Endoanal ultrasound showing intact internal and external sphincters (a) and lesions of the internal and external sphincters (b) (Courtesy G. Santoro; Treviso)
The anatomy and its potential defects can also be explored by magnetic resonance imaging (MRI). Whereas EAUS is widely available, relatively easy to perform, and considered an essential part of the initial diagnostic workup, MRI has limited availability and is considered part of an advanced diagnostic workup. Both imaging techniques help to differentiate muscular lesions from other causes.
9.5.5 Anorectal Physiology
Anorectal physiology studies may help to better define the dysfunctional component of the continence-maintaining function. They are essential to provide an objective assessment of anal sphincter pressures, rectal sensation, rectoanal reflexes, and rectal compliance, some of which may guide management . However some of the procedures are operator-dependent, the findings do not consistently correlate with symptom severity, and their value in decision making is limited and increasingly debated, although findings may help to monitor functional changes.
9.5.6 Anorectal Manometry
Anorectal manometry can assess and quantify muscular function of the smooth-muscle internal anal sphincter (resting pressure, length of the pressure zone) and the striated-muscle external anal sphincter (squeeze pressure), perception of rectal filling and distension (first sensation, urge to pass stool, maximal tolerable volume), compliance of the rectal reservoir, and the reflexive interaction of the rectum and anal sphincter (rectoanal inhibitory reflex). Even though the method is simple, techniques vary (water-perfused catheters, solid-state catheters, stationary pull-through, mechanical pull-through), and thus findings in different settings should be compared with caution. The normal values used by the particular lab must be considered.
9.5.7 Neurological Examination
Electromyographic recording of the striated muscles of the external anal sphincter and the pelvic floor differentiates muscular from neurogenic deficits and estimates the extent of reinnervation and denervation. It is rarely used for sphincter mapping because EAUS offers excellent access and painless imaging of sphincter morphology.
Pudendal nerve terminal motor latency (PNTML), which measures the conductance of the peripheral nerves by stimulating and recording evoked muscular contractions, helps to identify peripheral lesions of the pudendal nerve. Unilateral lesions can be distinguished from bilateral ones. Although normal values for conduction velocity are defined, their relation to clinical findings is weak, the technique is operator-dependent, and patient discomfort is noteworthy. Thus the role of PNTML in the assessment of FI remains controversial, and questions of the relevance of its findings have recently caused it to be used less.
9.5.8 Sensibility Testing
Anorectal sensitivity is often disturbed in neurogenic FI, and a clinical examination of the sensible anoderm with a needle and brush is part of the basic workup. Electrosensitivity and temperature sensitivity are complementary investigations of anal sensitivity. Rectal sensibility with balloon distension is part of anorectal manometry.
The defecation process can be imaged with dynamic standard imaging or MRI. Although it is not routine, defecography can be helpful if a patient who presents with FI has signs of an evacuation disorder (e.g., intussusception, enterocele, rectocele).
9.5.10 Continence Testing
General global continence tests are more of historical interest and have been widely replaced by the examinations described above. However, a first impression of anorectal continence function may be obtained by the simple application of a suppository or – more advanced – the instillation of porridge or mashed potato, which the patient holds for 15 min while walking around before defecating normally.
Adding to the above, FI can also coexist with other pelvic floor pathologies, such as rectal intussusception; patients can present with varying combinations and severity of urge and passive FI or leakage after defecation. Indeed, a high percentage of patients with rectal intussusception have FI, with up to 56 % presenting with this symptom alone . Although the exact mechanism remains unclear, it is postulated that rectal intussusception stretches the internal anal sphincter and also triggers the rectoanal inhibitory reflex, leading to a temporary reversal of the pressure gradient in the anal canal and soiling. The accompanying incomplete rectal emptying can also contribute to leakage after defecation.
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Only when all potential secondary causes are excluded should incontinence as such be addressed. Therapy should be adapted to the patient’s individual needs and expectations. The following general principles should be observed:
From conservative to invasive, surgical treatment is indicated if conservative means do not result in adequate symptom relief 
From less to more invasive
Conservative therapy is pragmatic, often based on a trial-and-error approach, and is adapted to the patient’s acceptance of, compliance with, and ability to handle the treatment. Conservative modes can also be adjuvant after operative therapy.
9.6.1 Conservative Therapy
Conservative therapy is considered first-line treatment unless it becomes evident during diagnosis that the cause, extent, and severity of the disease render it inappropriate. Conservative treatment aims to affect stool consistency, colonic transit, bowel emptying, sphincter function and its perception, and rectal filling. Various treatment options are available. They have evolved empirically, and limited data exist to prove their efficacy . A combination has been demonstrated to be clinically more effective than a single treatment .
Skin care (fastidious anal hygiene, skin care lotions or ointments, soft napkins, diapers)
Anal plugs: poorly accepted in general; only 10–20 % of patients use continence plugs regularly. They may be better tolerated in patients with reduced anal sensation owing to neurological impairment (spina bifida) . Recent results of a newly designed, flexible silicone plug indicate better acceptance and good improvement of FI .
