Faecal incontinence is defined as the inability to defer passage of faeces until an appropriate time. The maintenance of normal faecal continence is achieved by the interplay of functional anal sphincters, rectal compliance, anorectal sensation, and the composition of the faeces. The internal anal sphincter, a smooth muscle, is responsible for 80% of resting anal tone. It relaxes in response to rectal distension (rectoanal inhibitory reflex). The striated external anal sphincter is innervated by the pudendal nerve (S2, S3, S4). The external anal sphincter encircles the internal sphincter and continues cephaled as the puborectalis muscle (Anal canal and rectum.). Together, they function as a sphincter that exerts voluntary contraction when the intra-abdominal pressure is raised, such as in coughing or straining or when one wishes to defer defecation.
The anal canal has a rich sensory network to provide anorectal sampling to discriminate between gas, liquids and solids. Mechanoreceptors lie within the rectal wall and pelvic floor to detect rectal fullness. With reduction in rectal compliance as in Crohn's disease or radiation proctitis, diarrhoea may cause urgency at stool and further threaten continence, even if the sphincter mechanism is intact.
The causes of faecal incontinence are given in Causes of faecal incontinence.
Careful history with regard to the severity and nature of faecal incontinence is essential. Many patients are incontinent as a result of diarrhoea and urgency at stool. Neurological symptoms or any possible causative factors should be documented.
Careful examination of the perineum, anus and rectum should be performed, noting any scars, evidence of soiling, a patulous anus, perianal fistula or a rectal or uterine prolapse with straining. Digital rectal examination will provide a good assessment of the anal sphincters at rest and on voluntary contraction. Proctosigmoidoscopy is performed to exclude inflammatory bowel disease, neoplasia, mucosal prolapse and haemorrhoids.
Endo-anal ultrasound is an outpatient procedure using a rotating hand-held ultrasound probe inserted transanally. No special bowel preparation or sedation is necessary. This procedure is operator-dependent and its use is best restricted to major specialist colorectal centres.
Endo-anal ultrasound provides high resolution images of both the internal and external anal sphincters. Defects in the anal sphincters are clearly defined (Endo-anal ultrasound showing (A) normal and intact anal sphincters (IS, internal sphincter; ES, external sphincter) and (B) internal anal sphincter defect.) and may then be amenable to surgical repair.
This is performed using a balloon-tipped or microtransducer- tipped catheter inserted into the anal canal. The pressures produced by the internal sphincter (resting pressure) and the external sphincter (voluntary contraction pressure) are measured along the length of the anal canal. The length of the high pressure zone of the anal canal can then be defined.
Rectal sensation is measured by gradually distending a balloon in the rectum and recording when distension is first perceived. Compliance of the rectum and integrity of the rectoanal inhibitory reflex can also be documented.
While anorectal manometry provides interesting measurements for surgical research, it has not made a major impact on surgical management. It is generally restricted to use in specialist colorectal research and to aid in the management in complex cases.
Underlying pathology such as inflammatory bowel disease, cancer or rectal prolapse must be treated. Conservative treatment aims at producing a solid bulky stool. A low-fibre diet and codeine phosphate or loperamide are helpful. Daily phosphate enema may further reduce the risk of accidental soiling.
Pelvic floor exercises and biofeedback conditioning are used to strengthen the anal sphincters. These techniques are time-consuming and have not been proven to have a long-term benefit.
Surgery is undertaken when conservative treatment has failed or if there are identifiable sphincter defects clinically or on endo-anal ultrasound.
This is a direct repair of a defect of the anal sphincters. A perianal incision is made and both ends of the divided anal sphincters are then repaired either directly or in an overlapping fashion. About 85% of patients will derive some functional improvement after sphincter repair, if the pudendal nerve function is intact.
Injectable silicone biomaterial
This is a newly developed treatment by the Melbourne group for internal sphincter dysfunction. The silicone biomaterial is injected under guidance of endoanal ultrasound into the internal anal sphincter and the inter-sphincteric space. The injected silicone biomaterial (PTQTM) forms a template to allow ingrowth of collagen tissues, thereby increasing the bulk of the internal sphincter. Clinically it would take 6 to 8 weeks before any improvement in passive incontinence. Clinical improvement will continue up to 12 months after injection. The procedure is simple and can be performed under local anaesthesia with a mild sedative.
Sacral nerve stimulation
The innervation that controls defecation is mediated by S2, S3 and S4 nerve roots. Stimulation and modulation of the sacral nerves may increase the anal canal pressures through recruitment of the anal sphincter muscles. Melbourne is one of the pioneering centres to evaluate this particular approach and has reported outstanding success in patients with severe end-stage faecal incontinence. An electrode is inserted under fluoroscopic guidance to the S3 nerve root. Having established the optimal position of the electrode by eliciting the appropriate motor and sensory responses for S3, the electrode is connected to the stimulator. A screening phase for about 1 week is usually performed to establish the clinical benefits of sacral nerve stimulation, before a permanent neurostimulator is connected and implanted. The permanent neurostimulator is about the size of a cigarette lighter and is implanted subcutaneously in the buttock or lower abdominal wall. The procedure is safe and simple to perform.
Artificial bowel sphincter
Artificial bowel sphincter is a prosthesis using a fluidfilled, solid silicone device that is implanted around the anal canal with an occlusive cuff. A control pump is placed in the scrotum or labium to transfer fluid between the occlusive cuff and the presure-regulating balloon placed in the subcutaneous tissue of the abdominal wall. While artificial bowel sphincter can be successful in end-stage faecal incontinence, sepsis requiring removal of the prosthesis occurs in over one-third of patients. As a result, this is unlikely to be a popular treatment for faecal incontinence.