Causes of Genitourinary Prolapse - MBBS Notes

Definition

Pelvic Support Anatomy (Foundation for Understanding Causes)

1. Levator ani muscle complex - provides active tonic support; keeps the urogenital hiatus closed, compressing the urethra, vagina, and rectum against the pubic bone
2. Endopelvic fascia and ligaments - passive connective tissue support
3. Bony pelvis - anchor for all ligaments and muscles

DeLancey's Three Levels of Support

Pathophysiology

1. Direct Muscle Trauma (Levator Ani Injury)

• The levator ani maintains urogenital hiatus closure by tonic contraction
• Direct trauma or denervation reduces levator ani tone → widening of the urogenital hiatus → prolapse
• On MRI, up to 20% of primiparous women have visible levator ani muscle defects not seen in nulliparous women, confirming vaginal delivery as a major mechanism
• As prolapse progresses, the hiatus widens further (a vicious cycle)

2. Fascial/Ligamentous Failure (Endopelvic Fascia)

• When levator tone is lost, the full load falls on ligaments (endopelvic fascia)
• These eventually fail under sustained load
• Ligamentous injury/stretch occurs during: vaginal delivery, hysterectomy, chronic straining, aging
• Collagen metabolism is significantly altered in women with prolapse
• Altered collagen type I:III ratio leads to pelvic floor dysfunction
• Connective tissue disorders (Ehlers-Danlos syndrome, Marfan syndrome) are strongly linked to POP

3. Neuropathic Injury

• Two nerve supplies to the pelvic floor:
  • Pudendal nerve - urethral/anal sphincters and perineal muscles
  • S3-S5 nerve roots - levator ani muscles (direct branches)
• Pelvic floor nerve injury occurs most commonly during vaginal delivery
• Electromyography studies found levator ani neuropathy in 24% of women at 6 weeks and 29% at 6 months post-vaginal delivery
• Women who had elective caesarean sections showed almost no levator ani injury

Risk Factors / Causes (Classified)

A. Obstetric Causes (Most Important)

• Parity: Oxford Family Planning Study (17,000 women):
  • 2 deliveries: adjusted relative risk = 8.4
  • 4+ deliveries: adjusted relative risk = 10.85
  • Each additional delivery (up to 5) increases risk by 10-20%
• Mode of delivery:
  • Forceps delivery: OR 5.4 (highest risk)
  • Normal vaginal delivery: OR 2.9
  • Caesarean section: protective (reduces POP risk by ~46%)
  • Laboured caesarean (after labour) still carries elevated risk
• Young maternal age at first delivery (< 25 years) also increases risk
• Vacuum extraction and forceps have the highest associated ORs for symptomatic prolapse (OR 3.2 vs. caesarean-only group)
• Macrosomia (birth weight > 4000 g) was not consistently associated in all studies

B. Age / Menopause

• Prevalence of POP rises approximately 40% with each decade of life
• Women aged 60-79 have a significantly higher risk than those aged 50-59
• Risk of requiring surgery peaks in the seventh decade
• Oestrogen loss in menopause may contribute to weakening of fascial support, though studies have not consistently shown a direct association between hormonal status and POP

C. Obesity / Raised Intra-abdominal Pressure

• Chronic elevation of intra-abdominal pressure is a major mechanical cause
• Overweight (BMI 25-30): OR 2.51 for POP; Obese (BMI > 30): OR 2.56
• Obesity significantly increases:
  • Uterine prolapse: +40%
  • Cystocele: +57%
  • Rectocele: +75%
• Waist circumference ≥ 88 cm independently associated with rectocele and cystocele
• Similar mechanisms apply for: chronic cough (COPD, asthma), chronic constipation, heavy lifting, and intense physical activity

D. Previous Hysterectomy

• Associated with significantly increased risk of subsequent POP
• Cumulative risk of prolapse surgery after hysterectomy: 29/1000 women-years vs. 16/1000 in general population
• Risk rises from 1% at 3 years to 5% at 15 years post-hysterectomy
• Hysterectomy done for prolapse carries 5.5x higher risk of repeat POP surgery
• Failure to perform concomitant vaginal vault suspension at time of hysterectomy is a key contributing factor

E. Previous Pelvic Surgery

• Burch colposuspension: genitourinary prolapse as a sequel in 22.1% of women (range 9.5-38.2%)
• Retropubic suspensions alter vaginal and bladder base anatomy, may aggravate posterior vaginal wall weakness, predisposing to enterocele (incidence 3-17%)
• Paravaginal repair: recurrent cystourethrocele in 39% of cases

F. Connective Tissue Disorders

• Ehlers-Danlos syndrome and Marfan syndrome are strongly associated with POP
• Altered collagen composition (type I:III ratio) is found consistently in women with prolapse
• A family history of prolapse confers 5-fold increased risk among siblings

G. Racial/Ethnic Factors

• Lowest prevalence: Black/African-American women (OR 0.4-0.65)
• Highest prevalence: Hispanic women (OR 1.2-1.3) and Asian women (OR 2.18 for cystocele)
• Differences may relate to connective tissue structure and pelvic floor anatomy

H. Genetic/Hereditary Factors

• Women with a mother or sister with prolapse have a higher risk
• Fivefold increased risk among siblings of women with severe prolapse vs. general population

I. Chronic Constipation

• Independently and significantly associated with symptomatic prolapse
• 2.5-fold increased risk in population-based studies
• Chronic straining stretches and weakens pelvic floor ligaments and nerves

J. Other (Inconsistently Linked) Factors

• Smoking
• Heavy lifting (occupational/recreational)
• High-intensity physical activity
• Chronic pulmonary disease

Types of Prolapse (Quick Summary)

Summary Mnemonic: "COACH"

Key Points for Exam

1. POP cause is multifactorial - direct muscle trauma + fascial failure + neuropathy
2. Vaginal childbirth is the single most important risk factor (relative risk 8.4-10.85 with multiparity)
3. Caesarean section is protective - could prevent ~46% of POP cases
4. The levator ani muscle is the first line of pelvic support; its injury (trauma or denervation) is the initiating event
5. Once levator tone is lost, the ligaments bear all the load and eventually fail
6. Collagen I:III ratio alteration is consistently found in POP - supports a connective tissue component
7. Ehlers-Danlos and Marfan syndromes are classic examples of connective tissue risk
8. Level I loss → apical/uterine prolapse; Level II loss → cystocele/rectocele; Level III loss → urethral hypermobility/perineal descent
9. Hysterectomy done for prolapse carries the highest risk of needing future pelvic floor surgery (5.5x)
10. Chronic straining (constipation, chronic cough) is an underappreciated but significant cause