How is an anal fistula diagnosed?

By | August 8, 2018

An anal fistula is a health condition involving the presence of fistula in the anal or rectal area that can be diagnosed based on the presenting symptoms and physical findings. There are also several diagnostic tests that can be used to confirm the location of fistula and guide treatment decisions.

Physical Examination

A physical examination involves an examination of the anus and surrounding area to find the signs of a fistula. The opening of a fistula is usually a red and swollen spot that may leak pus.

When a fistula is predicted, the path of the fistula may be discovered, as the tunnel structure is usually hardened underside the skin. This may help to find any secondary tracts that may branch off of the main fistula tract.

It is very important to recognize the complete path of anal fistulas to make correct treatment decisions.

A rectal inspection may also be needed to assess the function of the sphincter muscles.

This is done by the doctor inserting a finger into the anus and rectum to palpate the fistula track and nearby tissue, for confirmation of infection or extension of the anal fistula.


Findings that can be indicative of fistula are:

A visible cavity of the fistula onto the skin

Pain and inflammation around the rectal area

Thickened skin because of chronic infection

Pus or bloody discharge from the anus or the neighboring skin

Other Testing

Additional tests may be needed to inspect the symptoms, mainly if there are more than one fistula tracts involved.

Anoscopy is done for endoscopic visualization of the inner side of the anus, including the inner opening of the fistula if present.

Flexible sigmoidoscopy is helpful in patients who may have Crohn’s disease or ulcerative colitis.

Anal endosonography can be used to see the fistula and its inner openings.

Proctoscopy can be done under general anesthetic, by using a proctoscope and a fistula probe to see inside the rectum and find any fistula there.

In Fistulography, X-ray imaging after the injection of a contrast dye may help to identify the fistula.

MRI is also very useful in visualizing the information of the anal fistula.

Computed tomography or CT scan may help to assess the level of inflammation in the rectal area with all details, that is useful for patients having Crohn’s disease.