Anal Fistulotomy 

Updated: Jun 28, 2022
Author: Vassiliki Liana Tsikitis, MD, MCR, MBA, FACS, FASCRS; Chief Editor: Kurt E Roberts, MD 



Anorectal abscess, which can be an incapacitating condition, originates from a cryptoglandular infection in the anal canal. Anal fistula, or fistula-in-ano, is a persistent, abnormal tract from the anal canal to the perianal skin; it is estimated to occur in 50% of patients with anorectal abscess.[1]

Anal fistulae are hollow tracts lined with granulation tissue connecting a primary (internal) opening inside the anal canal to a secondary (external) opening in the perianal skin. Obstruction of anal crypt glands leads to suppuration, which then forms a tract into an anorectal space; the direction taken determines the anorectal abscess location and hence the type of fistula. To understand the different types of anal fistulae (see Technical Considerations), clinicians must be familiar with the different anorectal spaces from which abscesses arise (see the image below).

Anorectal spaces. Anorectal spaces.

Whereas treating an abscess can be rather straightforward, treating an anorectal fistula can be difficult for the surgeon and frustrating for the patient. Treatment of anorectal fistulae also varies according to the location, severity, and chronicity of the fistula tract.


All anal fistulae should be treated surgically. The goal of treatment is to obliterate the internal fistulous opening, including associated epithelialized tracts, with minimal sphincter division (preservation of sphincter function) and prevention of recurrence.

The type of procedure performed depends on the type of fistula (see Technical Considerations). Thus, the first step in surgical treatment is to identify the anatomy, including the external and internal opening, and define the course of all tracts relative to the sphincter muscles. This maneuver almost always requires that the patient be anesthetized. The external opening is usually more apparent, and identifying the internal opening can be challenging.

Many principles and maneuvers have been devised to assist in this task, including the Goodsall rule, which is as follows (see the image below):

  • All fistula tracts with external openings within 3 cm of the anal verge and posterior to a line drawn through the ischial spines travel in a curvilinear fashion to the posterior midline; if the distance between the external opening and anal margin exceeds 3 cm, there is an increased chance of complicated extensions of the fistula tract
  • All tracts with external openings anterior to this line enter the anal canal in a radial fashion
The Goodsall rule. The Goodsall rule.

According to the literature, Goodsall’s rule accurately predicts the location of the internal opening in 49-81% of patients.[2] The external opening location can be a poor predictor of fistula location in patients with long fistula tracts, recurrent fistulae, or Crohn disease.[3, 4, 5]


All symptomatic anorectal fistulae require anal fistulotomy. The only exceptions are in patients with Crohn disease. The primary treatment for perianal Crohn fistulae is medical (eg, immunologic agents), and surgery is reserved for control of perianal sepsis, where less (eg, placement of draining setons) is more.[6]

Technical Considerations


Anatomy of anal canal and surrounding structures

A solid knowledge of the anatomy of the anal canal, the perirectal tissues, and the sphincteric muscles is a prerequisite for any operative treatment of anal fistula.

The surgical anal canal, which is approximately 2-4 cm long, is located between the anorectal ring (a palpable convergence of the internal sphincter, the deep external sphincter, and the puborectalis) superiorly and extends inferiorly to the anal verge (the junction of the anal canal and the hair-bearing keratinized perianal skin). The lining of the anal canal is composed of columnar cells, transitional epithelium, and non-hair-bearing squamous epithelium.

The anal canal is surrounded by two layers of funnel-shaped musculature. The inner muscular structure is the internal anal sphincter, which is the lowermost continuation of the inner, circular muscle layer of the rectum and is under involuntary control. The outer musculature is formed by the puborectalis (innermost fibers of the levator ani) and the external anal sphincter. The external anal sphincter has three parts—subcutaneous, superficial, and deep—and is under voluntary control.

The dentate line, which is about 1-2 cm proximal to the anal verge or the midportion of the anal canal, is the embryologic fusion point between endoderm and ectoderm and marks a separation between innervation, arterial-venous blood supply, and lymphatic drainage. At the level of the dentate line there exists a cryptoglandular complex, consisting of four to eight apocrine anal glands from the intersphincteric space that empty via anal ducts through the internal anal sphincter into the anal canal.

