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A fistula is a tract, a tunnel that begins inside the anal canal and burrows through the surrounding tissues out to the skin.
A perianal fistula can be short and superficial, not involving the anal sphincter (submucosal fistula) or can be long and deep, involving the just the internal anal sphincter (intersphincteric fistula) or both anal sphincters (transphincteric fistula or extrasphincteric). Most fistulae are low arising from low within the anal canal. Rarely fistulas are high, arising from above the anal canal (supralevator fistula).
Simple fistulae are those with a single tract that involves less than 30-50% of the external anal sphincter.
Complex fistulae, are those with multiple tracts, those that involve more than 30-50% of the external sphincter, those that involve the anterior half of the anus (in women), any fistula as a result of radiation or Crohn’s disease, and those arising in someone with already compromised sphincter function (i.e. weak anal tone prone to incontinence).
CAUSES OF FISTULA
Most fistulas are formed from an infection in the glands within the anal canal. As the infection spreads to the tissues outside the anus, an abscess forms. When this breaks open, or is drained, a fistula (tract) sometimes remains behind. Other common cause for fistula is Crohn’s disease.
A chronic discharge of malodorous pus from the perianal region is the usual feature of an anal fistula. This is often followed by a period of intense perianal pain that coincides with the time of abscess formation.
The diagnosis is made clinically, and confirmed by an Examination Under Anesthesia (EUA), where a probe is gently inserted into the fistula tract to confirm a communication between the outside perianal skin and the internal lining of the anal canal. Occasionally Endo Anal Ultrasound (EAU) or Magnetic Resonance Imaging (MRI) are needed to determine the number and direction of fistula tracts, and to determine the amount of muscle sphincter involved prior to any planned surgery.
The initial management of a fistula is to drain it. This is a small surgical procedure performed under local anesthesia with sedation where a silastic seton (similar in size and consistency to a rubber band) is passed through the fistula tract and tied in place. This allows any pus to drain, and inflammation to settle. A course of antibiotics may also be required. Within 6-12 weeks, the condition should be much improved, and you will be re-examined by the surgeon. There are 4 options at this point which include:
1. Remove the seton and hope that it heals (Crohn’s disease on biologic treatment)
2. Leave the seton in place awhile longer or indefinitely with or without periodic tightening; (Cutting and loose cutting seton)
3. Remove the seton and lay open the tract cutting the muscle; (Fistulotomy)
4. Remove the seton and remove the fistula tract (Fibrin plugs, LIFT, Advancement flap, and Tissue glue).
Although the wound can take months to heal completely, the pain usually subsides 2 or 3 weeks after the surgery. Nevertheless, pain can be minimized if post-operative instructions are followed properly.
Depending on the type of work you do, you may be able to return to work 2-4 weeks after the procedure.
The following complications can occur, but are not limited to:
(1) Some loss of control over gas or diarrhea based on the procedure:
The most serious involves the loss of some control over flatus (gas) or diarrhea. It usually goes away as the wound fills in and heals. However, permanent loss of some control can occur, requiring a second operation to repair the muscle.
(2) Recurrence of the Fistula:
The fistula can come back and the recurrence rate varies with the procedure.