A fistula is a tiny channel or tract that develops in the presence of inflammation and infection. It may or may not be associated with an abscess, but like abscesses, certain illnesses such as Crohn's disease can cause fistulas to develop. The channel usually runs from the rectum to an opening in the skin around the anus. However, sometimes the fistula opening develops elsewhere. For example, in women with Crohn's disease or obstetric injuries, the fistula could open into the vagina or bladder.
Since fistulas are infected channels, there is usually some drainage. Often a draining fistula is not painful, but it can irritate the skin around it. An abscess and fistula often occur together. If the opening of the fistula seals over before the fistula is cured, an abscess may develop behind it.
