A fistula is a tunnel that starts inside the anal canal, traverses (travels across) the anal sphincter muscle (which controls fecal continence), and exits onto the skin, just outside the anus. The underlying cause is most often from a perianal abscess (see our complete discussion on perianal abscesses) or less often from Crohn’s Disease, or OB trauma. Perianal abscesses typically begin as an infection of an anal gland located at the junction of the anus with the rectum. The infection can progress and result in an abscess located under the skin around the anus. These will either drain spontaneously or require surgical drainage. About 30-50% of the time the anal gland responsible for the infection will stay open (internal opening). This allows bacteria to accumulate which will then reform an abscess or drain through the opening in the skin around the anus (external opening).
Diagnosis: Most fistulas are easily diagnosed. Symptoms can be recurrent abscesses, recurrent drainage from one area, or persistent drainage from an area near the anus. On exam, we will see an opening in the skin around the anus (external opening). Occasionally, the tunnel itself can be felt through the overlying skin. While looking into the anal canal, we may be able to see an abnormal appearing anal gland (internal opening). At times, the internal opening is difficult to find in the office and may require an examination under anesthesia.
Classification: Fistulas are classified according to the amount of anal sphincter muscle the tunnel traverses. Fortunately, the great majority of fistulas involve only the lower end of the sphincter muscle, therefore involving only a small amount of the sphincter muscle (low inter or transphinteric fistula). This is of primary importance because the sphincter muscle is responsible for control of defecation so therefore it is important not to cut too much muscle or leakage or incontinence could occur. Because of this it is important that you work with a board certified colon and rectal surgeon who has significant experience in solving this type of problem.
Fistulotomy: This means to open the tunnel from the internal opening to the external opening. By doing this we eliminate the internal opening and open the tunnel for drainage. This allows your body to heal the fistula tract by removing both the source of the infection (internal opening) and the tunnel that allows bacteria to collect and grow. This procedure can be performed when the amount of sphincter muscle involved is small. This is usually performed as an outpatient procedure under local anesthesia with intravenous sedation. For more complex fistulas, other surgical techniques may need to be employed. (see below).
Seton: This is a heavy suture or a latex loop that enters the internal opening and exits the external opening and is tied as a loop. This is used to both stop abscesses from recurring by keeping the tunnel open on both sides, as well as slowly cutting through the muscle in cases where too much muscle is involved by the fistula to cut through at one time. This is typically reserved for either complex fistulae or for patients with multiple fistula due to Crohn's Disease (in this case the seton is kept in place for drainage, not to cut through the muscle). The seton can be tightened gently in the office to reduce the amount of muscle involved in the fistula. Think slow-motion fistulotomy. This is also typically performed as an outpatient procedure under local anesthesia with intravenous sedation. In our practice we tend not to use the seton that often for cutting, because although it works well in preventing incontinence, it can lead to a "gutter" type defect, leading to some leakage in the future.
Fibrin Glue: An alternative to the use of Seton's that we have been using in the practice for several years is fibrin glue. This situation occurs when the fistula tract involves an amount of sphincter muscle that can't be simply divided by fistulotomy, without adverse consequences. The fistula tract is initially scrapped to allow the glue to become adherent to the wall. The "glue" is then injected into the tunnel and the internal opening is closed. Your body then incorporates the glue and seals the tunnel off. The benefit is that no sphincter is divided (therefore no risk of control problems). The downside is the success rate is only about 50%. This is performed as an outpatient procedure under local anesthesia with intravenous sedation.
Endorectal Advancment Flap: This technique involves raising a portion of the rectal lining, sliding it over the internal opening and sewing it in place. This covers the internal opening with healthy tissue and stops bacteria from entering the tunnel. The fistula tract is scrapped out and filled with glue or a drain is left in place for 2-4 weeks. When we sew closed the internal opening and cover it with healthy tissue, the majority will heal. This procedure is reserved for the most complex of fistula tracts. This may be performed under local anesthesia with intravenous sedation or general anesthesia. Hospitalization is usually in order with a 1-2 day stay.
Pre-operative Preparation: For the simpler fistulas we typically will have our patient take two enemas prior to the procedure. The first should be administered about 2 hours prior to leaving for the hospital, and the second is administered about 1 hour prior to leaving for the hospital. It is important to hold the enema for about 5 minutes.
For the complex fistulas that will require an endorectal advancement flap, our patients will typically undergo a complete bowel prep with a clear liquid diet for 24 hours prior to the procedure, along with Fleets Phosphosoda®, and oral antibiotics.