The intersphincteric groove is the space between the internal and external anal sphincters. It can be palpated approximately 1 cm below the dentate line near the level of the anal verge. The anal margin is outside of the anal verge, and is characterized by radial skin folds, thicker skin, pigmentation, and skin with adnexal tissues.

For more information about the relevant anatomy, see Anal Canal Anatomy.

Classification of fistula types

The Parks classification system, which describes the fistula tracts in relation to the anal sphincter complex, defines the following four types of fistula-in-ano resulting from cryptoglandular infections[7] :

  • Intersphincteric
  • Transsphincteric
  • Suprasphincteric
  • Extrasphincteric

Intersphincteric fistulae (see the image below) account for about 70% of all anal fistulae; they usually result from a perianal abscess. The tract extends via the internal sphincter to the intersphincteric space and then out to the perineum. No external sphincter is involved. Other possible tracts include a blind tract with no perineal opening and a high tract to the lower rectum or pelvis.

Intersphincteric fistula. Intersphincteric fistula.

Transsphincteric fistulae (see the image below) account for about 25% of all anal fistulae; they usually arise from an ischioanal abscess. The tract traverses both internal and external sphincters and passes into the ischiorectal fossa and then to the perineum. Other possible tracts include a high tract with perineal opening and a high blind tract.

Transsphincteric fistula. Transsphincteric fistula.

Suprasphincteric fistulae (see the image below) account for about 5% of all anal fistulae; they usually result from a supralevator abscess. The tract arises in the intersphincteric space and courses superiorly above the puborectalis into the ischiorectal fossa and then to the perineum.

Suprasphincteric fistula. Suprasphincteric fistula.

Extrasphincteric fistulae (see the image below) account for only about 1% of all anal fistulae. Causes include iatrogenic injury from probing or penetrating injury to the perineum or rectum, Crohn disease, and carcinoma (or treatment thereof). The tract passes from the rectum above the levators and through the levator ani muscles to the perianal skin completely outside the sphincter mechanism.

Extrasphincteric fistula. Extrasphincteric fistula.

Additionally, anal fistulae can be classified as either simple or complex, as follows[5] :

  • Simple fistulae include intersphincteric fistulae and low transsphincteric fistulae that cross less than 30% of the external sphincter
  • Complex fistulae include high transphincteric fistulae (with or without a high blind tract), suprasphincteric fistulae, and extrasphincteric fistulae, in addition to recurrent fistulae; rectovaginal fistulae, fistulae involving multiple tracts, and anterior fistulae in women (higher risk for postfistulotomy incontinence); and fistulae associated with inflammatory bowel disease, radiation, malignancy, or preexisting incontinence

Periprocedural Care


Equipment required for anal fistulotomy may include the following:

  • Local anesthetic
  • Fistula probes
  • Methylene blue, hydrogen peroxide
  • Seton (Silastic vessel loop, suture)
  • Additional equipment, depending on the specific approach employed (fibrin glue or plug, bioprosthetic plug)

Patient Preparation

Local anesthesia (0.25% or 0.5% bupivicaine with 1:200,000 epinephrine injected circumanally and submucosally) with intravenous sedation can be used. General anesthesia may be required for airway control issues.

The patient is placed in a prone jackknife position, with the buttocks gently taped apart to afford better exposure.



Approach Considerations

No single technique is appropriate for the treatment of all anal fistulae. Treatment choice is tailored to the individual patient and fistula, specifically directed by the etiology and anatomy of the fistula, the severity of the symptoms, the patient's comorbid conditions (if any), and the surgeon's experience.

Treatment of fistula-in-ano is challenging. To improve healing rates, a clear understanding of the anatomy and accurate delineation of the tracts of the fistula with any potential extensions are paramount. Stem cells (see below) may provide a safe, successful approach to this difficult medical issue; however, available data are limited, and studies remain in progress.

