Figure 70-19. Goodsall’s rule for anal fistula.

Management

Options in the surgical treatment of an anal fistula include fistulotomy, cutting seton, fibrin glue,

collagen plug, ligation of the intersphincteric fistula tract (LIFT), and advancement flaps. Specific

treatment is dictated by the path of the fistula and the amount of sphincter complex that is involved in

the tract. Any division of the sphincter muscle during treatment of a fistula carries with it a risk of

impaired continence. Patients at higher risk of incontinence include those with pre-existing impaired

continence (elderly patients and women with a history of episiotomy) and patients with chronically

loose stools (colitis and Crohn’s disease). The location of the fistula is also important; the sphincter

complex is shorter anteriorly in women, and division of muscle here is particularly risky.

Simple submucosal, intersphincteric, and low transsphincteric fistulas may be managed with

fistulotomy with very low risk of postoperative incontinence. Under regional or general anesthesia, the

patient is placed in the prone jack-knife position. A fistula probe is inserted from the external opening to

identify the internal opening at the dentate line. If there is no significant muscle overlying the probe,

the tissue is incised and any granulation tissue is curetted. The wound is left open to heal by secondary

intention, or the wound may be marsupialized by suturing the wound edges to the tract.

Fistulas that involve a significant portion of the sphincter muscle (high transsphincteric and

suprasphincteric fistulas) are better managed in a staged fashion with the use of a seton. A seton is a

suture or vessel loop that is passed through the fistula tract and is tied to itself to form a ring between

the internal and external openings. The purpose of this is to facilitate drainage of the fistula and

promote wound contracture. Setons may be used as a bridge to a more definitive procedure, or may be

used in a “cutting” fashion. A cutting seton is tightened at regular intervals, gradually cutting through

the sphincter muscle. In theory, this leads to fibrosis of the sphincter muscle rather than a retracted

defect. This may be continued until the fistula has completely resolved, or a staged fistulotomy may be

performed to divide the remaining sphincter muscle.

In an effort to minimize postoperative incontinence, fibrin glue and collagen plugs have been used in

the treatment of anal fistulas. The mere existence of this plethora of therapeutic alternatives attests to

the lack of satisfactory efficacy with all of them. Fibrin glue is made of a combination of fibrinogen,

thrombin, and calcium. Injection of this into the fistula tract is thought to induce clot formation and

promote the growth of collagen to close the fistula. Short-term success rates have been reported as high

as 70%, however late recurrences despite initial healing are common.16 Fistula plugs made of porcine

submucosal collagen inserted into the fistula tract are intended to provide a scaffold for the growth of

fibroblasts to heal the fistula. Long-term healing with fistula plugs has also been disappointing, with

success rates of only 30%,17 however, success rates may be higher in long fistula tracts.

LIFT is a surgical technique that avoids division of the sphincter complex. With the patient in the

prone jack-knife position, a probe is passed through the fistula tract. An incision is then made in the

intersphincteric groove directly overlying the probe, and plane between the two muscles is dissected.

The fistula tract is then divided and ligated between the internal and external sphincter muscles. Success

with this procedure has been reported as high as 88%.18 If the LIFT procedure fails, the fistula often

recurs in the intersphincteric plane, thereby allowing treatment with a fistulotomy.

The use of endorectal advancement flaps has been advocated for high transsphincteric and

suprasphincteric fistulas, fistulas associated with inflammatory bowel disease, fistulas in patients who

have failed other treatments, and anterior fistulas in female patients. In this procedure, the fistula tract

is either cored out or curetted, and the internal opening is identified and excised. A full-thickness flap of

rectal mucosa and submucosa is raised and advanced, typically 1 cm below the level of the internal

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opening. It is important to maintain adequate blood supply by creating a flap, the base of which is twice

the width of the apex. Successful healing following an endorectal advancement flap has been reported in

as high as 90% of patients, although much lower in patients with Crohn’s disease and/or receiving

steroids.19

Anal Fistula Associated with Crohn’s Disease

Treatment of anal fistulas in patients with Crohn’s disease can be particularly challenging. Surgical

treatment of these fistulas is associated with poor wound healing and the risk of sphincter injury.

Medical treatment of the underlying Crohn’s disease is therefore extremely important in improving the

chance of fistula healing. Antibiotics such as ciprofloxacin and metronidazole have been shown useful; 8

weeks of oral metronidazole has reportedly eliminated drainage, erythema, and induration in up to 80%

of patients.20 Treatment with azathioprine and methotrexate have been shown to have little impact on

fistula healing. Infliximab, a monoclonal antibody against tumor necrosis factor-α, has been shown to be

effective in Crohn’s anal fistulas. Treatment with infliximab alone has been shown to reduce the number

of draining fistulas by half in 62% of Patients with Crohn’s disease (compared with only 26% of patients

treated with placebo).21 When combined with surgical intervention, fistulas in patients treated with

infliximab may heal faster than those treated with surgery alone.22

Surgical intervention in patients with Crohn’s anal fistulas should be conservative and limited initially

to adequate drainage with liberal use of draining setons. Although fistulotomy for subcutaneous fistulas

may be considered, active Crohn’s disease within the rectum is associated with poor outcomes. Due to

the high likelihood of recurrence or the development of additional fistulas, any division of the sphincter

muscle should be avoided. Once any infection has been drained and the underlying Crohn’s disease has

been optimally controlled with medication, repair with either an endorectal advancement flap or LIFT

may be an option. In rare cases of Crohn’s anal fistulas, fecal diversion with a stoma or proctectomy

may be warranted.

Rectovaginal Fistula

A rectovaginal fistula is a communication between the anterior wall of the anal canal or rectum and the

posterior wall of the vagina. Obstetrical injury is the most frequent cause of acquired rectovaginal

fistulas, however trauma, infection, and radiation may also result in their development (Table 70-3).

Rectovaginal fistulas can be classified according to their location (Fig. 70-20). In low fistulas, the rectal

opening is at or below the dentate line; in high fistulas, the vaginal opening is at or near the cervix. A

second classification system is based on the location, size, and cause of the fistula (Table 70-4).

Figure 70-20. Rectovaginal fistula classified by location. Fistulas are low when located at or just cephalad to the dentate line, high

when near the cervix, and mid when located in between.

ETIOLOGY

Table 70-3 Causes of Rectovaginal Fistula

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