Anal Fistula

An anal fistula is a communication between the internal anal canal and the skin outside the anus. There are various types of anal fistula and therefore many different treatments. Most anal fistulas can be managed easily. However, complicated ones require a lot of time, effort and thoughtful planning before successful treatment.

Anal fistula is more common in males than females with a ratio of 2:1 to 7:1. There is a maximal incidence between the third and the fifth decades. Fistulas are usually simple and due to an infected anal gland. Uncommonly, more complex fistulas may be secondary to other pathology such as Crohn’s disease.

The presence of a symptomatic anal fistula is an indication for operation because spontaneous healing is very rare. If fistulas are not treated, they can lead to recurrent abscesses and persistent discharge. The aim of fistula surgery is to cure the fistula with the lowest possible recurrence rate and minimal changes in continence. This requires knowledge of the primary track, the site of the internal opening, the amount of sphincter muscles involved and any secondary extensions. For the majority of fistulas, the above factors can be determined easily with clinical assessment. However, radiological investigations are required for complex fistulas prior to operation.

Treatment depends on the nature of the anal fistula. If the track is simple and low, it can usually be treated with a fistulotomy, which involves laying open the track. If the track is high and complex, it is usually treated with insertion of a seton (eg. silk or rubber threads) initially. Once inflammation around the track has settled and further assessment of the track is made, definitive surgery is then carried out to treat the fistula. This is usually in the form of a muscle flap such as a rectal advancement flap or a muscle-filling procedure. Fibrin glue has also been used to treat complex fistulas with some success.

Newer and better techniques are currently underway in the investigation of difficult anal fistulas. Recently, MRI has emerged again as a possible method for accurate determination of the nature of a complex fistula track.