Continuing Education Activity

An anorectal fistula is a connection between the anorectal canal and perianal area. It is a morbid condition that commonly occurs following perianal abscess drainage and requires thorough followup to diagnose and treat. Classification of fistulas is vital in guiding therapy. Surgical management is the mainstay of treatment, but knowledge of novel therapies and sphincter preserving approaches and preoperative imaging are essential elements to provide patients with multiple treatment options while preserving sphincter integrity. This activity covers diagnosis, classification, preoperative workup, and surgical management of anorectal fistulas. Also, it highlights the role of the interprofessional team in evaluating and improving care for patients with this condition.

Objectives:

• Describe the cryptoglandular theory of anal fistulas and other causes of anal fistulas.
• Outline preoperative risk factors for fecal incontinence in anal fistula surgery.
• Outline the advantages and disadvantages of anal fistula plugs.
• Identify patients who will benefit from referral to a gastroenterologist for workup of inflammatory bowel disease. Review and highlight the role of the interprofessional team in evaluating and improving care for patients with anorectal fistulas.

Introduction

Anal fistula occurs most commonly when the anal glands, which reside in the intersphincteric plane, become occluded and infected, resulting in a cryptoglandular abscess.[1] Whether surgically or spontaneously drained, a perirectal abscess may still result in a fistula in up to 40% of cases; however, spontaneously draining abscesses tend to have a higher fistula rate, up to 66%.[2][2] The mean incidence has been reported at 8.6 per 100,000.[3] The presence of an acute or chronic anal fistula can be distressing for patients and cause reduced quality of life.[4] They are commonly classified by anatomical location, as first described by Parks, Gordon, and Hardcastle in 1976.[5] Understanding anorectal anatomy and the classification of perirectal fistulas is paramount for their management.

Classification of Anorectal Fistulas

Anorectal fistulas are classified into transphincteric, high intersphincteric, suprasphincteric, and extrasphincteric types, based on the location of the tract in relation to the internal and external anal sphincters as described by Parks and Gordon.

Intersphincteric Fistulas:

Most abscesses form in the space between the internal and external sphincters, so intersphincteric fistulas end up being the most common. In this pattern, the tract passes through the internal sphincter before continuing outward to an external opening on the skin. A fistulotomy efficiently manages these (laying open of the fistulous tract) and rarely causes incontinence, as the treatment does not affect the external sphincter. Intersphincteric fistulas are the most common type of fistula, comprising 50-80% of all cryptoglandular fistulas.

Transsphincteric Fistulas:

Trans is a Latin word for “on the other side of.” So a trans-sphincteric fistula crosses to the other side of the external sphincter before exiting in the perianal area and thus involves both sphincters. Transsphincteric fistulas pose a challenge in management and often require more complex or staged treatment. However, the use of a seton to gradually “lower” the tract and reduce its involvement with the external sphincter may allow migration of the tract and a fistulotomy at a later date, while preserving the patient's continence. The extent of involvement of the external sphincter dictates the likelihood of postoperative incontinence, as a partial sphincterotomy is usually tolerated. Still, if the fistula involves the majority of the sphincter, then incontinence results after a complete division.

Suprasphincteric Fistulas:

These fistula tracts travel superior to the external sphincter and cross the puborectal muscle before changing course caudal to their external opening. Accordingly, they pass the internal sphincter and the puborectal muscle but spare the external sphincter. When these patients typically present with a perirectal abscess, it may not be visible on inspection, but they have tenderness on the digital rectal exam. Again, because of their high tract, a seton may be considered before fistulotomy in these cases. A fistulectomy is similar to fistulotomy but involves the removal of the entire fistula tract either sharply or with cautery. Historically, radical fistulectomy was the standard treatment for anal fistula; however, fistulotomy tended to be preferable as it preserved more sphincter function, was a less morbid procedure, and healed faster. However, more recently, with specialists performing the majority of fistula procedures, the outcomes of fistulectomy and fistulotomy appear similar. A recent meta-analysis published in 2016 of 6 randomized controlled trials comparing fistulectomy versus fistulotomy in low fistulas found no significant difference in recurrence in 5 trials and no significant difference in postoperative incontinence in 4 trials.[6]

Extrasphincteric Fistulas:

Extrasphincteric fistulas typically originate in the more proximal rectum rather than the anal canal and often develop as sequelae of prior procedures. The external opening appears in the perianal region, while the tract ascends to enter the anal canal above the dentate line.

