How is an anal fistula diagnosed?

Your doctor can usually diagnose an anal fistula by examining the area around the anus. He or she will look for an opening (the fistula tract) on the skin. The doctor will then try to determine how deep the tract is, and the direction in which it is going. In many cases, there will be drainage from the external opening.

Some fistulas may not be visible on the skin's surface. In this case, your physician may need to perform additional tests:

  • An anoscopy is a procedure in which a special instrument is used to see inside your anus and rectum.
  • Your physician may also order an ultrasound or MRI of the anal area to get a better view of the fistula tract.
  • Sometimes your surgeon will need to examine you in the operating room (called exam under anesthesia) to diagnose the fistula.

If a fistula is found, your physician may also want to do further tests to see if the condition is related to Crohn's disease, an inflammatory disease of the intestine. About 25% of people with Crohn's disease develop fistulas. Among these studies are blood tests, X-rays and colonoscopy. A colonoscopy is a procedure in which a flexible, lighted instrument is inserted into the colon via the anus. It is performed under conscious sedation, a type of light anesthetic.

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