Anal Fistula: Symptoms, Causes & Treatment

An anal fistula is a small abnormal channel or tunnel that forms between the inner lining of the anal canal or rectum and the skin surface around the anus. It differs from an anal fissure (a tear) and from hemorrhoids; a fistula is a fixed pathological channel connecting the inside to the outside.

An anal fistula arises in most cases as a result of a previous anal abscess, a collection of pus resulting from inflammation of the small glands inside the anal canal. When the abscess forms and is drained or bursts, a tunnel may remain connecting the source of infection inside to an opening on the skin, forming the fistula. It may sometimes be linked to other diseases such as Crohn's disease or chronic inflammation.

The main symptoms of a fistula are pus-like or bloody discharge from an opening near the anus, with recurrent pain, swelling, and redness, and symptoms may intensify when the opening blocks and a new abscess forms then ease when it drains, in a recurrent pattern. The problem is that a fistula does not heal on its own because the channel remains open, so treatment is surgical in the vast majority of cases. Surgery aims to close the channel and eliminate the infection while taking great care to preserve the continence (sphincter) muscles. The surgical technique varies by the fistula's location and its relationship to the sphincter muscle, so evaluation by a specialized surgeon is essential.

• Pus-like or bloody discharge from an opening near the anus.
• Recurrent pain, swelling, and redness around the anus.
• Irritation and itching of the surrounding skin.
• Sometimes fever when a new abscess forms.

• A previous anal abscess (the most common cause).
• Inflammation of the small anal glands.
• Inflammatory bowel diseases such as Crohn's.
• Sometimes infection, injury, or previous surgery.

• Clinical examination of the area, which usually reveals the fistula opening.
• Imaging (MRI or ultrasound) to determine the fistula's track and its relation to the sphincter.
• Evaluation to rule out Crohn's disease when suspected.

Surgical treatment (most cases)

• Procedures to close the channel and eliminate infection while preserving the continence muscles.
• The technique varies by the fistula's location, depth, and relation to the sphincter.

Supportive management

• Draining an accompanying abscess and antibiotics for infection.
• Treating the underlying disease such as Crohn's when present.

This content is educational and does not replace consulting a gastrointestinal or colorectal surgeon.

• Recurrent abscesses and infection.
• Fecal incontinence if the sphincter is affected (a risk careful surgery avoids).
• The fistula becoming complex and branched if treatment is delayed.

• Treating an anal abscess early and correctly.
• Follow-up after abscess drainage to detect fistula formation.
• Treating causative inflammatory bowel diseases.