An anal fistula (anorectal fistula) is one of the most common colorectal issues in the U.S. An anal or anorectal fistula is an inflammatory tract or connection between the anal canal and the perianal skin. Classic anal fistulas are the result of a perineal infection and abscess formation. These infections arise from the anal glands, which form a cryptoglandular abscess at the dentate line and then communicate outward to the perianal skin. The abscess or infections can spontaneously drain externally or be drained by a surgical incision and drainage procedure. After the drainage, a chronic tract can form that will intermittently drain or become infected again. Hidradenitis suppurativa, trauma, malignancy, tuberculosis, and Crohn disease can all express as fistulas as well, although these present as atypical fistulas. Initial treatment for all perianal pain and presumed perineal infections is an exam under anesthesia and drainage of the abscess. Over time the abscess should heal, and if there is continued drainage from a punctum or nodule at the perianal skin, then a fistula is presumed. There are multiple types of fistula tracts related to the anatomy through which the fistula courses. The fistula tract can either be deep or superficial to the external anal sphincter. The superficial tracts can simply be opened or unroofed with a fistulotomy to the anal gland, and the tract will heal by secondary intention. The deeper fistulas encompass more of the external anal sphincter and cannot be unroofed as that leads to fecal incontinence. Instead, these tracts should have a Seton (elastic band or heavy suture) placed through the tract, and this allows a slow process to cut through the tract as the deeper parts heal so that incontinence is less likely. A final option for chronic fistulas is a flap closure of the tract with advancement flaps. Patients with complex fistulas pose a challenge to the surgeon. Malignant fistulas will need an interprofessional team approach to rectal and anal cancers, which will involve chemotherapy and radiation therapy. Setons may be used as an adjunct to allow drainage so that abscess formation would not compromise patient care plans. Patients with Crohn disease who have fistula are a challenge. Setons would be the first line of therapy to make sure no abscess or perineal sepsis develops, then adjunct medication like steroids and Infliximab may be used chronically to assist remission of the disease and healing of the fistula tract(s). Hidradenitis suppurative and tuberculosis should be treated with antibiotics, and Setons are adjuncts to make sure the fistulas do not form abscesses during treatment. In some cases, the perineal fistula disease is so severe that fecal diversion with a colostomy assists healing and control of continued perineal infections.
Nottingham, J. M., Rentea, R. M. Anal Fistulotomy (Seton Placement) StatPearls , (2020).