Anal fistula

What is an anal fistula?

A fistula is a tunnel/channel between an opening in the anal canal (internal opening) and an opening at the level of the skin around the anus (external opening).

The average age is 40 years.

Men are affected twice as often as women.

The incidence of an anal fistula: 1,69 cases per 10,000 people.

García-Olmo D, Van Assche G, Tagarro I, Diez MC, Richard MP, Khalid JM, et al. Prevalence of anal fistulas in Europe: systematic literature reviews and population-based database analysis. Adv Ther. (2019) 36:3503–18. doi: 10.1007/s12325-019-01117-y

Most anal fistulas occur as a result of an anal abscess originating from anal glands located between the 2 sphincters (muscles) of the anus. As a result of infection and inflammation of the glands, an abscess develops.

Due to the progressing infection, the swelling increases and the abscess may press against the skin around the anus. It may empty spontaneously or after surgery.

When the abscess heals, an open connection may remain between the anal canal and the skin; this is referred to as an anal fistula.

Not every patient develops an anal fistula after an abscess.

+/- About 50% of patients develop a fistula after drainage of an abscess.

An anal fistula may present with similar symptoms as an anal abscess, but less acute and less painful.

A combination of the following symptoms may occur:

• Pain and swelling at the level of the skin.
• Fever.
• Fatigue.
• Irritation, redness at an opening near the anal canal.
• Intermittent drainage of foul smelling fluid through an orifice (pimple) around the perianal skin.

After drainage of an abscess, the patient usually complains of the following cycle of symptoms if a fistula develops:

• The wound does not heal completely and continues to seep intermittently
• A small swelling pimple forms on the healed wound of the abscess, which may cause discomfort/pain and redness. When the pimple (external opening) oozes foul smelling secretions, the pain goes away and the swelling subsides. Once the dirt loss is evacuated, the external opening closes and the cycle can repeat itself as long as the internal opening in the anal canal continues to feed the fistula. This cycle can repeat itself many times with intervals of weeks or months.

• With repeated infection, new fistulas may develop, increasing the risk of general infection.
• Chronic inflammation can increase the risk of cancer in the long term.

• No. It may also be decided not to treat an anal fistula if the risk of incontinence as a result of surgery is considered too high.

The most common types of fistula  are:

• Transsphincteric anal fistula: Fistula that (de)completely crosses both (external and internal) sphincters.
• Intersphincteric anal fistula: Fistula that runs between the external and internal sphincter.
• Superficial anal fistula: Fistula that does not pass through the sphincter.

Fistula can be complex with multiple tracts from an internal opening to multiple external openings.

The diagnosis is made based on the history of symptoms (history of abscesses, intermittent oozing of foul smelling secretions)

On clinical examination, an opening in the skin around the anus is observed (external opening of the fistula) .

On anuscopy, the internal opening can sometimes be visualized.

If a complex fistula is suspected, magnetic resonance or ultrasound of the anal canal may be requested preoperatively.

What are the different treatments for anal fistula?

High fistula tract

If it is a high anal fistula, traversing more than 30% of the anal sphincter, surgical treatments will aim to first, if necessary, control the infection and, in a second time, close the internal opening in the anal canal without compromising the patient’s continence.