Chapter 78 PATHOPHYSIOLOGY, DIAGNOSIS, AND TREATMENT OF DEFECATORY DYSFUNCTION

The domain of defecatory disorders is vast, and their treatment can be frustrating for the surgeon and the patient. Except for straightforward surgically correctible disorders, most diseases in this category have many causes and need treatment that encompass medical, behavioral, and surgical modalities. These patients often go from physician to physician seeking a cure for these complex disorders.

ANATOMY

Pathogenesis of the defecatory disorders can be a function of abnormal anatomy at the outlet. The anal sphincter complex is composed of the puborectalis, the internal anal sphincter, and the external anal sphincter. The puborectalis and the external anal sphincter are striated muscles that are primarily responsible for the process of defecation by voluntary relaxation. They are innervated by the S3 and S4 nerves. The internal anal sphincter accounts for about two thirds of the resting tone and is composed of smooth muscle. It is innervated by the autonomous nervous system. The external anal sphincter accounts for one third of the resting tone. Any process that causes a change in this normal physiology can lead to defecatory disorders.

MECHANISM OF DEFECATION

Storage is a function of the transverse colon. When the sigmoid colon is filled, the process of defecation commences with the propagation of stool into the rectum. Defecation occurs in response to the sensory stimulus generated by rectal distention that is received by receptors in the pelvic floor and anal transition zone; the rectum itself is not richly innervated by sensory nerves. The sensation of filling is normally perceived at a volume of 50 mL, and the maximum tolerated volume normally is about 200 mL. Rectal pressures should be more than the anal pressures for evacuation to take place, which is usually achieved by increasing the intra-abdominal pressure. The external anal sphincter and puborectalis relax, allowing fecal contents to be evacuated. If it is socially unacceptable at that time, the external anal sphincter contracts, and the sensation of the need to evacuate disappears.

DIAGNOSIS

History and Physical Examination

A detailed history and physical examination is the first step in diagnosing any defecatory disorder. The history should be tailored to the patient’s presenting symptoms. All patients should be asked about their current medications, and a history should be sought for all medical problems, especially diabetes, thyroid disorders, scleroderma, multiple sclerosis, stroke, dementia, food intolerance, and inflammatory bowel disease. The evaluation of a female patient with fecal incontinence should include a detailed obstetric history, including the number of vaginal deliveries, tears and episiotomies, unusual presentations, and prolonged labor. Other pertinent points are pad usage and number of accidents, symptoms of urinary incontinence, previous perineal surgery, back injuries, irradiation, and effect of symptoms on sexual behavior. Patients undergoing evaluation for constipation should be specifically asked about the duration of symptoms, the use of digitation to relieve symptoms, and factors that relieve or alleviate symptoms.

Physical examination of a patient with fecal incontinence should focus on the sphincters and pelvic floor. Scars are looked for, and the anal opening is assessed for any gaping. The anocutaneous reflex can be evaluated, providing a crude assessment of the nerves. The patient may then be asked to strain. Perineal descent and prolapsed hemorrhoids or prolapsed rectum should be looked for. A digital rectal examination with the patient squeezing assesses the tone, obvious defects, and muscle fatigue.

For a patient with constipation, the digital rectal examination evaluates increased tone with paradoxical contractions when straining and the presence of an internal intussusception and rectocele. In cases of rectal prolapse, inspection is important to differentiate a true rectal prolapse from prolapsing hemorrhoids, mucosal prolapse, or an anal or rectal polyp.

Enema

A tap-water enema in the office is a good and simple test to evaluate the sphincter tone in an incontinent patient. After administering the enema, the nurse documents the time the patient can hold the 100 mL of water. A patient with a suspected rectal prolapse is examined on the commode after the enema is given. The rectal prolapse may be seen while the patient strains on the commode. In a patient with irritable bowel syndrome, it may demonstrate urgency in the presence of normal tone.

