Fistula in ano or anal fistula is an abnormal opening on the buttocks other than the natural opening. This is usually the result of a previous or a present abscess which has failed to heal completely. It is more like a small bypass with 1 opening inside the anal canal and other outside on the skin of buttock. Fistulas can be broadly classified as Simple and Complex.
In most of the cases fistula is a sequel of a previous abscess or pus cavity. The pus formation is the result of an anal gland infection. When this abscess fails to heal completely, with or without treatment, a fistula develops. This track will get some stool pieces entering the track from time to time leading to infection and pus/ mucus discharge again and again this makes it a non-healing wound.
There is another opening in the buttock’s skin other than the natural opening. There is Pus discharge on and off; itching and redness around the opening.