Anal fistulas are small tunnels that begin inside the anal canal and end at the skin around the anus.
Anal fistulas usually form at the site of an infected anal gland. That infected gland creates an abscess, or a pocket of pus, which drains from the body by forming a fistula, or passageway.
Surgical drainage is the most common treatment for anal fistulas. However, some fistulas can be treated without surgery.
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What Is an Anal Fistula?
Anal fistulas are small tunnels or passageways connecting anal glands inside the anal canal to the skin around the anus. They're also called a fistula-in-ano.
Anal fistulas are usually the result of anal glands becoming blocked and infected.
When a blocked gland becomes infected, it fills with fluid, creating an abscess in the anal canal. As the abscess drains, it creates a fistula. Fistulas look like tiny holes in the skin around the anus.
Although fistulas are almost always the result of abscesses, not all abscesses become fistulas. About 50% of abscesses will develop fistulas. Abscesses that drain persistently for two to three months are typically considered fistulas.
Fistulas are benign, but they can cause serious discomfort, pain, and embarrassment. It is important to seek treatment for an anal fistula so that it does not become more infected or severe.
What are the types of anal fistulas?
Experts often classify anal fistulas by their location in relation to the internal and external sphincter muscles. These are the muscles that control bowel movements. The five types of anal fistulas according to this classification system are:
- Extrasphincteric — This is the least common type of fistula because it does not form at the site of an anal abscess. Instead, it begins in the rectum and passes around both sphincter muscles.
- Intersphincteric — This type of fistula first passes through the internal sphincter muscle and then uses the space between the internal and external sphincter muscles to travel to the skin around the anus. It is the most common type of fistula, accounting for 50% to 80% of all fistulas.
- Superficial — This type of fistula does not form at the site of an anal abscess. Instead, it forms below the anal glands and does not pass by the sphincter muscles at all.
- Suprasphincteric — This type of fistula passes through the internal sphincter muscle but then goes around the external sphincter muscle.
- Transsphincteric — This type of fistula passes through both the internal and external sphincter muscles.
The American Gastroenterological Association uses a simpler classification system. In this system, there are just two types of anal fistulas:
- Complex — Complex anal fistulas pass through both the internal and external sphincter muscles. They are often caused by conditions like cancer, inflammatory bowel disease, radiation, or chronic diarrhea. Complex fistulas have a high rate of recurrence, or a high chance of returning, and are more likely to result in incontinence issues.
- Simple — Simple anal fistulas are more superficial, involve little if any sphincter muscle, and can usually be treated successfully.
How common are anal fistulas?
Anal fistulas are diagnosed in about 8 of every 10,000 people each year. They are twice as common in men. People who are obese or have diabetes or an inflammatory bowel disease, like Crohn’s disease, are more likely to develop anal fistulas.
People with Crohn’s disease may develop a condition known as fistulizing Crohn’s disease. This is when many fistulas form and recur along areas of the gastrointestinal tract, including the intestines, the rectum, and the anus. When fistulas form around the anus, it’s known as perianal fistulizing Crohn’s disease.
Research shows that between 23% and 38% of people with Crohn’s disease may develop perianal fistulizing Crohn’s disease.
What causes an anal fistula?
Anal fistulas usually occur when a small gland just inside the anus becomes infected. That infected gland creates a pocket of pus, called an abscess. As the abscess drains, it forms a fistula, or passageway, to the skin around the anus.
Some conditions can make these types of anal gland infections more common, such as:
- Chronic diarrhea.
- Chronic sexually transmitted infection (STI).
- Colitis.
- Constipation.
- Inflammatory bowel disease.
- Radiation treatment in the area of the rectum or anus.
Sometimes, your provider can locate and drain an anal abscess before a fistula forms. This is usually successful. However, it’s possible that the passageway between the anal gland and the skin remains after your provider drains the abscess, eventually resulting in a fistula.
Anal fistula risk factors
The key risk factor for developing an anal fistula is having an anal abscess. Half of anal abscesses progress to anal fistulas.
Other conditions that can increase your risk for developing an anal fistula include:
- Cancer.
- Chronic diarrhea.
- Colitis.
- Crohn’s disease.
- Diabetes.
- Hyperlipidemia (high levels of lipids or lipoproteins in the blood).
- Infections around the anus.
- Obesity.
- Previous anal abscess.
- Radiation or surgery for anal cancer.
- Sedentary lifestyle.
