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A variety of different techniques may be employed surgically to treat fistula in ano but the basic aims of all are the destruction of the abnormal track that runs between the inside of the anal canal and the skin with restitution of the normal anatomy and function of the anal canal and sphincter mechanism.
In the main this is straightforward surgery which leads to the quick resolution of symptoms and rapid return to normal function but in a few cases treatment may be complicated and protracted.
The fistula track is identified, the tissue overlying it (skin, mucosa, sub-mucosa, fat and muscle) is then divided. This effectively opens up a portion of the anal canal onto the surrounding (peri-anal) skin. After thorough debridement the wound is then left to heal. This will require dressing changes and take a number of weeks.
The result is usually complete resolution of symptoms with healing. Clearly care must be taken when dividing muscles of the anal sphincter to avoid excessive injury and long term loss of function. Where too much muscle is found to be involved (particularly in female patients) the alternative treatments below are necessary.
Insertion of a Seton
A Seton is a thin loop of material (rubber, silk or nylon) that is passed along the fistula track from the skin of the peri-anal region into the anal canal and back through the anus, secured to itself outside. The loop is usually loose fitting but secure to allow all normal activities to continue without compromise. It allows drainage of infected material from the fistula track and prevents further abscess formation.
Walking particularly exerts gentle downward traction on the Seton which slowly cuts its way through the tissues that overly the fistula track. Because this occurs slowly, the tissues (including the sphincter muscle) have time to heal behind the Seton’s progressive cutting action (theoretically at least) maintaining the integrity and function of those tissues.
A Seton is usually removed at a further operation some months later, where a laying open procedure may be more safely carried. Less tissue and muscle is divided as a result. Occasionally a Seton may fall out spontaneously having completed it journey through the tissues and usually done its job.
A variety of materials biologic or synthetic (collagen/ complex polymers) are fixed into the fistula track once is has been thoroughly cleaned out. The ingrowth of normal components of the body tissues then occurs with healing of the fistula track.
Clearly unaffected body tissues including the sphincter mechanism are not injured and this offers an attractive alternative to the surgical treatments above. Unfortunately not all fistulas are suitable for a plug and failure rates are high.