An expert explains: What is an anal fistula?

In this informative article, highly experienced consultant general surgeon Mr Raj Harshen, who specialises in colorectal surgery, gives an expert guide to anal fistulas. The leading specialist details the causes behind the condition and the symptoms patients commonly experience. He also gives expert insight on how anal fistulas are diagnosed and how the best form of treatment is determined in each individual case.

What is an anal fistula?

An anal fistula is a small tunnel that connects an infected gland or abscess found inside the anal area to the skin on the outside of the anus.

What causes an anal fistula?

There are glands inside the anal canal which normally produce mucus. If these glands become clogged, they can form an abscess which may burst to the outside forming a fistula.

What symptoms will a patient likely experience?

Commonly patients describe a discharge which comes from somewhere around the anal opening. Patients can also experience pain around the anal opening and swelling like a small abscess. When the abscess eventually bursts, it then discharges pus or bloody pus. This can happen repeatedly in a cyclical fashion, where the discharge may settle down but will later flare up again after a few days or weeks. This repeated flaring up and discharging is very typical of an anal fistula.

What tests do doctors do to detect anal fistulas?

Anal fistulas are usually evident on clinical examination and when you examine the patient’s bottom, you can usually see an opening on the outside close to the anal opening. Additionally, on examining the anus itself, it is very often possible to also feel an inside opening, which is the tunnel from the inside to the outside of the fistula.

If a test is needed to confirm the diagnosis, an MRI scan can be used. The most important aspect of this imaging is to identify the relationship of the tunnel to the muscles around the anal opening. It’s crucial to investigate this before performing any kind of surgery as if the tunnel goes through the muscles, it requires very careful management. In these cases, we have to be very careful cutting or laying open the fistula because it can potentially weaken the anal muscles and cause the patient to become incontinent.

How are anal fistulas treated?

The best treatment option depends on whether the fistula is superficial or deep. If the fistula is superficial, this means it is located in front of the muscle or that it passes through very few fibres of the muscle. In that situation, a surgical procedure known as laying open can be used to cure the fistula.

If, however, the fistula goes through the muscle and is deeper, more careful attention is required. In this situation, we often put a thread, called a seton, through the fistula to drain it. Once the fistula is well drained and the seton is properly in place, it possible that the fistula will become superficial meaning it can be reassessed and eventually laid open in surgery.

In some cases, however, the fistula does not become superficial and remains deep even after being drained. When that occurs, one option is to leave the seton in place for a much longer duration or it may be possible to apply a fistula plug to try to close it off. More recently, innovative techniques have been developed which use laser to try to heal the fistula.

Mr Harshen a highly skilled consultant general surgeon with specialist expertise in colorectal surgery. If you are concerned about the symptoms of anal fistula or are seeking treatment and wish to discuss your options further, you can schedule a consultation with Mr Harshen by visiting his Top Doctors profile.