ANAL FISTULA

WHAT IS AN ANAL FISTULA?

An anal fistula is an abnormal connection, or tunnel, involving the tissues around the anus. The 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 can often be tiny – so small that many people may not be aware of it. In females, the skin opening can sometimes be near the vaginal opening.

Not everyone with an anal fistula will have an opening on the skin around the anus – some people may have a blind-ending tunnel which ends below the skin. This is termed a “perianal sinus”.

In many cases, an anal fistula will involve one single tunnel connecting the inside of the anus/rectum with the skin around the anus. In some cases, however, the disease is more complex. People can have multiple tracts, potentially with more than one opening on the skin, and some fistulae have “secondary tracts” or branches. It is important for the colorectal surgeon to fully understand the anatomy of an anal fistula before embarking on any surgical treatment.

An anal fistula at operation. The skin abnormality to the left of the anus is the external opening of the fistula.

WHY DO ANAL FISTULAE OCCUR?

We are all born with tiny glands within the anal canal, only about 1-2cm inside the anal opening. There are usually 10-20 of these oil glands; their function is thought to be related to lubrication of the anal canal to facilitate defecation.

Just like oil glands on the face, these glands can sometimes become blocked with thick secretions and then subsequently get infected.

When this happens, an abscess occurs, and pus from the abscess will follow the path of least resistance. The abscess will track under, in between, or through the adjacent anal sphincter muscle. Sometimes the abscess will travel into the fat around the anus (this is the padding we sit on – called the “ischiorectal fat”).

The abscess that forms is called a “perianal abscess” or “ischiorectal abscess” depending on its location, and this abscess will sometimes burst through the skin around the anus, leading to resolution. Sometimes the abscess will expand and only be drained by a surgeon when the patient presents for medical attention.

Of all patients who develop one of these abscesses, about 40% will go on to develop a fistula, regardless of what treatment is given to them at the time of the abscess. The fistula will occur between where the infection started, within the anal canal, and where the abscess drained to on the outside of the anus.

The exact reason why some people go on to develop a fistula after having an abscess around the anus, and some people don’t, is not fully understood. It is thought that premature healing of the skin and anal canal occurs, with infected fluid left within the perianal tissues with nowhere to go. The fluid then bursts back out through the openings which are trying to heal and the cycle continues, forming a fistula.

Other less common causes of anal fistulae

  • Crohn’s disease

About 20-30% of people with Crohn’s disease will develop an anal fistula in their life. In some of these people, the anal fistula will be their first symptom of Crohn’s disease; in fact 3% of people presenting with an anal fistula will ultimately get a diagnosis of Crohn’s disease. Your colorectal surgeon will always consider this when treating your anal fistula, and sometimes other tests may be required to make this diagnosis.

In Crohn’s anal fistulae, the fistulae are often more complicated than in “normal” anal fistulae, and the inside opening of the fistula is sometimes up in the rectum rather than in the anal canal. Treatment of Crohn’s anal fistulae is more difficult than in non-Crohn’s fistulae, and involves close collaboration between the treating colorectal surgeon and gastroenterologist.

  • Trauma

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

  • Radiotherapy

Patients who receive pelvic radiotherapy for malignancy can sometimes later develop anorectal problems, including anal fistula. Assessment by a colorectal surgeon is required to investigate this.

  • Tuberculosis/other infections

Rarely, unusual infections such as tuberculosis can cause anal fistulae.

  • Malignancy

Occasionally patients with previous bowel cancer can develop cancer within an anal fistula. This is rare.

  • Pelvic infection

Rarely, infections such as diverticulitis or appendicitis can cause an perianal fistula.

WHAT ARE TYPICAL SYMPTOMS OF AN ANAL FISTULA?

Usually, people with an anal fistula will recall having a painful lump (abscess) around the anus as their first symptom. This may have burst by itself, without a visit to the doctor, or they may have had to have an operation to have the abscess drained of pus.

When the fistula develops, people will usually feel that the problem around the anus has “never healed”. Common symptoms include intermittent pain and discharge of a small amount of pus/blood from the anal region. These symptoms can vary in frequency, from occurring every day to even once a year in some cases.

Occasionally, patients present to a colorectal surgeon having had an anal fistula for several years (particularly if they have only had mild symptoms from time to time). In other cases, there is significant suffering associated with the fistula.

Once someone has an anal fistula, they are at risk of developing further anal abscesses. If someone gives a story of having had more than one anal abscess, the colorectal surgeon will be highly suspicious of an underlying anal fistula being the problem.

