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Anal Abscess & Fistula

-Connie Pennington, MD


An anal fistula is a tract, or abnormal tunnel, that usually results from an anal abscess. There are several anal glands that line the anal canal. Anal glands produce mucus secretions to aid with bowel movements. When one of these glands becomes obstructed with fecal material and bacteria, or simply closed off, it can build up pressure and generate an anal abscess. An anal abscess presents with pain, pressure, and swelling that will either rupture spontaneously or need to be surgically drained. About 50% of these abscesses heal completely while the other 50% go on to form an anal fistula. A fistula in an abnormal tract between a gland inside the anal canal and the outside skin around the anus. They behave like a tunnel between the rectum and the skin that permits leakage and bleeding. The skin will frequently heal over and then build up pressure until drainage occurs again. This cycle may repeat itself every 4-5 weeks with intermissions. 


An anal abscess usually presents with anorectal pain, swelling, and fever. Spontaneous drainage may occur. Occasionally, rectal bleeding or urinary symptoms, such as trouble initiating a urinary stream or painful urination, may be present. Failure of an abscess to heal completley commonly presents with recurrent pain and sewelling followed by drainage. Fistula symptoms often cycle through weeks of building up pressure and draining and then acting as if they are healing for a few weeks only to have the cycle repeat itself.


A careful history regarding anorectal symptoms and past medical history are helpful, followed by a physical examination. Physical examination often reveals an external opening near the anal canal, that drains pus or blood, or may simply look like a dimple on the skin surface. In some cases there may be no external manifestation of an abscess, other than tenderness. A digital rectal exam may cause  pain and produce pus from the external opening. Some fistulas will close spontaneously and the drainage may be intermittent, making them hard to identify at the time of the office visit.

Classification of Anal Fistula

Anal abscesses are classified by their location in relation to the structures comprising and surrounding the anus and rectum: perianal, ischioanal, intersphincteric and supralevator. The perianal area is the most frequent and the supralevator the least. If any of these particular types of abscess spreads partially circumferentially around the anus or the rectum, it is termed a horseshoe abscess.

Fistulas are classified by their relationship to parts of the anal sphincter complex (the muscles that allow us to control our stool). They are classified as intersphincteric, transsphincteric, suprasphincteric and extrasphincteric. The intersphincteric is the most common and the extrasphincteric is the least common. These classifications are important in helping the surgeon make treatment decisions.

Diagnostic Studies

Most anal abscesses and fistula are diagnosed and managed on the basis of clinical findings. Occasionally, additional studies can assist with the diagnosis or delineation of the fistula tunnel. Anal ultrasound and CT scan can be used to further define an anal fistula, particularly a complex horseshoe variety, or those associated with inflammatory bowel disease. 

Treatment of Anal Fistula

Antibiotics alone are a poor alternative to drainage of the infection. Treatement of anal abscesses should always begin with surgical drainage. The quicker an abscess in drained, the less likely a fistula will develop. The routine addition of antibiotics to surgical drainage does not improve healing time or reduce the potential for recurrences in uncomplicated abscesses. There are some conditions in which antibiotics are indicated, such as patients with compromised or altered immunity or in the setting of extensive cellulitis (spreading of infection in the skin). The American Heart Association recommends the use of antibiotics for patients with prosthetic valves, previous bacterial endocarditis, congenital heart disease and heart transplant recipients with valvular pathology. A comprehensive discussion of your past medical history and a physical examination are important to determine if antibiotics are indicated. 

Surgical Treatment

Surgery is almost always necessary to cure an anal fistula. If the fistula is straightforward (involving minimal sphincter muscle), a fistulotomy may be performed. This procedure involves connecting the external opening with the internal opening and unroofing the tract, thereby excising the fistula and creating a groove that will heal from the inside out.

