Diagnosis at Mayo Clinic

By Mayo Clinic Staff


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Knowing the complete path of an anal fistula is important for effective treatment. The opening of the channel at the skin (external) generally appears as a red, inflamed area that may ooze pus and blood. This external opening is usually easily detected.

Finding the fistula opening in the anus (internal opening) is more complicated. Mayo specialists use the latest technology, including the following:

  • Endoscopic ultrasound uses high-frequency sound waves to produce detailed images of the sphincter muscles and other structures of the pelvic floor.
  • Fistulography is an X-ray of the fistula after a contrast solution is injected.
  • MRI may be used for fistulas that are very difficult to find.

Other options include:

  • Fistula probe, an instrument specially designed to be inserted through a fistula
  • Anoscope, a small endoscope used to view the anal canal
  • Flexible sigmoidoscopy, a procedure to rule out other disorders such as ulcerative colitis and Crohn's disease
  • An injected dye solution, which may help locate the fistula opening
May 06, 2015