Anal fistula surgery: fistulotomy, setons and what follows

A fistula forms when an infected gland near the anus drains but never fully closes, leaving a channel from the inside of the anal canal to a small opening on the skin. The NHS lists constant throbbing pain, worse when sitting, moving, passing a stool or coughing, skin irritation, foul-smelling discharge and sometimes pus or blood when opening the bowels. Swelling, redness and fever suggest an abscess.

Antibiotics can calm an infection, but they do not close the tunnel. The NHS says anal fistulas usually need surgery, and a Guy's and St Thomas' page describes surgery as the only curative treatment because the condition cannot heal independently.

The surgeon needs to know where the tunnel runs relative to the sphincter muscles that control the bowel. That is established by an examination, often under anaesthetic, and sometimes a scan beforehand. If an underlying cause such as Crohn's disease is suspected, other tests may be arranged, since the NHS lists Crohn's, diverticulitis and other conditions among less common causes.

A pre-operative health check and medical history review take place, and Guy's and St Thomas' advises that sphincter involvement cannot always be predicted beforehand. This is the reason surgeons sometimes plan in stages.

Fistulotomy: the NHS describes cutting open the whole length of the fistula so it heals into a flat scar. It suits tunnels that cross little or no sphincter muscle.

Seton: the NHS describes a piece of surgical thread placed in the fistula and left for several weeks to help it heal before a further procedure. Guy's and St Thomas' explains that a seton goes through the tunnel and is tied outside to allow drainage while protecting sphincter function, since the surgeon cannot always tell beforehand how much muscle is involved. It adds that setons cause minimal discomfort and do not prevent bathing, using the toilet or pregnancy.

• Complex or high tunnels may need staged surgery with a seton first.

• Other techniques, such as flaps or plugs, exist for some fistulas and your surgeon will say if they apply.

Surgery uses general anaesthetic according to the Guy's and St Thomas' page. Follow your fasting instructions, bring loose clothes and sanitary pads for discharge, and arrange for an adult to take you home.

The main specific concern is bowel control. Cutting through sphincter muscle can affect continence, which is why surgeons favour a seton for deeper tunnels. The NHS lists potential bowel incontinence among the features of fistulas themselves, and the Guy's and St Thomas' page says seton placement prevents the risk of incontinence when involvement is uncertain.

Other risks include bleeding, infection, an abscess forming again, the fistula returning or healing slowly, and general anaesthetic risks. The pages used here give no percentages, so none are quoted; ask your surgeon about recurrence and continence figures for your type of fistula.

The NHS says many people do not need to stay in hospital overnight, although some may need a few days. A Guy's and St Thomas' page says most patients go home the same day unless complications arise. Expect a draining wound and the need for dressings or pads for some time, with healing taking weeks rather than days. Neither source gave a precise healing time, so follow your team's advice.

Keep the area clean, take regular painkillers, avoid constipation and report any increasing pain, fever, spreading redness or new swelling to your GP, NHS 111 or the hospital. Call 999 for severe symptoms such as rapidly worsening pain with high fever and feeling very unwell.

Specialist colorectal surgeons treat fistulas in both settings. Waits, choice of surgeon and the arrangement for staged operations differ, so ask whether further procedures are included in a private quotation.

• Where does my tunnel run in relation to the sphincter?

• Do you recommend a fistulotomy or a seton, and why?

• How many stages might be needed?

• How will you look after my bowel control?