Anal incontinence (AI) is an involuntary loss of flatus, liquid, or solid stool that causes a social or hygienic problem (Abrams, 2005). This condition may lead to poor self-image and social isolation, thus significantly impairing quality of life (Johanson, 1996; Perry, 2002). Additionally, AI creates a substantial financial burden on patients and the health care system (Whitehead, 2001).
The definition of AI includes incontinence of flatus, whereas that of fecal incontinence (FI) does not. Not included in either definition is anal mucoid seepage. This type of fecal leakage tends to develop in those with a fully functional anal sphincter and intact cognition. It most often is associated with organic colonic disease or dietary sensitivity (Abrams, 2005).
Anal incontinence is common and affects all age groups. In contrast to previous beliefs, it affects men and women similarly (Heymen, 2009; Madoff, 2004; Nelson, 2004). The prevalence of AI increases with age and has been reported to reach 46 percent in older, institutionalized women (Nelson, 1998). In a systematic review of the literature, Macmillan and coworkers (2004) reported that the estimated prevalence of AI among community-dwelling adults ranges between 2 and 24 percent if flatal incontinence is included and between 0.4 and 18 percent if flatal incontinence is not. These wide variations are attributed to differences in definitions and in the surveyed cohort's age and to lack of validated questionnaires. In a multicenter trial that included seven geographically distinct sites in the United States, Boreham and associates (2005) reported the prevalence, risk factors, and quality of life effects of AI in women aged 18 to 65 years presenting for benign gynecologic care. The overall prevalence of AI in this cohort was 28 percent. In a recent study conducted by the Pelvic Floor Disorders Network, a validated FI severity scale was added to the National Health and Nutrition Examination Survey (NHANES) in 2005-2006 (Rockwood, 1999; Whitehead, 2009). The estimated prevalence of FI in the nationally representative sample of noninstitutionalized U.S. adults was 8.3 percent (18 million) and consisted of liquid stool incontinence in 6.2 percent, mucus in 3.1 percent, and solid stool in 1.6 percent. This survey confirmed the strong association between FI and age. The prevalence of FI increased from 2.6 percent in those aged 20 to 30 years up to 15.3 percent in subjects aged 70 years or older.
Pathophysiology of Defecation and Anal Continence
Normal defecation and anal continence are complex processes that require a competent anal sphincter complex, normal anorectal sensation, adequate rectal capacity and compliance, and conscious control.
This neuromuscular complex consists of the internal and external anal sphincter muscles and the puborectalis muscle (Figs. 38-9 and 38-21). Of these, the internal anal sphincter (IAS) is the ...