The St. James University Hospital (SJUH) classification is an imaging-based system that grades fistulas according to anatomy.[7] MRI plays a central role here: its superior soft-tissue contrast allows clear visualization of the sphincter complex and the fat planes of the perirectal and supra-levator spaces. MRI also facilitates more accurate identification of the internal opening because of its ability to image in multiple planes. Published in 2000 by Morris et al, the SJUH system mirrors the Parks classification in some areas while offering more detailed stratification based on MRI findings. Grade 1 represents a simple linear intersphincteric fistula, identical to the classic “intersphincteric” pattern in the Parks system. When a grade 1 fistula is associated with an abscess or a secondary tract, it is categorized as grade 2. Crossing of the external sphincter defines a grade 3, or trans-sphincteric, fistula. If a trans-sphincteric tract is accompanied by an abscess or secondary extension into the ischiorectal fossa, it is considered grade 4. A grade 5 fistula extends above or through the levator ani musculature, forming supra-levator or trans-levator pathways.[7] Importantly, MRI-based classification has been shown to predict surgical outcomes more reliably than intraoperative findings alone.[8]

Management generally aligns with the degree of sphincter involvement. Grade 1 and 2 fistulas are usually amenable to fistulotomy or fistulectomy; if an abscess is present, the abscess is incised and drained first. Persistent fistulas after resolution of acute infection are then treated according to their type. Grades 3 and 4 involve the external sphincter and may require seton placement followed by fistulotomy or a sphincter-sparing procedure such as LIFT or an endoanal advancement flap. Grade 5 fistulas often reflect atypical underlying pathology and warrant further evaluation before operative intervention. Fistulas related to Crohn disease require management tailored to the underlying inflammatory disorder and are addressed separately.

Etiology

A multitude of causes can lead to fistulas, but the well-known mnemonic "FRIEND" here aids memory. "F" for foreign body, "R" radiation, "I" infection or Inflammatory Bowel Disease, "E" epithelialization, "N" neoplasm, and "D" for distal obstruction (as is the case in the cryptoglandular theory). 

Foreign bodies in the rectum are often intentionally placed, such as a seton to lower a fistula tract, make it more localized, and aid healing. Radiation-induced fistulas are well known and are briefly discussed later in this topic. Infection is the most common cause of anorectal fistula and is thought to originate from a blockage of the anal glands and crypts. The 2 anal sphincters are separated by an avascular fatty areolar plane, which allows the spread and infiltration of an infection. Often, an abscess develops in this region and drains spontaneously via a fistula. Obstruction of the anal glands allows bacteria to proliferate and ultimately form a perirectal, anorectal, or perianal abscess. With or without surgical treatment of the anorectal abscess, there is a significant risk of fistula formation. In addition to an incision and drainage, a 5 to 10-day course of antibiotics has been shown to decrease the rate of fistula formation.[9]

A thorough understanding of anorectal anatomy is critical to understanding abscess-to-fistula development. The correct localization of the fistula relative to the sphincters is vital to correct operative management. The essential structures in the anorectal region include the rectum itself, anal glands, anal sphincters, and the levator ani, which is comprised of the puborectalis, pubococcygeus, and iliococcygeus. The anal canal lining is composed of stratified squamous epithelium distally, which changes to squamocolumnar epithelium proximally past the dentate line. Proximal to the dentate line is where the columns of Morgagni appear, which are folds of columnar glandular epithelium.

Anal fistulas are rarely a presentation of anal tuberculosis and should be suspected in endemic regions or nonhealing recurrent fistulas. Using polymerase chain reaction on pus samples is more sensitive than histopathology for detecting tuberculosis.[10][11] Anal fistulas in a younger patient, particularly if they are complex fistulas or multiple, should raise suspicion for Crohn disease.

Sexually transmitted infections (STIs) of the anus and rectum, usually secondary to anal receptive intercourse, may predispose individuals to perianal abscess and fistula. These anorectal STIs are most commonly caused by gonorrhea, chlamydia, as well as syphilis (Treponema pallidum) and herpes simplex.[12]

Radiation proctitis is another cause of anal fistulas. Radiation proctitis requires surgical intervention in less than 10% of cases, with fistula tracks to the vagina, urethra, and bladder being a common complication. Impaired microvascular healing often requires multiple treatment modalities, including local excision, flap reconstruction, and diversion of stool or urine from the site.[13] Patients with human immunodeficiency virus, with or without AIDS, are predisposed to anorectal disease and anal fistulas. These fistulas may lack internal openings and are sometimes in the absence of an underlying abscess.[14] In a study, fistula-in-ano accounted for 6% anorectal pathologies in HIV patients and was independent of the utilization of antiretroviral therapy.[15]

Complicated vaginal deliveries with 3rd or 4th-degree tears or the requirement of episiotomy may predispose to anal fistula; however, these fistulas often heal spontaneously. In nonhealing obstetric-related anal fistulas, surgical therapy is dependent on the location of the fistula as well as vaginal involvement. When distal to the dentate line, a recto-vaginal fistula becomes an ano-rectovaginal fistula. Causes include obstetrical trauma, typically associated with a traumatic vaginal birth. Patients who undergo episiotomy are at increased risk for sphincter injury and fecal incontinence.[16]

Although the majority of the resting anal tone is attributed to the involuntary internal sphincter, the external sphincter is vital to maintaining fecal continence and is comprised of striated voluntary muscle fibers. Three nerve branches innervate it: the external perineal nerve anteriorly, the inferior rectal nerve posteromedially, and, in 31% of cases, an additional posterior branch arising from either S4 or the inferior rectal nerve.[17]