Regulation of bowel emptying: laxative suppositories or retrograde lavage. The purpose of retrograde irrigation is twofold: to cleanse the distal bowel mechanically and to improve rectal reservoir function by distension and improved perception through a defined stimulus. Thus a rhythm of sufficient bowel emptying and time intervals free of fecal loss is established.
Regulation of stool consistency: low-fiber diet, meals that do not cause bloating, and constipating medication (e.g., psyllium, plantago ovata, loperamide, codeine). A paradoxical reaction may occur, and individual testing is advisable. In general, the aim should be behavioral training by a regular daily routine and regular defecation.
Pelvic floor muscle exercise: indicated in patients with reduced voluntary sphincter function. These exercises are recommended as an early intervention based on their low cost, the absence of morbidity, and evidence (although weak) suggesting efficacy. They should be taught under the guidance of a physiotherapist.
Biofeedback: based on the concept of operant conditioning. Visual or acoustic signals are used to teach the patient to be aware of and use specific physiologic functions and thus to recruit residual function. Both motor and sensory function can be addressed. The therapeutic effect is based on an increase in the strength and duration of contraction, an improvement in coordination and sensory perception, and the suppression of internal relaxation. Training should follow a strict protocol: after instruction the patient must train at home for some months. Success varies widely, and data are inconsistent. A recent randomized controlled trial failed to demonstrate the superiority of biofeedback over general conservative measures and good clinical management, despite a large body of uncontrolled studies supporting its efficacy. Thus the current consensus is that biofeedback is possibly effective but unproven . Because it is painless and risk-free, it can be recommended after other behavioral and medical management has failed to result in adequate symptom relief.
Anal electrostimulation: The periodic application of anal electrostimulation to strengthen the sphincter muscles passively remains controversial. Few, mostly anecdotal, experiences report variable improvements in heterogeneous patient groups. Neither recent nor randomized results from trials are available.
9.6.2 Operative/Interventional Therapy
The choice of surgical treatment is mainly guided by symptom severity and etiology and the structural integrity of the sphincter muscles.
22.214.171.124 Anal Sphincteroplasty
Direct sphincter reconstruction aims to reestablish function by closing a morphologic defect by coapting the dehiscent muscle. The term anal sphincter repair is used to describe primary repair of the anal sphincter immediately after direct trauma; anal sphincteroplasty describes a secondary or delayed reconstruction of the anal sphincter musculature when lesions were initially either unrecognized or functionally irrelevant, or when the outcome of primary repair was unsatisfactory. Only anal sphincteroplasty is discussed here.
Overlapping sphincteroplasty is the standard of care for disruption postpartum, postoperatively, or after trauma. Anterior sphincteroplasty after obstetric injury is the most common.
The patient is placed in either the prone jack-knife or lithotomy position.
Through a transverse incision on the perineum the dehiscent muscles are identified and mobilized. (Adequate mobilization is essential for tension-free approximation and adaptation.)
Suturing can either be overlapping or applied by direct adaptation  (Fig. 9.2).
Sphincteroplasty by muscular overlap
Separate identification and repair of the internal anal sphincter is technically challenging and has an unproven therapeutic effect.
A levatorplasty can be added, but vaginal narrowing needs to be avoided beause of the risk of dyspareunia.
A biological implant may be advantageous to reinforce the anal muscles .
Reported short- and mid-term success ranges from 43 to 89 %. Continence deteriorates with long-term follow-up . Patient satisfaction after 5–10 years is 40–45 %.
Predictors of poorer outcome are age ≥50 years, deep wound infection, and isolated external anal sphincter defects.
Coexisting neurogenic damage has repeatedly been discussed as a predictor of lower success, but this remains controversial and is not contraindicative.
Preoperative manometric variables do not predict outcome .
Adjuvant biofeedback therapy after surgery may improve quality of life and help sustain symptomatic improvement over time.
126.96.36.199 Pelvic Floor Repair
The aim of postanal repair is to increase the length of the anal canal and its high-pressure zone and to restore the anorectal angle, thus re-creating the flap-valve mechanism thought to contribute to continence. This concept was the treatment of choice in the 1970s and 1980s for patients presenting with incontinence owing to a generalized weakness of the pelvic floor and external anal sphincter without disruption. Initial symptomatic improvement did not last. Given the better surgical options available today, postanal or total pelvic floor repair cannot be recommended .
188.8.131.52 Sphincter Replacement/Substitution
Autologous and heterologous sphincter replacement procedures have been used in patients with failed sphincteroplasty, extensive soft-tissue damage, congenital abnormalities (such as anal atresia), or neurogenic damage. Nonstimulated muscle transpositions (such as uni- or bilateral gluteoplasty or graciloplasty) and stimulated transpositions (stimulated dynamic graciloplasty) have been used to create a neosphincter, or artificial neosphincters have been implanted. Only dynamic graciloplasty (DGP) and artificial bowel sphincters have gained broader clinical acceptance.
