Anal Fistula

Healthcare providers can find most anal fistulas during a physical exam, but sometimes the opening to the outside is closed. Your provider will also want to find the inside opening to the fistula, within your anus. This part might require anesthesia. If it hurts too much for your provider to touch or open your anus to examine the inside, they may have to examine you in the operating room under sedation.

To find the inside source of the fistula, your provider may use a lighted scope, like an anoscope or proctoscope (a longer scope that can visualize your rectum). Sometimes, they’ll inject hydrogen peroxide into the external opening to find the infection at the source of the fistula. The peroxide will interact with the infection and create bubbles or foam at the site. Finding the inside source can confirm the fistula.

Will I have any other medical tests?

Your healthcare provider might need to take imaging tests (radiology) to see the path of your fistula. This might mean:

• MRI (magnetic resonance imaging). An MRI is a noninvasive imaging test that provides high detail. This can help providers map the path of the tunnel and also see how it interacts with your muscles and other organs.
• Endoscopic ultrasound. As an alternative to MRI that produces similar images, an endoscopic ultrasound goes inside your anus with a tiny lighted camera and a tiny ultrasound probe.
• Fistulography. A fistulogram is an X-ray of your fistula that your healthcare provider takes after injecting dye into it. The dye will highlight the path of the fistula.

Your provider needs to know the pathway of your fistula in order to determine how to treat it. They’ll classify your fistula by its pathway.

What are the different types of anal fistulas?

Healthcare providers classify anal fistulas by where they’re located in relation to your anal sphincter muscles. These are the muscles that control your bowel movements, so it’s important to protect them. Your provider might refer to your anal fistula by a specific name based on its location, such as:

• Intersphincteric anal fistula: Passes through your internal anal sphincter muscle and then burrows out through the space between your internal and external sphincter muscles.
• Transsphincteric fistula: Travels through both layers of your anal sphincter muscles.
• Suprasphincteric fistula: Passes through your internal sphincter and then goes around your external sphincter.
• Extrasphincteric fistula: Goes around both sphincter muscles. This less common type usually originates from your rectum rather than your anus, so it doesn’t come from an anal gland.
• Superficial anal fistula: Travels from the lower part of your anal canal, below your anal glands, through the skin nearby, bypassing your muscles. This type doesn’t come from an anal gland.

You don’t have to know or remember what type of anal fistula you have, but the type will influence how your provider treats it. If it involves much of your sphincter muscles, the treatment might be more complicated. They have to be careful not to injure these muscles when they fix your anal fistula.