Anal Fistula

Introduction

An anal fistula is a small tunnel that runs between the inside of the anal canal (the last part of the bowel) and the skin around the anus. Most fistulas develop after an infection in one of the small glands inside the anus, which often first appears as a painful swelling called a perianal abscess. Once the abscess drains — either on its own, or after a doctor opens it — a narrow track can be left behind. That track is the fistula.

If you are reading this, you have probably already been told you have a fistula, or you have recently had an abscess and are being followed up to see whether one has formed. The next step is almost always a discussion about surgery, because fistulas rarely heal without it. This article explains what a fistula is, why it forms, the different surgical approaches doctors use, what recovery looks like, and what to expect in the longer term.

Anal fistula treatment involves a careful balance. Surgeons aim to close the tunnel and stop the infection from coming back, while protecting the muscles around the anus that control continence (your ability to hold in stool and gas). The choice of operation depends on exactly how the tunnel runs through those muscles, which is something your surgeon will work out using examination and imaging.

What Is an Anal Fistula?

To understand a fistula, it helps to picture the anatomy. Inside the anal canal, just above the opening, there is a ring of small glands. These glands normally produce mucus that helps with bowel movements. Sometimes one of these glands becomes blocked and infected, and the infection spreads outward through the tissue around the anus. This collection of pus is called a perianal abscess.

When the abscess drains, the infection often leaves a narrow channel behind. One end of the channel opens inside the anal canal (the internal opening), and the other end opens on the skin near the anus (the external opening). This channel is the fistula. Because stool and bacteria can keep entering the internal opening, the track tends to stay open and keep discharging fluid rather than healing on its own.

Shows the physical relationship between the internal opening, the fistula track through perianal tissue, and the external opening on the skin

Common symptoms of an anal fistula include:

• A small opening or bump on the skin near the anus that leaks pus, blood, or fluid
• Recurrent perianal abscesses — swellings that come, drain, and come back
• Skin irritation, itching, or staining of underwear
• Pain around the anus, often worse when sitting or during bowel movements
• A bad smell from the discharge
• In some cases, fever, especially during an active abscess

The discharge is often the most distinctive feature. Many patients describe it as a constant small amount of fluid that is hard to ignore and easy to feel embarrassed about. It is a common reason people delay seeking care, but it is also a condition surgeons treat routinely.

Why Do Anal Fistulas Form?

Most anal fistulas — roughly nine out of ten — are cryptoglandular in origin, meaning they start with an infection in one of the small anal glands as described above. These are sometimes called “ordinary” or “simple” fistulas, though the actual anatomy can still be complex.

The remaining fistulas have specific underlying causes that change how the condition is managed. These include:

• Crohn’s disease. This is a form of inflammatory bowel disease that can cause inflammation anywhere in the digestive tract, including around the anus. Crohn’s-related fistulas are often multiple, complex, and require both surgical and medical treatment.
• Previous surgery or trauma. Injury to the anal area, including obstetric (childbirth-related) tears or earlier anal surgery, can lead to fistula formation.
• Tuberculosis. In regions where tuberculosis is more common, including parts of India, TB can cause perianal fistulas. Doctors specifically test for this when the fistula behaves unusually or fails to heal.
• Cancer. Rarely, a chronic fistula may be linked with cancer of the anus or rectum, or the fistula track itself can develop cancerous changes over many years.
• Radiation. Radiotherapy to the pelvis can damage tissue and lead to fistulas.
• Hidradenitis suppurativa. This is a chronic skin condition that can affect the perianal area and produce tracks that look like fistulas.

Identifying the cause matters because it changes the treatment plan. A simple cryptoglandular fistula may be cured by a single, straightforward operation. A Crohn’s-related fistula may need long-term medication alongside surgery, and aggressive cutting operations are usually avoided because the tissue heals poorly.

Classification: Why the Type of Fistula Matters

Visually distinguishes the four Parks classification fistula paths relative to the sphincter muscles, helping understand why some fistulas are riskier to operate on than others.

