Anal fistula rarely presents as an emergency de novo, but rather as recurrent perianal suppuration. Fistula formation and recurrence following the first presentation of an anorectal abscess occurs in up to 50% of cases, and is more common with bowel-derived organisms such as Echerichia coli and Bacterioides fragilis. Other causes include Crohn’s disease, diverticular disease and, rarely, carcinoma.

A fistula is defined as an abnormal communication between any two epithelium-lined surfaces, in this setting between rectal lumen and perianal skin. Anal fistula is an abnormal tract or cavity communicating with the rectum or anal canal by an identifiable internal opening.


Various classifications of fistula-in-ano or anal fistula have been described. A simple and often used classification is that described by Parks et al. Intersphincteric and transphincteric fistulae are more frequently encountered than suprasphincteric, extrasphincteric, and submucosal types.

chiasmus diagram showing abba pattern
  • Intersphincteric fistula are the sequelae of a perianal abscess. The tract passes within the intersphincteric space (Figure X1).
  • Transphincteric Fistula-in-Ano develop from an ischiorectal abscess. The tract passes from the internal opening through the internal and external sphincters to the ischiorectal fossa (Figure X1).
  • Suprasphincteric Fistula-in-Ano results from a supralevator abscess. The tract passes above the puborectalis after arising as an intersphincteric abscess. The tract curves downward lateral to the external sphincter in the ischiorectal space to the perianal skin (Figure X1). A high blind tract may also occur in this variety and result in a horseshore extension.
  • Extrasphincteric Fistula-in-Ano pass from the rectum above the levators and through them to the perianal skin via the ischiorectal space (Figure X1). 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.
Table X1 | Classification of Anal Fistulas
  1. Simple low tract
  2. High blind tract
  3. High tract with rectal opening
  4. Rectal opening without a perineal opening
  5. Extrarectal extension
  6. Secondary to pelvic disease
  1. Uncomplicated
  2. High blind tract
  1. Uncomplicated
  2. High blind tract
  1. Secondary to anal fistula
  2. Secondary to trauma
  3. Secondary to anorectal disease
  4. Secondary to pelvic inflammation

Fistula-in-ano may also be classified as “simple” or “complex”. Complex anal fistula include transphincteric fistula that involve greater than 30% of the external sphincter, suprasphincteric, extrasphincteric, or horseshoe fistula, and anal fistula associated with inflammatory bowel disease, radiation, malignancy, preexisting fecal incontinence, or chronic diarrhea.

Simple anal fistulae have none of these complex features and generally include intersphincteric and low transphincteric fistula that involve <30% of the sphincter complex. Given the attenuated nature of the anterior sphincter complex in women, fistulae in this location deserve special consideration and may also be considered complex.


  1. 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 defecation, bleeding due to the presence of granulation tissue at the internal opening, swelling or decrease in pain with drainage.

Intermittent swelling, pain and even fever are due to fecal stasis in the tract; spontaneous rupture and drainage will result in improvement. More frequently, in the absence of acute suppuration, a fistula is seen as a draining sinus in the perineal area. A long history may result in the formation of several lateral secondary openings with a “watering-can” appearance.

  1. 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.

Goodsall's rule

According to Goodsall’s rule (Figure X2), an opening seen posterior to a line drawn transversely across the perineum will originate from an internal opening in the posterior midline. An interior 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 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 since 71% of these fistulas tracked to a midline anterior primary opening. This was especially true in women in whom fistulas with anterior external openings tracked in a radial fashion in only 31%.

Digital rectal examination may reveal an indurated cord-like 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. Posterior or lateral induration may be palpable indicating fistulas deep in the postanal space or horseshoe fistulas.

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 with sphincter division. Anoproctoscopy should be done prior to operation in an attempt to identify the primary opening. Sigmoidoscopy, colonoscopy, and CT, MR, or ultrasound imaging should be considered 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 a 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

  1. Imaging

Simple fistula-in-ano generally do not require diagnostic imaging to guide treatment. Alternatively, ultrasound, MRI, or fistulography, has proven useful in the assessment of occult anorectal complex or, in patients with Crohn’s disease, and in patients with recurrent fistulas who have undergone prior fistula surgery.

