Benign Anorectal: Abscess and Fistula

Transcription

1 13 Benign Anorectal: Abscess and Fistula Carol-Ann Vasilevsky and Philip H. Gordon Anorectal abscesses and fistula-in-ano represent different stages along the continuum of a common pathogenic spectrum. The abscess represents the acute inflammatory event whereas the fistula is representative of the chronic process. Abscess Anatomy Successful eradication of anorectal suppuration and fistulain-ano requires an in-depth understanding of anorectal anatomy. Essential is an understanding of the existence of potential anorectal spaces 1 (Figure 13-1A). The perianal space is located in the area of the anal verge. It becomes continuous with the ischioanal fat laterally while it extends into the lower portion of the anal canal medially. It is continuous with the intersphincteric space. The ischioanal space extends from the levator ani to the perineum. Anteriorly it is bounded by the transverse perineal muscles; the lower border of the gluteus maximus and the sacrotuberous ligament form its posterior border. The medial border is formed by the levator ani and external sphincter muscles; the obturator internus muscle forms the lateral border. The intersphincteric space lies between the internal and external sphincters and is continuous inferiorly with the perianal space and superiorly with the rectal wall. The supralevator space is bounded superiorly by peritoneum, laterally by the pelvic wall, medially by the rectal wall, and inferiorly by the levator ani muscle. The deep postanal space is located between the tip of the coccyx posteriorly and lies below the levator ani and above the anococcygeal ligament (Figure 13-1B). At the level of the dentate line, the ducts of the anal glands empty into the anal crypts. Some 80% of the anal glands are submucosal in extent, 8% extend to the internal sphincter, 8% to the conjoined longitudinal muscle, 2% to the intersphincteric space, and 1% penetrate the internal sphincter. 2 Pathophysiology Etiology Ninety percent of all anorectal abscesses result from nonspecific cryptoglandular infection whereas the remainder result from the causes as listed in Table According to the cryptoglandular theory championed by Parks, 3 abscesses result from obstruction of the anal glands and ducts. Obstruction of a duct may result in stasis, infection, and formation of an abscess. Persistence of anal gland epithelium in part of the tract between the crypt and the blocked part of the duct results in the formation of a fistula. Predisposing factors include diarrhea and trauma in the form of a hard stool. Associated factors may be anal fissures, infection of a hematoma, or Crohn s disease. Classification Abscesses are classified according to their location in the aforementioned potential anorectal spaces: perianal, ischioanal, intersphincteric, and supralevator (Figure 13-2). Perianal abscesses are the most common type whereas supralevator abscesses are the rarest. Pus can also spread circumferentially through the intersphincteric, supralevator, or ischioanal spaces, the latter via the deep postanal space, resulting in a horseshoe abscess. Evaluation and Treatment Symptoms Pain, swelling, and fever are the hallmarks associated with an abscess. The patient with a supralevator abscess may complain of gluteal pain. 4 Rectal bleeding has been reported. Severe rectal pain accompanied by urinary symptoms such as dysuria, retention, or inability to void may be suggestive of an intersphincteric or supralevator abscess. 192

2 13. Benign Anorectal: Abscess and Fistula 193 TABLE Etiology of anorectal abscess Nonspecific Cryptoglandular Specific Inflammatory bowel disease Crohn s disease Ulcerative colitis Infection Tuberculosis Actinomycosis Lymphogranuloma venereum Trauma Impalement Foreign body Surgery Episiotomy Hemorrhoidectomy Prostatectomy Malignancy Carcinoma Leukemia Lymphoma Radiation FIGURE Anorectal spaces. A Coronal section. B Sagittal section. (From Vasilevsky CA. Anorectal abscess and fistula-in-ano. In: Beck D, ed. Handbook of Colorectal Surgery. 2nd ed. Copyright 2003 by Taylor & Francis Group LLC (B). Reproduced with permission of Taylor & Francis Group LLC (B) in the format Textbook via Copyright Clearance Center.) Treatment General Principles Essentially, the treatment of an anorectal abscess involves incision and drainage. Watchful waiting under the cover of antibiotics is ineffective and may allow the suppurative process to progress resulting in the creation of a more complicated abscess and thus possible injury to the sphincter mechanism. Rarely, delay in diagnosis and management of anorectal abscesses may result in life-threatening necrotizing infection and death. 5 Physical Examination Inspection will reveal erythema, swelling, and possible fluctuation. It is crucial to recognize that no visible external manifestations will be present with the intersphincteric or supralevator abscesses despite the patient s complaint of excruciating pain. 1 Although digital examination may not be possible because of extreme tenderness, palpation, if possible, will demonstrate tenderness and a mass. With a supralevator abscess, a tender mass may be palpated on rectal or vaginal examination. 4 Anoscopy and sigmoidoscopy are inappropriate in the acute setting. FIGURE Classification of anorectal abscess. (Reprinted from Vasilevsky CA. Fistula-in-ano and abscess. In: Beck DE, Wexner SD, eds. Fundamentals of Anorectal Surgery. London: WB Saunders, copyright 1998, with permission from Elsevier.)