HOW COMMON ARE ANAL FISTULAE?

The lifetime risk of developing an anal fistula is about 1 in 1000. The disease tends to me more common in men, and the most common age group is 20-50.

Often it is young and otherwise healthy people who develop an anal fistula, and in most cases it is due to bad luck. The disease has nothing to do with hygiene. The only known risk factor is cigarette smoking, although many people who develop the disease are non-smokers.

WHAT TESTS ARE REQUIRED FOR SOMEONE WITH AN ANAL FISTULA?

It is important that someone with an anal fistula is treated by a colorectal surgeon. Colorectal surgeons have subspecialty training in anal surgery and the operations for anal fistulae can be delicate.

The aim of treatment of all anal fistulae is to try to cure the fistula, whilst at the same time preserving normal anorectal function. Surgery to treat anal fistula has a risk of compromising anal continence, and as such we spend much time at Brisbane Colorectal discussing the goal of treatment, options available and risks of each approach. People who have had previous anal surgery, or females who have had traumatic childbirths, may already have damage which is important to diagnose before any surgery is done.

A clinical examination by a colorectal surgeon, along with a detailed history, provides most of the information required for treatment of an anal fistula. Occasionally, other tests give further information on the anatomy of a fistula, or an assessment of anorectal function. These include MRI scans, endoanal ultrasound, anal manometry, colonoscopy, and examination under general anaesthetic. Your colorectal surgeon has the expertise to advise you on what tests may be required for your anal fistula.

CAN AN ANAL FISTULA HEAL BY ITSELF?

Generally, once an anal fistula is formed it will not heal by itself. There are, however, many people whose symptoms are so infrequent from their anal fistula that it never really causes a problem. These people could be considered “cured” of their fistula in that it does not cause them any trouble, but there may be a risk of further symptoms in the future, even years later. In these situations we generally recommend no treatment as the problem is so infrequent that any surgery is not justified.

In cases of Crohn’s disease-related anal fistulae, the fistula can be “controlled” by some medication used for Crohn’s disease, such as “biologics” with no surgery required. It is best to discuss this with your colorectal surgeon who will collaborate with your gastroenterologist.

WHAT ARE THE TREATMENT OPTIONS?

Once you have been assessed and diagnosed with an anal fistula, your colorectal surgeon will advise you on what treatment options there are. The aim is to cure the anal fistula, but at the same time preserve normal anorectal function.

Sometimes in patients with frequent blockage and infection of their anal fistula, a “draining Seton” is placed across the fistula before a definitive repair is performed. This involves a short operation under general anaesthetic, with the placement of a small plastic tube or silk thread (called a “Seton”) through the tunnel of the fistula. Usually, the Seton is visible on the outside of the anus, but tends to be tolerated very well by patients. It can sometimes interfere with cleaning of the anus after going to the toilet and occasionally patients prefer to have a shower after using their bowels when they have a Seton in place. The Seton keeps the skin openings of the fistula open and encourages drainage of the fluid, preventing any infection.

A Seton is frequently used as a temporary measure to control a fistula, prior to definitive surgery; but in some cases if the Seton is tolerated very well by the patient it is also an option for longer-term management.

seton image

There are many types of operations to choose from for anal fistulae. The main problems with all these operations are that none of them are able to provide a 100% guarantee of success and healing of the fistula, with no risk to normal continence and function of the anus. We will explain this to you in detail at the time of your consultation.

At Brisbane Colorectal we will often recommend a combination of procedures, giving the patient a maximal chance of healing of the fistula. This may require a longer operation, or a longer hospital stay, but with a better chance of successful healing of the fistula. Different anal fistulae are best served with different operations, and we tailor the surgery we recommend to each patient’s fistula depending on a number of factors.

Some of the operations more commonly used are listed below (this is not an exhaustive list). All of these surgeries are performed under general or spinal anaesthetic:

  • Fistulotomy (“Laying open of the fistula”)

A fistulotomy is performed for anal fistulae which are near the surface of the body. The operation is done as a day procedure. An incision is made through the skin over the tunnel of the fistula, and in doing so the fistula is turned into an external wound, which will then heal from the base up. Healing usually takes about 3 weeks to occur on average, and a small scar is left instead of the fistula. This scar usually fades over several weeks/months.

This operation is only performed if there is plenty of anal sphincter muscle left above the surgical wound, and the risk of any future minor leakage is very small. It has a very high success rate of approximately 95% for complete healing.

  • LIFT procedure (“Ligation of the Intersphincteric Fistula Tract”).

