A fistula is an abnormal tract or passage connecting two parts of the body or the inside to the surface of the skin. In the case of an anorectal fistula, the tract usually connects the inside of the anorectal canal to a drain in the skin.

Signs and Symptoms



A fistula is diagnosed by locating the external opening and tracing the tract to its internal opening (or vice versa) using a fistula probe (a soft piece of wire).

Differential Diagnosis


Once the course of the fistula has been traced with a fistula probe, outward traction of the probe will reveal the course and depth of the fistula to inspection.

Superficial fistulas can be treated using minor surgical techniques, involving careful incision along the course of the tract to open the fistula. An electric cutting current is useful for this purpose. The edges of the fistula are then shaved off using electrodessication in order to promote healing from the inside out and to discourage premature healing of the outer surface.

Care must be taken to avoid cutting too much of the anal sphincter muscle, in order to prevent post-operative anal incontinence.


Anorectal fistulas seldom resolve without surgical treatment. Untreated fistulas may revert to abscesses.

Recurrence after surgery is common (20% or more). Surgical removal of too much muscle, especially high in the anal canal or with repeated surgery, is associated with the risk of anal incontinence.

ICD-9 Codes

565.1Anal fistula