Anal Fistula

Diagnosis

Knowing the complete path of an anal fistula is critical for effective treatment. Most often, the external opening of the channel is easily detected, while finding the internal opening can be more complicated.

The external opening usually appears as a red, inflamed area that may ooze pus and blood. Sometimes the fistula can be felt as a hard core.

Despite the best efforts, sometimes the fistula's path may not be clear until surgery.

At Mayo Clinic, tools used for diagnosis of anal fistulas include:

• Fistula probe — An instrument specially designed to be inserted through a fistula.
• Anoscope — A small endoscope (tube with a tiny camera at the end) used to view the anal canal.

Diagnostic tools used for more complicated fistulas include:

• Diluted methylene blue dye — Dye is injected into the fistula in an operating room.
• Fistulography — Injection of a contrast solution into a fistula followed by an X-ray of the affected area.
• Magnetic resonance imaging (MRI) — Reserved for the most difficult to find fistulas.
• Endoscopic ultrasound

Flexible sigmoidoscopy may be used to rule out other disorders such as ulcerative colitis or Crohn's disease.

Read more about flexible sigmoidoscopy, and MRI on MayoClinic.com.