What are the pelvic support structures in a typical adult female patient?

Pelvic Support Structures in Adult Females

The female pelvic support system consists of two integrated mechanical frameworks: a supporting system comprising the levator ani muscle, arcus tendineus fasciae pelvis, and adipose cushion pillar, and a suspension system formed by neurovascular structures with their associated endopelvic fascial condensations. 1

Primary Muscular Support Components

Levator Ani Muscle Complex

• The levator ani muscle divides into horizontal and vertical components at the medial attachment of the fibrous visceral sheath 1
• The puborectalis portion attaches at the superior pubic ramus above the arcus tendineus fasciae pelvis 1
• The anterior half of the iliococcygeus originates at the level of the arcus tendineus fasciae pelvis but descends from it before reaching the ischial spine 1
• MRI with high-resolution T2 images reliably detects and quantifies levator ani muscle defects with high interobserver reliability, and these defects correlate with symptoms of pelvic organ prolapse and histories of vaginal reconstructive surgery or episiotomy 2

External Anal Sphincter

• The external anal sphincter forms the lower outer half of the striated muscle sphincter layer, while the puborectalis forms the upper outer half 3
• The external anal sphincter is continuous with the rectum at the anorectal junction 3
• Endoanal MRI can evaluate external anal sphincter thickness to predict outcomes after sphincter repair 2

Fascial and Ligamentous Support Structures

Endopelvic Fascia

• The fibrous visceral sheath of the endopelvic fascia covers both the bladder and upper vagina, binding these structures together 1
• Perivascular sheaths and pelvic nerve plexuses are reinforced by condensed endopelvic fascia, suspending the pelvic organs posterolaterally 1
• The endopelvic fascia constitutes the first principal layer of the pelvic floor 3

Urethral Support Structures

• The female urethra has no direct ligamentous fixation to the pubic bone 4
• The ventro-lateral aspect of the urethra is enclosed by the ventral parts of the levator ani, its fasciae, and a ventral urethral connective tissue bridge connecting both sides 4
• Dorsally, the urethra is intimately connected to the vaginal wall 4
• MRI allows direct visualization of urethral ligaments and other support structures 2

Uterosacral Ligaments

• The uterosacral ligaments are critical anatomical structures that support the uterus and apical vagina within the pelvis 5
• When these structures become overstretched, weak, or exhibit laxity, pelvic organ prolapse occurs 5

Vaginal Support Structures

• Secondary vaginal support defects, including lateral and apical vaginal wall displacement, are visible on MRI 2
• The fibrous visceral sheath binds the bladder and upper vagina together as a functional unit 1

Additional Support Components

Adipose Cushion Pillar

• A well-circumscribed adipose cushion pillar in the ischioanal fossa and its anterior recess supports the horizontal part of the levator ani muscle and presses the vertical part against the pelvic viscera 1

Arcus Tendineus Fasciae Pelvis

• The arcus tendineus fasciae pelvis serves as a key attachment point for the levator ani muscle components 1
• It forms part of the primary supporting system along with the levator ani muscle and adipose cushion pillar 1

Additional Pelvic Floor Layers

• The perineal membrane (urogenital diaphragm) constitutes the third principal layer 3
• The superficial transverse perineii forms the fourth principal layer 3
• The perineal body and a fibro-elastic network add additional support 3

Clinical Significance

Elastic Fiber Homeostasis

• Elastic fibers turn over slowly in most adult tissues but undergo massive remodeling in reproductive organs through pregnancy and birth 6
• Failure to maintain elastic fiber homeostasis causes inability of reproductive tissues to replenish elastic fibers after parturition, leading to pelvic organ prolapse, vaginal wall weakening, and lower urinary tract dysfunction 6
• Lysyl oxidase-like-1 (LOXL1) expression is highly regulated in the reproductive tract and diminishes during aging, contributing to pelvic floor disorders 6

Imaging Assessment

• MRI provides comprehensive anatomic evaluation with high soft-tissue contrast resolution, allowing assessment of pelvic organs, bladder, urethra, urethral ligaments, and pelvic floor muscles and fascia 7
• Global assessment of all pelvic compartments allows repair of all defects during a single procedure, including those hidden on physical examination 2