Epidemiology

An anorectal fistula is relatively uncommon and has an incidence of 1-8 per 10,000 persons every year. In the western hemisphere, up to 25% of cases may be associated with Crohn disease.[18] It is twice as common in males as in females and usually presents in the 3rd to 5th decades of life. Some risk factors for perirectal fistula include obesity, diabetes, hyperlipidemia, a history of anorectal surgery, and even excess salt intake.[19] 

Smoking has also been associated with perianal abscess and fistula development and recurrent anal fistula in certain procedures.[20][21][22] Patients who are younger than age 40 or who have recurrent anal abscesses may be predisposed to the development of an anal fistula.[23]

Pathophysiology

An anal fistula, which is an epithelialized connection between the anal canal and external peri-anal area, is characterized by inflammatory tissue and granulation tissue. The distal obstruction prevents the fistula from healing. Because cells are continually being turned over, there is constant debris in the fistula tract, which causes obstruction and prevents healing. The use of a seton and its role in allowing fistulas to heal is evidence of this, as setons maintain constant drainage of the fistula and usually result in the fistula migrating and healing.

Histopathology

Histologic analysis of fistula tissue should be sent when an atypical etiology, such as an infectious or malignant etiology, is suspected. In general, tissue from anal fistula surgery is not usually sent for pathologic analysis, as it does not contribute to the management unless there is an occult process. A study of 84 patients treated for anal fistula evaluated the yield of histopathological analysis in the routine assessment of tissue from anal fistula surgery, found a low positive rate for this tissue except in the setting of a recurrent fistula or when HIV, tuberculosis, or Crohn disease was suspected.[24] The majority of fistula tracts demonstrate pathology. In cases of Crohn disease, noncaseating granulomas may be seen, and if tuberculosis is present, an acid-fast bacilli test is helpful for diagnosis.

History and Physical

A thorough history, complete review of systems, and physical exam are essential for determining the cause of fistula in patients who have not recently had a perirectal abscess drained. Patients with inflammatory bowel disease may be tender on an abdominal exam and provide a history of bloody diarrhea, abdominal pain, or systemic symptoms such as weight loss or fever. A complete sexual history is vital as lymphogranuloma venereum can, in some instances, cause a perianal fistula.[25]

A history of malignancy or radiation to the pelvis is essential, as fistulas from radiation are well-documented, and treatment should be coordinated with the patient’s cancer care. A history of rash or multiple new sexual partners should prompt suspicion of syphilis. A patient with a chronic cough or a history of tuberculosis could present with the disease as an anorectal fistula, particularly if he or she is from an endemic region. Multiple draining fistulas, fistulas in abnormal locations, and chronic or recurrent fistulas should raise concern for a systemic process.

Typical complaints include itching, drainage, discomfort, and possible pain with defecation on presentation. Patients who had an abscess that was inadequately drained may present with a fistula and recurrent perianal abscess. The surgical and procedural history is vital, as a history of anorectal procedures is associated with the development of an anorectal fistula.

A perianal exam and anoscopy in the office are necessary for evaluating concurrent abscesses, assessing external fistulous openings, and other anorectal diseases such as fissures or hemorrhoids. On inspection, a small opening outside the anus with or without visible drainage may be seen. The drainage may be serous, serosanguinous, bloody, purulent, or fecal matter, depending on the location of the fistula. Around the opening, hypertrophied tissue may be present, suggesting a developed tract; this is sometimes palpated on digital rectal exam. The digital rectal exam is also essential to assess for tenderness, which may suggest an occult abscess. 

Evaluation

Imaging: An anorectal fistula is a clinical diagnosis, but imaging is useful for assessing the course of the fistulous tract or its etiology. Imaging studies include endoanal ultrasound, computed tomography of the pelvis, computed tomography fistulography, and MRI of the pelvis.

Endoanal Ultrasound

Endorectal ultrasound is also a useful modality for assessing an abscess, with similar sensitivity but lower specificity than MRI.[26] The introduction of hydrogen peroxide into the external fistulous opening canal improves the accuracy of endoanal ultrasound in identifying both fistulous tracts and occult abscesses. It may be equivalent to anal MRI in the diagnosis of fistulous tracts.[27][28][29][30] It is a less expensive modality than MRI and can be performed in the office, facilitating its use for patients with chronic fistulas, such as Crohn disease patients who require long-term follow-up.

Computed Tomography scan and Computed Tomography Fistulogram

Computerized tomography is useful for identifying abscesses and drainable fluid collections, as it is quick and readily available in most clinical scenarios. Although it is not as sensitive or specific as pelvic MRI for the classification of anal fistulas.[31] In the clinical setting where an acute infection of an anal fistula or an underlying abscess is suspected and timely diagnosis is needed, a computed tomography scan may be the most appropriate imaging modality to expedite diagnosis and treatment.[32]

In the outpatient setting, computed tomography fistulography is a useful and efficient modality for preoperatively identifying fistula tracts.[33] However, it requires expert radiologists to read the images as well as a skilled surgeon being available to inject the contrast for the exam. It may be a cost-saving when compared to MRI. It should be considered in complex anal fistula preoperative planning when trying to save costs or in patients who are reluctant or unable to undergo an MRI. Multidetector computed tomography has been used with similar efficiency to identify fistulous tracts and underlying abscesses.[34]

Magnetic Resonance Imaging (MRI)

MRI of the pelvis assists in identifying fistulous tracts and occult abscesses, and in characterizing the proximity of tracts to the internal and external sphincters to coordinate effective planning. Although computed tomography of the pelvis is useful for evaluating underlying abscesses, it is less sensitive than MR in identifying fistulous tracts.[35] MRI has been shown in various studies to aid operative planning and reduce fistula recurrence or the need for additional operations, as it allows the surgeon to identify occult fistulous tracts and plan for a more extensive procedure when necessary. 