184.108.40.206 Dynamic Graciloplasty
In adults the simple transposition of the gracilis muscle around the anus failed to achieve sufficient clinical effect because of fibrosis and the inability for proper activation and durable contraction. The addition  of continuous low-frequency electrical stimulation of the supplying nerve with an implantable stimulator consisting of electrodes, an impulse generator, and a remote control device shows various results:
The phenotype of the transposed muscle is transformed from fast-twitch, fatigable type II fibers to the slow-twitch, fatigue-resistant type I fibers, which are capable of sustained contraction and mimic the physiological characteristics of continuous anal canal closure.
Increased anal canal closure pressure results from this continous contraction.
The neoanal sphincter opens when the stimulator is switched off – a voluntary act similar to voluntary bowel emptying.
The longevity of an impulse-generator battery is limited; thus operative replacement is mandatory. The procedure of dynamic graciloplasty (DGP) is complex and associated with high morbidity, and the most frequent complication is infection that ultimately mandates removal of the implanted foreign material and the need for operative reintervention . Outcomes are best in specialized centers.
Depending on the underlying etiology, success rates of DGP in cohort studies range from 55 to 83 % and are best with pathophysiological conditions that are not associated with impaired sensory function. Multicentee trials have shown a poorer functional outcome .
DGP has also been used for total anorectal reconstruction after abdominalperineal excision for low rectal or recurrent anal cancers. Its relevance is now considerably reduced.
220.127.116.11 Artificial Bowel Sphincter
Artificial sphincters are designed to reinforce or replace the anal sphincter. Three models – prosthetic bowel sphincter, the soft anal band system from the Agency for Medical Innovations, and the Acticon Neosphincter (American Medical Systems, Minnetonka, MN) – are available on the market. Artificial bowel sphincter (ABS) results have been reported only for the Acticon Neosphincter . Its use is supported in the current recommendations of both the National Institute for Health and Clinical Excellence and the American Society of Colon and Rectal Surgeons [1, 30].
An ABS is a silicone device that restores anal canal closure by means of an inflatable cuff placed around the lower rectum or upper anal canal and connected to a pressure-regulating balloon implanted in the retropubic space. The patient controls the balloon via a pump placed for convenient accessibility in the labia majora or scrotum .
The deflation of the cuff is limited to several minutes. Refilling allows a pressure gradient between the pressure balloon and the cuff.
Reported success rates range from 50 to 75 %. Continence for liquid and solid stool can be achieved, but the complication rate is high. In up to 30–50 %, infection and technical failure have resulted in device removal . The revision rate increases with the duration of follow-up. The system can be reimplanted, with success rates comparable to those of the first implantation.
Despite their high complication rates, DGP and the ABS remain alternatives to the creation of a stoma in severe end-stage FI. Certain conditions influence the preference of one over the other; for example, the success of DGP depends on intact innervation of the gracilis muscle. Trophic alterations of the perineal or perianal area carry an increased risk of infection if foreign material is implanted.
Exclusion criteria for these procedures include morbid obesity, insulin-dependent diabetes mellitus, Crohn’s disease, pelvic sepsis, radiation proctitis, and the practice of anoreceptive intercourse. It is also vital that all patients be adequately motivated and have sufficient manual dexterity to operate the devices independently.
18.104.22.168 Sacral Nerve Stimulation/Sacral Neuromodulation
Sacral nerve stimulation (SNS) aims to recruit residual function of the anorectal continence organ . Prerequisites are residual sphincter function and an existing neuromuscular connection to the sphincter, which is tested by observing the voluntary squeeze or reflex activity after a pin prick.
The system consists of a fully implantable electrode placed close to a target nerve at the level of the sacral spinal nerves, most commonly S3 or S4, and connected to an impulse generator placed in a subcutaneous pocket (Fig. 9.3), which can be programmed and activated via telemetry. The mechanism of action is complex and multifactorial; the effect of SNS is not limited to the anorectal continence organ and the large bowel, affecting the somatomotor, somatosensory, and autonomic nervous systems; it also seems to affect the central nervous system, which controls bowel and sphincter activity.
Sacral spinal nerve stimulation
Patients are selected for permanent SNS with the help of a limited period of test stimulation with an external impulse generator:
A 3-week screening phase of peripheral nerve evaluation, during which patients document bowel habits in standardized bowel diaries, permits evaluation of the clinical effect of SNS.
Two techniques are available for testing: temporary electrodes to be removed after test stimulation and electrodes that can remain for chronic stimulation if testing is successful. These quadripolar, so-called tined lead electrodes are placed under fluoroscopic guidance. Both types of electrodes are connected to an external pulse generator for the duration of the test period.
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