3 194 C.-A. Vasilevsky and P.H. Gordon Operative Management Incision and Drainage Perianal abscesses can be effectively drained under local anesthesia. 4,6 After the most tender point has been determined, the area is infiltrated with 0.5% lidocaine with 1:200,000 epinephrine. A cruciate or elliptical incision is made and the edges are trimmed to prevent coaptation which may result in poor drainage or recurrence (Figure 13-3). No packing is required. Most ischioanal abscesses can be incised and drained in a similar manner with the site of incision shifted close to the anal side of the abscess, minimizing the complexity of a subsequent fistula. Large ischioanal or horseshoe abscesses often require drainage with the patient under a regional or general anesthetic and in the prone jackknife or left lateral (Sim s) position. The location of infection is often in the deep postanal space. Access to this space may be achieved by a midline incision between the coccyx and anus, spreading the superficial external sphincter to enter the space. An opening is made in the posterior midline and the lower half of the internal sphincter is divided to drain the anal gland in which the infection originated. 4 Counter-incisions are made over each ischioanal fossa to allow drainage of the anterior extensions of the abscess (Hanley procedure) 5,7 (Figure 13-4). Because the diagnosis of an intersphincteric abscess is entertained when the patient presents with pain out of proportion to the physical findings, an examination under anesthesia is mandatory to completely assess the cause of the pain. Once the diagnosis is established, either by palpation of a protrusion into the anal canal or by needle aspiration in the intersphincteric plane, treatment consists of dividing the internal sphincter along the length of the abscess cavity. The wound is then marsupialized to allow adequate drainage and quicker healing. Before the treatment of a supralevator abscess, it is essential to determine its origin because it may arise from an upward extension of an intersphincteric or an ischioanal abscess, or downward extension of a pelvic abscess. 1,4 The treatment in each case will be different. If the origin is an intersphincteric abscess, it should be drained through the rectum by dividing the internal sphincter and not through the ischioanal fossa, because this will result in the creation of a suprasphincteric fistula. However, if it arises from an ischioanal abscess, it should be drained through the perineal skin and not through the rectum; otherwise, an extrasphincteric fistula will occur (Figure 13-5). If the abscess is of pelvic origin, it may be drained through the rectum, ischioanal fossa, or abdominal wall via percutaneous drainage depending on the direction to which it is pointing. Catheter Drainage An alternative method of treatment for selected patients is catheter drainage. Patients suitable for this technique should not have severe sepsis or any serious systemic illness. 8 The patient is placed in the prone jackknife position or left lateral FIGURE Drainage of abscess. A Injection of local anesthesia. B Cruciate incision. C Excision of skin. D Drainage cavity. FIGURE Drainage of horseshoe abscess.

4 13. Benign Anorectal: Abscess and Fistula 195 FIGURE Drainage of a supralevator abscess. (Sim s) position. The skin is prepared with a proviodineiodine solution and the fluctuant point of the abscess is selected. Local anesthesia consisting of 0.5% lidocaine with 1:200,000 epinephrine is injected in a 1-cm area of skin and a stab incision is made to drain the pus. The lidocaine should be injected into the skin around, rather than immediately over, the point of maximal fluctuation because the acid environment may otherwise preclude adequate anesthesia (Figure 13-6A). A 10- to 16-French soft latex mushroom catheter is inserted over a probe into the abscess cavity. When released, the shape of the catheter tip will hold the catheter in place, obviating the need for sutures. The external portion of the catheter is shortened to leave 2 3 cm outside the skin with the tip in the depth of the abscess cavity (Figure 13-6B). This reduces the chances of the catheter falling out of or into the abscess cavity. A small bandage is placed over the catheter. Several portions of this technique deserve further comment. First, the stab incision should be placed as close as possible to the anus, minimizing the amount of tissue that must be opened if a fistula is found after resolution of inflammation (Figure 13-6A). Second, the size and length of the catheter should correspond to the size of the abscess cavity (Figure 13-7A). A catheter that is too small or too short may fall into the wound (Figure 13-7B). Third, the length of time that the catheter should be left in place requires clinical judgment. Factors involved in this decision should include the size of the original abscess cavity, the amount of granulation tissue around the catheter, and the character and amount of drainage. If there is doubt, it is better to leave the catheter in place for a longer period of time. FIGURE Catheter drainage of an abscess. A Stab incision. B Catheter in abscess cavity. trace the suppurative process because of the presence of pus. Primary fistulotomy eliminates the source of infection and decreases the rate of recurrence, obviating the need for subsequent surgery with the potential to decrease disability and morbidity. Fucini 11 reported no recurrences in 51 of 58 primary Primary Fistulotomy A point of controversy is whether primary fistulotomy should be performed at the time of initial abscess drainage. Proponents 5,9 11 believe that in the acute phase one can better FIGURE Catheter in an abscess cavity. A Correct size and length of catheter. B Catheter too short.