Anal Physiology Testing

Anal physiology testing has two parts. The first is manometry, which records resting and squeeze pressures and evaluates rectal sensation by documenting the time of first sensation of rectal filling and maximum tolerated volume. Rectal compliance also can be calculated. Paradoxical pressures in the rectum can be recorded during squeeze and strain, and they also can be demonstrated on electromyography by identifying the external anal sphincter contraction. Balloon expulsion tests can demonstrate rectal inertia or loss of coordination among the rectum, pelvic floor, and anal sphincters.

The second part of the test evaluates pudendal nerve terminal motor latency. The test uses the St. Marks electrode and records electrical impulses when the pudendal nerve is stimulated. The amplitude of the wave reflects the voltage, which is low or absent in neurologic disorders.

Anorectal Ultrasound

Endoluminal ultrasound is the single most important test to demonstrate sphincter defects. The normal sphincter is shown in Figure 78-1. Sphincter defects may be those of the internal anal sphincter or external anal sphincter (Fig. 78-2), or both (Fig. 78-3). Thinning of the internal anal sphincter is easily demonstrable. After sphincteroplasty, the repaired sphincter can be evaluated with this test.

Figure 78-1 Normal anal ultrasound. EAS, external anal sphincter; IAS, internal anal sphincter.

Figure 78-2 Defect in the external anal sphincter.

Figure 78-3 Defect in the internal and external anal sphincters.

Colon Transit Study

Transit studies specifically demonstrate slow-transit constipation. This assessment reflects motility of the colon but not the rectum. The patient swallows capsules with radiopaque markers. The markers are followed on day 1, 2, 4, and 7. Demonstration of markers in the right and left colon on day 7 indicates slow transit of the fecal matter on the right side, supporting a diagnosis of colonic inertia. If markers are aggregated on the left side, the problem may be redundancy of the left colon or outlet obstruction.

Defecating Proctogram

Patients with constipation and symptoms suggesting obstructive defecation syndrome are subjected to a test in which contrast is instilled in the rectum, small bowel, vagina, and bladder. Patients defecate in a radiolucent commode, and serial radiographs are taken to demonstrate perineal descent, cystocele, enterocele, internal intussusception, and rectal prolapse.

Dynamic Magnetic Resonance Imaging

Dynamic magnetic resonance imaging (MRI) is a test that replaces the defecating proctogram. Contrast is instilled in the vagina and rectum, and serial MR images are taken with the patient straining. Newer imaging techniques use upright MRI scans with the patient seated and evacuating in the sitting position. This test can evaluate pelvic descent, rectal diameter before and during straining, the width of the pelvic hiatus, presence of enteroceles and sigmoidoceles, and prolapse of the uterus and bladder.¹ It may become the confirmatory test for obstructive defecation. Cine radiography can give a dynamic picture of the process of evacuation, and it can demonstrate prolapse of the anterior wall of the rectum.

Colonoscopy

All colonic pathology must be excluded before undertaking for-mal treatment of any defecatory disorder. Colonoscopy should be part of the workup of all patients older than 50 years and patients with any suspicion of mucosal pathology.

Barium Enema

A barium enema is warranted when the anatomy of the colon needs to be defined. It may be of use in cases of rectal prolapse to demonstrate a redundant sigmoid colon, necessitating a sigmoid colectomy.

FECAL INCONTINENCE

Pathophysiology

Injury to the muscle complex or the nerves that supply them can result in a loss of continence. The most common etiologic factor is childbirth injury. Other causative factors are listed in Table 78-1.

Table 78-1 Causes of Fecal Incontinence

Sphincter injury

Childbirth trauma

Surgical trauma

Rectal injury, traumatic

Irradiation

Congenital causes

Colonic causes

Decreased rectal compliance

Neurogenic causes

Peripheral disorders (e.g., diabetes)

Functional causes

Other causes

Diarrhea

Myopathy

Treatment of Fecal Incontinence

The treatment of fecal incontinence is based on the severity of symptoms, the anatomy of the sphincter mechanism, and the presence of nerve damage. An algorithm for management is provided in Figure 78-4, but treatment options depend on the availability of certain procedures and on the patient’s comorbidities.