This operation is used for anal fistulae which are deeper inside the anus. A small incision is made in between the internal and external anal sphincter muscles, and the fistula tract is identified, sutured closed on each side and divided. This surgery carries a minimal risk to anorectal function, and a success rate of 50-60%.

  • Mucosal/anodermal advancement flap

In this operation, closure of the internal opening of the fistula, inside the anal canal, is performed. A small flap of tissue is created and this is used to ensure a complete closure of the internal opening, ultimately leading to healing. Again success rates are about 50-60%. Small dissolvable sutures are used and eventually the area scars up after healing.

  • Video-assisted anal fistula tract surgery (VAAFT)

Video-assisted anal fistula tract surgery is used as an “adjunct” to some fistula operations at Brisbane Colorectal. A small endoscope is passed into the anal fistula itself, and fistula tract is irrigated with fluid to remove any debris. The inner lining of the fistula tract is then cauterized to create a fresher wound and definitive repair is then performed. VAAFT may increase the success of fistula repair surgery, particularly for more longstanding fistulae, and we offer this at Brisbane Colorectal as a novel technique.

  • Core fistulectomy

Anal fistula surgery aims to offer the best chance of complete healing for the patient. Removal of some, or all, of the fistula tract itself can sometimes lead to this if it can be done without injury or damage to the remaining anal tissue. At Brisbane Colorectal, we usually aim to remove as much of the anal fistula tract as possible, as much as can be safely done without damage to the anal sphincter. This leads to an increased chance of cure.

  • Negative pressure drainage of the fistula wound

A new technique for anal fistula surgery used at Brisbane Colorectal involves “negative pressure therapy”. At the time of fistula surgery, a tiny tube is placed into the surgical wound, secured to the skin and connected to a low pressure suction device. This allows any residual fluid from the anal fistula or the surgery itself to be gently sucked out of the wound. This fluid, if left undrained, may accumulate and burst through the fistula repair leading to failure. In selected cases we have found our success rates for anal fistula surgery have improved by using this technique.

  • Anal fistula plug

An anal fistula plug is sometimes used for complex anal fistulae and fistulae between the anus/rectum and the vagina. An anal fistula plug is a specially designed, completely absorbable, material made in the shape of an anal fistula. At the operation, the anal fistula plug is gently placed into the anal fistula and used to completely fill the fistula tunnel. The internal opening is then closed, and the body grows scar tissue into the mould of the anal fistula plug as it slowly dissolves. The advantage of the procedure is that the risk is very low. Success rates are about 30-40%.

  • Draining Seton

Some people prefer to live with a small Seton across their anal fistula (see above). This may be suitable for patients with very complex fistulae, previous failed surgery, or for patients with Crohn’s disease-related anal fistulae. Whilst the fistula remains, some people find this a suitable management strategy, avoiding further surgery.

  • Cutting Seton

A cutting Seton is another option for people with complicated anal fistulae. Whilst not used much these days, a cutting Seton remains a reasonable option for patients with fistulae which are difficult to heal.

In this procedure, a silk thread is passed around the fistula and tied together snugly. The procedure is mildly/moderately uncomfortable afterwards for a few days, and the cutting Seton works by gradually pulling the fistula closer to the skin. The body replaces the tissue behind it with scar tissue. The downside is that the procedure needs to be repeated several times (usually between 3-7 times) and it takes months for the fistula to finally reach the skin and heal completely. There is a small risk of disturbed anal function and hence this procedure is only used selectively for complex fistulae.

WHAT FOLLOW-UP IS REQUIRED AFTER ANAL FISTULA SURGERY?

Unfortunately, there is no guarantee of success with anal fistula surgery, regardless of what operation has been performed. At Brisbane Colorectal we will continue to see our anal fistula patients until healing has been achieved, and we are always available should any further problems arise in the future.

For patients who have had a anal fistulotomy (“laying open of the fistula”), we usually see patients 6 weeks after surgery to ensure the wound is completely healed. If it has not, we will make a plan to facilitate healing and occasionally our wound therapists become involved in patient care if needed.

Following any definitive fistula operation, there is a risk of a fistula coming back, out to 6-12 months following the surgery. 80% of fistula “recurrences” occur within 6 months of the surgery, and this can manifest as another abscess, the skin re-opening, or another fistula forming.

DO I NEED A COLONOSCOPY IF I HAVE HAD AN ANAL FISTULA?

Most of the time, no. Your colorectal surgeon may choose to recommend a colonoscopy, however, if Crohn’s disease is suspected or if there is another reason to have a colonoscopy.