Chapter 20 — Anal Incontinence
Anal incontinence means involuntary loss of control over flatus, liquid stool, or solid stool. It ranges from occasional minor soiling to complete loss of control. It is one of the most distressing conditions in anorectal practice, and one of the most likely to be underreported by the patient. This chapter explains anal incontinence in full. It covers presentation, examination, differential diagnosis, investigations, and the general principles of management. Two later chapters build on this one: Chapter 21 covers obstetric sphincter injury specifically, and Chapter 22 covers secondary sphincter repair in full technical detail.
20.1 What Is Anal Incontinence
Anal incontinence is the involuntary loss of control over the contents of the rectum. It exists on a wide spectrum. At the mild end, a patient may notice occasional soiling of underwear, or difficulty controlling flatus. At the severe end, a patient may have no control at all over the passage of solid stool.
The condition can affect flatus, liquid stool, solid stool, or any combination of these. A patient may also describe urgency, meaning a sudden, difficult-to-control need to defecate, as well as, or instead of, frank leakage.
This condition carries a heavy social and psychological burden. Many patients restrict their daily activities significantly because of it, and many are reluctant to describe it fully unless asked directly and sensitively.
20.2 Why It Happens
Sphincter injury is a common cause. This can follow childbirth, particularly a difficult or assisted delivery, described fully in Chapter 21. It can also follow previous anorectal surgery. This can happen if a sphincterotomy or other procedure divides more of the sphincter than intended. It can also happen if the sphincter is inadvertently damaged during surgery for another condition, such as fistula-in-ano, described in Chapter 12.
Nerve injury can impair sphincter function even when the muscle itself is structurally intact. This can follow childbirth, or chronic straining over many years. It can also follow damage to the nerves supplying the pelvic floor, from another cause such as diabetes or spinal disease.
Structural conditions elsewhere in the anorectal region can also cause incontinence. Rectal prolapse, described in Chapter 14, can prevent the sphincter from closing properly. Large, prolapsing haemorrhoids, described in Chapter 10, can have a similar effect, allowing seepage around the bulk of tissue.
Reduced rectal capacity, from inflammatory bowel disease or previous radiotherapy, can leave the rectum unable to store stool normally, leading to urgency and leakage.
Overflow incontinence is an important and distinct cause, particularly in an elderly or immobile patient. Hardened stool becomes impacted in the rectum, and liquid stool leaks around this impacted mass. This looks like incontinence, but the underlying problem, and its correct treatment, is entirely different from a true sphincter or nerve problem.
Severe or persistent diarrhoea, from any cause, can overwhelm even a normally functioning sphincter.
20.3 Classification
Anal incontinence is usually classified by severity, and by the type of leakage.
Minor incontinence — occasional difficulty controlling flatus, or occasional soiling, without regular loss of solid stool.
Major incontinence — regular, involuntary loss of liquid or solid stool.
Passive incontinence — leakage without warning or awareness.
Urge incontinence — a strong urge to defecate, with leakage before the patient can reach a toilet.
A validated scoring system, such as the Wexner incontinence score, is commonly used to record severity. This gives a standardised, reproducible way to track the patient's response to treatment over time.
20.4 Presentation
Follow the history-taking method described in Chapter 2. Ask directly and specifically about incontinence. As with the digital splinting described in Chapter 16, many patients will not volunteer this symptom unless asked plainly.
Ask specifically what is lost: flatus, liquid stool, solid stool, or a combination.
Ask about frequency, and about the use of pads or other protection.
Ask whether leakage happens with warning, described as urge incontinence, or without warning, described as passive incontinence.
Ask about obstetric history in every female patient. Include the number of deliveries. Ask whether any delivery was difficult, prolonged, or assisted with forceps or vacuum.
Ask about previous anorectal surgery, chronic diarrhoea, diabetes, and any neurological condition.
Ask about the impact on daily life. This helps judge severity, and matters greatly to the patient, even when it does not change the underlying diagnosis.
20.5 Examination
Follow the sequence described in Chapter 3.
Inspection, described in Chapter 4, may show perianal soiling, or scarring from previous surgery or childbirth. It may also show a patulous or gaping anus, or a rectal prolapse visible on straining.
Digital rectal examination, described in Chapter 5, should assess resting tone, which reflects internal sphincter function, and squeeze tone, which reflects external sphincter function. A palpable gap or defect in the sphincter ring, particularly anteriorly, suggests a structural sphincter injury.
Examine specifically for a coexisting rectal prolapse, described in Chapter 14, or large prolapsing haemorrhoids, described in Chapter 10. Correcting either of these may substantially improve incontinence, without any direct surgery on the sphincter itself.
In a patient with suspected faecal impaction and overflow incontinence, examination will typically reveal a rectum loaded with hardened stool.
20.6 Differential Diagnosis
Overflow incontinence from faecal impaction — described in Section 20.2. This must be actively excluded, since its treatment, disimpaction and a bowel regimen, is completely different from the treatment of true sphincter or nerve-related incontinence.
Rectal prolapse — described in Chapter 14, as both a cause of incontinence and a condition that can coexist with it.
