An anal fistula is a small abnormal tunnel or passage that forms between the skin around the anus (perianal skin) and inside the rectum or anus. It’s a condition that often develops after an anal abscess, which is a collection of pus from an infection in the anal glands. 

“When the abscess doesn’t heal properly, it may develop into a fistula,” says Nebraska Medicine colon and rectal surgeon Rishi Batra, MD. “The majority of anal fistulas are a result of a prior anal abscess that occurred.” 

Symptoms of an anal fistula

“Most patients will notice drainage from around the anus,” says Dr. Batra. “The drainage can be foul-smelling with the appearance of blood or pus. If an infection is present, patients may also experience pain in the anal area or fever.”

Other symptoms of anal fistulas may include: 

• Pain or discomfort around the anus, especially when sitting, coughing or passing stool.
• Swelling or tenderness.
• Itching or irritation.
• Discharge, blood or pus usually with a foul odor. 
• Possible fecal incontinence. 

If left untreated, anal fistulas can cause chronic pain and potential repeat infections.

What causes anal fistulas?

Anal fistulas are often caused by infected anal glands, but can also result from other underlying conditions. An anal abscess occurs when an anal gland is infected due to poor hygiene or certain sexually transmitted infections. If an abscess doesn’t heal properly, anal fistulas can occur. Other less common causes can include:

• Surgery complications near the anus.
• Anal gland infections.
• Inflammatory bowel disease or Crohn’s disease. 
• Trauma or injury, such as surgery, childbirth or an anal fissure. 
• Previous radiation therapy for the treatment of anal cancer.
• Accumulation of bacteria. 

How are anal fistulas treated?

Because anal fistulas rarely heal on their own, surgical treatment is usually necessary. A health care provider, often a gastroenterologist or colorectal surgeon, will evaluate your condition to determine the best treatment plan.

“Fistulas are treated based on the cause and exact location of the fistula within the anal canal,” says Dr. Batra. “The anatomy of the fistula is very important.”

Treating a fistula can be more complex if it’s located near anal sphincter muscles. It’s important to minimize damage to external and internal sphincter muscles so there’s no risk of incontinence. Fistulas can vary in complexity; simple fistulas are easier to treat and involve one tract, while complex fistulas require more intricate surgeries. Complex fistulas need careful evaluation and may require an MRI or endorectal ultrasound to get a clear view. 

An anal fistula surgery, a fistulotomy, is the most common and effective treatment for simple fistulas that don’t involve anal sphincter muscles. A colorectal surgeon opens the fistula tunnel to rid the infection so it can heal properly. Other treatment options include:

• Seton placement – a surgical thread or wire in the fistula tract to tighten over time and heal from the inside out.
• Advancement flap surgery – a flap of tissue used to cover the fistula. 
• Antibiotics – used to treat bacterial infections but not cure fistulas. 
• Healthy diet – helps to prevent recurrent abscesses.

When to see a health care provider

“Patients should seek a health care provider if they have persistent anal pain, unusual drainage, fever, chills or fatigue,” says Dr. Batra.

If you’ve had a prior anal abscess that didn’t heal properly or a fistula that isn’t improving, see a health care provider for a physical exam to prevent any complications and discuss possible surgical options.