A fistula is an abnormal connection between two bodily surfaces. An anal fistula is an abnormal tract that forms between the anal canal (interior of the anus) or rectum and the skin around the anus. It usually manifests initially as a perianal abscess (collection of pus near the anus).
What cause anal fistula?
An anal fistula normally starts when an anal gland becomes blocked and infected. Instead of breaking back into the anus, the infection breaks through to the skin next to the anus and creates a tunnel. As long as this internal opening stay open, the fistula usually will not heal. An anal fistula may also occur following the draining of an abscess, mainly because the internal opening was not obvious at that time and was not treated.
What are the symptoms?
Some fistulas start as a small pimple around the anus. This bursts and pus and/or blood are discharged. It then heals, but the pimple can form and burst again after some time. A fistula may also develop after an abscess has been drained. The wound heals well initially, but it may not close completely even after a long time. In some cases, though the skin heals, swelling would occur under the scar and pus gets discharged when the scar bursts.
How is it diagnosed?
A history of repeated swelling and discharge can point towards the diagnosis of a fistula, and an examination of the area may reveal the presence of the channel that leads from the skin into the anus. In some complex cases, additional imaging such as endoanal ultrasound or magnetic resonance imaging (MRI) may be required to see the entire length of the fistula tract to plan for treatment.
What are the treatment options?
Surgery is often necessary to cure an anal fistula, with the most straightforward procedure being lay open fistulotomy. The surgeon does this by cutting a small portion of the anal sphincter muscle to open up the entire tunnel, which will then heal from within. For deeper fistulas, this method is not suitable due to the potential risk of incontinence. Alternative methods include:
- Ligation of intersphincteric fistula tract (LIFT): dividing the tract as it passes between the two layers of sphincter muscles
- Fistula plugs: using a prosthetic material to fill up the tract and allow the growth of new tissues to replace the material
- Fibrin glue: a non-surgical treatment option, where the glue is injected into the fistula to seal the tract
- Seton: placing a suture (seton) around the tract to facilitate controlled drainage of the pus in the tract; this is only a temporary measure to clear the infection
- Video-assisted anal fistula treatment (VAAFT): inserting a videoscope through the opening to view the entire tract, and closing the internal opening, which comes with the added benefit of not having to make a long incision over the skin