Figure 78-4 Algorithm for the management of fecal incontinence. Sacral stimulation has been used successfully in some centers. Although listed, graciloplasty no longer available in the United States. IBD, irritable bowel disease. *Sacral stimulation has been used successfully in some centers. **Not available in the US.

Treatment of Minor Incontinence

A thorough history and physical examination are the first step in treatment to rule out inflammatory bowel disease, irritable bowel disease, and neurologic disorders. Minor incontinence can be treated with medical management ² using bulking agents, which can change the consistency of stool and lead to evacuation as a mass movement. They are started in small doses to prevent abdominal distention and bloating, and they are gradually in-creased to achieve the desired effect. Other agents that are used slow the gastrointestinal motility. They tend to constipate the patients because they decrease the bulk of the stool during the increased transit time. Loperamide hydrochloride (Imodium) is the commonly used medication, and it may be started in doses of 2 mg before breakfast and advanced to a maximum of 16 mg daily as warranted. Diphenoxylate hydrochloride (Lomotil) is another drug that may be used, especially if diarrhea is the main symptom. It is started in doses of 1 tablet once or twice daily and may be advanced to 1 or 2 tablets three or four times daily.

Amitriptyline ³ has been used for idiopathic fecal incontinence. It acts through an anticholinergic mechanism, increasing intrarectal pressures. Phenylephrine cream is an α₁-adrenergic blocker that has not been approved by the U.S. Food and Drug Administration (FDA). Used in some studies in strengths of 10% to 40%, it has been shown to increase resting pressures for 1 to 2 hours.⁴

Other treatment modalities include the use of regular (even daily) enemas, which evacuate the rectum until it fills again. Bulking agents may be used in conjunction to prevent seepage between enemas.

Biofeedback and Kegel Exercises

Kegel exercises are an integral part of the treatment of fecal incontinence, but they are ineffective as the sole treatment. They may benefit to patients with very mild incontinence and those with easy fatigability of the sphincter and no sphincter defect.

Biofeedback training consists of retraining the patient’s re-sponse using visual, auditory, and sensory stimuli. It consists of strength training of the external sphincter, retraining the sphincter to coordinate rectal distention with external anal sphincter contraction, and sensory training of the rectal mucosa to be able to sense earlier when the rectum receives contents. It is done in the office by a trained therapist using the electromyographic apparatus to retrain and strengthen the sphincter, and a rectal balloon is used for sensory stimulation training. Some studies have shown improvement after biofeedback therapy.⁵ Biofeedback has been shown to benefit patients after sphincter repair.⁶

Treatment of Moderate Fecal Incontinence with an Intact Sphincter

Secca Procedure

The Secca procedure involves radiofrequency stimulation of the muscular layer of the anal canal and lower rectum. It has been hypothesized that the procedure causes stimulation of collagen deposition and remodeling over time, which can improve symptoms of fecal incontinence.

The procedure is done under conscious sedation. After local anesthesia is injected, radiofrequency is delivered by means of a specialized probe that contains needles that pierce the mucosa and submucosa. In about 64 separate punctures, the radiofrequency is applied beneath the mucosal surface. Contraindications to this procedure include inflammatory bowel disease, a history of depression, collagen vascular disease, acute infections, pudendal neuropathy, and a history of pelvic irradiation.⁷

Sacral Stimulation

Sacral nerve stimulation is FDA approved in the United States for stress urinary incontinence, and it is being evaluated under a research protocol for fecal incontinence. It produces constant stimulation of the sacral nerves, resulting in an increase in resting tone and squeeze pressures. In this procedure, a temporary stimulator is implanted as a first step, and if the patient improves, a permanent device is implanted. It has gained popularity in Europe, where it has been available for many years.⁸

Perianal Bulking Agents

Bulking agents instilled in the perianal area are being studied.⁹ They work by increasing the internal bulk of the sphincter, preventing seepage of stool. An optimal bulking agent should be nonbiodegradable, should not migrate, and should be removable if the need arises.

Treatment of Moderate to Severe Fecal Incontinence due to a Defect in the Sphincter Mechanism

Overlapping Sphincter Repair: Sphincteroplasty

Any fixable defect of the sphincter complex should be considered for repair. Because it is difficult to determine which patient will benefit, consideration should be given to all those with a defect.