In a study of 54 patients with perianal Crohn’s disease in which MRI and operative/clinical findings were compared, all of the abscesses and 82% of the fistulas were correctly identified by MRI. In another 2014 study, MRI had a positive predictive value (PPV) of 93% and a negative-predictive value of 90% for anorectal abscess and a sensitivity of over 90% for fistula-in-ano.

Surgical Treatment

Anal fistulas do not heal spontaneously without surgery. As anal fistulas are the result of infection of the anal glands, in 90% of cases the “infecting source” (i.e. the anal gland and duct) must be removed to allow healing of the tract.

A precise definition of the anatomy of the fistula should be obtained before treatment. An approved method is sonography. Surgery must achieve the following goals:

  1. Preservation of continence
  2. As little cicatrisation as possible

Various methods have been described. The choice must be adapted to the course of the tract in relation to the sphincter. In order to avoid subsequent incontinence, it is crucial to know if there has been any sphincter damage, particularly in women; therefore, preoperative sonography is necessary. Even if there is total continence at the time of fistula operation, aging of the muscular system can result in incontinence.

  1. One-Stage Fistulotomy and Fistulectomy

Fistulotomy involves the deroofing or laying open of a fistulous tract along a probe. Fistulectomy consists of the excision of all of the fistulous tract, granulation and dense fibrous tissues. Fistulectomy creates larger wounds and a greater separation of the ends of the sphincter, resulting in a longer healing time and increased risk of incontinence.

Fistulectomy and fistulomy are easy to perform in cases of perineal, intersphincteric and low transsphincteric fistulas. If the fistulous tract crosses the external sphincter, a lay-open technique or fistulotomy results in some sphincter damage, depending on the amount of sphincter that is divided.

  1. Healing by Second Intention

After excision or incision of a fistulous tract, with more or less extensive excision of the skin, and after removing the intersphincteric anal gland, the wound is left open for healing by second intention.

Wounds are irrigated or washed several times a day and dressed by a nurse during the hospital stay or by the patients themselves. The application of petrolated gauze or dressings impregnated with antibiotics or wound-healing medium is not needed.

  1. Primary Suture

There are several reasons why primary suture of wounds resulting from fistulectomy is unsound:

  • A contaminated haematoma may develop and lead to infection and recurrence of a fistula.
  • Exploration of any secondary or deep tract may be difficult.
  • If skin is excised, the suture will be under tension, with a risk of becoming loose.

After excision of the internal opening, partial suture at the level of the pectineal line and anoderm may nevertheless achieve haemostasis, speed up healing time and prevent an anal keyhole deformity. The outer part of the excision is left open to ensure drainage.

  1. Two-Stage Fistulectomy

For transsphincteric fistula in a low or a high location and for suprasphincteric fistulas, a two-stage procedure should usually be planned. In the first stage, the original abscess is exposed within the intersphincteric space. The relationship between the primary tract and the external sphincter and the puborectalis muscle must be determined. If the tract is low and if a sufficient amount of external sphincter is left above, as fistulotomy may be performed in the same session; the fistulous tract may be curetted or cored out. This tract may close spontaneously.

If there are doubts about the amount of sphincter left, the external tract outside the sphincter and within the ischiorectal space is excised widely to allow good drainage. The external sphincter is denuded for 1–2 cm. Seton drainage made of a vessel loop is passed through the tract across the external sphincter and tied loosely. No bridge of skin or anoderm should be left between the anal excision and the ischiorectal incision. The wounds are drained and dressed. The amount of functioning muscle enclosed by the seton is estimated later when the patient is conscious.

  1. Long-Term Seton Drainage

Seton drainage can be left in place for many months. It can represent a definitive treatment in case of Crohn’s disease, preventing recurrent abscess formation. Long-term seton drainage has proved helpful in managing anorectal sepsis secondary to AIDS.