Severe haemorrhoidal disease — described in Chapter 10, which can cause seepage that is sometimes mistaken for true incontinence.
Diarrhoeal illness — a temporary cause of loose stool overwhelming continence, rather than an underlying sphincter problem.
20.7 Investigations
Anorectal manometry, described in Chapter 8, measures resting and squeeze pressures directly. It helps confirm whether the internal sphincter, the external sphincter, or both are underperforming.
Endoanal ultrasound identifies a structural sphincter defect, and is particularly useful when planning sphincter repair, described fully in Chapter 22.
Pudendal nerve studies may be considered when a nerve-related cause is suspected, particularly when the sphincter appears structurally intact on imaging, despite poor function.
Defecography, described in Chapter 8 and Chapter 16, is useful when a coexisting rectal prolapse or obstructed defecation is suspected alongside incontinence.
20.8 Principles of Management
Treat any identifiable underlying cause first. Disimpact an overflow incontinence. Treat a diarrhoeal illness. Correct a rectal prolapse, described in Chapter 14, or treat significant haemorrhoidal disease, described in Chapter 10, if either is contributing.
Conservative measures are the correct first step in most patients without a major structural defect. These include dietary modification, bulking agents, anti-diarrhoeal medication such as loperamide to firm up loose stool, and a structured bowel training programme.
Pelvic floor physiotherapy and biofeedback training, described in Chapter 16 for pelvic floor dyssynergia, is also valuable here. It strengthens and retrains the sphincter and pelvic floor muscles, even without a structural defect.
Surgical treatment is considered when conservative measures fail, and depends on the underlying cause. A defined anterior sphincter defect, most often from obstetric injury, is addressed by sphincteroplasty. This is introduced briefly below, and described in full technical detail in Chapter 22. Incontinence without a clear structural defect, or incontinence that persists after sphincter repair, may be considered for sacral nerve stimulation.
20.9 Surgical and Device-Based Options
Overlapping sphincteroplasty repairs a defined defect in the sphincter ring, most commonly located anteriorly after obstetric injury. The torn ends of the sphincter are identified, overlapped, and sutured together, restoring a complete muscular ring. This technique, and the specific injury it most often treats, are described in full in Chapters 21 and 22.
Sacral nerve stimulation involves implanting a small electrode near the sacral nerve roots, delivering continuous mild electrical stimulation. It improves continence by modulating the nerve signals controlling the pelvic floor and rectal sensation, rather than by repairing the sphincter muscle directly. It is considered for incontinence without a clear structural defect, and for incontinence that persists despite a technically successful sphincter repair.
Injectable bulking agents are placed around the anal canal. They can improve minor incontinence by narrowing the canal slightly. The effect is often partial, and may not be lasting.
A stoma remains an option of last resort. It suits severe, disabling incontinence that has not responded to other measures. It offers a definitive solution when quality of life has been severely affected.
20.10 Special Situations
Overflow incontinence in an elderly or immobile patient — needs disimpaction and a structured bowel regimen. Surgery has no role here, and offering it would not address the true underlying problem.
Obstetric sphincter injury — described fully in Chapter 21, including the specific management of a fourth-degree tear at the time of delivery.
Incontinence after previous anorectal surgery — review the original operative details carefully. This may reflect a technical sphincter injury during that earlier procedure. Re-examine exactly how much sphincter was divided at that time.
Failed previous sphincter repair — described in Chapter 22, under secondary repair.
20.11 Complications of Treatment
Sphincteroplasty carries a risk of wound infection, and a risk that the repair itself may break down or stretch over time, with symptoms gradually returning.
Sacral nerve stimulation carries a risk of infection at the implant site. Lead migration can also occur. This sometimes needs a further procedure to reposition or replace the device.
Injectable bulking agents carry a small risk of infection or migration of the injected material, and their effect can diminish over time.
20.12 Common Mistakes to Avoid
Failing to ask directly about incontinence, and missing the diagnosis because the patient did not volunteer it unprompted.
Treating overflow incontinence as if it were a true sphincter problem, without first checking for and treating faecal impaction.
Proceeding to sphincter surgery without first identifying and treating a coexisting, more easily correctable cause, such as rectal prolapse or significant haemorrhoidal disease.
Offering surgery before a genuine trial of conservative treatment and pelvic floor physiotherapy.
20.13 Recording and Follow-Up
Record the type and severity of incontinence. Ideally, use a standardised score such as the Wexner incontinence score. Also record the suspected cause and the examination findings. For example: "Anal incontinence to liquid stool, Wexner score 12, anterior sphincter defect palpable on DRE, history of forceps delivery. Plan: endoanal ultrasound, pelvic floor physiotherapy trial, review in 6 weeks." Arrange follow-up to track the response to treatment over time. Use the same scoring system at each visit, for a fair comparison.
20.14 Why This Chapter Matters
Anal incontinence is common, genuinely treatable in most patients, and yet frequently hidden by patients too embarrassed to raise it unprompted. Asking directly, distinguishing true incontinence from overflow, and correcting any treatable underlying cause first, together form the foundation of good management. The next chapter turns to the single most common structural cause of this condition: obstetric anal sphincter injury.