Anal Fistula
What is Anal Fistula?
An anal fistula is an abnormal connection between the lining on the inside of the anal canal (back passage) and the skin near the anus.
Most anal fistulas are caused by an abscess (a collection of pus) which has developed in the anal canal (back passage). Just inside the anus there are small glands. When these glands get blocked, they can become infected and an abscess can develop.
A fistula is a small tunnel that forms under the skin and connects a previously infected anal gland to the skin on the buttocks outside the anus. The pus can drain away onto the skin on its own or by an operation. A fistula happens when the track, made by the pus on the way to the surface of the skin, stays open. Surgery is usually needed to treat an anal fistula, sometimes preceded by an endo anal ultrasound.
Treatment for Anal Fistula
Surgery:
Surgery for anal fistula is performed under a general anaesthetic. To lessen the risk of bowel incontinence (passing a motion without wanting to) treatment may involve several operations over a number of months. The type of surgery needed will depend on where the fistula is and its relation to the muscle that controls the passage of motions call the anal sphincters.
If the fistula is below, or crosses the lower part of the sphincter muscles, your surgeon will cut it open to the skin and leave the wound open so that it can heal with healthy tissue. This is referred to as laying open the fistula.
If the fistula has branches that pass through the upper part of the sphincter muscles your surgeon may place a special stitch called a Seton stitch, in the fistula to allow pus to drain easily. This is done instead of laying open the fistula as this would require cutting a big proportion of the sphincter muscle and therefore damage the continence mechanism of the back passage. By placing a Seton suture the infection is controlled and the body slowly (over many months) heals the tract by trying to push the stitch towards the surface of the skin minimising the scarring and therefore not damaging the sphincters. This may need to be followed by further operations in future, including insertion of a fistula plug.
A fistula plug is an operation where the fistula tract is plugged with a special material to try and block it and allow it to heal without cutting the sphincters.
Endo anal ultrasound
This is a specialist type of imaging. A thin probe is inserted into the anus and rectum. An ultrasound scanner is built into this probe and circumferential images can be taken of the lower most part of the bowel and the anus. This is a very useful addition to a clinical examination and other scans such as MRI.
Endoanal ultrasound is used to look for:
1) Anal fistula
A scan can be very useful in showing the anatomy and direction of the fistula and therefore its relation to the sphincter mechanism of the back passage. This allows decisions to be made about how to best treat the fistula with subsequent surgery.
2) Infection
A scan is very sensitive to looking for pockets of infection or abscesses around the anus.
3) Assessment of large polyps in the rectum
Sometimes prior to surgery for large polyps/tumours in the rectum an Endoanal ultrasound is performed to further characterise the lesion and help plan treatment.
4) Anatomy
Some surgery involves operating on or very close to, the sphincter muscle (the muscle which controls continence). The endoanal ultrasound is very useful in looking at the length and thickness of this sphincter in order to help guide the surgeon through an operation. It can also be used in this role to look for any hidden damage to the muscle, for example following tears during childbirth.
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Basingstoke Colorectal
The Hampshire Clinic
Basing Road
Basingstoke RG24 7AL
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01256 354747