Overview of neurophysiology.

UI is the symptomatic complaint of the involuntary loss of urine and can develop because of anatomic and functional abnormalities of the lower urinary tract (LUT). The LUT is composed of the bladder and urethra, supported by a complex system of neural innervation and musculofascial support in the lower pelvis. It functions with the integration of many components, including the central nervous system (CNS), the peripheral nervous system, bladder smooth muscle, bladder stroma, suburothelial and intradetrusor interstitial cells, bladder urothelium, urethral smooth muscle, pelvic floor striated muscles, and the external urethral sphincter (EUS).

Pelvic parasympathetic nerves arise at the sacral level of the spinal cord, stimulate the bladder, and relax the urethra. Lumbar sympathetic nerves inhibit the bladder body and stimulate the bladder base and urethra. Pudendal nerves stimulate the EUS. These nerves contain afferent (sensory) as well as efferent axons.

Urethral and sphincter pathophysiology and anatomy.

The urethra is part of the bladder outlet, along with the pelvic floor musculature. The urethra has components of smooth muscle and striated muscle (rhabdosphincter or EUS). The periurethral striated muscle is part of the pelvic floor muscle complex. The EUS is composed of two parts. The periurethral striated muscle of the pelvic floor contains fast-twitch and slow-twitch fibers. The striated muscle of the distal sphincter mechanism contains predominantly slow-twitch fibers and provides >50% of the static resistance. In addition to striated muscle, the EUS appears to contain smooth muscle, which receives noradrenergic innervation. Investigators have shown that stimulation of the hypogastric nerve elicits myogenic potentials in the EUS.

In the male, the membranous urethra extends from the prostatic apex through the pelvic floor musculature (including the EUS) until it becomes the bulbous and penile urethra at the base of the penis. The male EUS covers the ventral surface of the prostate in a crescent shape proximal to the verumontanum, then assumes a horseshoe shape distal to the verumontanum, and is crescent shaped at the bulbar urethra.

In women, the urethra extends throughout the distal third of the anterior vaginal wall from the bladder neck to the meatus. The bulk of the muscle responsible for sphincteric control in women is circular striated muscle located in the proximal urethra and/or mid-urethra. A network of vascular subepithelial tissue/estrogen sensitive submucosa in women contributes to a urethral seal effect and promotes continence. The female EUS covers the ventral surface of the urethra in a horseshoe configuration.

Urinary continence is maintained during elevations in intraabdominal pressure by means of passive transmission of abdominal pressure to the proximal urethra along with a guarding reflex involving an active contraction of striated muscle of the EUS. The most common causes of intrinsic sphincteric deficiency (ISD) are iatrogenic, although, less commonly, neurologic disease can directly affect sphincter function.

Types of urinary incontinence.

Stress urinary incontinence (SUI) is the complaint of involuntary loss of urine with physical exertion (i.e., walking, straining, exercise, sneezing, coughing) or other activities that cause a rise in intraabdominal pressure. SUI in women is unlikely to be caused solely by anatomic laxity of the anterior vaginal wall and may be also due to poor intrinsic (physiologic) sphincteric function.

Urgency urinary incontinence (UUI) is the complaint of involuntary urine loss associated with urgency. It can, occasionally, be noted on physical exam as the observation of involuntary leakage from the urethra synchronous with the sensation of a sudden, compelling desire to void that is difficult to defer. This may be accompanied by detrusor overactivity incontinence, a urodynamic diagnosis, although this does not have to be present to establish a diagnosis of UUI. Any neurologic process interrupting the normal suprapontine inhibition of the pontine micturition center may result in neurogenic detrusor overactivity (NDO) and cause UUI.

Mixed urinary incontinence (MUI) is the complaint of involuntary urine loss associated with urgency as well as activities causing a rise in intraabdominal pressure. Postural UI is the complaint of involuntary urine loss associated with a change in position (typically from sitting or lying down to standing). Nocturnal enuresis is the complaint of involuntary urine loss occurring during sleep and should be distinguished from urgency incontinence. Continuous UI is the complaint of continuous urine loss, day and night, typically seen with fistula of the lower urinary tract involving the vagina (i.e., vesicovaginal and ureterovaginal fistulae). Insensible UI is the complaint of urine loss when the patient is unaware of how or precisely when the urine loss occurred. Coital incontinence is the complaint of involuntary loss of urine with sexual intercourse. It may occur with initial penetration, intromission, and/or during orgasm. Poor emptying from detrusor underactivity or detrusor areflexia (causing overflow incontinence ) can also cause UI ( Table 16.1 ).

Types of prolapse.

POP refers to the downward displacement of the pelvic organs, which results in protrusion of the uterus and/or the different vaginal compartments and their surrounding organs, such as the bladder, the rectum, or the bowel. It results from the loss of support of one or more compartments of the vagina ( Fig. 16.1 ). The levator ani muscles, and their interaction with endopelvic fascia, are an important component of the pelvic organ support.

Levels of support.

Anterior compartment prolapse corresponds to the descent of the anterior vaginal wall. Most commonly, this represents the descent of the bladder ( cystocele ), but it can also represent an anterior enterocele, especially after prior reconstructive surgery. Apical prolapse corresponds to the descent of the uterus (uterine or cervical prolapse) or, in a posthysterectomy patient, the vaginal cuff. It can include the small intestine (enterocele). Posterior compartment prolapse is a weakness of the posterior vaginal wall and can involve the rectum (rectocele) but can also include the small bowel or colon even in the presence of an intact uterus. Procidentia refers to total vaginal eversion with complete uterine or vaginal cuff prolapse. POP occurs most frequently in the anterior compartment, followed by the posterior compartment, and least commonly in the apex.

Risk factors.

Vaginal childbirth, advancing age, and obesity are the most established risk factors for POP. The risk of POP increases with every additional vaginal childbirth, and forceps delivery further increases the risk of developing POP. Cesarean section seems to be protective against prolapse, but the degree of protection is unclear. The incidence and the prevalence of POP increase with advancing age with women 60–69 and 70–79 years of age having a higher risk of prolapse than women ages 50–59 years. Hysterectomy is associated with an increased risk of developing POP. Additionally, POP is more common in white and Hispanic women than African American women.