What Are Anal Fistulas?
Anal fistulas are small, abnormal tracts that run from the inside of the anus to the skin around the anus.
They are usually the result of a blocked and infected anal gland. Instead of the infection breaking through back into the anus, it breaks through to the skin around the anus, thus creating a tunnel. As long as the internal opening remains open, the fistula usually will not heal.
An anal fistula may declare itself after drainage of a previous anal abscess, and the wound does not heal properly. This could be because there was already an internal opening at the point, but it was not apparent when the abscess was being drained. As a result, there will be a persistent drainage of pus from the incision, and the wound will not heal and close completely. In other cases, the skin heals, but soon develops a swelling under the scar. When the scar bursts, pus will be discharged.
Other less common causes of anal fistulas include:
- Inflammatory bowel disease (Crohn’s disease)
Symptoms of Anal Fistulas
- Recurring symptoms are the hallmark of an anal fistula
- Pain, swelling and redness near the anus
- Oozing of pus
Types of Anal Fistulas
Medically, the fistulas are classified according to the location of the tracts, such as intersphincteric, transsphincteric, supralevator, etc.
A simpler way to put it is:
- Simple Fistula – where there is only a single tract involving a small amount of muscle, with one opening low in the anal canal and a single external opening at the skin around the anus
- Complex Fistula – where the tract has branches and there are more than one opening on the skin, or the tract involves a substantial amount of anal muscles
How Are Anal Fistulas Diagnosed?
Most of the time, repeated swelling and discharge around the anus can point towards the diagnosis of an abscess, and closer examination of the area may reveal the tract that leads from the skin around the anus into the anal canal.
However, in some complex fistulas, additional imaging scans such as an endoanal ultrasound (the insertion of a small ultrasound probe into the anus) or magnetic resonance imaging (MRI) may be needed to view the entire length of the fistula and identify features such as depth and direction of the tract.
Learn more about this medical condition at Dr Ho Kok Sun's main Anal Fistula and Anal Surgery page.