Surgeons classify fistulas based on how the tunnel runs in relation to the anal sphincter muscles. The sphincters are two rings of muscle — an internal and an external sphincter — that keep the anus closed. Damaging too much of these muscles can lead to faecal incontinence (loss of control over stool or gas), which is why the relationship between the fistula and the sphincters drives almost every surgical decision.

The most widely used classification is Parks’ classification, which describes four main types:

• Intersphincteric: the track runs between the internal and external sphincters. This is the most common type and is usually the simplest to treat.
• Trans-sphincteric: the track crosses through both sphincter muscles. Treatment depends on how much muscle is involved.
• Suprasphincteric: the track loops up and over the external sphincter before coming down to the skin. Less common, and more complex.
• Extrasphincteric: the track runs outside the sphincters entirely. This is rare and often associated with an underlying cause like Crohn’s disease, trauma, or pelvic infection.

Doctors also describe fistulas as simple or complex. A simple fistula is typically a low intersphincteric or low trans-sphincteric track involving only a small amount of muscle, with a single tunnel. A complex fistula involves more muscle, has multiple tracks or branches, sits high in the anal canal, is linked with Crohn’s disease, or has recurred after previous surgery. Complex fistulas usually need more cautious, sphincter-preserving operations.

How Anal Fistulas Are Diagnosed

Diagnosis usually starts with a careful history and an examination of the anal area. Your doctor will look for an external opening, feel for a track under the skin (which can sometimes be felt as a firm cord), and perform a digital rectal examination. They may also use a small instrument called a proctoscope to see the inside of the anal canal.

For most fistulas, especially complex or recurrent ones, imaging is helpful to map the track before surgery. The two most commonly used investigations are:

• MRI of the pelvis. This is generally considered the most informative imaging test for fistula. It shows the path of the track, any side branches or abscess cavities, and the relationship to the sphincter muscles. Major colorectal society guidance, including from the American Society of Colon and Rectal Surgeons (ASCRS), supports MRI for complex or recurrent fistulas.
• Endoanal ultrasound. A small ultrasound probe is placed inside the anal canal to produce images of the sphincters and the fistula track. It is particularly good at showing the sphincter anatomy.

In some cases, a final assessment is made under anaesthesia, immediately before surgery. This is called an examination under anaesthesia (EUA). With the patient relaxed and pain-free, the surgeon can probe the fistula thoroughly and decide on the best operation in real time.

If Crohn’s disease or another underlying condition is suspected, additional tests — such as colonoscopy, blood tests, or tests for tuberculosis — may be added.

Treatment: Why Surgery Is Usually Needed

Once a fistula has formed, it almost never closes by itself. The internal opening keeps the track contaminated, and the body cannot fully heal it. Antibiotics can settle a flare of infection but do not cure the fistula. For these reasons, surgery is the main treatment.

The goals of surgery are, in order of priority:

1. Drain any active infection
2. Close the fistula track so it cannot keep discharging
3. Preserve continence by protecting as much sphincter muscle as possible
4. Prevent recurrence

There is a real tension between the second and third goals. The most reliable way to close a fistula is to open the entire track (a fistulotomy), but this cuts through muscle. If too much muscle is divided, continence can be affected. So surgeons select the operation based on the type of fistula, the amount of muscle involved, the patient’s age and previous continence, and whether there is an underlying cause like Crohn’s disease.

Surgical Approaches for Anal Fistula

Several different operations exist for anal fistula. None is best for every situation; the choice depends on the anatomy and the patient. Below are the most widely used approaches.

Fistulotomy

Fistulotomy is the oldest and most reliable operation. The surgeon opens the entire fistula track from the external opening to the internal opening, lays it open as a groove, and lets it heal from the bottom up over several weeks. Cure rates are very high.

The trade-off is that fistulotomy divides whatever muscle the track passes through. For low, simple fistulas with little muscle involvement, this is usually safe and is considered the first-line treatment by most colorectal guidelines. For higher or more complex tracks, fistulotomy carries a meaningful risk of incontinence and is generally avoided.

