Perianal abscess & fistula

A perianal abscess is a collection of pus that builds up in the tissue around your back passage, usually because one of the small glands inside the anal canal has become infected. An anal fistula is a small tunnel or channel — often like a tiny burrow — that forms between the inside of the anal canal and the skin around it. Around 30–50% of people who have had an abscess go on to develop a fistula afterwards. Both conditions are common, and both have good treatments available.

An abscess usually comes on quite suddenly. You will likely notice a tender, swollen, red area around your back passage — it can be quite painful. Sometimes a fever or feeling unwell comes with it. The important thing to know is that an abscess will not go away on its own or with antibiotics alone — it needs to be drained. This is done as a day procedure under a general anaesthetic, and relief is usually immediate afterwards. At the same time, the area can be examined (called an examination under anaesthetic, or EUA) to check whether a fistula has already started to form.

A fistula usually makes itself known through a persistent or on-and-off discharge of fluid from a small opening near your back passage, or through recurring abscesses. It may also cause ongoing discomfort in the area. Fistulas are described by how deeply the tunnel passes through the sphincter muscles (the ring of muscle that gives you bowel control). The technical names — intersphincteric, transsphincteric — describe this, and the surgeon will explain which type you have. Understanding exactly where the fistula is — sometimes with the help of an MRI scan — is important because it shapes the surgical plan.

Treatment is carefully tailored to your specific situation. The key question is always: how much of the sphincter muscle does the fistula pass through?

For a simple, shallow fistula, a procedure called a fistulotomy — where the tunnel is gently laid open — works very well and heals reliably.

For a deeper or more complex fistula, where cutting through too much muscle at once could affect your bowel control, the treatment is done in stages. A seton (a soft surgical thread) is often placed first, kept loose to keep the tract open and controlled while preparing for a more definitive repair later.

Other options for complex fistulas include the LIFT procedure (ligation of the intersphincteric fistula tract — a sphincter-preserving technique that seals the inner opening without cutting through muscle) and an advancement flap repair (where a small patch of healthy tissue is used to close the internal opening).

If you have Crohn's disease (a type of inflammatory bowel disease), you may be more likely to develop fistulas, and they tend to be more complex. Managing a Crohn's-related fistula involves close teamwork between your surgical and gastroenterology teams. Treatment usually combines medication for the Crohn's itself with surgical steps like an EUA, seton placement, and careful long-term monitoring. See the dedicated Crohn's Perianal Disease page for more detail on this combined approach.

Protecting your bowel control is the number one priority in every fistula decision Mr Nguyen makes. He uses MRI imaging when needed to map exactly where the fistula is before planning surgery. Simple fistulas are treated definitively; more complex ones are managed in careful stages — usually with a seton first — to keep your continence safe throughout the process. Mr Nguyen will talk you through the whole plan at your consultation, including how many steps are likely and a realistic timeframe. There are no surprises — you will always know what to expect next.

If you have a painful, swollen, red area around your back passage, please seek urgent assessment — this is most likely an abscess and needs to be drained soon. Do not wait for a routine appointment. If you have ongoing discharge from the area, a history of recurrent abscesses, or have been told in the past that you have a fistula, please make an appointment to be reviewed — even if things are not extremely painful right now.

If your GP is concerned about an acute abscess, you may be sent straight to hospital for drainage — this is the immediate priority and gives prompt relief. For a fistula or recurrent symptoms, your GP will send a referral and most patients are seen within one to two weeks. At the consultation, a careful history is taken, the area is examined, and in many cases an examination under anaesthetic and an MRI are arranged to map the fistula tract precisely before committing to a definitive plan.

Fistula treatment is often staged. The first step is usually drainage of any active infection, sometimes with a soft seton left in place to keep things settled while the tissues calm down. Once the inflammation has settled — typically over weeks to months — a definitive repair is planned, with the technique chosen to balance healing the fistula against protecting your continence. A follow-up appointment is arranged after each stage to confirm progress, and your GP will be kept informed throughout.