Anal Fistula

What is an anal fistula?

An anal fistula, also known as a fistula-in-ano, is a small, infected tunnel that forms between the skin around the anus and the inside of the anal canal. The vast majority of anal fistulas result from a previous or recurrent anorectal abscess. When an anal abscess does not heal completely after draining, a persistent channel can remain, leading to a fistula.

The fistula tract has an internal opening inside the anal canal (usually at the dentate line where the anal glands are located) and an external opening in the skin around the anus. This tunnel can cause persistent drainage, pain, and recurrent infections if not properly treated.

Common Symptoms

The symptoms of an anal fistula can be constant or may come and go.

• Persistent Drainage: The most common symptom is a constant or intermittent drainage of pus, blood, or stool from an opening near the anus. You may notice this on your underwear.
• Pain and Swelling: The area around the anus can be painful, swollen, and tender. The pain is often throbbing and may get worse when sitting or having a bowel movement.
• Skin Irritation: The skin around the anus may become irritated and itchy from the drainage.
• Recurrent Abscesses: The external opening of the fistula may temporarily close, causing pus to build up and form a painful abscess that eventually drains on its own or requires surgical drainage.
• Fever and Feeling Unwell: If an abscess develops, you may experience systemic symptoms like fever, chills, and fatigue.

What causes an anal fistula?

Most anal fistulas are caused by a clogged and infected anal gland, which leads to an abscess. The fistula is the tunnel that forms as the pus from the abscess tries to find a path to drain out to the skin.

• Cryptoglandular Abscess: This is the cause for about 90% of anal fistulas. It starts with an infection in one of the small glands just inside the anus. The infection forms an abscess, and as it drains, a fistula tract can be left behind.
• Crohn's Disease: This inflammatory bowel disease can cause inflammation and ulceration anywhere in the digestive tract, including the anal area, leading to abscesses and complex fistulas.
• Other Causes: Less common causes include trauma, radiation therapy for pelvic cancers, sexually transmitted infections, tuberculosis, and cancer.

How is an anal fistula diagnosed?

Diagnosing an anal fistula usually starts with a clinical evaluation.

• Physical Examination: A doctor can often diagnose a fistula by examining the area around the anus. They will look for an external opening on the skin. A gentle digital rectal exam may be performed to feel for the fistula tract and to locate the internal opening.
• Anoscopy: A small, lighted instrument is used to look inside your anus and rectum to find the internal opening of the fistula.
• Imaging Tests: For more complex fistulas, imaging may be needed to see the full path of the tunnel. This is important for planning surgery.
  • Magnetic Resonance Imaging (MRI): MRI of the pelvis is very effective at mapping the fistula tract and its relationship to the sphincter muscles.
  • Endoanal Ultrasound: An ultrasound probe is inserted into the anus to create an image of the fistula and surrounding muscles.
• Examination Under Anesthesia (EUA): In some cases, a surgeon may need to take you to the operating room to fully explore the fistula tract while you are under anesthesia. This is often the most accurate way to diagnose the fistula's anatomy and plan the best surgical approach.

How is an anal fistula treated?

Surgery is almost always necessary to cure an anal fistula. The goal of surgery is to eliminate the fistula tract while preserving the anal sphincter muscles to maintain bowel control. The choice of procedure depends on the fistula's location and complexity.

• Fistulotomy: This is the most common and effective treatment for simple fistulas that do not involve much of the sphincter muscle. The surgeon cuts open the entire length of the fistula, allowing it to heal from the inside out as a flat scar.
• Seton Placement: For complex fistulas that involve a significant portion of the sphincter muscle, a seton (a piece of surgical thread or rubber) may be placed through the fistula tract. A 'draining' seton is left in place for several weeks to allow the infection and inflammation to resolve before a definitive repair. A 'cutting' seton is tightened over time to slowly cut through the muscle, allowing the fistula to heal behind it.
• LIFT Procedure (Ligation of Intersphincteric Fistula Tract): This sphincter-sparing procedure involves making an incision in the intersphincteric space, identifying the fistula tract as it passes between the internal and external sphincter muscles, and then ligating (tying off) and dividing it.
• Advancement Flap: The internal opening of the fistula is covered with a flap of healthy tissue taken from the rectal wall. This is another sphincter-sparing option for complex fistulas.
• Fistula Plug or Fibrin Glue: A plug made of biological material or a special glue is used to fill the fistula tract. The success rates for these methods are variable.

Self-Care and Recovery

After fistula surgery, proper wound care is important for healing.

• Sitz Baths: Soaking the anal area in warm water several times a day can help with pain and keep the area clean.
• Pain Management: Your doctor will recommend pain medication. Over-the-counter pain relievers are often sufficient.
• Diet: Eat a high-fiber diet and drink plenty of fluids to keep your stools soft and avoid straining during bowel movements.
• Wound Care: Follow your surgeon's instructions for wound care. This may involve placing gauze in or over the wound. You will have some drainage from the wound for several weeks as it heals.

Can an anal fistula heal on its own without surgery?
It is very rare for a true anal fistula to heal completely on its own. While symptoms may come and go, the underlying tunnel usually remains and will likely cause problems again in the future. Surgery is the only reliable way to cure a fistula.

Will I be incontinent after fistula surgery?
The risk of incontinence depends on the complexity of the fistula and the type of surgery performed. For simple fistulas treated with fistulotomy, the risk is very low. For more complex fistulas requiring sphincter-sparing procedures, surgeons take great care to preserve the muscles that control bowel movements. Your surgeon will discuss the specific risks with you based on your individual anatomy.

What happens if I don't get my fistula treated?
If left untreated, an anal fistula will likely continue to cause persistent drainage, pain, and recurrent abscesses. Over time, a simple fistula can become more complex, potentially branching into multiple tracts and making future surgery more difficult.

• Johnson EK, Bernier G. Cryptoglandular Abscess and Fistula. In: Steele SR, Hull TL, Hyman N, Maykel JA, Read TE, Whitlow CB, eds. The ASCRS Textbook of Colon and Rectal Surgery. 4th ed. Springer; 2022:249-270.
• National Institute of Diabetes and Digestive and Kidney Diseases. Colonic & Anorectal Fistulas. Accessed September 28, 2026. https://www.niddk.nih.gov/health-information/digestive-diseases/anatomic-problems-lower-gi-tract/colonic-anorectal-fistulas
• Mayo Clinic. Anal Fistula. Published August 12, 2021. Accessed October 11, 2025. https://www.mayoclinic.org/diseases-conditions/anal-fistula/symptoms-causes/syc-20352871