MRI is a compelling preoperative tool, particularly in complex fistulas and those with an external opening greater than 2 cm from the anus.[36] MRI is very sensitive and specific in diagnosing fistulous tracts and characterizing their internal and external openings.[37][38][39][40][41] In a study by Garg et al of 229 patients, MRI changed the preoperative diagnosis in half of the simple fistulas and in over a third of the complex fistulas.[42]

It is efficacious for identifying postoperative complications, such as an abscess or recurrent fistula, particularly at or after 12 weeks postoperatively.[43] In complex fistulas, the utilization of a balloon rectal channel catheter improves the accurate identification of internal openings.[44] Buchanan & colleagues found that the usage of MRI to plan surgery was associated with decreased recurrence of fistulas by facilitating a complete initial operation.[45] In a case-control study of 41 patients comparing computed tomography fistulography to MR preoperatively, internal openings were more readily identified by MRI than by computed tomography fistulography (85.3% vs 68.2%); the combination of both imaging modality findings was most consistent with operative findings.[31]

Laboratory Findings

Basic laboratory panels should be obtained in patients, including a complete blood count and a comprehensive metabolic panel. Low hemoglobin may indicate underlying anemia, which could be secondary to inflammatory bowel disease or a gastrointestinal malignancy. Leukocytosis may reveal an underlying infectious process or occult abscess, as well as an elevated C-reactive protein—other blood tests for inflammatory bowel disease, rapid plasma reagin, and others.

Treatment / Management

Current Management Options for Anorectal Fistula

Treatment Options for Anorectal Fistula

The treatment for a fistula depends on etiology. Still, in general, an exam under anesthesia is typically indicated to identify the fistulous tract using a lacrimal probe and methylene blue or hydrogen peroxide. When the fistulous tract is detected, if the cause is known to be an abscess or otherwise, excellent results have been achieved with a fistulotomy during the initial operation, which has been shown to decrease the need for additional procedures.

Fistulotomy Versus Fistulectomy

 A fistulotomy is the gold standard for an acute anal fistula and entails first identifying the tract of the fistula using a probe. The patient is placed in a lithotomy or prone jackknife position. Deep sedation or general anesthesia is used. The anus and perianal area are prepped with Betadine. A local anesthetic is injected at the start of the procedure to help reduce postoperative pain and may help separate tissue planes. A digital rectal exam is performed. A Lonestar retractor or a Park's retractor is placed. The fistula tract is identified by probing the external opening using a lacrimal probe. Then an injection of methylene blue and/or hydrogen peroxide into the external opening using a small angiocatheter reveals the internal opening and whether there are multiple internal openings. The probe is kept through the external and internal openings, and the sphincters are carefully identified and their involvement assessed. If the external sphincter is not involved, a fistulotomy is performed. Division of the external sphincter should be avoided at best to preserve continence; however, if a necessary division of the lower segment is associated with acceptable postoperative continence rates.[46]

Being careful to avoid the external sphincter and simply splaying open the fistulous tract using a Bovie cautery or sharp dissection. Electrocautery is then used to obliterate the epithelialized tract as much as possible, and the wound is left open to heal. Fistulotomy healing rates have been reported as high as 94% in some series.[47]

A newer procedure used for high transphincteric or suprasphincteric fistulas is fistulectomy with sphincter reconstruction. In this procedure, the sphincter is divided where the fistula tract is, and after excision of the fistula tract, the sphincter is re-approximated with absorbable sutures. Recent studies have shown promising results with this technique for high- and complex-fistula cases, with healing rates approaching 90% and incontinence rates of 2%.[48] Further utilization of this technique and studies on its outcomes are necessary to expand its use.

