Anal Fistula
What is an anal fistula?
An anal fistula is an abnormal tract that originates from within the anal canal and tunnels to open on to the skin on the edge of the anus. In doing so it will cross through a variable amount of sphincter muscle which is the key factor in determining appropriate surgical management.
Fistulas can be simple, meaning a short superficial tract or they can be more complex with deeper, branching tracts.
Why did I get a fistula?
Most fistulas are the result of an infection in one of the anal glands (cryptoglandular theory). As the infection evolves it forms a tract out towards the skin and either creates an abscess or fistula (or both).
Those with Crohn’s Disease or ulcerative colitis are at higher risk of developing anal fistulas. Rarely is an anal fistula related to cancer.
What are the symptoms of a fistula?
Most fistulas will either initially present as a painful abscess or a purulent (pus) discharge. Some may notice passage of faeces or wind through the fistula tract.
What investigations are required?
For most the diagnosis is clear on examination alone. The first line management is usually surgery. For more difficult, complex or recurrent fistulas you may require an MRI scan or colonoscopy.
What are the treatment options?
Conservative measures and antibiotics
Antibiotics are often prescribed prior to seeing a surgeon though this will seldom fix the fistula. Whilst the discharge may subside a bit, it will usually recur once the antibiotics are ceased.
Surgery
Surgery is the mainstay of fistula management. The initial step is referred to as an Examination Under Anaesthesia (EUA), meaning we assess the fistula tract whilst you are under a general anaesthetic. In doing so we attempt to identify the tract with both the external and internal openings, whilst making an assessment to how much of the sphincter muscle is included within the fistula tract. Depending on the location around the anal canal, depth of fistula and gender, the fistula can be deemed as simple or complex.
Fistulotomy: This is the simplest method of fixing a fistula. It is only suitable for fistulas that are relatively superficial and only crossing a smaller portion of the sphincter muscle. It involves cutting down (laying open) on to the tract through the skin and sphincter muscle. It leaves an open wound that will usually take several weeks to heal. Depending on the degree of sphincter muscle involvement, a fistulotomy may cause impairment in continence. A fistulotomy is the most common procedure performed and has the highest success rate.
Seton insertion: A seton is a sialastic band that is passed through the fistula and anal canal and tied together. A “loose seton” as the name implies is tied loosely and helps to drain pus. It is often a temporary measure to control infection before a more definitive procedure is performed. A “cutting seton” is tied tightly. The tightness of the seton will slowly cut through the sphincter muscle and allow it to gradually heal in the process.
Ligation of Intersphincteric Fistula Tract (LIFT Procedure): This involves an incision in the perianal skin over the fistula and locating the tract as it crosses between the two sphincter muscles. Both ends of the tract are tied and then the tract divided.
Anal mucosal advancement flap: This involves mobilising the anal liming (mucosa) on the inside of the anal canal and suturing it over the top of the internal opening.
Fistula plug: This is less commonly performed nowadays. It involves a biological (pig intestine) mesh plug that is sutured within the tract.
Fistula glue: Again this is seldom performed now and involves filling the tract with tissue glue that promotes healing.
What surgery is right for me?
The various options will be discussed with you at your first consultation with a surgeon. Often the first step is to assess the fistula tract under an anaesthetic (EUA) and decide if it is a simple fistula that is suitable for a fistulotomy or a complex fistula that first requires a seton insertion. If the latter of these is the case then a plan will be put in place for definitive management of the fistula at a later date.
Fistula surgery can be frustrating for both patient and surgeon. Recurrences are unfortunately common and multiple procedures are sometimes required for complex fistulas.