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Although definitions are inconsistent, anal incontinence (AI) is most commonly defined as an involuntary loss of flatus, mucus, or fecal material that causes a social or hygienic problem (Abrams, 2018; Sultan, 2017). The definition of AI includes incontinence of flatus, whereas that of fecal incontinence (FI) does not. From a consensus workshop, a more patient-centered term “accidental bowel leakage” was suggested for communication with patients (Bharucha, 2015).
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AI can lead to poor self-image and isolation, and the social and quality-of-life effects of AI are significant (Johanson, 1996). Additionally, AI raises the likelihood that an older patient will be admitted to a nursing home rather than cared for at home (Grover, 2010).
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AI is common. From one national survey, the prevalence of FI in women approximated 9 percent using 2005 through 2010 data (Wu, 2014). Of affected individuals, liquid stool incontinence was noted in 6.2 percent, mucus in 3.1 percent, and solid stool in 1.6 percent (Whitehead, 2009). The prevalence of FI rose from 2.6 percent in those aged 20 to 30 years to 15.3 percent in subjects aged 70 years or older. In older, institutionalized women, AI prevalence may reach 46 percent (Nelson, 1998). Notably, FI is also not significantly associated with race or ethnicity, education level, income, or marital status (Whitehead, 2009).
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Normal defecation and anal continence are complex processes that require: (1) a competent anal sphincter complex, (2) normal anorectal sensation, (3) adequate rectal capacity and compliance, and (4) conscious control. Logically, mechanisms responsible for FI include anal sphincter and pelvic floor weakness, reduced or enhanced rectal sensation, diminished rectal capacity and compliance, and diarrhea (Bharucha, 2015). In many patients, these factors are additive.
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Muscular Contributions
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Essential contributors to fecal continence include the internal and external anal sphincters and the puborectalis muscle (Figs. 38-9 and 38-21, p. 799). The internal anal sphincter (IAS) is the thickened distal 3- to 4-cm longitudinal extension of the colon’s circular smooth-muscle layer. It is innervated by the autonomic nervous system and provides 70 to 85 percent of the anal canal’s resting pressure (Frenckner, 1975). As a result, the IAS contributes substantially to the maintenance of fecal continence at rest.
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The external anal sphincter (EAS) consists of striated muscle and is primarily innervated by somatic motor fibers that course in the inferior anal (rectal) branch of the pudendal nerve (Fig. 25-1A). The EAS provides the anal canal’s squeeze pressure and is mainly responsible for maintaining fecal continence when continence is threatened. At times, squeeze pressure may be voluntary or may be induced by increased intraabdominal pressure. In addition, although resting sphincter tone is generally attributed to ...