Defecation is normally a private function, which is performed at socially acceptable times chosen by the individual. Bowel control is learned in early childhood, and failure of bowel control may be associated with loss of independence, reduced self-esteem, social isolation, a sense of inadequacy or helplessness, and clinical depression.

The incidence and prevalence of anal incontinence (AI) is difficult to estimate. Surveys report widely differing figures. Sampling biases may result in significant underestimation in some populations and overestimation in others. For example, embarrassment may cause anally incontinent individuals to deny their symptoms in self-reporting surveys. On the other hand, surveys in which people over the age of 65 are represented by nursing home occupants may overestimate the prevalence in geriatric populations (1). Similarly, the reported prevalence of AI in younger, obstetric populations is suspected to be underestimated because a proportion of these patients may have injuries that go unrecognized, or these individuals experience transient fecal incontinence. Lastly, a standardized definition of AI does not exist. Currently, the reported prevalence varies according to the definition used. In several papers, “fecal incontinence” refers to the exclusive loss of feces, while the term “anal incontinence” is used for incontinence inclusive of flatus and stool (1). In addition, the threshold for the frequency of incontinence varies. Some surveys include individuals who admit to any anal incontinence in the past 1 year, while other surveys focus only on individuals who report incontinence of liquid or solid stool in the past month. Data collection methods also affect the quality of information obtained. Although face-to-face interviews offer the greatest potential for accurate data collection, some individuals are uncomfortable disclosing private information to a live examiner. Conversely, paper questionnaires can be difficult to complete for impaired patients.

Macmillan et al (1) performed a systematic literature review on the prevalence of AI (including flatal incontinence) and fecal incontinence in community-dwelling individuals. These investigators retrieved 1,517 articles and identified 16 that fit their inclusion and exclusion criteria. Overall, these studies estimate the prevalence of AI to be 2% to 24% and the prevalence of fecal incontinence to be 0.4% to 18%. Only 3 of the 16 studies employed a design that minimized significant sources of bias; these studies focused on fecal incontinence and had a much smaller prevalence variation than the other 13. The estimated prevalence of fecal incontinence in these particular trials ranged from 11% to 15%.

Fecal incontinence has a multifactorial etiology, and in gynecologic practice, the majority of patients with AI have obstetric trauma as the principal cause of their symptoms. Many of these women have anal sphincter defects (2). However, patients typically present years after the presumed obstetrical insult, which implies that compensatory continence mechanisms degrade with time.

Sultan et al (3) reported that 35% of a group of primiparous women who were demonstrated to have had intact sphincters antepartum had sphincter defects observed on endoanal ultrasound 6 weeks after vaginal delivery. More concerning was their observation that 13% of the primiparous women developed fecal incontinence or fecal urgency after delivery. Pretlove et al (4) followed a cohort of postpartum patients and found that 61% of patients with recognized sphincter defects were symptomatic
postpartum. The patients were not stratified according to parity or age. Faltin et al (5) performed immediate postpartum endoanal ultrasound in 150 primiparous women. They identified clinically undetected anal sphincter tears in 42 of 150 women (28%). In a postal questionnaire 3 months postpartum or more, fecal incontinence was reported by 22 women (15%). The odds ratio of those who had clinically undetected sphincter tears was 8.8 for the development of fecal incontinence.

In addition to sphincter defects, vaginal delivery is associated with pudendal neuropathy, particularly during a prolonged or difficult second stage of delivery. A proposed mechanism of injury is that nerve damage results from traction or compression. This damage may develop into impaired rectal evacuation with the need to strain, perineal descent, and subsequent fecal and urinary incontinence. Other common conditions seen by an obstetrician-gynecologist that are associated with fecal incontinence are presented in Table 22.1.

While there is no universally accepted scoring system for AI at present, several scoring systems have been described and used in different trials. These include the Cleveland Clinic Florida Fecal Incontinence Scale (Wexner) (6), Fecal Incontinence Severity Index (FISI) (7), Fecal Incontinence Quality of Life Score (FIQL) (8), Gastrointestinal Quality of Life Index (GIQLI) (9), as well as non-disease-specific instruments such as the Short Form-36 (10).

The detailed pathophysiology and evaluation of AI are covered in Chapters 20 and 21.

The maintenance of fecal incontinence involves complex interaction between higher centers (frontal cortex) and intact neural pathways between the spinal cord and pelvic muscles and sphincters. These, together with several other physiologic mechanisms, work to result in bowel control, allowing defecation to occur voluntarily at socially acceptable times. Degeneration or injury at any of these levels can result in fecal incontinence; hence there are a variety of etiological factors (Tables 22.2 and 22.3).

Specifically, obstetric-related fecal incontinence can result from pudendal nerve damage by compression or stretching, in addition to physical disruption of the anal sphincter mechanism from perineal lacerations. Postmenopausal estrogen deficiency may also affect levator muscle and pelvic floor strength.

The goal of the evaluation process is to understand the specific pathophysiology in the individual patient in an effort to identify any easily treatable contributing condition and develop an appropriate treatment plan. Thorough assessment begins with a detailed history and physical examination. Prior instrumented deliveries, gastrointestinal disease, and neurological history should be noted. Levator strength should be assessed, as well as the presence of pelvic or rectal prolapse, hemorrhoids, fistulas, and any abnormal or absent reflexes or sensation. A focused neurological examination is essential as well as an appropriate assessment of any suspected diarrheal disease.

Investigative tools for the evaluation of AI include anorectal manometry, endoanal ultrasound, defecography, endoscopy, and pudendal nerve latency tests; a description of these tests can be found in Chapter 21.

Because obstetrical trauma is the most common etiology of AI in women, prevention should be focused on the management of labor and delivery. There is an association between sphincter disruption and episiotomy (both midline and mediolateral). When episiotomy must be performed for obstetrical indications, the mediolateral approach should be preferred in an effort to avoid direct injury to the anal sphincters (11). There is also a well-established association between operative delivery using forceps and anal sphincter trauma. Avoidance of episiotomy and use of vacuum-assisted vaginal delivery (as opposed to forceps) when operative delivery is indicated, as well as maintaining a low threshold for cesarean delivery for labor dystocia, may be protective (12).

Before embarking on an extensive work-up and committing to specific treatments for AI, it is prudent to identify and address any gastrointestinal conditions that may contribute to fecal incontinence.

Treatments for AI include medical therapy, behavioral therapy in the form of biofeedback therapy, and surgery. A significant issue in the management of AI is the differing opinion on what constitutes successful treatment. This is due to a lack of consistent outcome measures. The use of post-treatment questionnaires in some studies relies on vague and subjective quantification such as “improved,” while in other studies there is variation in the inclusiveness of the definition of incontinence with respect to gas, liquid, or solid stool.