  1. Seton Drainage and Secondary Fistulotomy or Staged Fistulotomy

Seton drainage allows healing of the external wound with fibrous bridging the external sphincter outside the fistulous tract. When complete healing of the external wound is achieved (from several weeks to 6 months later), a fistulotomy may be performed; the muscle may be divided even at the level of the puborectalis sling, preventing the sphincter edges from retracting and minimizing the risk of post-operative incontinence. Special attention is required for female patients.

  1. Cutting Seton

Different techniques have been proposed:

  1. A no. 1 nylon seton suture is fixed to a rubber band anchored to the posteromedial thigh via a safety pin and adhesive tape. The tension on the seton is adjusted for minimal discomfort and maximal effectiveness.
  2. The monofilament seton is replaced by a rubber band. This band is tied progressively every 2-3 weeks to slowly cut the external sphincter and puborectal sling.
  3. The monofilament seton, replaced by a rubber band, is tied every 2–4 weeks using a Barro band ligator.

The aim of such a treatment is to cut the muscular mass surrounded by the seton slowly in a similar way to a wire cutting slowly through an ice cube. By reason of a very high incontinence rate, the cutting seton is inadvisable. Furthermore, this method is very displeasing for the patients.

  1. Fistulotomy and Primary Occlusion of the Internal Ostium with Mucosal Flap Advancement

This procedure consists of a conventional fistulectomy, an opening of the intersphincteric space through a particle excision of the internal sphincter, and occlusion of the former primary orifice of the fistula with mucosal flap advancement. This technique has been used for transsphincteric and for suprasphincteric fistulas.

The complication rate is still high: suture dehiscence of the flap occurs in 9–20%, the recurrence rate varies from 8 to 17%, and significant impairment of continence develops in 21–43% of patients. Continence disorders result from the opening of the intersphincteric space and partial resection of the internal sphincter.

  1. Sliding Flap Advancement

The prevalent procedure for transsphincteric and supralevatoric fistulas is the sliding flap advancement technique. The perianal fistular tract has to be excised funnel-shaped up to the external sphincter. A transanal incision has to be applied distal to the primary orifice and a flap is formed that ideally contains muscular mucosa.

The primary orifice is excised. The intersphincteric space is curetted. The gap through the external and internal sphincters is closed by separate stitches of absorbable material starting from the anal lumen. The size of the flap varies according to different authors. It must have a base twice the width of the apex, but the length should be as short as possible to reduce the risk of ischaemia.

The flap is sutured to the lower edge of the mucosa. The suture line must lie distal to the previous muscle closure. The external wound is left open. If the wound below the pectineal line cannot be completely closed, the flap is sutured to the muscles below the previous opening. No stom is necessary, but a medical treatment with the aim of soft, formed faeces is administrable.

The external wound should be cleansed at least twice daily with saline and disinfectant solution. This technique preserves a greater amount of sphincter than any other; it minimizes star formation, avoids anatomic deformities such as keyhole deformity, and does not require any intestinal diversion. The success rate is very high (Table X1), and if the fistula recurs, the procedure should not be repeated within 3–6 months.

Functional results confirm that this technique does not change the median maximal resting pressure or the resting-pressure profile of the anal canal, because the external sphincter is preserved and no keyhole deformity is created.

Table X1 | Results of sliding flaps in the treatment of anal fistulas
ReferenceYearTreated (n)Success rate (%)
Oh [62]19831587
Wedell et al. [91]19873096
Jones et al. [41]19873969.2
Koscinski and Marti [44]19926997
Oritz and Marzo [64]200010393

The technique is used for chronic fistula; it can also be performed as the second stage after incision and drainage of a fistulous abscess with a seton. This technique has also been advocated in cases of fistula occurring in patients suffering from Crohn’s disease; if anorectal mucosa is only minimally inflamed and if Crohn’s disease is under control with or without reduced amount of steroids, success rates of over 60% can be expected.

  1. Anocutaneous Advancement Flap Repair

According to the sliding flap advancement procedure, the concept arose of sliding the flap from the perianal region orally instead of moving it from the rectum downwards. After excision of the inner fistula orifice, the intersphincteric part has to be ablated. The external fistular tract has to be excised up to the external sphincter ani. A U-shaped flap of perianal skin and adjacent subcutaneous fat is designed for prevention of flap ischaemia.