5 196 C.-A. Vasilevsky and P.H. Gordon fistulotomies when internal openings could be identified. No major incontinence was reported, but impaired control of flatus was seen in 17%. In eight patients in whom only incision and drainage were performed because of failure to identify an internal opening, recurrences were reported in 87%. 11 Opponents 6,12 are reluctant to perform primary fistulotomy in the presence of acute inflammation because the search for an internal opening may lead to creation of false passages resulting in neglect of the main source of infection. Failure to identify an internal opening has been reported to occur in as high as 66% of patients. 10 In addition, 34% 50% of patients who present with an abscess for the first time will not develop a fistula. 6,12 Thus, primary fistulotomy in these patients would be unnecessary and may result in needless disturbances of continence. Of those patients whose abscesses are drained, 11% may develop a fistula whereas 37% may develop a recurrent abscess. 6 This is most often observed in conjunction with ischioanal abscesses. 6 The search for an internal opening converts the operative procedure from one that can be performed under local anesthesia to one that requires regional or general anesthesia. A prospective, randomized trial of drainage alone versus drainage and fistulotomy for acute perianal abscesses with proven internal openings revealed that incision and drainage alone demonstrated no statistical significance in recurrence compared with concurrent fistulotomy although there was a tendency to recurrence in the former group. 13 Another prospective study advocated a conservative approach in the treatment of anorectal abscess, reserving fistulotomy as a second-stage procedure if necessary. 14 If the internal opening of a low transsphincteric fistula is readily apparent at the time of abscess drainage, primary fistulotomy is feasible with the following exceptions: 1) patients with Crohn s disease, 2) patients with acquired immunodeficiency syndrome (AIDS), 3) elderly patients, 4) patients with high transsphincteric fistulas, and 5) women with anterior fistulas and episiotomy scars. The decision to perform a primary fistulotomy should be individualized but should only be attempted by a surgeon with a sound knowledge of the regional anatomy. Insistence upon finding a fistula may encourage creation of a false passage and unnecessary division of sphincter muscle. 11 As will be seen in the discussions of the use of fibrin glue ranal plug in the treatment of fistula-in-ano further on in this chapter, many of the former proponents of primary fistulotomy have abandoned this approach and have instead elected to await the appearance of a fistula after drainage only to treat it with fibrin glue ranal plug so as to avoid cutting any sphincter muscle. Antibiotics There is little if any role for antibiotics in the primary management of anorectal abscesses except as an adjunct in patients with valvular heart disease or prosthetic valves, extensive soft tissue cellulitis, prosthetic devices, diabetes, immunosuppression, or systemic sepsis. Postoperative care Patients are instructed to continue with a regular diet and to take a bulk-forming agent, non-codeine-containing analgesic, and sitz baths. Patients are generally seen in follow-up in 2 4 weeks or for intersphincteric or supralevator abscesses, 2 weeks postoperatively. Those patients in whom catheter drainage has been performed are seen within 7 10 days after the procedure. If the cavity has closed around the catheter and drainage has ceased, the catheter is removed. If the cavity has not healed, the catheter is left in place or replaced with a smaller one. In all cases, patients are observed until complete healing has occurred. Complications Recurrence After incision and drainage, ischioanal and intersphincteric abscesses are associated with the development of recurrent abscesses or fistulas in as many as 89% of patients. 6,14,15 Recurrence is more likely to occur in patients with a history of abscess drainage 6,14,15 perhaps because the natural barriers to infection have been destroyed. Reasons for recurrence of anorectal infections include missed infection in adjacent anatomic spaces, the presence of an undiagnosed fistula or abscess at initial abscess drainage, and failure to completely drain the abscess. 5 If a patient waits too long for follow-up after catheter drainage, the skin may seal and a second incision may be required to retrieve the catheter or redrain a recurrent abscess. Failure to detect a primary opening at the time of primary fistulotomy and abscess drainage may result in persistence of the infection. Extra-anal Causes Extra-anal disease should be considered once the usual causes of recurrence have been ruled out. Hidradenitis suppurativa and downward extension of a pilonidal abscess should be considered. 1 A prospective review of recurrent anorectal abscesses by Chrabot et al. 16 reported hidradenitis in one-third of patients with recurrent abscesses. In addition, the possibility of Crohn s disease should be suspected. Incontinence Incontinence may result after incision and drainage of an abscess either from iatrogenic damage to the sphincter or inappropriate wound care. Continence may be compromised if the superficial external sphincter is inadvertently divided during drainage of a perianal or deep postanal abscess in a patient with preoperative borderline continence. Drainage of a supralevator abscess may lead to incontinence if the puborectalis is inappropriately divided. 17 Prolonged packing of a drained abscess may impair continence by preventing the development of granulation tissue and promoting the formation of excess scar tissue. 18

6 13. Benign Anorectal: Abscess and Fistula 197 Although advocated to decrease recurrence rates, primary fistulotomy may result in unnecessary division of sphincter muscle in acutely inflamed tissue. Schouten and van Vroonhoven 14 reported a 39% rate of continence disturbances in a prospective, randomized trial. Special Considerations Necrotizing Anorectal Infection Rarely, anorectal abscesses may result in necrotizing infection and death. Factors thought to be responsible include delay in diagnosis and management, virulence of the organism involved, bacteremia and metastatic infections, or underlying disorders such as diabetes, blood dyscrasias, heart disease, chronic renal failure, hemorrhoids, and previous abscess or fistula. 5 Symptoms and Signs Spreading soft tissue infection of the perineum can be classified into two groups. 19 The first group includes anorectal sepsis in which the infection extends superficially around the perineum resulting in necrosis of skin, subcutaneous tissue, fascia, or muscle. Perianal crepitation, erythematous, indurated skin, blistering, or gangrene may be present (Figure 13-8). A black spot may appear early and indicates a widespread necrotizing infection. 