An anal fistula is an abnormal tract between the anal canal and the skin around the anus. It may cause symptoms such as pain or discomfort, and leak blood or pus. It usually results from previous anal abscesses (cryptoglandular), and can be associated with other conditions including inflammatory bowel disease (such as Crohn's disease) and cancer.
Anal fistulas can be classified according to their relationship with the external sphincter. A fistula may be complex, with several openings onto the perianal skin. Intersphincteric fistulas are the most common type and cross only the internal anal sphincter. Trans-sphincteric fistulas pass through both the internal and external sphincters.
Treatment of an anal fistula commonly involves surgery. The type of surgery depends on the medical history, extent, location and complexity of the fistula in relation to surrounding muscles. The aim is to drain infected material and encourage healing. If the fistula does not heal completely, another surgical procedure may be needed. For simple intersphincteric and low trans-sphincteric anal fistulas, the most common treatment is a fistulotomy or laying open of the fistula tract (involving muscle division that may affect continence). For high and complex (deeper) fistulas that involve more muscle, with a high risk of faecal incontinence or recurrence, surgery aims to treat the fistula and preserve sphincter-muscle function. Techniques include a 1‑stage or 2‑stage seton (suture material or rubber sling) either alone or in combination with fistulotomy, ligation of an intersphincteric fistula tract, creating a mucosal advancement flap, injecting glue or paste, or inserting a fistula plug (in line with NICE's interventional procedures guidance on fistula plug).
Endoscopic ablation of an anal fistula is a less invasive procedure than surgery. It aims to preserve sphincter-muscle function and faecal continence. It may be done in combination with surgical techniques such as creating a mucosal advancement flap.
The procedure is usually done as a day case using spinal or general anaesthesia. With the patient in the lithotomy position, a fistuloscope is inserted into the fistula tract from the external opening. A continuous jet of irrigation solution is used, which allows optimal visualisation of the fistula tract, the internal opening and any secondary tracts or abscess cavities. When the fistuloscope exits through the internal opening to the rectal mucosa, 2 or 3 stitches are inserted to isolate the internal opening. Under direct vision, an electrode is passed through the fistuloscope and the material in the fistula tract is cauterised from the external to the internal opening. All necrotic material is removed using a fistula brush and a continuous jet of irrigation solution. The fistuloscope is removed and the internal opening closed by suturing, stapling or by creating a cutaneous mucosal flap.