The gap in the sphincteric apparatus is closed by resorbable suture material and the flap is inserted into the defect. The perianal skin heals by second intent. Although the recurrence rate is quite high (20–25%) and incontinence occurs in 30% of cases, this method remains accepted as therapy for recurrent fistulas when a rectal flap cannot be implemented.

  1. Fistulotomy and Primary Sphincteral Reconstruction

In the case of refractory recurrent fistulas that cannot be incised due to their relationship with the sphinceric apparatus, it is a moot point whether another surgery with a diverting stoma will work out or a fistulotomy be performed. If such a recurrent fistula is treated for a long time with a seton and retention of pus can be expected and the local inflammation is healed. In this situation, a fistulotomy and primary sphincteral reconstruction is the proper option.

  1. Technique for Intramural or Intermuscular Fistura

Intramural or intermuscular fistulas may extend from the pectineal line high up into the rectum. If the tract below the anorectal ring is adequately opened and destroyed, the remaining tract above the ring will close spontaneously. If an abscess is present, a seton drainage may be applied for several days or weeks before the tract is opened. If the intramural abscess constitutes a diverticular extension of a transsphinteric fistula, it must be opened in the first stage of a two-stage fistulectomy.

  1. Extrasphincteric Fistula

These fistulas may have a cryptoglandular origin, but occur more frequently as a result of Crohn’s disease and as a complication of probing too deeply and surgical drainage of an abscess. In the case of Crohn’s disease, a permanent seton should be kept in place for several months to prevent the formation of an abscess and to promote the growth of an epithelial lining.

If the patient does not respond to this treatment or to metronidazole and 6-mercaptopurine, proctectomy must be considered. If the extrasphincteric fistula has a traumatic origin, a sliding flap advancement, or a low anterior resection with coloanal anastomosis must be considered.

  1. Horseshoe Fistula

Horseshoe fistula is one of the most difficult conditions that an anorectal surgeon has to face. The primary fistulous opening is usually in a posterior midline crypt. It not previously drained by a seton, the primary tract is deroofed through a sagittal incision at the tip of the coccyx.

The posterior anal space is opened. The Y-shaped portion of the tract in the postanal space, below the anococcygeal raphe, is excised. The remaining transsphincteric tract is drained with a seton. The secondary openings are excised through radial incisions. The tracts are excised or curetted but not deroofed in order to prevent large scars.

As soon as the lateral wounds have closed, the primary tract may be excised or cored out. This constitutes one of the best indications for a sliding flap in order to prevent any iatrogenic sphincter damage in the posterior midline and any keyhole deformity.

Post-operative Care After Fistulectomy

At the end of an operation for fistula, the wounds are kept apart with a gauze dressing soaked in antiseptic. Baths, showers or wound irrigations are recommended three to four times daily. In order to promote the healing from the depth of the wound, the skin edges should not have made contact so that new fistula information is avoided. The wound must be kept clean.

Application of antibiotics to improve the prognosis is discussed. Better results are expected if the patient was pretreated 5 days preoperatively. A post-operative antibiotic treatment may be reasonable under clean conditions, although the total duration of this therapy remains unclear.

Weekly inspection should be carried out by the surgeon. Pocketing and early bridging of the wounds must be avoided. Silver nitrate may be applied to prevent overgranulation and early bridging. Sphincter function must be evaluated soon after surgery, especially if seton drainage is in place. Bowel action should only be delayed in the case of a sliding flap. Bulky laxatives must be given to allow passage of stools without straining and to reduce pain. Non-steroidal anti-inflammatory drugs are useful to reduce local pain.

Results and Complications After Treatment

Satisfactory results may be achieved in the treatment of anal fistula. Results depend on the type of fistula. The healing time varies from 6 weeks for the low type to 16 weeks or more for the complex variety. Fistula surgery should be reserved for experienced surgeons in order to reduce as much as possible the high incidence of recurrence and prevent continence. Three main post-operative complications may occur after treatment of an anal fistula: recurrence, incontinence and mucorectal prolapsed.