20 The second group includes sepsis in which the preperitoneal or retroperitoneal spaces have become involved. 19 Subtle signs may be present which include abdominal wall induration, tenderness, or a vague mass. It is important to realize that systemic symptoms such as fever, tachycardia, and vascular volume depletion may precede the appearance of overt signs of infection. 21 Treatment Treatment consists of vigorous intravenous fluid hydration, restoration of electrolyte balance, and insertion of a Foley catheter. Accompanying coagulopathy, respiratory insufficiency, and FIGURE Necrotizing anorectal infection. renal failure must be aggressively treated. Invasive monitoring and ventilatory support may be necessary. 22 Pus or necrotic tissue from the infected region must be cultured for aerobes and anaerobes. A Gram stain can be used to distinguish between the presence of clostridial and nonclostridial organisms. 23 Empiric broad-spectrum antibiotic therapy should be instituted regardless of Gram stain and culture results. The chosen antibiotic regimen should be effective against staphylococci and streptococci, Gram-negative coliforms, Pseudomonas, Bacteroides, and Clostridium. For Gram-positive rods seen on Gram stain, antibiotics administered should include sodium penicillin G in doses of million units per day and an aminoglycoside. Tetanus toxoid should also be administered. 22 Surgical treatment consists of wide radical debridement until healthy tissue is encountered. The goals of surgical debridement are to remove all nonviable tissue, halt the progression of infection, and alleviate the systemic toxicity. 21 It is crucial to realize that the preoperative skin changes may be minimal compared with the operative findings which may include edema, liquefactive necrosis of subcutaneous tissues, watery pus formation, and extensive necrosis of underlying fascia. 22 Reexamination under anesthesia is usually necessary because this is the only manner by which adequate wound examination can be conducted. 22 The need for colostomy is a debatable issue and has been recommended if the sphincter muscle is grossly infected, if there is colonic or rectal perforation, if the rectal wound is large, if the patient is immunocompromised, or if incontinence is present. 19,21 Whereas some authors 23 believe that colostomy is seldom necessary, fecal diversion may also be accomplished with the use of a medical colostomy consisting of enteral or parenteral nutrition. Controversy also exists with regard to the need for urinary diversion by suprapubic catheterization. It has been suggested that this may be indicated in the presence of known stricture and urinary extravasation with phlegmon. 24 Although antibiotics and adequate surgical drainage are thought to be sufficient, the use of hyperbaric oxygen (HBO) has been advocated as an adjunct to treatment, particularly in patients with diffuse spreading infections who do not have chronic obstructive pulmonary disease. 25 It is postulated that HBO has a direct antibacterial effect on anaerobic bacteria by diminishing the effect of endotoxins and optimizing leukocyte phagocytic function. 20 HBO may also promote wound healing by facilitating fibroblast proliferation. 25 HBO is delivered as 100% oxygen through an oronasal mask or endotracheal tube at 3 atm for one or two cycles each lasting 2 hours. If HBO is to be used as an adjunctive therapy, appropriate surgical intervention with wide debridement cannot be compromised because ischemic tissue cannot be salvaged by HBO. 21 Despite aggressive surgical and multidisciplinary management of anorectal sepsis, mortality rates ranging from 8% to 67% have been reported. 19,21 This high mortality rate is attributable in part to the aggressive nature of the infection and to the underlying comorbid diseases that are present in these

7 198 C.-A. Vasilevsky and P.H. Gordon patients. 21 Mortality rates are 2 3 times higher in diabetics, in elderly patients, and in patients in whom treatment is delayed. 21 Anal Infection and Hematologic Diseases Acute anorectal suppuration poses an interesting and often life-threatening problem in patients with acute hematologic diseases. In patients with acute leukemia, mortality rates of 45% 78% have been reported. 26 There is a definite relationship between the number of circulating granulocytes and the incidence of perianal infection in patients with hematologic diseases. In one study, patients with neutrophil counts below 500 per cubic millimeter had an incidence of anorectal infections of 11% whereas those with counts greater than 500 per cubic millimeter had an incidence of 0.4%. 27 Glenn et al. 28 reported that 63% of anorectal infectious episodes occurred when fewer than 500 neutrophils were present per cubic millimeter. The risk of developing anorectal infection in this patient population has been found to be related to the severity and duration of the neutropenia. 26 The most important prognostic indicator was the number of days of neutropenia during the infectious episode. 28 The most common presenting symptoms include fever which precedes pain, and urinary retention. Point tenderness and poorly demarcated induration constitute the earliest signs, 26 whereas external swelling and fluctuation often appear late in the course of infection. 28 Controversy surrounds the treatment of acute anorectal infections in patients with hematologic malignancies. Surgery has generally been avoided because what may seem to be simple incision and drainage may produce scant or no pus and may instead cause hemorrhage, poor wound healing, or expanding soft tissue infection. 28 Any patient with perianal pain is assumed to have a perianal complication and is started on precautionary measures which consist of no digital rectal examinations, suppositories, or enemas. 29 Sitz baths, stool softeners, bulk agents, and analgesia are advised. On aspiration of most abscesses in this group, the most common organisms have been found to be Escherichia coli and group D streptococcus. 28 Consequently, infections are successfully controlled with a third-generation cephalosporin combined with anaerobic coverage or an extended spectrum penicillin in combination with an aminoglycoside and an anti-anaerobic antibiotic. This combination has been associated with an 88% success rate. 28 Barnes et al. 26 recommend an aggressive surgical approach. Through this approach, 13 of 15 patients who were severely neutropenic with neutrophil counts of fewer than 100 per cubic millimeter recovered with incision and drainage. It must be noted that these patients were found to have extensive soft tissue infection. Because appropriate antibiotic coverage has been found to control infection successfully, surgery has generally been recommended only if there is obvious fluctuation, progression of soft tissue infection, or persistent sepsis after a trial of antibiotic therapy. 