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Anal Fistula
Anal Fistula
Anal Fistula

The lining of the anus has multiple glands which produce mucus to help lubricate the stools as it passes through. When the opening of the gland becomes blocked, the gland becomes swollen and infected. Like a pimple on the face, the gland can burst through and discharges the infection into the anal canal. For an anal fistula, the gland breaks through to the skin next to the anus instead of breaking back into the anus, thus creating a tunnel.

A fistula is an abnormal connection between two body surfaces. An anal fistula is an abnormal connection or a small tunnel connecting the anal gland from which the abscess arose to the skin of the buttocks outside the anus. As long as the internal opening does not close up, the fistula does not heal on its own.

Some fistulas start as a small pimple around the anus. This bursts and some pus, with or without blood, is discharged. It then heals, but after a period of time, the pimple can form and burst again.

Another way that the fistula may manifest would be after an abscess has been drained. The wound nicely heals initially, but even after a long time, does not close completely. In some cases, the skin heals, but soon, a swelling may appear under the scar, and when the point in the scar bursts, pus comes out.

Most of the time, a history of repeated swelling and discharge can point towards the diagnosis of the abscess, and examination of the area may even reveal the presence of the tract that leads from the skin into the anus. It is quite common that fistulas may get misdiagnosed by the lay person as hemorrhoids, as both can cause pain and some bleeding.

For some complex fistulas, additional imaging such as endoanal ultrasound (by putting a small ultrasound probe into the anus) or magnetic resonance imaging (MRI) may be required to see the entire length of the fistula tract.

Surgery is almost always necessary to cure an anal fistula. The most straightforward fistula surgery is lay open fistulotomy. This entails cutting a small portion of the anal sphincter muscle to open up the entire tunnel, which will then heal from inwards to outwards.

For the deeper tracts, cutting open the muscle is not advisable as this may lead to incontinence. Some methods of treatment would include:
  • 1. Ligation of Intersphincteric Fistula Tract (LIFT) – this entails locating the tract between the two layers of muscle, and separating and tying off the two ends of the tract.
  • 2. Fistula plug – this uses a prosthetic material that fills up the entire tract and allows new tissues to grow into the tract to replace the material, thereby closing up the tunnel.
  • 3. Fibrin glue – this uses a “glue” to seal up the tunnel.
  • 4. Seton – a seton is a stitch (suture) that is placed around the tract. This allows the pus in the tract to come out along the seton, while at the same time, the seton slowly cuts through the muscle below and allows the muscle above it to heal. A second operation may then be required to cut through the rest of the muscles once it is safe enough to do so without risks of incontinence.
  • 5. Video Assisted Anal Fistula Treatment (VAAFT) – this is one of the latest techniques available for treatment of complex fistulas. It allows the surgeon to put a video scope through the opening to look at the entire tract and follow it to the opening on the inside. The opening on the inside is then closed, and the tract is cleaned out using the brush and a probe through the video scope. This has an added benefit that there will be no long cut over the skin.
Although fistula surgery is usually relatively straightforward, the potential for complication exists, and is preferably performed by a specialist in colon and rectal surgery. This operation needs to be done with care, as cutting too much muscle will lead to loss of control of bowel movement. Most of the time, fistula surgery can be performed on an outpatient basis – or with a short hospital stay.

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Ho Kok Sun Colorectal

Colorectal Surgeon

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Mount Elizabeth Medical Centre
#12-09, Singapore 228510

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