  1. Recurrence

Recurrence of anal fistula in cases of cryptograndular origin is essentially due to failure to remove the correct anal gland. The internal opening may not be found and part of the tract may be buried under the granulation tissue, including the epithelial remnants. A recurrence rate of up to 10% is observed. It is also difficult to assess the adequacy of the initial management from reports in the literature. If a fistula has been adequately treated and still recurs, the possibility of Crohn’s disease must be considered.

  1. Incontinence

Partial early post-operative incontinence is frequent after surgery of any fistulous tract and is the result of inflammation, tissue deformity, pain and the dressing. If the sphincter has been divided, the initial weakness regresses, and continence has proved to be adequate within 2–3 weeks.

As many as one-third of the patients have some permanent disturbance in anal continence, varying from loss of flatus control to severe faecal incontinence.

To prevent incontinence, there must be a sufficient time interval between the two operative sessions in a two-stage procedure. Division of the sphincter muscle must be kept to a minimum. In cases of transsphincteric fistula, a sliding flap is preferable to long and high fistulotomies. The sliding flap procedure reduces the risk of alteration of sphincter function, as proven by clinical and manometric studies. If sphincter division results in persistent incontinence, sphincter repair must be considered.

  1. Prolapse of the Rectum

Mucosal prolapsed frequently occurs after sphincter division below the anorectal ring. The hypertrophic mucosa tends to obliterate the post-operative deformity. This prolapsed is usually asymptomatic and should not be excised. If the anorectal ring has been divided, rectal prolapsed with incontinence may occur. An abdominal rectopexy with suture of the levator ani must be considered.

New and Alternative Procedures

The surgery of anal fistulas is challenging and the results depend on the fistular course in relation to the sphincteric apparatus, the side tracts of the fistulas, the possible underlying disease (Crohn’s disease) and last but not least on the surgeon’s skill. Laying open of fistulas with a transsphincteric course involving a large amount of sphincter muscles is rejected at the expense of better results due to the risk of post-operative incontinence. Therefore, again and again new techniques are proposed.

  1. Local Antibiotic Collagen Treatment

As a fistula before epitheliasation is a chronic inflamed duct, it seems evident that antibiotic treatment will improve the results. In a randomized study with 83 patients, 42 were treated with a gentamycin-collagen sponge placed under the flap and the fistular tract, respectively. No benefit was shown by this treatment compared with the solely surgically treated group.

  1. Fibrin Glue

The idea of duct closure by glue is appealing. However, a precondition of definite healing is the absence of epitheliasation, as is seen in the early stages of anovaginal or rectovaginal fistulas.

Furthermore, the inflammation with its proteolytic processes must not dissolve the glue before time. This method is technically very simple. A fine thread is pulled through the fistular tract and a plastic cannula is placed close to the internal orificium.

After removal of the thread, the fibrin is injected into the duct by the cannula as it is pulled back slowly. The results of this method are not persuasive; although in particular cases a 100% success rate is reported, other authors report 0% success, a result that is consistent with our own experience. Nevertheless, an attempt using glue therapy can be made as there is no morbidity and the option of subsequent surgery is not affected.

The attempt was made to apply fibrin glue as an adjunct to flap repair. A randomized study showed no advantage of this technique.

  1. Fistular Plug

A further very new development is the use of a lyophilized pork submucosa plug (Surgisis AnoFistula Plug). The bioabsorbable xenograft has inherent resistance to infection, evokes no foreign-body or giant-cell reaction and is repopulated with host cell tissue within 3–6 months.

United States Food and Drug Administration approval was given in April 2005. The fistular duct is purified with a disinfectant solution without being enlarged. A thread is pulled through the fistular tract and attached to the tip of the cone-shaped plug. The plug is pulled through the anal canal into the fistula so that the large base is positioned under the internal fistular orifice. This has to be fixed so that the mucosa seals over the plug. Protruding parts have to be cut at the level of the skin. The wound is left open on the external surface.

First results show a promising success rate of 87%. In a randomized study the healing rate was found to be significantly higher than with the fibrin glue procedure. Even in cases of Crohn’s disease, very good results of 80% healing were reported. Unfortunately, recent studies do not indicate as good results.

See also:
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