- Trauma.
Anal fistula complications
When caught right away, fistulas can usually be treated successfully. However, if left undiagnosed or untreated, fistulas can lead to complications such as:
- Cancer — Chronic inflammation, like the inflammation caused by an anal fistula, is a risk factor for cancer. Researchers have found anal cancer in longstanding fistulas.
- Fecal incontinence — Fistulas that pass through sphincter muscles or fistulas that require a surgeon to cut your sphincter muscles can result in fecal incontinence. This is when you have trouble holding or controlling your bowel movements.
- Fistula extension — Sometimes, an anal fistula will begin to drain in new directions, creating new branches or tracts of fistula tunnels. These fistulas are much more difficult to treat and more likely to involve the sphincter muscles.
- Recurrent abscess — Left untreated, fistulas allow glands to continue becoming infected and cause abscesses.
- Serious infection — In rare cases, untreated fistulas can result in a serious or systemic infection such as sepsis.
How can I reduce my risks of developing an anal fistula?
It’s important to remember that some anal fistulas are caused by underlying conditions or unforeseen circumstances that you would not be able to predict or prevent. However, there are some lifestyle changes you can make to reduce your risk of developing an anal fistula.
These lifestyle guidelines include:
- Having an active lifestyle — Anal fistulas are more likely to develop in people who live a sedentary lifestyle or are sitting for long periods of time every day. If you work at a desk job or spend a lot of your day sitting, take frequent breaks to stand up and walk around as much as you can. This helps take pressure off the anal area and lowers the risk of developing a fistula.
- Having healthy bowel movements — Constipation and straining while going to the bathroom can aggravate a fistula or contribute to the development of a new one. Talk with your medical provider if you experience irregular or infrequent bowel movements and feel the need to strain during them. Drinking water, eating fiber-rich foods, and staying active can also help promote more regular bowel movements.
- Maintaining a healthy weight — Obesity is a risk factor for anal fistulas because of the added pressure of weight in the anal area. Talk with your doctor to make sure you are eating a rich, colorful diet. Emphasize fruits, vegetables, protein, and healthy fats.
- Quitting smoking — Smoking can prolong any healing process and can interfere with your body’s ability to fight infections. If you are experiencing an anal fistula, it is best to quit smoking to give your body the best chance at fully healing and avoiding a recurring fistula.
- Seeking medical attention quickly — Do not wait if you experience pain, redness, swelling, or discharge around the anus. Talk to your doctor to receive prompt medical care before the infection worsens.
- Using proper hygiene — Wash your hands with warm water and soap after every bowel movement, and thoroughly and regularly wash your body. This can reduce the risk of infection in the anal area.
What Are the Signs and Symptoms of an Anal Fistula?
The most common symptoms of an anal fistula are:
- Drainage of blood, pus, mucus, or stool from an opening near the anus.
- Fever, chills, or feeling ill.
- Frequent anal abscesses.
- Pain or tenderness in the rectum or anus, usually when sitting or having a bowel movement.
- Swelling, redness, or irritation around the anus.
When should I see a doctor about my anal fistula symptoms?
If you suspect you have an anal fistula or are experiencing any of the above symptoms, you should call your provider right away. It’s important to catch and treat the infection before it gets worse or leads to complications.
How Do You Diagnose an Anal Fistula?
Your provider will most likely discuss your symptoms and medical history before performing a physical examination to diagnose an anal fistula. This exam will include looking at, around, and possibly inside your anus to find signs of a fistula.
Typically, the external opening of an anal fistula can be seen on the skin surrounding the anus — it looks like a tiny hole. But your provider will likely order tests to see where the fistula originates and what path it takes to the skin. This will help to determine the best treatment option.
Tests to diagnose an anal fistula
- Anal examination under anesthesia — This may be necessary so a provider can thoroughly examine the fistula without causing too much discomfort.
- CT scan — This painless and noninvasive imaging test uses a series of x-rays and a computer to create a detailed map of the fistula’s path and openings.
- Endoscopy — This imaging test uses high-frequency sound waves to view the muscles and tissues around the anus and identify the fistula’s path.
- Fistulography — This test uses injected contrast to find the fistula’s path using x-ray.
- MRI — This painless and noninvasive imaging test uses strong magnets and radio waves to create images. It can show more detailed images of the tunnel’s path and the other muscles and tissues around the anus.
How Do You Treat an Anal Fistula?