Compared with other operations, fistulotomy is associated with higher healing rates and a lower need for additional surgeries. Fistulotomy has historically been considered the gold standard for fistula therapy; however, its use varies. It has excellent first-time healing rates.[49] Results of fistulotomy versus fistulectomy are variable, with some studies favoring fistulotomy over fistulectomy because of faster healing time but similar complication rates.[50] Fistuolotomy with marsupialization has been associated with shorter duration of wound discharge and decreased healing time compared to fistulectomy, due to significantly smaller wound size. It may also decrease bleeding rates.[51] A study using endoanal ultrasound to assess internal and external sphincter lengths postoperatively found that sphincter mechanism injury occurred more often during fistulectomy than during fistulotomy.[52]

A meta-analysis of 6 randomized controlled trials comparing the 2 showed no significant difference in healing rates or postoperative complications.[6] In patients undergoing fistulotomy, a sphincter-sparing approach may yield improved functional outcomes.[53] Recurrence of fistula-in-ano after a fistulotomy is usually seen within 12 months after the index operation.[54] Patients who are at high risk for postoperative incontinence, such as females, patients with a prior history of anorectal procedures, and pre-existing poor sphincter control, should be considered for a sphincter-sparing procedure. Complex fistulas, while amenable to fistulotomy and fistulectomy, may be associated with poorer outcomes, as for a trans-sphincteric fistula, division of the sphincter is necessary for an adequate fistulotomy or fistulectomy. Performing preoperative anal manometry is a useful tool for predicting postoperative functional outcomes as well as guiding the type of fistula surgery to minimize sphincter-related complications.[55] In an international survey of surgeons who treat anal fistula, 80% considered fistulotomy as the gold standard.[56]

Seton-Primary Drainage of the Fistula

Seton placement works by the simple concept of allowing a fistula to adequately drain so that healing by secondary intention, from internal to external, may occur. A seton may be placed in the operating room once both the internal and external openings of a fistulous tract are known, and the tract is probed with a lacrimal probe. By allowing the tract to drain and keeping the seton in place continuously, the tract slowly migrates from a deeper or higher location to a more superficial tract. There are various kinds of setons, mainly simple setons, which may be small vessel loops placed loosely. Setons may be used as the primary treatment for a fistula or as a staged procedure, and the patient returns to the operating room for a fistulotomy after their high fistula has converted to a low fistula.

For a cutting seton, a suture is placed and is tied snugly to encourage the migration of the tract. As the wound migrates, the seton becomes loose, and it is then tied again more snugly in the office at intervals. A loose seton, typically a vessel loop, the patient may regularly turn to assist the healing, and these are effectively similar to cutting setons.[57] Setons are an effective definitive therapy for high trans-sphincteric fistulas with complete healing rates up to 98%.[58][59][60][61] They can also be used as effectively as a staged procedure. Setons are highly effective in patients with Crohn disease as well.[62]

In an extensive study of 372 patients in Saudi Arabia with high anal fistulas, the combination of a cutting seton and a 0-silk suture, placed after a partial fistulotomy, achieved exceptional healing rates of 97% with no fecal incontinence and a low recurrence rate of 2.4%.[63] In a study of high trans-sphincteric fistulas in the US, the daily rotation of a silk suture seton by the patient was an effective means of treating these fistulas, with 0 patients experiencing incontinence of stool.[64] Of patients with high trans-sphincteric fistulas treated with setons, recurrent fistulas, supra-levator extension, or horseshoe fistulas have a higher propensity for recurrence.[65] Setons have also been shown to be successful in supra and extra-sphincteric fistulas.[66] Advantages are the preservation of the sphincter and the ability to treat high or complex fistulas with a simple technique. Preserving the internal sphincter intraoperatively may further reduce postoperative incontinence rates.[67] Setons have been shown to have significantly higher healing rates than fibrin glue treatment.[68]

Some disadvantages of setons include frequent follow-up, being cumbersome for patients, being uncomfortable for patients, and long healing times of up to 6 months or longer. In a study of 55 patients who failed seton therapy for their fistula, an endorectal advancement flap had superior short-term results than a LIFT.[69]

Ligation of Intersphincteric Fistula Tract (LIFT)

Description: 

The LIFT procedure was first described by Rojanasakul & colleagues in 2007, in which 18 patients with intersphincteric fistulas were successfully treated using this novel technique. The method involves identifying the intersphincteric groove (ISG), identifying the internal and external openings of the fistula, followed by careful dissection of the portion of the fistula tract within the intersphincteric groove. The dissection can be carried out using cautery and or small scissors. Once the tract is dissected and is clamped with a right-angle clamp, it can be safely suture-ligated within the ISG close to the internal sphincter while preserving the integrity of both the internal and external sphincter musculature. It is then ligated with an absorbable suture. Distal to its ligation, the tract is sharply divided, as confirmed by injection of saline or hydrogen peroxide through the external opening. Any remnant of the intersphincteric tract is carefully removed, and finally, a small incision on the external opening is made to facilitate drainage. The wound over the ISG is precisely approximated with a few simple absorbable sutures.[70] The LIFT procedure can also be safely performed using a lateral approach, with acceptable healing rates of up to 75%.[71]

This technique is specific to trans-sphincteric fistula tracts. Still, it can also be used for other complex fistulas with a tract through the ISG, such as horseshoe or suprasphincteric fistulas.

LIFT is an effective surgical modality for high and complex anal fistulas with healing rates ranging from 40-100% and very low or absent sphincter dysfunction, with larger cohorts demonstrating first-time healing around 75% of the time.[72] Failures of the operation are usually attributed to incorrect identification of the intersphincteric portion of the fistula tract. In a systematic review and meta-analysis that included 1295 patients comparing LIFT to anal advancement flap, there was no significant difference in cure rates for both cryptoglandular and Crohn disease-associated fistulas; however, LIFT showed better continence preservation.[73] Both groups had acceptable cure rates: 61% in Advancement flap patients and 53% in LIFT patients.

