Anal Fistula

An anal fistula is an abnormal connection, or tunnel, involving the tissue around the anus.

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On this page, we’ll answer the following questions:


In more detail, what is an anal fistula?

This abnormal connection is usually between a small opening inside the anal canal, or sometimes the rectum, and another opening on the skin around the anus.

The opening on the skin around the anus is often really tiny – in fact, most pepole are unaware it’s there. In females, this skin opening can sometimes be near the vaginal opening. Not everyone with an anal fistula will have this opening. Instead, some may have a tunnel which ends below the skin. This is called a perianal sinus.

In many cases, an anal fistula involves one single tunnel connecting the inside of the anus / rectum with the skin around the anus.

However, in some cases, the disease is more complex.

People can have multiple tracts, potentially with more than one opening on the skin, and some fistulas have secondary tracts or branches. It’s crucial the conorectal surgeon fully understands the anatomy of an anal fistula before commencing any surgical treatment.

There is a one-in-a-thousand chance of developing an anal fistula in your lifetime.  Anal fistulas tend to be more common in men, affecting those aged 20-50 years the most.

What causes an anal fistula?

We’re all born with tiny oil glands within the anal canal. There are typically 10-20 of these glands, which help to lubricate the anal canal to facilitate defecation.

Like oil glands on the face, these glands can sometimes become blocked with thick secretions which can become infected.

When this happens, an abscess forms. This abscess is called a perianal abscess or a ischiorectal abscess depending on its location. (The fat around the anus, which is the padding you’re sitting on right now, is called the ischiorectal fat.)  

Sometimes, this abscess will burst through the skin around the anus, and will no longer be a problem. However, other times the abscess will expand and the patient will need medical attention. In such cases, the pus will need to be drained by a surgeon.

In around 40% of cases where people have developed one of these abscesses, they will develop a fistula. This will happen regardless of the treatment given to them at the time of the abscess. The fistula will be between where the infection started within the anal canal, and where the abscess drained to, on the outside of the anus.

If you’re wondering why 40% of people go on to develop a fistula after having an abscess around the anus, and 60% don’t, there is no one clear answer. One possible answer is infected fluid is left within the perianal tissues with nowhere to go. This fluid then bursts back out through the openings which are trying to heal, and the cycle continues, forming a fistula.

Often is it young and healthy people who develop an anal fistula, simply due to bad luck! Anal fistulas have nothing to do with hygiene.

The only known risk factor is cigarette smoking, although many people who develop an anal fistula do not smoke.

Here are other causes of anal fistula, which are less common. 

Crohn’s disease

About 20-30% of pepole with Crohn’s disease will develeop an anal fistula in their lifetime.

It’s not uncommon for an anal fistula to be someone’s first symptom of Crohn’s disease. Around 3% of those who present with an anal fistula are ultimately diagnosed with Crohn’s.

Your colorectal surgeon will always consider this when treating your anal fistula, and sometimes further testing will be needed to make this diagnosis.

In someone with Crohn’s disease, the anal fisula will tend to be relatively complicated, and the inside opening of the fistula is sometimes further up inside the rectum rather than in the anal canal. Treatment in these cases is more difficult, and involves close collaboration between the colorectal surgeon and the gastroenterologist.


Penetrating trauma to the perineum or rectum can occasionally result in an anal fistula.


Patients who receive pelvic radiotherapy for malignant conditions can sometimes develop anorectal problems later on, including anal fistula. Proper assessment by a colorectal surgeon is needed to investigate this.

Tuberculosis / other infections

In rare cases, unusual infections such as tuberculosis can cause an anal fistula.


Patients with previous bowel cancer can develop cancer within an anal fistula. This is a rare occurrence.

Pelvic infection

Infections such as diverticulitis or appendicitis can cause an anal fistula. This is also very rare.

Do I have an anal fistula?

People with an anal fistula will usually describe a painful lump around the anus as their first symptom. This lump was an abscess, and it may have burst without a visit to the doctor, or they may have had an operation to have the abscess drained of pus.

When the fistula subsequently develops, it will usually feel like the problem around the anus has never properly healed. There may be intermittent pain and discharge of some blood / pus from the anal region.

These symptoms can vary in frequency – from happening daily to once a year. That’s why some patients present to a colorectal surgeon having had an anal fistula for several years. In other cases, there is significant suffering caused by the anal fistula.

Once someone has had an anal fistula, they are at risk of developing further ones. If a patient explains they have had more than one anal abscess, the colorectal surgeon will suspect an underlying anal fistula is the cause.

Can an anal fistula heal on its own?

Generally speaking, no. Once an anal fistula has formed it will not heal by itself.

However there are many people whose anal fistula symptoms are so infrequent that it never really causes a problem. It’s understandable that these people could be considered cured of their anal fistula since it doesn’t cause them any trouble, but there is a risk of further symptoms later on.

In these cases, at Brisbane Colorectal we generally recommend no treatment as the problem is so infrequent that surgery is not justified.

When the anal fistula is related to Crohn’s disease, the fistula can be managed by some medication taken for Crohn’s, such as biologics. No surgery is required. However, it is always best to discuss this with your colorectal surgeon, who will work closely with your gastroenterologist.

What’s the treatment for an anal fistula?

Once you’ve been diagnosed with an anal fistula, your colorectal surgeon will advise you on treatment options. The aim is to cure the anal fistula and preserve normal anorectal function.

If an anal fistula is causing a patient problems and interfering with their everyday life, or if it’s frequently blocked and infected, surgery is the best option. Simple fistulas are treated with an anal fistulotomy, where the fistula tract is opened up and drained, helping it to heal from the inside out.

If an anal fistula passes through a significant amount of anal sphincter muscle,  the insertion of a draining seton is a good option. This is a thin piece of surgical thread that, once inserted, stays in the fissure for a few weeks. This keeps the fissure open and promotes healing, while not risking damage to the anal sphincter muscles which are so important for anal continence. Once drained, your doctor will discuss a treatment plan with you to cure the fistula.

This may involve the use of tighter setons to cut through the fistula slowly, or carrying out more than one fistulotomy procedure, where one section of fistula can be worked on at a time.

You will be sedated for these procedures, or in some cases the procedure is performed under a general anaesthetic, so you won’t be in pain. In most cases, patients go home on the same day as their surgery, and there may be some pain for a few days afterwards.

All cases are different, and depending on your situation, a combination of treatments might be recommended. We will work with you to ascertain the best treatments so you can get on with life and the things you enjoy.

Do I need a colonoscopy if I’ve had an anal fistula?

In most cases, you won’t need a colonoscopy. However, your colorectal surgeon may choose to recommend one if Crohn’s Disease is suspected, or for some other reason.

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