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Anal fistula

What is an anal fistula (aka fistula-in-ano)?

An anal fistula is an abnormal communication between the inside of the bowel (anus) and the external skin around the anus.

What causes an anal fistula?

Most commonly they occur following a perianal abscess. The infection results in a tract between the inside of the anus and the outside where the abscess ruptured or was surgically drained. Patients with Crohn's disease can develop multiple complex anal fistulas.

How do I know if I have an anal fistula?

If you have had a perianal abscess drained and the wound has never fully healed, i.e. you have a small wound that keeps discharging fluid more than one month after the abscess drainage, then you may have an anal fistula. Symptoms include persistent purulent and possibly blood-stained fluid discharge from around the anus. The fistula may dry up for a few days – weeks and then a pressure build up occurs and it ruptures draining externally again.

How to you diagnose an anal fistula?

Usually the diagnosis is suspected clinically after consultation in the office. Confirmation is performed with an examination under anaesthesia (EUA) in the operating theatre. At that time an assessment is performed of the fistula including how much sphincter muscle is involved. This is needed to determine how to heal the fistula. Often a seton drain will be placed through the fistula tract at the time of surgery. For more complex fistulas an MRI scan and/or endoanal ultrasound can be very useful.

What is a seton?

A seton is like a rubber band. It is a narrow silicone band placed through the fistula tract and is tied to itself to stop it falling out. A seton allows the fistula to keep draining externally to prevent recurrence of the abscess.

What are the treatments options for an anal fistula?

Surgery is almost always required for cure. This can involve a fistulotomy (laying open of the fistula tract) where the tract is cut open leaving a wound that gradually scars and heals. This is most effective treatment for healing a fistula (>90% success rates), however cannot be performed if a large amount of sphincter muscle is involved, as division of the muscle can cause incontinence.

Other surgical procedures include a mucosal advancement flap (MAF), ligation of the intersphincteric fistula tract (LIFT), fistula plugs, and more. Often several operations are needed to heal the fistula.