Seton Placement

• Loose (draining) seton: kept loose to allow the track to drain continuously. This calms inflammation, prevents new abscesses, and is often used as a first step in complex fistulas, Crohn’s-related fistulas, or while planning a definitive operation later. A loose seton can stay in place for months.
• Cutting seton: tightened gradually over weeks so that it slowly cuts through the muscle. As it cuts, scar tissue forms behind it, which is thought to reduce the risk of incontinence compared with cutting all the muscle at once. Cutting setons are used less often today because newer sphincter-preserving techniques have become available, but they remain an option.

Setons are particularly common in Crohn’s disease, where keeping the track drained and avoiding aggressive cutting is generally preferred while medical therapy works on the underlying inflammation.

LIFT Procedure (Ligation of the Intersphincteric Fistula Track)

The LIFT procedure is a sphincter-preserving operation developed for trans-sphincteric fistulas. The surgeon makes a small cut in the groove between the internal and external sphincters, finds the fistula track running between them, ties it off on both sides, and removes the segment in between. The sphincter muscles themselves are not cut.

LIFT avoids the continence risk of fistulotomy. Success rates reported in clinical studies are reasonable but lower than fistulotomy, and some patients need a further procedure if the fistula recurs.

Advancement Flap

In an advancement flap, the surgeon closes the internal opening of the fistula by lifting a flap of healthy tissue from inside the anal canal (made of mucosa, with or without some muscle) and stitching it over the opening. The external track is cleaned out separately.

This is another sphincter-preserving option, often used for higher or more complex fistulas where fistulotomy would be unsafe. It has reasonable success rates in experienced hands, with a relatively low risk of incontinence, though some patients describe minor changes in anal sensation afterwards.

Fibrin Glue

With this approach, a biological glue is injected into the cleaned fistula track to seal it. The procedure is simple, sphincter-preserving, and can be repeated. However, long-term cure rates have been disappointing in clinical studies, and fibrin glue is now used less often as a stand-alone treatment.

Fistula Plug

A fistula plug is a small cone of biological material placed inside the cleaned track to seal it and act as a scaffold for healing tissue. Like fibrin glue, it preserves the sphincter and can be repeated. Success rates have varied widely in published series, and current guidance from major colorectal societies describes plugs as an option in selected cases rather than a routine first choice.

VAAFT (Video-Assisted Anal Fistula Treatment)

VAAFT uses a thin telescope (fistuloscope) passed along the fistula track. The surgeon can see the inside of the track on a screen, identify the internal opening, destroy the lining of the track, and close the opening. It is minimally invasive and sphincter-preserving. It is used in a range of complex fistulas, often combined with closure of the internal opening by sutures, stapler, or a flap.

FiLaC (Fistula-tract Laser Closure)

FiLaC uses a laser fibre passed into the fistula track. The laser energy seals and closes the track from the inside. It is minimally invasive, preserves the sphincter, and recovery is generally fast. As with other newer techniques, reported success rates vary and it is often used in selected cases or in combination with other procedures.

Stem Cell Therapy

For complex Crohn’s-related fistulas that have failed other treatments, injection of mesenchymal stem cells into the cleaned track is an option that has been studied in clinical trials and is approved in several countries. Availability varies.

Staged Treatment

Many complex fistulas are treated in more than one stage — for example, a loose seton first to settle the infection, followed weeks or months later by a definitive operation such as LIFT or advancement flap. Staged treatment can give better results in difficult cases.

Preparing for Surgery

Anal fistula surgery is usually done as a day-case or short-stay procedure, although complex operations may require an overnight stay. Preparation typically includes:

• Pre-operative assessment. A review of your general health, current medications, allergies, and any previous anaesthetic problems.
• Imaging and examination findings are reviewed to plan the operation.
• Bowel preparation. Many surgeons ask for a small enema before surgery rather than a full bowel cleanout, though practice varies.
• Fasting for a set number of hours before anaesthesia, as instructed by your team.
• Medication review. Blood thinners, certain diabetes medications, and some other drugs may need to be adjusted. Always tell your team about every medicine and supplement you take.
• Stopping smoking, ideally for several weeks before surgery, supports better wound healing.