Future directions

Adipose-derived stem cells

The potential treatment for fistula-in-ano with adipose-derived stem cells (ADSCs) has been explored by few international groups. In a pilot trial, expanded ADSCs (eADSCs) were obtained from subcutaneous fat by means of liposuction, a process that yields more stem cells than bone-marrow aspiration.[8] The technique is described as including the following steps:

  • Identification of the fistula tract and internal opening
  • Curettage of the fistula tract and suture closure of the internal opening
  • Injection of the suspension of stem cells into the walls and tract of the fistula
  • Sealing of the tract with fibrin glue

It has been thought that the biologic properties of eADSCs would suppress inflammation and enhance wound healing. Initial results were promising, with 71% of recipients reporting closure of the fistula; however, the healing rate decreased from 62.5% to 33% at 1 year and 3 years after the procedure. Although injection of eADSCs provides a rather safe treatment without a substantial risk of incontinence or any other adverse effects, it does not seem to yield better healing results than application of other biomaterial products.

Anal Fistulotomy

The first surgical step is to classify the fistula type by identifying the primary and secondary openings. Examination under anesthesia may be all that is needed to identify the internal opening. A probe can then be gently passed through to the external opening to define the tract. This maneuver almost always requires that the patient be anesthetized.

Care must be taken in passing a probe from an external opening to an internal one; this step can result in iatrogenic injury and creation of a false tract. Goodsall’s rule can help in guiding this maneuver. Diluted methylene blue, hydrogen peroxide, or both can be injected into the external opening to facilitate identification of the internal opening at the dentate line.

Once the anatomy is defined as either simple or complex, the techniques discussed below may be employed. In general, complex fistulae are treated with more conservative approaches because fistulotomy is associated with a high incidence of postoperative incontinence.

Surgery for simple fistula-in-ano

Simple fistula has been defined by the American Society of Colon and Rectal Surgeons (ASCRS) as having the following characteristics[5] :

  • Includes a single, nonrecurrent tract that crosses less than 30% of the external sphincter
  • Is not an anterior fistula in women
  • Occurs in patients without impaired continence, a history of Crohn disease, or previous pelvic irradiation.

These fistulae, which include intersphincteric and low transsphincteric fistulae, are typically treated by means of primary fistulotomy (also known as the "lay open technique"), which results in resolution of symptoms in 90% of patients.

A probe is inserted into the tract, and the overlying tissue is then divided. Division of the internal sphincter alone does not usually compromise fecal continence. The base of the wound is then curetted and left open to heal by secondary intention. Marsupialization can be performed and may improve the rate of wound healing, as well as decrease bleeding potential.[1, 9] Fistulectomy (fistula tract resection) is associated with larger defects, longer healing time, and higher risk of incontinence without lower recurrence rates. Supplemental treatments with sitz baths and fiber therapy can improve healing after fistulotomy.

Surgery for complex fistula-in-ano

Complex anal fistulae may include high transphincteric fistulae, suprasphincteric fistulae, extrasphincteric fistulae, and fistulae with various associated comorbid conditions.

A number of treatment options may be considered. Seton placement is commonly employed. Continence-preserving approaches include the following:

  • Fibrin glue
  • Anal fistula plug
  • Endoanal or endorectal advancement flaps
  • Ligation of intersphincteric fistula tract (LIFT) procedure

These continence-preserving procedures are associated with relatively high recurrence rates (30-50% overall).[10]

Seton placement or staged fistulotomy

A seton, which can be a nonabsorbable suture, a rubber band, or a Silastic vessel loop, is passed through the fistula tract and secured to itself externally. The use of cutting setons, in which the seton is progressively tightened in the office until it eventually cuts through the fistula tract (see the image below), can also be considered.

Seton. Seton.

In the treatment of complex fistulae, setons are usually placed loosely to allow drainage and control sepsis, and seton placement is then followed by a secondary procedure (eg, endoanal advancement flap, fibrin glue, or plug) to avoid division of the sphincter muscle.

Postoperative continence changes range from 0% to 54% in patients treated with two-stage procedures or cutting setons, and incontinence to flatus is more common than stool incontinence.[11, 12, 13]

Fibrin glue

Fibrin glue is easy to use, avoids sphincter division, can be repeated with low risk, and does not preclude the use of other methods of treatment.

The procedure starts with identification of the internal and external openings of the fistula tract. The tract is cleaned and debrided with a curette or gauze. A commercially available preloaded syringe is introduced into the tract, and fibrin glue is slowly injected until it is seen exuding from the internal opening. Time is usually given to allow the reaction to stabilize the clot.