The technique involves a semicircular incision about 1 to 1.5 cm beyond the anal verge. For obstetric injuries, this arc spans about 200 degrees in a semicircular fashion, mirroring the anus. The branches of the pudendal nerves that innervate the external sphincter approach the muscle from the posterolateral position. To avoid nerve injury, the arc of the incision should not extend to the extreme posterolateral position. The rectovaginal septum is dissected, and care is taken to avoid making buttonhole defects in the anal canal or rectum. Occasionally, the only part of the perineal body that remains is the vaginal and anal mucosa, and dissection in this situation can be difficult.

The dissection is carried laterally to the ischiorectal fat. A finger placed in the vagina or rectum and dissecting from lateral to medial may facilitate the dissection. Any tears in the anal mucosa are repaired with 4-0 chromic suture. The ends of the sphincter are usually dissected with scar in the midline (or midportion of the injury). This scar is divided in the middle, leaving two ends of sphincter with scar attached. It is important to divide the scar but to not trim it from the ends of the sphincter, because this will provide tensile strength when the repair is done. If the internal and external muscles are injured, it is preferable to repair them as one unit. If the internal sphincter is intact, divide and repair only the external sphincter.

The levator ani muscles may be plicated at this point using 1-0 or 2-0 delayed absorbable sutures. This may lengthen the anal canal. The vagina should be checked after the levator plication to ensure that a ridge or narrowing did not occur with levator plication, because this may contribute to dyspareunia. If the internal anal sphincter was intact, plication can be done before the sphincteroplasty if there is redundant internal sphincter.

The sphincter ends that have been sufficiently mobilized to allow overlapping of the muscle are grasped. Some authorities ^10,¹¹ advocate merely approximating the muscles, but if possible, overlapping the muscle ends is preferred using 2-0 polyglactin sutures, placing mattress sutures for the sphincteroplasty. Approximately six sutures (three on each side) are used. The repair tightens the anal canal such that only an index finger may be admitted. During the procedure, the wound may be irrigated with antibiotic solution. The skin edges are closed in a V-Y fashion, starting laterally and leaving the center open for drainage. If there is a significant amount of dead space, a 0.5-inch Penrose drain can be inserted and then removed postoperatively.

Postoperatively, we keep patients on intravenous antibiotics for 2 to 3 days and withhold oral intake. Because sitz baths macerate the skin edges, they are avoided, but showers are permitted. We do not use constipating drugs. The Foley catheter is removed on postoperative day 2, and the patient is allowed a high-fiber diet just before discharge. At discharge, patients are placed on Metamucil, Citrucel, or Konsyl daily. Additionally, they take 1 ounce of mineral oil each morning. If they do not move their bowels by postoperative day 7, they take 1 ounce of milk of magnesia twice daily until their bowels begin to function. Because they undergo a complete bowel cleansing before surgery, patients may not move their bowels for several days after surgery.

A diverting stoma is used at the discretion of the surgeon. Preoperatively, this should be discussed with patients who have had previous failed repairs, have concomitant inflammatory bowel disease, have severe diarrhea, or need an extremely complicated repair. A stoma does not ensure success but may aid a successful outcome in such patients.¹²

Initial functional improvement can be anticipated in 80% to 90%¹³^–¹⁵ of patients. Pudendal nerve damage is associated with suboptimal results.¹³ Age does not seem to significantly affect results,¹² although erratic bowel problems such as urgency and diarrhea may lead to continued incontinence. Wound infection occurs in up to a fourth of patients¹⁵ but does not usually adversely affect the outcome unless the sphincter repair sutures become disrupted. Complete disruption of the skin sutures usually heals by secondary intention with adequate wound care.

Long-term follow-up suggests that about 40% of patients undergoing a repair are expected to be continent without further surgery.¹⁶ In patients needing a repeat overlapping sphincter repair due to disruption of the initial repair, evidence suggests that satisfactory outcome can be achieved.¹⁷