28 With severe neutropenia of fewer than 500 neutrophils per cubic millimeter, low-dose radiation therapy of rads for a period of 1 3 days has been suggested. Spontaneous drainage or subsidence of induration has been found to occur in 3 5 days. 29 A randomized, controlled study, however, has failed to confirm the utility of this approach. 30 Anorectal Sepsis in the Patient Positive for the Human Immunodeficiency Virus Patients who are human immunodeficiency virus (HIV) positive and present with abscesses require drainage either by incision and drainage or use of catheter drainage. Because these patients are immunosuppressed, adjunctive antibiotics should be used. Efforts should be directed at keeping wounds small because these patients are at risk of poor wound healing. 31 An increased incidence of perianal sepsis 32 may be observed in HIV-positive patients. Serious septic complications or uncommon presentations of anorectal sepsis were found in 13% of patients who initially presented with anorectal suppuration in one study. 31 In another study, perianal sepsis was associated with in situ neoplasia. 33 Fistula-in-ano Familiarity of the surgeon with the anatomy of the anorectal area and with the pathogenesis and classification of fistulas is essential for their adequate management. Pathophysiology Etiology A fistula is defined as an abnormal communication between any two epithelium-lined surfaces. A fistula-in-ano is an abnormal tract or cavity communicating with the rectum or anal canal by an identifiable internal opening. Most fistulas are thought to arise as a result of cryptoglandular infection. Classification The most helpful yet complicated classification of fistula-inano is that described by Parks et al. (Table 13-2). It has been suggested that its use is particularly applicable to the treatment of recurrent fistulas. 10 Intersphincteric Fistula-in-ano This fistula is the result of a perianal abscess. The tract passes within the intersphincteric space (Figure 13-9A). This is the most common type of fistula and accounts for approximately 70% of fistulas. 34 A high blind tract passing from the fistula tract to the rectal wall may occur; in addition, the tract may also pass into the lower rectum. The infectious process may pass into the intersphincteric plane and terminate as a blind tract. There is no downward extension to the anal margin, and

8 13. Benign Anorectal: Abscess and Fistula 199 TABLE Classification of fistula-in-ano Intersphincteric Simple low tract High blind tract High tract with rectal opening Rectal opening without perineal opening Extrarectal extension Secondary to pelvic disease Transsphincteric Uncomplicated High blind tract Suprasphincteric Uncomplicated High blind tract Extrasphincteric Secondary to anal fistula Secondary to trauma Secondary to anorectal disease Secondary to pelvic inflammation thus no external opening is present. Infection may also spread in the intersphincteric plane to reach the pelvic cavity to lie above the levator ani muscles. Lastly, an intersphincteric fistula may originate in the pelvis as a pelvic abscess but manifest itself in the perianal area. Transsphincteric Fistula-in-ano In its usual variety, this fistula results from an ischioanal abscess and constitutes approximately 23% of fistulas seen. 34 The tract passes from the internal opening through the internal and external sphincters to the ischioanal fossa (Figure 13-9B). A high blind tract may also occur in this situation in which the upper arm of the tract may pass toward the apex of the ischioanal fossa or may extend through the levator ani muscles and thereby into the pelvis. One form of transsphincteric FIGURE Classification of fistula-in-ano. A Intersphincteric. B Transsphincteric. C Suprasphincteric. D Extrasphincteric. fistula is the rectovaginal fistula. This is discussed further in Chapter 14. Suprasphincteric Fistula-in-ano This fistula results from a supralevator abscess and accounts for approximately 5% of fistulas in some series. 34 The tract passes above the puborectalis after arising as an intersphincteric abscess. The tract curves downward lateral to the external sphincter in the ischioanal space to the perianal skin (Figure 13-9C). A high blind tract may also occur in this variety and result in a horseshoe extension. Extrasphincteric Fistula-in-ano This constitutes the rarest type of fistula and accounts for 2% of fistulas. 34 The tract passes from the rectum above the levators and through them to the perianal skin via the ischioanal space (Figure 13-9D). This fistula may result from foreign body penetration of the rectum with drainage through the levators, from penetrating injury to the perineum, or from Crohn s disease or carcinoma or its treatment. However, the most common cause may be iatrogenic secondary to vigorous probing during fistula surgery. 4 Evaluation and Treatment Symptoms A patient with a fistula-in-ano will often recount a history of an abscess that has been drained either surgically or spontaneously. Patients may complain of drainage, pain with defecation, bleeding caused by the presence of granulation tissue at the internal opening, swelling, or decrease in pain with drainage. Additional bowel symptoms may be present when the fistula is secondary to proctocolitis, Crohn s disease, actinomycosis, or anorectal carcinoma. 35 Systemic diseases such as HIV, carcinoma, and lymphoma should be entertained. 35 Physical Examination The external or secondary opening may be seen as an elevation of granulation tissue discharging pus. This may be elicited on digital rectal examination. In most cases, the internal or primary opening is not apparent. The number of external openings and their location may be helpful in identifying the primary opening. According to Goodsall s rule (Figure 13-10), an opening seen posterior to a line drawn transversely across the perineum will originate from an internal opening in the posterior midline. An anterior external opening will originate in the nearest crypt. Generally, the greater the distance from the anal margin, the greater the probability of a complicated upward extension. Cirocco and Reilly 36 found that Goodsall s rule was accurate in describing the course of anal fistulas with a posterior external opening. It was inaccurate in patients with anterior external openings because 71% of these fistulas tracked to a midline anterior primary opening. This

