What is an Anal Fistula ?
An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the anus (where poo leaves the body).
They’re usually the result of an infection near the anus causing a collection of pus (abscess) in the nearby tissue. When the pus drains away, it can leave a small channel behind. Anal fistulas form when an anal abscess, that’s drained, doesn’t heal completely.
Anal fistulas can cause unpleasant symptoms, such as discomfort and skin irritation, and will not usually get better on their own. Surgery is recommended in most cases
Different types of anal fistulas are classified by their location. The various types include:
- Intersphincteric fistula. The tract begins in the space between the internal and external sphincter muscles and opens very close to the anal opening.
- Transphincteric fistula. The tract begins in the space between the internal and external sphincter muscles or in the space behind the anus. It then crosses the external sphincter and opens an inch or two outside the anal opening. These can wrap around the body in a U shape, with external openings on both sides of the anus (called a horseshoe fistula).
- Suprasphincteric fistula/ Extrasphincteric fistula. These are less common and more complex to treat and can only be diagnosed with specialist investigations.
Symptoms of an anal fistula
- skin irritation around the anus
- a constant, throbbing pain that may be worse when you sit down, move around, poo or cough
- smelly discharge from near your anus
- passing pus or blood when you poo
- swelling and redness around your anus and a high temperature (fever) if you also have an abscess
- difficulty controlling bowel movements (bowel incontinence) in some cases
- People who may have experience with recurring anal abscesses may have an anal fistula. The external opening of the fistula is usually red, inflamed, oozes pus, and is sometimes mixed with blood although this may be difficult for you to see yourself.
When to get medical advice
See a Specialist if you have persistent symptoms of an anal fistula. They’ll ask about your symptoms and whether you have any bowel conditions.
Colorectal Specialist will need to examine your anus and gently insert a finger inside it (rectal examination) to check for signs of a fistula.
You may need further tests to confirm the diagnosis and determine the most suitable treatment.
These may include:
- a proctoscopy, where a special telescope with a light on the end is used to look inside your anus.
- an ultrasound scan, MRI scan or CT scan.
- Sometimes your surgeon will need to examine you in the operating room (called exam under anaesthesia) 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.
Tools used to rule out other disorders such as ulcerative colitis or Crohn’s disease include:
- Flexible sigmoidoscopy. A thin, flexible tube with a lighted camera inside the tip allows doctors to view the lining of the rectum and sigmoid colon as a magnified image on a television screen
- Colonoscopy. Similar to sigmoidoscopy, but with the ability to examine the entire colon or large intestine
Causes of anal fistulas
Most anal fistulas develop after an anal abscess. You can get one if the abscess does not heal properly after the pus has drained away.
Less common causes of anal fistulas include:
- Crohn’s disease – a long-term condition in which the digestive system becomes inflamed
- diverticulitis – infection of the small pouches that can stick out of the side of the large intestine (colon)
- hidradenitis suppurativa – a long-term skin condition that causes abscesses and scarring
- infection with tuberculosis (TB) or HIV
- a complication of surgery near the anus
What Treatments are available for anal fistula?
The chosen treatment depends on the severity of your symptoms, their medical history and the type of fistula. Each fistula is different in terms of the path it takes through the muscles in the anus (sphincter muscles). The muscles are in two layers (internal and external) and a fistula can travel through or between these layers. Some complex fistulas can have side branches as well as one main tract.
Surgery allows all the infection to drain while at the same time avoiding damage to the delicate sphincter muscles around the anus as these muscles are important for maintaining bowel control (continence).
It is important to realise that a fistula is often difficult to treat. More than one operation is commonly needed to get a fistula to heal. Sometimes a fistula can be so difficult to heal that the focus of treatment is to allow them to drain well to improve symptoms.
- Fistulotomy: This involves making a cut along the length of the fistula it allows all infection to drain and leaves an open wound that takes 1 to 2 months to heal completely. However, it does involve cutting some of the sphincter muscle and if too much muscle is damaged it can result in incontinence. It is the most commonly performed operation for anal fistula, but it is only recommended for those people whose fistula does not involve too much sphincter muscle.