If you are diagnosed with an anal abscess that has not yet become a fistula, it can be treated in a provider's office using a local anesthetic. A provider will drain the pus through an opening made in the skin near the anus.
A large or deep abscess may need drainage in the operating room. Hospitalization may be necessary for people susceptible to more serious infections, such as those with diabetes or decreased immunity.
Medications for anal fistulas
While antibiotics cannot repair an anal fistula, they are important to its treatment. Antibiotics can help to clear infections and relieve symptoms.
Nonsurgical treatments for anal fistulas
Collagen plug
A collagen plug is a nonsurgical procedure that helps to close and heal an anal fistula. Your provider will first clean the tunnel and then block the internal opening with a plug of collagen protein. The collagen allows for the growth of new, healthy tissue that will eventually close the fistula.
Fibrin glue
While you are usually under general anesthesia for this procedure, it is not considered a surgery.
First, your provider will clean the fistula and close the internal opening with stitches. Then, they'll fill the tunnel with fibrin glue, which gets absorbed into the body as the fistula heals.
Surgery for anal fistulas
The type of surgery your provider recommends will likely depend on the location and severity of your fistula.
Endorectal advancement flap
During an endorectal advancement flap procedure, your surgeon will remove the infected tissue around the internal opening of the fistula. Then, your surgeon will cut a healthy piece of skin from your rectum and use it to cover the opening of the fistula. The fistula can then heal from the inside out.
This procedure is often used because it reduces the amount of sphincter muscle cut.
Endoscopic ablation
During an endoscopic ablation, your provider will insert a long, thin tube called an endoscope into the fistula. An electrode is then passed through the endoscope and used to cauterize, or seal, the tunnel.
Fistulotomy
If your fistula is too deep for simple drainage but not too severe, it can usually be treated using a fistulotomy. During this procedure, your surgeon will cut the internal opening of the fistula and possibly a small part of a sphincter muscle, and clean the infected area. Then, they'll flatten the tunnel and stitch it in place.
Most fistulotomy surgeries can be performed on an outpatient basis.
Fistulectomy
During a fistulectomy, your surgeon will completely remove the fistula, or tunnel. Surgeons don't perform this often because it increases the likelihood of damage to the sphincter muscles. However, a fistulectomy can be necessary if you are experiencing decreased bowel function.
Ligation of the intersphincteric fistula tract (LIFT)
A LIFT is a two-stage procedure often used when the fistula tract involves too much sphincter muscle. Instead of cutting and further damaging the sphincter muscles, your surgeon uses the space between them to access the internal fistula opening.
Your surgeon will place a surgical string made of silk or latex in the fistula tunnel to keep it open. This is called a seton drain placement. Once drainage is complete — sometimes weeks later — your surgeon can remove the drain and infected tissue and close the fistula with stitches.
Seton drain placement
During a seton drain placement, your surgeon will place a surgical string made of silk or latex in the fistula tunnel to keep it open. Later, the surgeon can remove the drain and use a fistulotomy or another procedure to close the tunnel.
If a chronic condition like Crohn's disease is causing your fistula, your surgeon may leave the drain in place.
How effective is surgery for an anal fistula?
Simple anal fistula surgery, such as a fistulotomy, has a success rate of more than 90%.
While anal fistula surgery is usually successful, that does not mean that anal abscesses or fistulas will not recur. It is important to practice healthy habits — such as good hygiene, diet, and exercise — to prevent anal fistulas from reappearing. If symptoms begin again, call your provider right away.
How long does it take to recover after surgery for an anal fistula?
After fistula surgery, you may experience mild to moderate discomfort for the first week. The discomfort can be controlled with pain medication. In fact, you may feel well enough to return to regular activity right away.
Most providers recommend soaking the affected area in warm water three or four times a day and wearing a gauze pad to prevent the drainage from soiling your clothes. Some people may want to use stool softeners to make bowel movements easier. However, bowel movements should not affect healing.
Questions to Ask Your Doctor
If you believe you have an anal fistula or you have been diagnosed with an anal fistula, you may want to ask your doctor these questions:
- Do I have an anal fistula or an anal abscess? How can you tell the difference?
- What type of anal fistula do I have?
- What treatment options are available for my fistula, and which do you recommend for me?
- What should I expect during recovery, and how long will it take to return to normal activities?
- What are the risks if my anal fistula is not treated or if it comes back after surgery?
