Anal fistulas are small channels or connections that form between the rectum and skin near the anus. Anal fistulas often develop from an acute infection of an anal gland, located inside the anal opening. The infection causes an abscess to form, which then develops into a fistula or channel leading from the gland to an opening on the skin around the anus.
Anal fistulas may also be caused by surgery, Crohn's disease, radiation therapy, sexually transmitted disease, and other conditions.
Anal fistulas may appear as swollen inflamed sores near the anus from which pus, clear liquid, stool, or blood may drain. They may also appear as a painful lump near the anus and can be accompanied by signs of an infection such as fever or chills.
Individuals with an infection of the anal gland, and/or an abscess often develop fistulas. Individuals with Crohn's disease have a tendency to develop anal abscesses and fistulas.
Fistulas must be carefully diagnosed to determine their exact internal location. A physician will usually use a small instrument known as an anoscope to view the anal canal. If the fistula is complex or in an unusual spot, a contrast solution or dye may be injected into the fistula to display its path or imaging studies such as an MRI or endorectal ultrasound may be used.
In order to rule out Crohn's disease or ulcerative colitis, a colonoscopy or sigmoidoscopy may be used to view a larger part of the colon.
Most fistulas require surgery to drain the area of infection using a seton or a fistulotomy. For a fistulotomy, the fistula is surgically opened, flushed out, and stitched open or left as is to heal. Depending on the location of the fistula, there can be a minimal risk of developing minor fecal incontinence with fistulotomy.