Some cons of the LIFT is the potentially high recurrence rates reported in studies approaching 40%.[74]

The benefits of the LIFT procedure include the ability to operate on patients with prior fistula surgeries, preservation of continence, a small incision and scar, and compatibility with reoperation if needed. Patients with a history of multiple fistula surgeries, a longer fistula tract, smokers, or those with obesity are at higher risk for failure of the operation.[75]

Advancement Flap for Anal Fistula

The advancement flap for anal fistula is an earlier technique for treating complex anal sphincters that has remained an important surgical option through the years despite many variations in technique and combinations of this technique with others. Rectal advancement flap, or mucosal advancement flap: this procedure is commonly performed by covering the internal opening of the fistula with rectal mucosa after coring out the fistula tract. Usually, the external opening is left open to drain. It has been shown to achieve acceptable healing rates with low recurrence (<10% in patients) and is a viable option for patients who have had prior fistula surgeries.[76] The shape of the endorectal flap, which can be elliptical or rhomboid, does not appear to affect outcomes.[77] For higher or more proximal fistulas, a transanal approach (TAMIS, transanal minimally invasive surgery) can be used to facilitate easier and more extensive mobilization of a long rectal flap.[78] Compared to seton placement, the RAF may have a lower recurrence and wound infection rates.[79] Partial or full-thickness flaps are superior to mucosa-only flaps in some studies, with lower failure rates. This is generally attributed to the improved blood supply of the flap, as the underlying circular smooth muscle contains significant vasculature.[80][81]

Despite the usually high rates of fistula recurrence in Crohn disease patients, RAF is another treatment option, provided there is adequate drainage before the flap procedure.[82] Crohn disease patients treated with immunologic therapy seem to have improved outcomes with this operation.[83] Smoking is linked to higher failure rates of advancement flap repairs and an increased risk of fistula recurrence. Horseshoe fistulas are likewise associated with poorer healing and a greater likelihood of repair failure.[84] There are multiple variations of advancement flaps published in the literature, with the type necessary determined by the type of fistula present. For instance, the rectal advancement flap, in combination with sphincteroplasty, has been effectively used to treat rectovaginal fistulas secondary to obstetric procedures.[85]

Anal Fistula Plug

An anal fistula plug is another sphincter-sparing procedure that can be used in patients at high risk of incontinence or with complex fistulas. Plugs can be made of fibrin, porcine, or other biologic absorbable materials. Adequate drainage of the fistula must take place before placing any foreign body to minimize the risk of anal sepsis. For fistula plug surgery, the internal and external openings of the fistula are first identified, and a probe is placed through them. This is sometimes followed by a mini-debridement of the track using a "fistula brush" or curette. A suture is easily pulled through the track, and the plug is threaded through it.

The plug is sutured in place in the internal opening to the mucosa and the internal anal sphincter, such that the mucosa covers it entirely. In contrast, the external fistula opening is left open to drain. Anal fistula plugs have been widely controversial, with studies being inconsistent in outcomes. A large randomized controlled trial comparing fistula plugs with surgeon preference for transphincteric fistulas in the United Kingdom found similar healing rates but higher costs in the anal plug group, with no difference in fecal incontinence or quality-of-life scores between the 2 groups.[86] Healing rates for complex fistulas treated with anal fistula plug as a primary therapy range 13-60%, with most studies quoting around 55%.[87][88][89][90] They tend to have higher recurrence rates of fistula than other surgeries for anal fistula as well. In a randomized controlled trial comparing fistula plug versus mucosal advancement flap, the fistula plug had a recurrence rate of 66%.[91] Besides lower healing rates, absorbable fistula plugs have been associated with postoperative anal sepsis.[92] Studies supporting anal fistula plugs have shown cost-effectiveness compared with endoanal advancement flap repair, but only in small samples.[93] In a randomized controlled trial of 104 patients with Crohn disease, the anal fistula plug was not superior to the removal of the seton.[94] Because the results of studies have varied widely, it is still recommended in some international guidelines for the treatment of Crohn disease anal fistulas and recognized as a treatment option for these patients by the ASCRS guidelines.

Video-Assisted Anal Fistula Treatment (VAAFT)

Video-Assisted Anal Fistula Treatment (VAAFT) is an emerging modality for treating anal fistulas. It involves placing a tiny endoscope, a "fistuloscope," through the external opening of the fistula tract, and then exploring the tract for its internal opening. Any contiguous tracts or abscesses are identified. Diathermy is used to obliterate the tract under direct visualization, and, similar to plug therapy, the tract is debrided with a brush. The internal opening is closed with sutures after localization and debridement. In a study of 73 patients treated for complex cryptoglandular fistulas, VAAFT was associated with decreased pain, shorter length of stay, and reduced wound secretions, and could be repeated safely in patients who failed initial VAAFT.[95] Further studies may provide more insight into this novel technique. 

