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Introduction

Urinary incontinence affects well over 13 million adult women in the United States. It is estimated to affect 30-40% of American women during their lifetime. Despite its prevalence and estimated costs in excess of $19.5 billion annually, up to 70% of women do not seek help for incontinence, primarily because of social embarrassment or because they are unaware that help is available. Because of increasing awareness by both patients and physicians, the societal concept that incontinence is part of the "normal" aging process is no longer acceptable. Advances in modern medicine during the last 80 years have increased the life expectancy of women well into the eighth and ninth decades. We are caring for patients longer and better than ever, effectively managing chronic medical problems such as hypertension, cardiovascular disease, and diabetes, enabling women to enjoy longer and more productive lives. This results in a large population of women living up to one-third of their life after menopause, thereby introducing a whole host of medical issues and health concerns. A prime example of this is the problem of urinary incontinence, which has become more prevalent as the population of aging women grows. In this section we focus on the evaluation and treatment of women with urinary incontinence.

The urinary and reproductive tracts are intimately associated during embryologic development. The lower urinary tract can be divided into 3 parts: the bladder, the vesical neck, and the urethra (Fig 45-1). The bladder is a hollow muscular organ lined with transitional epithelium designed for urine storage. The bladder musculature consists of 3 layers of smooth muscle, which are densely intertwined and constitute the detrusor muscle. The bladder stays relaxed to facilitate urine storage and contracts periodically to completely evacuate its contents when appropriate and acceptable. At the bladder base is the trigone, which is embryologically distinct from the bladder.

The 2 ureteral orifices and the internal urethral meatus form the boundaries of the trigone. The trigone has 2 distinct muscular layers: superficial and deep. The deep layer shares a similar cholinergic autonomic innervation as the detrusor muscle, whereas the superficial layer is densely innervated by noradrenergic nerves. This distinct difference in receptor distribution is important, as it provides opportunities to target more specific sites for pharmacotherapeutic intervention. The superficial detrusor layer extends muscular fibers that contribute to the distal urethra and posterior to the proximal urethra. The urethral "sphincter" itself is not a well-delineated structure; rather, it is a complex and intricate meshwork of intertwining smooth and striated muscle fibers that functionally responds neurophysiologically to variable degrees of vesicle pressures and facilitates urine storage and voiding.

The female urethra is approximately 3-4 cm long. The composition and support of the urethra and bladder neck play key roles in the function and maintenance of urinary continence. Together the striated urethral and periurethral muscles compose the extrinsic urethral sphincter mechanism. The urethral sphincter, along with the levator ani, function in the reflex contraction. The urethra is surrounded by dense vasculature that contributes to the urethral mucosal seal and urethral closure pressure. An abundance of submucosal glands are found along the dorsal surface. Most of the urethral diverticula arise from this area. The uroepithelium is stratified squamous (Fig 45-2).