If you have Crohn’s disease or are taking medications that suppress the immune system, your gastroenterologist and surgeon will coordinate the timing of surgery.

What Happens During Surgery

1. Examines the area under anaesthesia to confirm the anatomy
2. Identifies the external and internal openings, often using a fine probe
3. Decides on (or confirms) the planned procedure based on the actual findings
4. Performs the chosen operation — for example, lays open a low track, places a seton, performs a LIFT, raises a flap, or applies a laser or plug
5. Cleans the wound, controls any bleeding, and places a simple dressing

Recovery depends heavily on the type of operation performed. In general:

• Pain is usually moderate for the first few days and is managed with simple painkillers and, in some cases, short courses of stronger medication. Pain is often worse during the first bowel movement after surgery, which is normal.
• Discharge from the wound is expected, especially after fistulotomy, where an open groove heals from the inside out. A pad may be needed in the underwear for several weeks.
• Sitz baths — sitting in warm water for ten to fifteen minutes, two to three times a day — help keep the area clean, soothe discomfort, and encourage healing. Most surgeons recommend starting them the day after surgery.
• Bowel movements should be kept soft. A high-fibre diet, plenty of fluids, and stool softeners or fibre supplements as advised will reduce straining.
• Return to work ranges from a few days for simple cases to two to three weeks for more complex operations, depending on the type of work and how you feel.
• Wound healing after a fistulotomy can take six to twelve weeks for full closure. Sphincter-preserving operations heal more quickly on the surface but need similar time for the deeper track to seal.
• Sexual activity and exercise are usually resumed gradually, in line with comfort and your surgeon’s advice.

You will typically be reviewed in clinic a few weeks after surgery, and again later to confirm healing. If you have a seton in place, your follow-up plan will be tailored to the staged plan.

Risks and Complications

Anal fistula surgery is generally safe, but every operation carries risks. The most important specific risks to understand are:

• Recurrence. The fistula can come back, particularly with complex tracks or after sphincter-preserving operations. Recurrence may need further surgery.
• Faecal incontinence. Some loss of control over gas, liquid, or solid stool can occur if sphincter muscle is divided or damaged. The risk depends on the operation, the amount of muscle involved, prior surgeries, and underlying continence. Sphincter-preserving operations are designed to minimise this risk, though minor changes in control can still occur.
• Bleeding from the wound, usually minor.
• Infection, including a new abscess.
• Delayed wound healing, particularly in smokers, people with diabetes, or those on immune-suppressing medications.
• Anal stenosis (narrowing of the anal canal) — rare but possible after extensive surgery.
• Anaesthetic risks, which your anaesthetist will discuss separately.

The risk profile is one of the main reasons surgeons take time to explain the planned operation and the reasons behind it. Patients with complex fistulas should expect a frank discussion about the chances of cure versus the risks to continence.

Life After Anal Fistula Surgery

For most people, successful surgery means the end of the constant discharge, pain, and recurrent abscesses. Many describe it as a major improvement in daily life and confidence.

Longer-term considerations include:

• Watching for recurrence. Symptoms to look out for include new swelling, new discharge from the previous area, or pain similar to the original abscess.
• Continence changes. Most patients have normal or near-normal control after sphincter-preserving operations. If you notice any difficulty holding gas or stool, mention it at follow-up — there are exercises, pelvic floor physiotherapy, and other treatments that can help.
• Ongoing care for underlying conditions. If your fistula was related to Crohn’s disease or another condition, continuing that treatment is central to preventing further problems.
• Diet and bowel habits. Keeping stool soft and avoiding constipation is helpful in the long term.

Anal Fistula in Children

Anal fistulas in children are uncommon but not rare, and they behave differently from adult fistulas. They are seen most often in infant boys under one year of age, usually following a perianal abscess. The exact cause is not fully understood, but theories include abnormal anal gland anatomy in early infancy and differences in immune function.

