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Stress Urinary Incontinence in Women (1/3)

• Stress urinary incontinence in women (1/3): definition and etiology
• Stress urinary incontinence (2/3): symptoms and diagnostic work-up
• Stress urinary incontinence (3/3): medical and surgical treatment

Definition of stress urinary incontinence

The International Continence Society (ICS) defines urinary incontinence as "the complaint of any involuntary loss of urine". Stress urinary incontinence is urine leakage, which is associated with increased abdominal pressure and insufficient urethral sphincter mechanism. The main symptom of stress urinary incontinence is the loss of urine on exertion, sneezing or coughing.

Epidemiology of stress urinary incontinence

Vaginal deliveries are a risk factor for stress urinary incontinence:

The prevalence of incontinence in nulliparous women is 10%, after cesarean section 16% and in women with vaginal deliveries 21%. Comparative studies between cesarean sections and vaginal deliveries found a different prevalence of stress incontinence: 7% (cesarean sections) vs. 12% (vaginal deliveries).

Age is a risk factor for urinary incontinence:

There is a significant rising prevalence of urinary incontinence with age. For all forms of incontinence, the prevalence is 4.5 to 53% for women, 1.6 to 24% for men, depending on age.

Etiology and Pathogenesis of Stress Urinary Incontinence

Components of the bladder sphincter mechanism:

Components of the bladder sphincter are the urethral closure pressure caused by the sphincter muscles, and active and passive pressure transmission during the elevation of abdominal pressure.

Urethral closure pressure:

Urethral closure pressure is mainly created by the external sphincter muscle (striated muscle) and internal sphincter muscle (smooth muscle) [see section bladder anatomy].

Passive pressure transmission:

If the abdominal pressure rises, additional pressure is applied on the bladder sphincter without muscle contraction of the pelvic floor. The passive pressure transmission is enabled by the connective tissue suspension of urethra, bladder and vagina.

Active pressure transmission:

If the abdominal pressure rises, contraction of the striated muscles of the pelvic floor and bladder sphincter causes an increase in urethral closure pressure.

Causes of Stress Urinary Incontinence:

Any defect causing a reduced urethral closure pressure and/or impaired pressure transmission with rising abdominal pressure will cause stress urinary incontinence. The most common causes of stress incontinence are a hypermobile urethra and/or an intrinsic sphincter deficiency (hypotonic urethra).

Hypermobile urethra:

The caudal displacement of the urethra due to rising abdominal pressure into the extraabdominal compartment leads to lack of passive pressure transmission, opening of the bladder neck and thus to stress urinary incontinence.

The stability of the suburethral connective tissue is a crucial factor for continence under stress. Vaginal deliveries increase the risk of stress urinary incontinence due to damage to the connective tissue, muscle tearing and damage to the innervation of the pelvic floor and sphincter muscles. The defects lead also to pelvic floor deficiency and prolapse of the pelvic organs.

Pelvic organ prolaps is a clinical sign for stress urinary incontinence, but it may also mask the symptom incontinence. The prolapse may cause kinking and obstruction of the urethra. An excessive kinking of the urethra may lead to residual urine and urinary retention. After correction of prolapse, incontinence may become clinically relevant. The effect of hysterectomy on stress incontinence is controversial.

Intrinsic sphincter deficiency :

Insufficiency of the urethral sphincter, regardless of the cause, is called intrinsic sphincter deficiency.

• Neurogenic causes of intrinsic sphincter deficiency: most common for sacral and peripheral lesions of the sphincter innervation [see also section neurogenic bladder dysfunction].
• Scarring in the region of the proximal urethra and bladder neck: after incontinence surgery.
• Age and estrogen deficiency lead to atrophy of the urethral mucosa with deterioration of sphincter closure pressure.

Chronic elevated abdominal pressure:

Diseases or circumstances which elevate the abdominal pressure aggravate existing stress urinary incontinence: e.g. COPD, obesity or carrying heavy loads.

Integral theory of stress urinary incontinence by Petros and Ulmsten:

The integral theory of stress urinary incontinence by Petros and Ulmsten relates symptoms to anatomical defects of the pelvic region. The vagina acts like a hammock under the urethra and bladder and plays a central role in the mediation of urinary continence and in the prevention of urge symptoms. The proximal urethra is the zone of critical elasticity, this elasticity is essential for bladder filling, scarring or distention causes urgency. Depending on the location of the pelvic floor defects, various symptoms and therapeutic consequences may be distinguished.

References

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  Deutsche Version: Belastungsinkontinenz der Frau