assess integrity, especially postpartum

• MRI: High-resolution pelvic MRI may show perineal body volume, integrity, and its relation to surrounding defects in pelvic floor disorders