Although early results were promising, recurrence was found to be common. In a randomized controlled trial by Lindsey et al, fibrin glue was associated with higher healing rates (69% vs 13%) than conventional treatment (fistulotomy or loose seton with or without subsequent advancement flap) for complex fistulae.[14] In nonrandomized studies using fibrin glue for complex disease, overall healing rates ranged from 10% to 67%.[15, 16, 17, 18]

Despite fibrin glue's relatively low success rate in complex disease, its low morbidity makes it worth considering for initial therapy.

Anal fistula plug

The bioprosthetic anal fistula plug, manufactured from porcine small intestine, is used to close the primary internal opening. It serves as a matrix for the obliteration of the fistula tract (see the image below).

Fistula plug technique. Fistula plug technique.

After identification of the internal and external openings of the fistula, the tract is cleaned and debrided with a curette or gauze. The conical plug is pulled, starting from the internal opening with the narrow end first, into the tract until the internal opening is blocked. It is then sutured into place. The external opening is not completely sealed, so as to allow continued drainage of the fistula.

This technique has inherent appeal in that it is simple to perform and avoids sphincter division. It seems to work best with long tracts without active sepsis. Success rates in the limited studies vary but are usually lower than 50%.[19, 20]

Endoanal or endorectal advancement flaps

The goal of advancement flap procedures for anal fistulae is to obliterate the internal opening and leave the tract and external opening to drain and heal secondarily while avoiding sphincter division.

The first step is identification of the openings, followed by curettage of the tract. Any fibrous tissue around the internal opening is excised. The incision is begun distal to the internal opening. A segment of proximal healthy anorectal mucosa, submucosa, and some muscle is mobilized to allow tension-free coverage of the internal opening. To maintain the blood supply, the base of the flap should be twice the tip of the flap. The distal tip harboring the fistula opening is then excised. (See the image below.)

Anorectal advancement flap. A) Transsphincteric fi Anorectal advancement flap. A) Transsphincteric fistula-in-ano. B) Enlargement of external opening and curettage of granulation tissue. C) Mobilization of flap and closure of internal opening. D) Suturing of flap covering internal opening.

Healing is observed in 66-87% of patients, with recurrence rates ranging from 13% to 56%.[5, 9]

Ligation of intersphincteric fistula tract (LIFT) procedure

The LIFT procedure is a sphincter-sparing approach that involves ligation and division of the fistula tract in the intersphincteric space.

A seton is usually placed weeks before the operation to allow fibrosis of the tract. The procedure begins with a curvilinear incision in the intersphincteric groove. The fistula tract is identified and dissected out. The fistula tract next to the internal opening is ligated with absorbable suture. The lateral tract is curetted and then suture-ligated externally to the first ligation site. The tract is divided, and the remnant of the tract or infected gland is removed. Tract division is confirmed by injection or probing. The external opening can be widened for drainage if needed.

Success rates have ranged from 61% to 94%, with little morbidity, a healing time of 4-8 weeks, and only rare occurrences of fecal incontinence. The LIFT procedure can be used for simple or complex fistulae. Factors associated with LIFT failure include a fistula tract length greater than 3 cm, obesity, and previous fistula procedures.[9, 21]

Modifications to the originally described procedure above include omission of tract excision, advancement flap, fibrin glue, or anal plug at time of LIFT.

Comparisons of these procedures have been performed retrospectively, but prospective randomized data is needed to determine the optimal treatment.[22] Overall, LIFT is technically a more challenging procedure than the other available options, but it has the advantage of allowing treatment of a fistula without any division of the sphincter.


Results of fistula surgery can vary considerably, depending on the chronicity and the complexity of the fistula and on the experience of the surgeon.

Patients with high transsphincteric fistulae and females with anterior fistulae present complex problems to the surgeon, in that postoperative incontinence rates after fistulotomy can be significant.[23] As a general rule, the internal sphincter and about 30% of the external sphincter can be sacrificed in the posterior quadrant, as long as the puborectalis is not compromised. Not all patients, however, have the same quality of sphincter function; results may therefore vary.

Preoperative anorectal physiology tests, such as endoanal ultrasonography and anorectal manometry, can delineate the anatomy of the sphincteric complex and may predict the functional outcome of fistula surgery.[24]