Diagnosis and Tests
How is an Anal Fistula Diagnosed?
The Colorectal Surgeon can find most anal fistulas during a physical exam, but sometimes the opening to the outside is closed. Your surgeon will also want to find the inside opening to the fistula, within your anus. If it hurts too much for your surgeon to touch or open your anus to examine the inside, they may have to examine you in the operating theatre under sedation - this is called an EUA (examination under anesthesia).
To find the inside source of the fistula, your surgeon 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 Colorectal Surgeon 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 non invasive 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 surgeon takes after injecting dye into it. The dye will highlight the path of the fistula.
Your surgeon needs to know the pathway of your fistula in order to determine how to treat it. They’ll classify your fistula by its pathway.