(See also Evaluation of Anorectal Disorders.)
Fistulas arise spontaneously or occur secondary to drainage of a perirectal abscess. Most fistulas originate in the anorectal crypts. Predisposing causes include
Fistulas in infants are congenital and are more common among boys.
Rectovaginal fistulas may be secondary to Crohn disease, obstetric injuries, radiation therapy, or cancer.
A history of recurrent anorectal abscess followed by intermittent or constant discharge is usual. Discharge material is purulent, serosanguineous, or both. Pain may be present if there is infection. On inspection, one or more secondary openings can be seen. A cordlike tract can often be palpated. A probe inserted into the tract can determine the depth and direction and often the primary opening.
Diagnosis of anorectal fistula is by examination. Sigmoidoscopy should follow if there is suspicion of Crohn disease (see diagnosis of Crohn disease).
(See also the American Society of Colon and Rectal Surgeons' clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula.)
In the past, the only effective treatment was surgery, in which the primary opening and the entire tract are unroofed and converted into a “ditch.” Partial division of the sphincters may be necessary. Some degree of incontinence may occur if a considerable portion of the sphincteric ring is divided. Alternatives to conventional surgery include advancement flaps, biologic plugs, and fibrin glue instillations into the fistulous tract. More recently, the ligation of intersphincteric fistula tract (LIFT) procedure, where the fistula tract is divided between the sphincter muscles, has gained acceptance as an alternative more likely to preserve continence.
If diarrhea or Crohn disease is present, fistulotomy is inadvisable because of delayed wound healing. For patients with Crohn disease, metronidazole, other appropriate antibiotics, and suppressive therapies can be given (see treatment of Crohn disease). Infliximab is effective in closing anal fistulas caused by Crohn disease.