A perianal fistula is a communication that occurs between the rectum or anal canal and the perianal skin, usually in the vicinity of the anus. Perianal fistula is a disease of high incidence, occurs in more men than women and is usually initially diagnosed between the ages of 30 and 50.
Origin and types of fistulas
This communication is called a fistulous tract, originating in an internal fistulous orifice, inside the anus, and ending in the external fistulous orifice, in the perianal skin. Based on the cryptoglandular theory, most fistulas have their origin in an obstruction of glands inside the anal canal, whose function is to lubricate it to allow the exit of feces. More rarely, fistulas are related to trauma, anal fissure, Crohn’s disease or previous surgical interventions in the anal region.
On its way from the inside of the anus to the skin, this fistulous tract crosses the anal sphincter, which is responsible for the correct continence of bowel movements. Fistulas are classified according to the area where the fistulous tract crosses the anal sphincter.
Fistulas: symptoms
Generally, the first symptom of a perianal fistula is the appearance of a perianal abscess. This is a pocket of pus under the skin near the anus. This abscess usually requires surgical drainage as initial treatment. Subsequently between 25% and 50% of patients will develop an established fistula. In this case, the most common symptoms are:
continuous or intermittent discharge, which sometimes stains the patient’s underwear; pain in the area where the external fistulous orifice is located, especially in the days prior to the discharge and perianal humidity which, if maintained over time, causes itching and stinging in the area of the fistula.
Differences between fistulas and hemorrhoids
The typical characteristic of a fistula is oozing, with a yellowish-white material. The pain may be unrelated to bowel movements and may be relieved when oozing occurs.
Hemorrhoids, on the other hand, may produce bleeding, the patient may notice a “lump” coming out after straining during bowel movements or feel more intense pain in case of hemorrhoidal thrombosis.
Treatment of the fistula
In the case of a perianal fistula, the only definitive treatment in Coloproctology is surgery. As we have said before, if the diagnosis is made by the appearance of a perianal abscess, the treatment is surgical drainage. This operation, although apparently simple, it is important to perform it correctly since this will determine a shorter fistulous tract and will avoid the appearance of fistulas with several tracts.
Once the fistula has been established, it is important to know the relationship between the fistulous tract and the anal sphincter, since an injury to the sphincter could cause it to malfunction and lead to permanent fecal incontinence. If after the physical examination we have doubts about the location of the fistulous tract, we will perform an endoanal ultrasound or an MRI to know the relationship between the fistula and the anal sphincter.
If there is suppuration and significant inflammation that makes exploration difficult, it may be necessary to place a drain (lax line) that the patient will carry until the definitive intervention.
Simple perianal fistulas (the tract crosses only the internal sphincter and the lower part of the external sphincter) are treated by fistulotomy. In this operation, the coloproctologic surgeon will cut the skin and part of the sphincter muscle until the fistulous tract is reached, putting the fistulous tract flat so that it can heal from the inside to the outside. It is possible that during the fistula operation the surgeon may modify the technique if it seems to him that it may cause a risk of incontinence.
In cases of complex perianal fistulas (involving more than half of the external sphincter or having several tracts) different techniques are available. The common aspect of all these techniques is the absence of sphincter section. The simplest techniques are based on filling the fistulous tract with different materials (fibrin glue injection or plugs) that seek to heal the tract. On other occasions we will perform an endoanal advancement flap in order to obliterate the internal fistulous orifice or a LIFT technique (ligation of the fistula in the intersphincteric space). These techniques, although they protect anal continence, have variable possibilities of fistula recurrence.
Prevention of fistulas
Most fistulas are caused by obstruction of glands located inside the anal canal. There are no measures to prevent this obstruction, but it is important for the surgeon to evaluate and treat correctly any suspected perianal abscess in order to avoid the development of complex fistulas. In the same sense, it is important the correct treatment of anal fissures, which sometimes are the beginning of a subsequent fistula.
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