9 200 C.-A. Vasilevsky and P.H. Gordon initial surgery, to determine the relationship of the fistula tract to the sphincter mechanism, and to reveal the site of sepsis in a recurrent fistula, all serving to decrease recurrence rates associated with fistula surgery. Imaging may take the form of fistulography, computed tomography (CT) scan, endoanal ultrasound, and magnetic resonance imaging (MRI). FIGURE Goodsall s rule. was especially true in women in whom fistulas with anterior external openings tracked in a radial manner in only 31%. 36 Digital rectal examination may reveal an indurated cordlike structure beneath the skin in the direction of the internal opening with asymmetry between right and left sides. Internal openings may be felt as indurated nodules or pits leading to an indurated tract. 36 Posterior or lateral induration may be palpable indicating fistulas deep in the postanal space or horseshoe fistulas. 35,36 Bidigital rectal examination will define the relationship of the tract to the sphincter muscles and provides information as to preoperative sphincter tone, bulk, and voluntary squeeze pressure which need to be assessed preoperatively because of a possible risk of incontinence. 17,35 Fistulography Fistulography, which involves cannulation of the external opening with a small feeding tube and injection of water-soluble contrast may be useful in the evaluation of recurrent fistulas or in Crohn s disease where previous surgical forays or disease may have altered anorectal anatomy 38 (Figure 13-11). Contrast is introduced at low pressures for fear of tissue disruption. This may not allow secondary tracts to fill with contrast. It is difficult to distinguish between an abscess located high in the ischioanal fossa and one located in the supralevator space. In addition, the level of the internal opening may be difficult to see because of the absence of precise landmarks. Contrast may reflux into the rectum wrongly suggesting an extrasphincteric tract with a rectal opening thus resulting in injudicious probing. Accuracy rates in identifying the internal openings and extensions in one study were found to be 16%, whereas a subsequent study found fistulography to be useful in 96%. 38,39 Its use resulted in altered surgical management or revealed other surgical pathology in 48%. 38 It was found, for reasons outlined previously, to have a false-positive rate of 12%. 39 Fistulography is invasive and potentially may result in the dissemination of sepsis. Investigations Anoscopy should be done before operation in an attempt to identify the primary opening. Sigmoidoscopy should be performed to locate a proximal internal opening and to exclude underlying pathology such as proctitis or neoplasia. Colonoscopy or barium enema and a small bowel series are indicated in patients who have symptoms suggestive of inflammatory bowel disease and in patients with multiple or recurrent fistulas. Although anal manometry is not generally required, it may be useful as an adjunct to planning the operative approach in women with previous obstetric trauma, in an elderly patient, a patient with Crohn s disease or AIDS, or in a patient with a recurrent fistula. 37 The role of preoperative imaging is to demonstrate clinically undetected sepsis, to serve as a guide at the time of the FIGURE Fistulogram. Arrowheads indicate fistula tract.

10 13. Benign Anorectal: Abscess and Fistula 201 CT Scan CT scanning performed with intravenous and rectal contrast is a noninvasive method used to assess the perirectal spaces. Its use may be to distinguish an abscess requiring drainage from perirectal cellulitis. It does not permit visualization of tracts in relation to the levators. Endoanal Ultrasound The role of endoanal ultrasound is to establish the relation of the primary tract to the anal sphincters, to determine if the fistula is simple or complex with extensions, and to determine the location of the primary opening. It may aid in the identification of complex fistulas and may serve as an adjunct in the evaluation of complex suppuration to assess the adequacy of drainage 40 (Figure 13-12a). A prospective study that compared this modality to digital examination found that although endosonography was able to detect a large portion of intersphincteric and transsphincteric tracts, it was unable to detect primary superficial, extrasphincteric and suprasphincteric tracts or secondary supralevator or infralevator tracts. 41 A study conducted 10 years later 42 using a 10-mHz probe along with injection of hydrogen peroxide into the tract, was able to identify the internal opening in 93%. Although this investigative modality is rapid and well tolerated, it is operator dependent and scars or defects caused by previous sepsis, surgery, or trauma will confuse ultrasonographic interpretation and make delineation of fistula tracts difficult. 41 The concomitant use of hydrogen peroxide (Figure 13-12b) or Levovist 43 at the time of ultrasound examination has been found to improve its accuracy. Magnetic Resonance Imaging MRI in the form of endoanal coil, body coil, and phase array coil (Figure 13-13) may be of value in the assessment of patients with complex fistulas and in those with anatomic distortion resulting from previous surgery. Because MRI can provide multiplanar visualization of the sphincter muscles, differentiation of supralevator from infralevator lesions is easier. 44 MRI has been found to accurately delineate the presence and course of a primary fistulous tract but also demonstrates the site and presence of any secondary extensions. 45 It also provides the most accurate imaging technique of localizing the site of the internal opening because its location can be inferred from the proximity of the tract in the intersphincteric space. 45 A prospective study that compared the accuracy of MRI in the preoperative assessment of anal fistulas to operative findings found concordance rates of 88% for the presence and course of the primary tract, 91% for the presence and site of secondary extensions or abscesses and 97% for the presence of horseshoeing, and 80% for the position of the internal openings. 45 In the same study, failure of healing in 9% was found to be related to pathology missed at the time of surgery which had been documented on preoperative MRI. 45 Difficulties in interpretation, however, may occur because neural and vascular structures could be mistaken for fistulas and chemical shift artifacts may simulate a fistula filled with fluid. 46 The use of the endoanal coil has been found to be superior to external MRI for the identification of complex sphincter anatomy especially in the demonstration of the morphology of the internal and external sphincters 47 ; however, definition may fall off outside the sphincter and may fail to show the tracts that lie beyond its range. It is also painful. A prospective study comparing hydrogen peroxide endoanal ultrasound to endoanal MRI found good agreement for the classification of the primary fistula tract and the location of the internal opening. These results also demonstrated good agreement with the surgical findings enabling both to be reliable for the preoperative evaluation of fistulas. 48 FIGURE A Anal endosonogram; arrows indicate fistula tract; B with hydrogen peroxide; arrows indicate better delineation of fistula tract. (Courtesy Dr. Julio Faria.)