- Seton: A seton is a stitch that is threaded along the fistula. This does not allow the fistula to heal but it does allow some of the infection to drain easily. A seton controls symptoms and allows the fistula to stabilise prior to planning further operations. Setons are often used for fistulas that involve too much muscle to be treated by a fistulotomy operation. Some fistulas require several operations to get them to heal and this usually involves a combination of seton operations and other secondary options such as LIFT, advancement flap, paste or VAAFT (see below).
- LIFT: LIFT stands for ‘litigation of the inter-sphincteric fistula tract”. This operation making a cut around the anus and finding the fistula between the different layers of sphincter muscle. Once found the fistula is tied off. This operation can be effective but is not suitable for all types of fistula.
- Advancement Flap: For some fistula, the lining of the lower bowel (inside the anus) can be lifted up, as a flap, and used to cover the opening of the fistula. Like the LIFT procedure, an advancement flap can be effective and the risk of damage to the sphincter muscles is low.
- Plugs and paste: A plug is a thin strip of material made from collagen that is pulled into the fistula to block and plug the space. Similarly, a paste made from collagen can be squeezed into the fistula tract to block it. It is thought that these techniques can be effective in some cases but probably not those fistulas that contain side branches. Again, the risk of damage to the sphincter muscle is low.
- VAAFT: This stands for video assisted anal fistula treatment and involves passing a very small camera along the path of the fistula. This allows the path to be seen (including side any branches) and washes out all the infective material. Cautery (heat treatment) is then performed to clean and close the fistula. The procedure can be repeated in the future if necessary and the risk of damage to the sphincter muscle is low.
- Laser treatment / Radiofrequency ablation (RFA): A wire can be passed along the path of the fistula that delivers heat treatment from either a laser or an electrical current at the frequency of radio waves. This heat treatment attempts to clean and close the fistula tract.
- The operation: Anal fistula operations are usually performed as a day case procedure under a brief general anaesthetic, or a spinal anaesthetic (a needle into the back.) You may have a pre-assessment appointment before the operation to ensure that you are fit enough for the procedure. Just before the operation, you may be given an enema (some liquid inserted into the anus to empty the lower bowel.)
Following the operation, you may have a dressing (particularly if you have had a fistulotomy operation.) You will be monitored for a few hours in recovery before being discharged home. You will be given some painkillers to take home with you. The painkiller codeine can cause constipation so you may be given some laxatives with this.
Operation risks: All operations carry some degree of risk.
The main risks are:
- infection – this may require a course of antibiotics; severe cases may need to be treated in hospital
- recurrence of the fistula – the fistula can sometimes recur despite surgery
- bowel incontinence – this is a potential risk with most types of anal fistula treatment, although severe incontinence is rare one in 10 people may experience some degree of incontinence to gas and liquid (wet wind.)
The level of risk will depend on things like where your fistula is located and the specific procedure you have.
Speak to the surgeon about the potential risks of the procedure they recommend
After the operation: After a few days provided you feel well and the pain is controlled, you should be able to resume normal activities including driving, heavy lifting and going back to work. If you have dressings, you may need these to be changed or removed by the nurse at your GP practice.
Some fistulas may need several operations to allow them to fully heal. You may be booked for a planned operation (especially if your operation involved putting a seton along the fistula) or you may be seen in the clinic.
Is any follow-up treatment necessary for an anal fistula?
Most fistulas respond well to surgery. After the surgery, your surgeon may recommend that you soak the affected area in a warm bath, known as a sitz bath, and that you take stool softeners or laxatives for a week.
Since you may also have some pain or discomfort in the area after surgery, your physician will usually inject local anaesthetic such as lidocaine to decrease your discomfort, and may prescribe pain pills. If opioids are prescribed, they are usually used for a very short period.
If the abscess and fistula are treated properly and heal, they will probably not come back.
Can an anal fistula be prevented?
You can greatly reduce your risk of an anal fistula by avoiding constipation, keeping your stools soft and going to the toilet to open your bowels as soon as you feel the urge to go. To help your bowel work properly and keep your stools soft, it’s important to drink lots of fluid and get regular physical exercise.