2 The condition, current treatments and procedure
2.1 An anal fistula is an abnormal tract between the anal canal and the skin around the anus. It usually results from previous anal abscesses (cryptoglandular) and can be associated with other conditions such as inflammatory bowel disease and cancer. It may cause symptoms such as pain or discomfort in the anal area, and leakage of blood or pus. Anal fistulas can be classified according to their anatomical relationship with the external sphincter. Intersphincteric fistulas are the most common type and cross only the internal sphincter. Trans-sphincteric fistulas pass through the internal and external sphincter.
2.2 Treatment of anal fistulas commonly involves surgery. The type of surgery depends on the location and complexity of the fistula. For intersphincteric and low trans-sphincteric anal fistulas, the most common treatment is a fistulotomy or laying open of the fistula tract. For deeper fistulas that involve more muscle, and for recurrent fistulas, a seton (a piece of suture material or rubber sling) may be used, either alone or with fistulotomy. Setons can be loose (designed to drain the sepsis but not for cure), or snug or tight (designed to cut through the muscles in a slow controlled fashion). Fistulas that cross the external sphincter at a high level are sometimes treated with a mucosal advancement flap or other procedures to close the internal opening. Other options for treating anal fistulas are to fill the tract with glue or paste.
2.3 Bioprosthetic plug insertion for anal fistula aims to leave the sphincter muscles intact, allowing the use of subsequent treatments if needed.
2.4 The procedure is usually done using general anaesthesia. The fistula tract is identified using a probe or by imaging techniques, and it may be irrigated. A conical plug, usually made of porcine intestinal submucosa, is pulled into the tract until it blocks the internal opening. It is sutured in place at the internal opening. The external opening is not completely sealed so that drainage of the fistula can continue. The plug acts as a scaffold into which new tissue can grow.