Anal Fistula in Crohn Disease

Fistulizing disease in Crohn patients is a severe disease to treat, but early recognition and diagnosis are critical to effective therapy. These patients should be referred to a gastroenterologist and receive anti-TNF alpha therapy as their primary treatment for fistula disease. After medical treatment, if the fistula persists, setons are the most commonly used primary surgical option in these patients, with reasonable healing rates after anti-TNF alpha therapy.[96] Crohn disease patients often are misdiagnosed and have delays in care, and also may experience prolonged waiting periods to obtain their medications; thus, a comprehensive care team may be more effective in the management of these patients.[96] Infliximab is the primary treatment for these patients. In patients receiving infliximab therapy, higher drug levels have been associated with improved healing rates.[97][98] Patients with Crohn disease are likely to have concomitant proctitis, which is revealed by preoperative imaging. A study of 126 patients with anal fistulas who underwent preoperative MRI found that MRI findings of concomitant rectal inflammation were more closely associated with Crohn disease.[99]

The International Organisation for Inflammatory Bowel Diseases (IOIBD) global consensus guidelines emphasize the importance of evaluation of the rectum in these patients as their disease may often affect the rectal mucosa and anorectal area simultaneously. In a study of 36 pediatric and adult patients with fistulizing Crohn disease, a cutoff of 2.5 cm on MRI predicted who would respond to infliximab therapy and who would persist with illness.[100] A few studies have reported effective healing rates of 67% to 90% with combined seton and anti-TNF alpha therapy in Crohn disease patients, though these were retrospective.[101][102] A large meta-analysis comparing the healing of primary seton versus infliximab failed to determine which was superior, as the studies varied in outcomes.[103]

Differential Diagnosis

The differential diagnosis for anal fistula includes, first, all common anorectal conditions seen in a primary care provider's office or in a general or colorectal surgeon's office:

• Anal fissure
• Anal warts
• Condyloma acuminate
• Hemorrhoids
• Perianal abscess
• Solitary rectal ulcer syndrome

In addition to these, there are infectious, benign, and malignant processes that may present as or appear as an anal fistula, such as:

• Crohn disease
• Hidradenitis suppurativa
• Anal cancer
• Atypical presentation of anal sexually transmitted diseases can mimic anorectal fistula. Anorectal sexually transmitted infections include syphilis, herpes, gonorrhea, or chlamydia, as well as granuloma inguinale caused by Calymmatobacterium granulomatosis.[25][104][25]
• In HIV positive patients presenting with symptoms of anal fistula, the diagnosis of potential Kaposi sarcoma as well as lymphoma.[105][106]

Prognosis

The prognosis of anorectal fistulas varies depending on etiology. In anal fistulas of cryptoglandular origin, healing rates for simple fistulas approach 80%, and those of complex fistulas are around 60% for sphincter-preserving operations. Setons have been used with much success, achieving healing rates of 80% to 90% after 6 months, but these are measured after 6 months. In general, a fistula that is treated with a fistulotomy or fistulectomy, depending on the wound size, should be entirely healed by 12 weeks. If drainage increases or persists through the twelfth week, the fistula may recur or fail to close completely. Causes for failure of surgical therapy include incomplete division of the fistula in a fistulotomy or incomplete resection or obliteration of the tract in a fistulectomy. In the LIFT procedure, leaving a long fistula tract behind and incomplete ligation of the fistula tract are possible causes of failure. In anal-cutaneous or rectal mucosal advancement flap techniques, if the flap fails, the fistula may recur or not heal properly. Smoking is a risk factor for failure of treatment with flap, as well as Crohn disease.[107] This is often secondary to the inadequate blood supply of the flap, as evidenced by improved healing rates when the muscular layer is used in the flap. 

Failure of anal fistula plugs to allow fistulas to heal can be attributed to several factors, including incomplete internal coverage, incomplete debridement of the fistula tract, and premature dislodgement of the fistula plug. Setons removed too early may lead to the fistula not healing if the tract has not migrated sufficiently to allow it to heal. Some setons may lead to a lower fistula that then requires a fistulotomy for complete healing to occur. 

Depending on the initial procedure performed, additional procedures are used to treat recurrent fistula. When a fistula recurs, an MRI is helpful to determine its course, and an exam under anesthesia should be performed to characterize the fistula tract. Treatment is based on the type of fistula present, which may be different on recurrence than on a complex fistula. Because the risk of incontinence is increased with repeated anorectal surgeries, a sphincter-preserving approach is best utilized in the treatment of recurrent fistula, mainly if a fistulotomy or fistulectomy was the primary treatment. The LIFT procedure is an option for recurrent fistulas. A repeat LIFT, an advancement flap, or a seton may be performed after a failed LIFT procedure. A study that evaluated outcomes of 53 patients who failed the LIFT procedure and went on to undergo an endorectal advancement flap or fistulotomy staged with a seton showed a 50% healing rate.[108] Among patients with a high transphincteric fistula, those with a horseshoe extension may have improved success with anal advancement flap repair.[84]

