Fistulotomy and Setons

Graham Williams, Consultant Surgeon, New Cross Hospital Wolverhampton

Powerpoint File

The aims of surgical treatment of an anal fistula are to eradicate the fistula, without compromising anal continence. To this end, a number of surgical techniques may be employed, depending on the complexity of the fistula and the proportion of the sphincter muscle involved by the primary fistula tract. Selection of the most appropriate technique depends on a variety of factors. These include:-

The extent and proportion of sphincter involvement (internal vs. external sphincter involvement)

The position of the fistula (anterior sphincter shorter than posterior)

The sex of the patients (females have a shorter anal sphincter, especially anteriorly and also potential for pre-existing obstetric damage)

Previous anal surgery (previous sphincter damage, especially previous fistula surgery)

Pre-existing bowel disorders (loose stools harder to control)

Crohn's disease (potential for recurrent sepsis and unhealed wounds)

Thus assessment of a patient with an anal fistula requires a detailed history and careful examination of the anal area to assess the fistula and anal sphincters. Useful investigations include hydrogen peroxide enhanced endoanal ultrasound scanning and MRI scanning. Ano-rectal physiology probably adds little further information to clinical examination, as it is always wise to adopt a cautions surgical approach if sphincter integrity appears diminished either from the patient's history of borderline control or from physical examination.

The majority of anal fistulas are simple, low fistulas, which involve only the lower part of the anal sphincters and form simple tracts. Such a fistula will involve only the internal sphincter (intersphincteric) or a small proportion (<25%) of the external sphincter (transsphincteric). These fistulas can be laid open with expectation of healing of the fistula and at most only minor alteration in anal control. The technique requires careful probing of the fistula tract and confirmation of the quantity of sphincter involved by palpation and direct observation during fistulotomy. Fistulotomy is preformed by incising the skin, anoderm and sphincter muscle down onto the probe. Care should be taken to identify any high blind extension in the intersphincteric space, which if missed, can lead to recurrence of the fistula. A smaller, shallower wound is produced by suturing the cut edge of the tract to the adjacent skin and anoderm edge (marsupialisation).

Complex fistulas, which involve more sphincter muscle, follow a tortuous course or are associated with un-drained abscess cavities, are more difficult to treat. It is in these situations that fistulotomy is likely to result in significant problems with anal control.

A variety of techniques have been developed to deal with high or complex fistulas of which use of a seton is the most popular. Using a seton is an ancient treatment for an anal fistula and Hippocrates gave a description of one use for a seton, which is little changed today. A seton can be used in a variety of ways to treat a fistula.

[1] Loose seton (drainage)

The aim of a loose seton is to keep the external opening of the fistula patent, allowing discharge to the exterior of any infected material from the fistula tract, preventing an abscess developing in the fistula. There are a number of reasons a loose seton may be inserted. (i) to make it easier to identify the fistula tract at subsequent surgery. (ii) to act as a drain to allow acute sepsis to settle before definitive surgery is performed, such as a rectal advancement flap repair. (iii) to act as a drain to settle sepsis, before the seton is removed, in the expectation that the fistula will heal, once sepsis is controlled. (iv) a loose seton can be used for permanent drainage of a difficult fistula. Whilst the fistula will not heal using this method, it is an effective way of controlling sepsis and improving quality of life. A loose seton is very useful in anal Crohn's disease. A variety of materials can be used as a loose seton. Fine silastic tubing or plastic vascular sloops are particularly suitable. Nylon suture material is best avoided as it is hard, and the sharp, cut end can cause pain if it digs into the perianal skin.

[2] Tight seton (cutting)

Problems with anal control after laying open a high fistula are thought to result from springing apart of the ends of the sphincter muscle. The idea of a tight, cutting seton is to divide the muscle slowly by pressure necrosis caused by a tight band round the sphincter muscle. Fibrosis induced by the seton round the muscle prevents wide separation of the muscle ends. However, there is little evidence to support this theory, even though in practice high fistulas can be treated in this manner with limited impairment of continence. The seton can be used to divide the involved muscle completely. When it is inserted, the skin and anoderm overlying the fistula tract should be incised to limit pain when the seton is tightened. The author performs internal sphincterotomy at the site of the internal opening to make sure that the intersphincteric space is adequately drained and any high blind tract in the intersphincteric space is dealt with. As the seton works through the sphincter it needs to be tightened. This can be achieved by a variety of means. A simple method is to apply haemorrhoid bands to the seton, behind the knot. An alternative approach is to leave a tight seton in place for a few weeks to induce fibrosis as it partially divides the sphincter muscle. At a later date, the seton can be removed and the residual fistula tract is laid open by simple fistulotomy.

Fistulotomy and seton techniques remain the mainstay of the armamentarium of the surgeon treating anal fistulas.

Further Reading:

Williams J.G., MacLeod C.A., Rothenberger D.A., et al., Seton treatment of high anal fistulae. British Journal of Surgery 1991; 78: 1159-61,

McCourtney J.S.,Finlay I.G., Setons in the surgical management of fistula in ano. British Journal of Surgery 1995; 82: 448-52,

Garcia-Aguilar J., Belmonte C., Wong D.W., et al., Cutting seton versus two-stage seton fistulotomy in the surgical management of high anal fistula. British Journal of Surgery 1998; 85: 243-5,

Balogh G., Tube loop (seton) drainage treatment of recurrent extrasphincteric perianal fistulae. American Journal of Surgery 1999; 177: 147-9,

Joy HA, Williams JG. The outcome of surgery for complex anal fistulas. Colorectal Diseases 2002;4: 254-261

Zbar A. Long-term outcome following loose-seton technique for external sphincter preservation in complex anal fistula (Br J Surg 2004; 91: 476-480). Br. J. Surg. 2004;91(8):1073.

Buchanan GN, Owen HA, Torkington J, et al. Long-term outcome following loose-seton technique for external sphincter preservation in complex anal fistula.. Br. J. Surg. 2004;91(4):476-80.