11 202 C.-A. Vasilevsky and P.H. Gordon FIGURE Phase array MRI. A White arrowhead indicates levators; black arrowhead indicates fistula tract to rectum; black arrow shows tract crossing levator. B Arrowhead indicates tract going to skin. A prospective trial comparing the use of the endoanal coil to the body coil found that surgical concordance for the endoanal coil was 68% versus 96% for the body coil, presumably because of field of view limitations. 49 This can be overcome with the use of the phase array coil which has a larger field of view and may be useful in Crohn s disease and recurrent fistulas. 50 Buchanan et al., 51 in a prospective study to determine the impact of MRI with primary fistulas, found that MRI changed the surgical approach in 10%. In another study with respect to recurrent fistulas, recurrence rates were found to be higher for those surgeons who never used MRI. 52 They concluded that MRI-guided surgery can decrease recurrence rates by 75% in surgery for recurrent fistulas. Treatment General Principles The principles of fistula surgery are to eliminate the fistula, prevent recurrence, and preserve sphincter function. Success is usually determined by identification of the primary opening and dividing the least amount of muscle possible. Several methods have been proposed to identify the primary opening in the operating room 1,4 : 1. Passage of a probe or probes from the external opening to the internal opening or vice versa. 2. Injection of a dye such as dilute solution of methylene blue, milk, or hydrogen peroxide, and noting their appearance at the dentate line. Although methylene blue may stain surrounding tissues, diluting it with saline or hydrogen peroxide will obviate this problem. 3. Following the granulation tissue present in the fistula tract. 4. Noting puckering of an anal crypt when traction is placed on the tract. This may be useful with simple fistulas but is less successful in the more complicated varieties. Operative Management Lay-open Technique For the treatment of simple intersphincteric and low transsphincteric fistulas, the patient is placed in the prone jackknife position after induction of a regional anesthetic. Local anesthesia consisting of 0.5% lidocaine or 0.25% bupivacaine hydrochloride with 1:200,000 epinephrine is injected along the fistula tract for hemostasis after insertion of an anal speculum. Use of bupivacaine provides analgesia of longer duration than most regional anesthetics. A probe is inserted from the external opening along the tract to the internal opening at the dentate line. The tissue overlying the probe is incised and the granulation tissue curetted and sent for pathologic evaluation. A gentle probe is used to identify any high blind tracts or extensions, which are unroofed, if found. If desired, the wound may be marsupialized on either edge by sewing the edges of the incision to the tract with a running locked absorbable suture. There is no need to insert packing if an adequate unroofing has been accomplished (Figure 13-14A C).

12 13. Benign Anorectal: Abscess and Fistula 203 Seton The problem of preserving anal continence and treating the fistula is more complicated when managing high transsphincteric fistulas. If the tract is seen to cross the sphincter muscle at a high level, the use of the lay-open technique in combination with insertion of a seton is safer. A seton may be any foreign substance that can be inserted into the fistula tract to encircle the sphincter muscles. Materials frequently used include silk or other nonabsorbable suture material, Penrose drains, rubber bands, vessel loops, and silastic catheters. 17 The lower portion of the internal sphincter is divided along with the skin to reach the external opening and a nonabsorbable suture or elastic suture is inserted into the fistulous tract. The ends of the suture or elastic are tied with multiple knots to create a handle for manipulation (Figure 13-15). This form of seton, known as a cutting seton, is tightened at regular intervals to slowly cut through the sphincter. This allows the tract to become more superficial, converting a high fistula into a low one. The proximal fistulotomy subsequently heals by stimulating fibrosis behind it reestablishing continuity of the anorectal ring to prevent separation of the sphincter muscle at a second-stage repair 8 weeks later when the remaining external sphincter is divided. The seton also allows delineation of the amount of remaining muscle thus enabling improved postoperative assessment by outlining the tract. A seton may also be used as a drain which is left loosely in place to facilitate prolonged drainage. Specific indications for seton use include the following: 53 1) to identify and promote fibrosis around a complex anal fistula that encircles most or all of the sphincter mechanism; 2) to mark the site of a transsphincteric fistula in cases of massive anorectal sepsis where the normal anatomic landmarks have been distorted; 3) anterior, high transsphincteric fistulas in women. Because the FIGURE Technique of laying open. A Insertion of probe and incision of tissue overlying probe. B Curettage of granulation tissue. C Marsupialization of wound edges. FIGURE Seton.