Setons used as the primary treatment should be considered a staged procedure and followed by a fistulotomy. Anal fistula plug procedure that has failed may be followed by a seton, advancement flap, LIFT, or even fistulotomy, depending on the location of the fistula. A failed flap may be repeated using tissue from a different site. VAAFT is a safe treatment option when repeated after a failed initial VAAFT, with higher healing rates on the repeat procedure.[109]

Complications

Complications of anal fistula surgery include:

• Recurrence of fistula
• Incontinence to flatus or stool
• Chronic draining wound
• Anal stricture

A large meta-analysis examined risk factors for recurrence of anal fistula after fistula surgery, including a high transanal fistula, horseshoe extensions, and multiple fistula tracts, as well as a history of anal procedures or failure to identify the internal opening of the fistula intraoperatively.[110] In a study of 251 patients with high transphincteric fistulas treated with loose setons, a history of fistula surgery, horseshoe fistula, and anterior fistula were risk factors for recurrence.[65]

Risk Factors for fecal incontinence after fistula surgery include a history of anorectal procedures, female gender, complex fistulas, and preoperative incontinence. Fistulotomy should be avoided in fistulas, which are grades 3 or 4 as complex fistulas are associated with higher rates of postoperative incontinence.[111] Performing anal manometry can be helpful preoperatively in determining which patients should undergo a sphincter-sparing approach, as patients who exhibit signs of incontinence before surgery are more likely to have worsened function postoperatively.[112] A history of incisions and drainage or multiple fistula surgery is associated with a higher risk of worsened postoperative sphincter function, as well as the type of operation performed, a fistulotomy or a sphincter-sparing procedure.[113]

Female sex is a risk factor for postoperative incontinence. Treatment of incontinence to flatus and stool involves biofeedback therapy and sacral nerve stimulation. A systematic approach to fecal incontinence has been proposed, with initial treatment consisting of bulking agents and increased dietary fiber, followed by pelvic floor muscle training with biofeedback therapy. If these are not effective, then more invasive options, including surgical sphincteroplasty, magnetic anal sphincter, or implantation of an artificial anal sphincter, may be considered. Only in patients who have exhausted all non-invasive and invasive options is a colostomy offered for recalcitrant fecal incontinence.[114]

The best remedy for any complication is prevention. One way to prevent incontinence is to minimize the number of procedures a patient requires for his or her fistula and to tailor therapy for high-risk patients. Counseling patients preoperatively on the risks of fecal incontinence and obtaining preoperative anal manometry are all useful for stratifying patients preoperatively. Obtaining preoperative imaging to more accurately classify fistulas before surgery should also be considered.

Deterrence and Patient Education

Anal abscesses are a common condition and may result in anal fistula in up to 40% of cases, and the majority of anorectal fistulas are cryptoglandular in origin. Prevention of anal abscesses likely, therefore, decreases anal fistula. Patient education on a healthy diet and exercise to prevent diabetes is an essential component of this. Since anorectal sexually transmitted infections may cause anorectal fistula, education about safe sex practices, particularly in the homosexual community, is a necessary aspect of preventing these diseases.

Educating the general public on the warning signs of Crohn disease, such as weight loss, abdominal pain, bloody diarrhea, or extra-intestinal manifestations, may aid early diagnosis of Crohn disease and, hopefully, with proper medical management, decrease the suffering of this patient population with anal fistula. Expanding access to healthcare is essential to prevent complications of anal abscess, as untreated abscesses are more likely to result in a fistula. Educating patients on proper hygiene and skincare of the perianal region, such as daily showering and washing after soiling, may also help prevent this morbid condition.

Enhancing Healthcare Team Outcomes

Patient-centered care involves the patient in preoperative discussions and in the decision-making process. Educating patients preoperatively may aid decision-making and help manage postoperative expectations. General Surgeons see and manage the majority of patients with anal fistulas; however, involving a colorectal surgeon in complex cases is essential, as they are more specifically trained in these conditions than general surgeons. For example, ACGME requirements for graduating general surgery residents require only 20 anorectal procedures; however, accredited colorectal surgery fellowships require 60 anorectal procedures, including 20 fistula procedures.

Colorectal surgeons are also trained in the treatment of fecal incontinence and thus are better equipped to diagnose and treat this potentially preventable complication. There is evidence that the care of anal fistulas in patients with Crohn disease is improved when a multidisciplinary team is utilized, as these patients often have difficulty obtaining their required medications and other issues with care.[96][115] Coordination between primary care providers and specialists is important for these patients' care and for early diagnosis of anal fistula. 

A Cochrane review published in 2010 showed that concomitant fistula treatment at the time of incision and drainage of abscesses decreased fistula or abscess persistence without increasing complications. There is a shortage of evidence on comprehensive care for fistulas that are not secondary to Crohn disease, but with improved imaging techniques and the knowledge that MRI may alter operative outcomes, coordination between surgeons and radiologists is becoming essential for effective planning for patients with complex disease.

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Disclosure: Mercy Jimenez declares no relevant financial relationships with ineligible companies.

Disclosure: Nageswara Mandava declares no relevant financial relationships with ineligible companies.