Key points for parents:

• Many infant fistulas resolve on their own as the child grows, particularly in the first year or two. Conservative management with warm sitz baths and good hygiene is often the first step.
• Surgery in children is usually a simple fistulotomy when needed, and outcomes are generally very good.
• In older children, a fistula that does not behave like a typical infant fistula should prompt consideration of underlying causes, particularly Crohn’s disease.
• Specialist care from a paediatric surgeon or paediatric colorectal team is appropriate for fistulas in children.

Parents often worry that the condition signals something serious. In otherwise healthy infants with a simple perianal fistula, the long-term outlook is excellent.

Frequently Asked Questions

Can an anal fistula heal without surgery?

True fistulas almost never close on their own in adults. Antibiotics can settle infection temporarily, and a draining seton can keep symptoms under control, but the track itself does not seal without surgical treatment. Infant fistulas are a partial exception, as many do close as the child grows.

How long will the discharge last after surgery?

Some wound discharge is normal while the area heals. After a fistulotomy, discharge can continue for several weeks until the wound closes. After sphincter-preserving operations, surface discharge usually settles within one to two weeks, though deeper healing continues for longer.

Will I be able to control my bowels after surgery?

Most patients have normal continence after appropriately chosen surgery. Sphincter-preserving operations are specifically designed to protect bowel control. If sphincter muscle has to be cut, your surgeon will discuss the likely effect with you before the operation. Minor changes — such as occasional difficulty holding gas — are the most common form of any continence change, and many of these can be improved with pelvic floor exercises.

What is a seton, and why do I have to live with one for so long?

A loose seton is a thin thread kept in place to drain the fistula track. It is left in for weeks or months when the fistula is complex, when there is active infection that needs to settle, when an underlying condition like Crohn’s is being treated medically, or as part of a planned two-stage treatment. While the thread is in place, the area stays drained and infection is much less likely, but the fistula is not yet cured.

Is anal fistula the same as a haemorrhoid?

No. Haemorrhoids are swollen blood vessels in and around the anus. A fistula is an infected tunnel between the anal canal and the skin. They can cause some overlapping symptoms — such as discomfort or staining of underwear — but they are different conditions with different treatments.

Can a fistula come back after successful surgery?

Yes, it can. Recurrence rates depend on the complexity of the original fistula and the type of operation. Simple fistulas treated with fistulotomy have very low recurrence rates; complex fistulas treated with sphincter-preserving methods can recur more often. If symptoms return, further treatment is possible.

Does an anal fistula cause cancer?

Long-standing chronic fistulas, particularly those present for many years without successful treatment, carry a small risk of cancerous change within the track. This is rare, but it is one reason doctors usually recommend treating fistulas rather than leaving them indefinitely.

Can I exercise or have sex after fistula surgery?

Most patients return to gentle activity within days and to normal exercise within a few weeks, guided by comfort and the surgeon’s advice. Sexual activity, including anal-area contact, is typically resumed once the wound has healed enough to be comfortable. Your team will give you specific guidance based on your operation.

Conclusion

An anal fistula is a treatable condition. The discharge, recurrent abscesses, and discomfort that bring most people to see a doctor can almost always be resolved with the right operation, and for many patients the improvement in everyday life after successful surgery is significant.

The most important part of treatment is matching the operation to the anatomy — balancing a good chance of cure against protecting the muscles that control continence. Simple, low fistulas often respond well to a single straightforward operation. Complex fistulas, fistulas linked with Crohn’s disease, and recurrent fistulas usually need a more careful, sometimes staged approach, with sphincter-preserving techniques chosen to keep continence intact.

If you have been diagnosed with an anal fistula, the next step is a detailed discussion with a colorectal surgeon about the type of fistula you have, the imaging findings, the operation being considered, and the expected recovery. Understanding the trade-offs in advance makes the path through treatment much easier to navigate.