Types of Fistula

Fistulas are classified by where they run in relation to the sphincter muscles that control the anus. The type decides which treatment is safe.

Parks classification of anal fistula

• Intersphincteric. Runs in the space between the inner and outer sphincter muscles. The most common type.
• Transsphincteric. Crosses both sphincter muscles to reach the skin. Treatment needs more care to protect continence.
• Suprasphincteric. Goes up over the top of the sphincter and then down. Less common.
• Extrasphincteric. Lies outside the sphincter muscles. Rare and complex.

Simple versus complex

• Simple (low) fistulas cross little or none of the sphincter muscle and are easier to treat.
• Complex (high) fistulas cross a large amount of muscle, have several tracts, or are linked to Crohn's disease, previous radiation or recurrent disease. They carry a higher risk of recurrence and incontinence.

Other kinds of fistula

The word fistula is also used for other abnormal connections, such as between the bowel and bladder, the vagina and the rectum, or arteries and veins in dialysis. These need their own assessment.

How types are found

A surgeon examines the area and may use an MRI scan or an endoanal ultrasound to map the tract. Sometimes an examination under anaesthesia is needed.

Ayurvedic classification

Classical texts describe several bhagandara types, such as shataponaka and ushtragriva. These names are traditional and do not map neatly onto modern types, so they are not a basis for choosing treatment.

Knowing the exact type helps the surgeon choose the safest operation.