A fistula is an abnormal tunnel that connects the inside of the anal canal to the skin near the anus. It usually begins as an infection in one of the small glands inside the canal. That infection forms an abscess, and when the abscess drains, the tract that is left behind becomes the fistula. Understanding this sequence, from gland to abscess to fistula, explains almost everything about how the condition behaves.

What causes an anal fistula?

The great majority arise from a blocked, infected anal gland, what surgeons call cryptoglandular disease. A few have other causes, such as inflammatory bowel disease, previous surgery or injury. Whatever the origin, the common thread is an infection that found a path to the skin and left a tunnel behind. The relationship between the early abscess and the later fistula is covered on the perianal abscess page.

Symptoms to recognise

The typical picture is a recurring boil-like swelling near the anus that discharges pus or blood, often with pain, irritation and a small persistent opening that weeps. Many patients describe a cycle of improvement and flare-up. The full range of complaints is set out on the anal fistula symptoms page.

Types of fistula

Not all fistulas are the same. They are classified by how the tract runs in relation to the sphincter muscles that control continence, and this classification drives the choice of operation. The simpler tracts are straightforward to treat; the ones that involve more muscle need a more careful, sphincter-preserving approach. The detail is on the anal fistula types page.

Treatment options

A fistula needs a procedure; there is no reliable medical cure for the tract itself. The art lies in clearing the fistula while protecting the sphincter, because continence matters as much as healing. Modern options range from sphincter-preserving laser treatment to traditional techniques, and they are compared on the anal fistula surgery page. Our preferred minimally invasive approaches include laser (FiLaC) and VAAFT.

Why treatment should not be delayed

A fistula left alone tends to persist, flare and occasionally form new tracts, which makes later treatment harder. Early assessment by a surgeon experienced in proctology gives the best chance of a simple, sphincter-sparing cure. A condition that shares some symptoms, an anal fissure, can also cause perianal pain and bleeding and is worth distinguishing.

How an anal fistula is diagnosed

Diagnosis rests on the pattern, recurring discharge from a persistent opening near the anus, confirmed by examination. A surgeon experienced in anorectal disease can usually identify a fistula and gauge its likely course on assessment, and where the anatomy is uncertain, imaging or examination under anaesthesia maps the tract before any definitive treatment. This mapping is not a formality; it is the single biggest factor in a successful outcome, because treating a fistula without knowing how it runs in relation to the sphincter is the main reason some recur. The classification this produces is explained on the anal fistula types page.

The abscess-to-fistula story

Most fistulas begin life as an acute infection. An anal gland becomes blocked and infected, pus collects, and the result is a painful perianal abscess. Draining that abscess relieves the pain, but in a proportion of people a tunnel remains once the infection settles, and that tunnel is the fistula. Recognising this sequence explains why a fistula and an abscess are managed in stages: settle the acute infection first, then treat the tract that may follow. It also explains why recurring discharge after an abscess is the signal that a fistula has formed.

Why protecting the sphincter is central

Everything in modern fistula surgery turns on one balance: clearing the tract while preserving the sphincter muscles that control continence. A tract that crosses significant muscle cannot simply be cut open without risking control, which is why sphincter-preserving techniques have become so important. The decision depends entirely on how much muscle the tract involves, the classification on the types page, and it is the reason experience matters more here than in almost any other proctological condition.

The modern treatment toolbox

Treatment has shifted decisively toward sphincter-preserving methods. Laser treatment (FiLaC) seals the tract from within without cutting muscle, and VAAFT lets the surgeon treat the tract under direct video view, both detailed on their own pages and compared on the anal fistula surgery page. For complex or branching tracts, a seton is sometimes placed first as a staged step to drain the fistula and let inflammation settle before definitive treatment. Traditional fistulotomy still has a place for simple, low tracts. The right choice is the least invasive technique that reliably cures the fistula while protecting continence.

Recurrence and what reduces it

Fistulas can recur with any technique, and being honest about that helps set expectations. The commonest reasons are a missed internal opening, an unrecognised side branch, or treating before inflammation has settled, all of which careful assessment and staged management address. Choosing the right method for the tract type, mapping the anatomy fully, and treating completely give the best chance of lasting healing. How recovery differs by technique is on the recovery page.