The surgery may be performed at the same time as drainage of an abscess, although sometimes the fistula doesn’t appear until weeks or years after the initial drainage. Fistulotomy is a long-standing treatment with a high success rate. This high success rate must be balanced, however, with the potential changes to a patient’s continence (ability to control stool), as the more anal sphincter muscle is divided in a fistulotomy, the greater the risk of changes in continence. Therefore, the surgeon must assess whether a fistulotomy is appropriate for a given patient.

In addition to fistulotomy, there are a number of other surgical treatment options for anal fistula which do not involve division of the sphincter muscles. Fibrin glue injection is one such option, in which fibrin glue is injected into the fistula tract to obliterate the tract with the intention of becoming incorporated in the surrounding tissue. It has the advantage of avoiding dividing any sphincter muscle, thereby preserving continence. While there is a relatively high failure rate with this approach, it does not “burn any bridges” (risk affecting continence) and may be repeated.

An anal fistula plug is an elongated piece of material that is placed throughout the length of the fistula tract to fill the tract space and incorporate itself into the tissue around it. The plug also has the advantage of not requiring division of the sphincter muscle. However, like the fibrin glue, it has a relatively low success rate, with the majority of studies reporting success less than 50%.

An endoanal advancement flap is a procedure usually reserved for complex fistulas or for patients with an increased potential risk for suffering incontinence from a traditional fistulotomy. In this procedure, the internal opening of the fistula is covered over by healthy, native tissue in an attempt to close the point of origin of the fistula. Recurrence rates have been reported to be up to 50% of cases. Certain conditions, such as Crohn’s disease, malignancy, radiation history and previous attempts at repair, increase the likelihood of failure. Smokers also are less likely to heal in the anal area. Although the sphincter muscle is not divided in this procedure, mild to moderate incontinence has still been reported.

Most of the operations can be performed on an outpatient basis, but in selected cases, may require hospitalization. Consider identifying a specialist in colon and rectal surgery who will be familiar with a number of potential operations to treat the fistula.

​Placement of a Seton

If a significant amount of sphincter musculature is involved in the fistula tract, a fistulotomy may not be recommended as the initial procedure. The goal is to treat the fistula, but not compromise the anal sphincter muscles. In complex fistulas a drain, or seton may be placed.  A seton is a thin piece of rubber or suture which is placed through the entire fistula tract and the ends of the seton (or drain) are brought together and secured, thereby forming a ring around the anus involving the fistula tract. The seton may be left in place for variable lengths of time (or indefinitely in selected cases), with the purpose of providing controlled drainage, thereby allowing all the inflammation to subside and form a solid tract of scar along the fistula tract. This is associated with minimal pain and normal bowel function. Once all the inflammation has resolved, and a mature tract has formed, one may consider all the various surgical options detailed above as staged procedures.

Treatment of Fistula's in Crohn’s disease

Anal fistulas are very common in Crohn’s disease, which is a chronic inflammatory condition that can affect any part of the gastrointestinal tract. Patients with Crohn’s disease are at increased risk for fecal incontinence because anorectal Crohn’s disease tends to recur and may lead to multiple operations involving the sphincter muscle. It is important to acknowledge that the primary treatment of Crohn’s perianal fistulas is medical, with surgery reserved for treating infection and, occasionally, as a supplement to medical therapy. The treatment should be individualized to the specific patient and incorporate factors that may increase the potential for fecal incontinence.


Pain after surgery is controlled with pain medications, fiber and bulk laxatives. Patients should plan for time at home using warm water baths for the first few days. It is also important avoiding constipation that can be associated with prescription pain medication. Down time really depends on the complexity of the surgery. Many people return to normal activity in about a week. More complex fistulas will take a longer recovery time and can take 6-8 weeks to completely heal.


Unfortunately, up to 50% of abscesses may re-present as another abscess or as a frank fistula at some point in one's lifetime. Despite proper treatment and apparent complete healing, fistulas can potentially recur, with recurrence rates dependent upon the particular surgical technique utilized. Should similar symptoms arise, suggesting recurrence, please call for an immediate evaluation, as abscesses and fistulas are generally easier to treat the smaller they are on presentation.

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