Anal fistula

Anal fistula, or fistula-in-ano, is an abnormal connection between the epithelialised surface of the anal canal and (usually) the perianal skin.

Anal fistulae originate from the anal glands, which are located between the two layers of the anal sphincters and which drain into the anal canal. If the outlet of these glands becomes blocked, an abscess can form which can eventually point to the skin surface. The tract formed by this process is the fistula.

Abscesses can recur if the fistula seals over, allowing the accumulation of pus. It then points to the surface again, and the process repeats.

Anal fistulas per se do not generally harm, but can be very painful, and can be irritating because of the pus-drain (it is also possible for formed stools to be passed through the fistula); additionally, recurrent abscesses may lead to significant short term morbidity from pain, and create a nidus for systemic spread of infection.

Surgery is considered essential in the decompression of acute abscesses; repair of the fistula itself is considered an elective procedure which many patients elect to undertake due to the discomfort and inconvenience associated with a draining tract.

Symptoms

Anal fistulae can present with many different symptoms:

• Pain
• Discharge - either bloody or purulent
• Pruritus ani - itching
• Systemic symptoms if abscess becomes infected

Diagnosis

Diagnosis is by examination, either in an outpatient setting or under anaesthesia (referred to as EUA - Examination Under Anaesthesia). The examination can be an anoscopy.

Possible findings:

• The opening of the fistula onto the skin may be seen
• The area may be painful on examination
• There may be redness
• An area of induration may be felt - thickening due to chronic infection
• A discharge may be seen
• It may be possible to explore the fistula using a fistula probe (a narrow instrument) and in this way it may be possible to find both openings of the fistula

Treatment

There are several stages to treating an anal fistula:

Definitive treatment of a fistula aims to stop it recurring. Treatment depends on where the fistula lies, and which parts of the anal sphincter it crosses.

There are several options:

• Doing nothing - a drainage seton can be left in place long-term to prevent problems. This is the safest option although it does not definitively cure the fistula.

• Lay-open of fistula-in-ano - this option involves an operation to cut the fistula open. Once the fistula has been laid open it will be packed on a daily basis for a short period of time to ensure that the wound heals from the inside out. This option leaves behind a scar, and depending on the position of the fistula in relation to the sphincter muscle, can cause problems with incontinence. This option is not suitable for fistulas that cross the entire anal sphincter.
• Cutting seton - if the fistula is in a high position and it passes through a significant portion of the sphincter muscle, a cutting seton may be used. This involves inserting a thin tube through the fistula tract and tying the ends together outside of the body. The seton is tightened over time, gradually cutting through the sphincter muscle and healing as it goes. This option minimizes scarring but can cause incontinence in a small number of cases, mainly of flatus. Once the fistula tract is in a low enough position it may be laid open to speed up the process, or the seton can remain in place until the fistula is completely cured.
• Seton stitch - a length of suture material looped through the fistula which keeps it open and allows pus to drain out. In this situation, the seton is referred to as a draining seton.The stitch is placed close to the ano- rectal ring – encourages healing and makes further surgery easy.
• Fistulotomy - till anorectal ring
• Colostomy - to allow healing
• Fibrin glue injection is a method explored in recent years, with variable success. It involves injecting the fistula with a biodegradable glue which should, in theory, close the fistula from the inside out, and let it heal naturally. This method is perhaps best tried before all others since, if successful, it avoids the risk of incontinence, and creates minimal stress for the patient.
• Fistula plug involves plugging the fistula with a device made from small intestinal submucosa. The fistula plug is positioned from the inside of the anus with suture. Small intestinal submucosa stimulates the body to close the fistula from the inside out. According to some sources, the success rate with this method is as high as 80%. As opposed to the staged operations, which may require multiple hospitalizations, the fistula plug procedure requires hospitalization for only about 24 hours. Currently, there are two different anal fistula plugs cleared by the FDA for treating ano-rectal fistulas in the United States. This treatment option does not carry any risk of bowel incontinence. In the systematic review published by Dr Pankaj Garg, the success rate of the Fistula Plug is 65-75%.^[1]
• Endorectal advancement flap is a procedure in which the internal opening of the fistula is identified and a flap of mucosal tissue is cut around the opening. The flap is lifted to expose the fistula, which is then cleaned and the internal opening is sewn shut. After cutting the end of the flap on which the internal opening was, the flap is pulled down over the sewn internal opening and sutured in place. The external opening is cleaned and sutured. Success rates are variable and high recurrence rates are directly related to previous attempts to correct the fistula.
• LIFT Technique is a novel modified approach through the intersphincteric plane for the treatment of fistula-in-ano, known as LIFT (ligation of inter sphincteric fistula tract) procedure. LIFT procedure is based on secure closure of the internal opening and removal of infected cryptoglandular tissue through the intersphincteric approach. Essential steps of the procedure include, incision at the intersphincteric groove, identification of the intersphincteric tract, ligation of intersphincteric tract close to the internal opening and removal of intersphincteric tract, scraping out all granulation tissue in the rest of the fistulous tract, and suturing of the defect at the external sphincter muscle.^[2] The procedure was developed by Thai colorectal surgeon, Arun Rojanasakul, Colorectal Division Department of Surgery, Chulalongkorn University in Bangkok, Thailand. The first reports of preliminary healing result from the procedure were 94% in 2007 ^[3]
• VAAFT Technique: This technique involves use of an endoscope, i.e Fistuloscope and involves two stages. First the scope is introduced thru' external opening and to identify the internal opening where the light is reflected on the anal wall. This is the Diagnostic step. Then a suture [purse string] is taken around the internal opening so as to close it snugly. A semicircular stapler or linear stapler can be used also. Then the fistula tract is debrided with fistula brush and scrappings sent for HPE. A fibrin glue injected near the inner end[now closed] and coagulation of the whole wall is done with the electrode. Simultaneously, the scope is withdrawn and the therapeutic procedure is over.

Infection

Some patients will have active infection when they present with a fistula, and this requires clearing up before definitive treatment can be decided.

Antibiotics can be used as with other infections, but the best way of healing infection is to prevent the buildup of pus in the fistula, which leads to abscess formation. This can be done with a seton - a length of suture material looped through the fistula which keeps it open and allows pus to drain out. In this situation, the seton is referred to as a draining seton.

See also

• Pilonidal cysts/sinuses, another condition in which infected perianal "holes" or openings may appear

References