Anal Fistula

(Fistula in Ano)

A sinus tract between the rectum and the skin.

Fistulas commonly result from a perianal or ischiorectal abscess caused by inflammation of rectal crypts or glands. Inflammatory diseases (eg, Crohn's disease, tuberculosis, lymphogranuloma) may cause fistulas. Intraperitoneal lesions (eg, diverticulitis, Crohn's disease of the small intestine or colon) may cause fistulas that track into the perineum. Trauma can produce fistulas that track into the vagina.

Symptoms, Signs, and Diagnosis

The main symptom is perirectal pain with pus or blood seen on toilet paper or emanating from an opening on the medial buttock.

Most anal fistulas open near the anus. If the external opening is adjacent to the posterior half of the anus, the tract almost always runs into the rectum exactly in the posterior midline. However, if the opening is adjacent to the anterior half, the tract runs radially into the rectum (Goodsall's rule).

During initial examination, probing the entire tract may be possible, but locating the internal opening is usually difficult until surgery. Because of the many possible causes, microscopic examination of excised tissue is imperative.

Treatment

When the fistula connects with the anorectum just above the anal verge, the tract can be exposed with little risk of damage to the sphincter; this simple procedure is curative. However, when the internal opening is high, a seton (a silk suture or a rubber or polymeric silicone band) should be used to avoid damaging the sphincter and causing incontinence. The seton is passed through the tract into the rectum and is tied. It gradually cuts through the tissues, leading to fibrosis and fixation.