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 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 usually 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 procedure 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. Another option for treating an anal fistula is to fill the tract with a plug or glue.
2.3 The use of collagen paste for closing an anal fistula is done using general anaesthesia and with the patient in the lithotomy position. The fistula tract is de-epithelised and granulation tissue is removed, then it is cleaned with dilute hydrogen peroxide followed by saline. A guiding catheter is connected to a syringe containing the paste and the other end is inserted into the external opening of the fistula. The paste is injected into the fistula until it is visible at the internal opening, and then the guiding catheter is slowly withdrawn. The internal opening of the fistula is closed using resorbable stitches. The external opening is partially closed, using resorbable stitches if needed, to allow any inflammatory fluid to drain out without allowing the collagen paste to escape.
2.4 The paste fills the exact shape of the tract, which is intended to reduce the risk of it being expelled from the body when defaecating.
2.5 It is a less invasive procedure than traditional surgery and the aim is to allow the fistula to heal while preserving sphincter function.