13 204 C.-A. Vasilevsky and P.H. Gordon puborectalis is absent in this area and the external sphincter is quite tenuous, primary fistulotomy may result in incontinence; 4) the presence of a high transsphincteric fistula in a patient with AIDS in whom healing is known to be poor; 5) to avoid premature skin closure and formation of recurrent abscesses and promote long-term drainage in patients with Crohn s disease. In these patients, a silastic catheter can be left in place for a prolonged period of time to promote epithelialization of the fistula tract or tracts; 6) when there is suspicion that primary fistulotomy will result in incontinence such as in those patients with multiple simultaneous fistulas, patients who have undergone multiple prior sphincter operations such as fistulotomy or internal sphincterotomy, and in elderly patients with weakened sphincter muscles. Another option available to treat transsphincteric fistulas without division of muscle involves the use of a dermal island flap. 54 Division of muscle was able to be avoided in 90%; however, a 23% failure rate was reported. This was found to be more likely in males, patients who had previous treatment of their fistulas, patients with large fistulas requiring combined flaps, and patients who underwent simultaneous fibrin glue injection. Treatment of suprasphincteric fistulas requires an appreciation that the tract involves the entire external sphincter complex as well as the puborectalis muscle. Laying open the entire tract would render the patient incontinent. Thus, several methods have been proposed to manage this fistula without the ensuing devastating consequences. The use of a seton has been advocated in combination with division of the internal sphincter and the superficial portion of the external sphincter to the external opening. The seton is placed around the remaining external sphincter as was previously described. 55 A modification of this approach has been proposed by Kennedy and Zegarra 56 in which an internal sphincterotomy is performed, followed by opening of the tracts outside the external sphincter without division of any portion of the external sphincter which is encircled by a seton to promote fibrosis and assure adequate drainage. Complete healing using the latter approach has been reported in 66% with posterior fistulas and in 88% with anterior fistulas. 56 Parks and Stitz 55 obtained healing in 63%. Another method that has been proposed to treat this type of fistula is the anorectal advancement flap which will be described. The horseshoe variety of the suprasphincteric fistula also presents the problem of complete sphincter involvement combined with the presence of multiple external openings a great distance from the cryptoglandular source. Treatment consists of identification of the internal opening and proper drainage of the postanal space as was previously described. The horseshoe extensions are enlarged for counter-drainage and the granulation tissue is curetted. The treatment of an extrasphincteric fistula depends on its etiology. If the fistula arises secondary to an anal fistula, a secondary opening above the puborectalis is thought to be iatrogenic because of extensive probing of a transsphincteric fistula. The lower portion of the internal sphincter is divided and the rectal opening is closed with a nonabsorbable suture. A temporary colostomy may be necessary but a medical colostomy consisting of preoperative mechanical and antibiotic bowel preparation followed by enteral feeding may suffice. If the fistula is the result of entrance of a foreign body, it must be removed, drainage must be established, the internal opening closed, and a temporary colostomy constructed to decrease rectal pressure. This type of fistula may also be a manifestation of Crohn s disease. Treatment will depend on the nature of the anorectal mucosa and drainage may be assisted by placement of a seton. Finally, the fistula may be the result of downward tracking of a pelvic abscess which must be drained so that the fistula can heal. Anorectal Advancement Flap When the traditional laying-open technique may be inappropriate, for example, in anterior fistulas in women, in patients with inflammatory bowel disease, in patients with high transsphincteric and suprasphincteric fistulas, as well as in those with previous multiple sphincter operations, multiple and complex fistulas, the use of an anorectal advancement flap has been advocated 57 (Figure 13-16A D). Advantages of this technique include a reduction in the duration of healing, reduced associated discomfort, lack of deformity to the anal canal, as well as little potential additional damage to the sphincter muscles because no muscle is divided. 17 After full mechanical and antibiotic bowel preparation, the patient is placed in the prone jackknife or left lateral position. Under a regional or general anesthetic, after insertion of a Foley catheter, the fistula tract is identified with a probe and either cored out or curetted. The internal opening is identified and excised. The external opening is enlarged to allow for drainage. A full-thickness flap of rectal mucosa, submucosa, and part of the internal sphincter is raised. The residual internal opening is closed with absorbable suture. The flap is then advanced 1 cm below the internal opening. The tip of the flap containing the fistulous opening is excised and the flap is sewn into place with absorbable sutures ensuring that the mucosal and muscular suture lines do not overlap. The base of the flap should be twice the width of the apex to maintain good blood supply. Successful results have reported in more than 90% of patients. 58 Factors associated with poor outcomes include Crohn s disease and steroids. 59 Cigarette smoking was found to be another significant variable in another study. 60 Fistulectomy Although excision of the fistula or fistulectomy was thought to be a satisfactory method of treatment of fistula-in-ano, its use is no longer recommended. Larger wounds are created significantly prolonging wound healing time. 61 A greater separation of muscle ends occurs 1 and there is greater risk of injuring or excising underlying muscle 57 thereby increasing the risk of incontinence. Schouten and van Vroonhoven 14