Anal Fistula

An anal fistula is a small tunnel that forms between the inside of the back passage (anus or lower rectum) and the skin around the outside. Most fistulas develop as a result of an infection that started in one of the small glands just inside the anus. When this infection forms a collection of pus (an abscess) and the abscess drains — either on its own or after surgical drainage — a fistula tract can remain behind.

Fistulas vary considerably in their complexity. A simple fistula follows a short, straight path through a small amount of the sphincter muscle. A complex fistula may have multiple branches, pass through more of the sphincter muscle, or be associated with conditions such as Crohn’s disease, previous surgery, or radiation treatment. The type of fistula you have will guide which treatment your surgeon recommends.

Common symptoms include:

• Persistent or intermittent discharge of pus, blood, or fluid from an opening near the anus
• Pain, swelling, or irritation around the back passage
• A tender lump or swelling near the anus
• Skin soreness, redness, or rash around the external opening
• Occasionally, fever or feeling generally unwell — particularly if a new abscess is forming

Your surgeon will take a careful history of your symptoms and perform a clinical examination. Depending on the complexity of your fistula, further investigation may be recommended:

• MRI scan of the pelvis — the most accurate method to map the fistula tract and its relationship to the sphincter muscles
• Examination under anaesthetic (EUA) — allows thorough assessment and is often combined with initial treatment such as seton placement
• Endoanal ultrasound — a scan performed within the back passage to visualise the sphincter muscles and fistula tract

Treatment depends on the type, position, and complexity of your fistula, as well as your overall health and continence function. There is no single approach that suits all patients — your surgeon will discuss the most appropriate option for your individual situation.

1. Seton Drainage

A seton is a soft thread or suture that is passed through the fistula tract and tied loosely in a loop. It is one of the most commonly used initial treatments for fistulas that involve a significant amount of sphincter muscle.

How it works: The seton keeps the tract open, allowing drainage and preventing abscess formation. Over weeks to months, it promotes gradual fibrosis (scarring) around the muscle, which may reduce the risk to continence if the tract is subsequently divided. A seton is often used as a staging procedure — a first step while planning a definitive repair.

The procedure is usually performed under general or spinal anaesthetic as a day case. The seton is left in place and reviewed in clinic. It can be left long-term for drainage and symptom control in patients where other options carry too high a risk to continence.

Recovery: Most patients return home the same day and can resume light activities within a few days. The seton is generally well tolerated, though you may notice some discharge and mild discomfort while it is in place.

2. Fistulotomy

A fistulotomy involves surgically laying open the entire fistula tract so that it heals from the inside out. It is the most straightforward and reliably curative option — but it is only suitable when the fistula passes through a small amount of sphincter muscle, so that dividing the tract carries minimal risk to continence.

How it works: The surgeon uses a probe to identify the tract, then cuts along its length, converting the tunnel into an open groove. The wound is left open to heal gradually over several weeks. Healing is reliable, and recurrence rates after a successful fistulotomy are very low.

Recovery: Most patients go home the same day. The wound requires dressing changes, and your nurse or district nurse team will support you with wound care. Full healing typically takes 4–8 weeks depending on the size and depth of the fistula.

Suitability: Your surgeon will carefully assess how much sphincter muscle the fistula involves before recommending a fistulotomy. If too much muscle would be divided, a sphincter-sparing procedure will be discussed instead.

3. Collagen Plug

A collagen plug (also called a fistula plug or bioprosthetic plug) is a small, cone-shaped device made from purified animal collagen. It is inserted into the fistula tract and acts as a scaffold for the body to grow new tissue, ideally closing the tract from the inside.

How it works: The plug is advanced through the tract and anchored at the internal opening. It dissolves over time and the body’s healing response fills the tract with fibrous tissue. No sphincter muscle is cut.

Published studies report healing in approximately 50–60% of cases. It is generally considered a good first-line sphincter-sparing option because, if it does not work, it does not preclude other treatments. The procedure is usually performed under general anaesthetic as a day case.

Recovery: Most patients return home the same day with minimal discomfort. You may notice some discharge initially while the plug integrates.

4. Laser Ablation (FiLaC — Fistula-tract Laser Closure)

FiLaC is a minimally invasive technique in which a specially designed radially emitting laser probe is passed along the fistula tract and slowly withdrawn while emitting laser energy. The laser destroys the lining of the tract and causes it to seal shut. No sphincter muscle is divided.

How it works: Under general or spinal anaesthetic, the laser fibre is introduced into the fistula and activated as it is gradually pulled through the tract. The heat generated ablates (destroys) the tract wall and promotes closure. The internal opening is typically closed with a small suture or flap at the same time.

Published results suggest success rates of approximately 60–70% in carefully selected patients. Because no muscle is cut, the risk to continence is very low. The procedure can be repeated if needed and does not close off other treatment options.

Recovery: Day case procedure. Discomfort is generally mild. Most patients return to normal activities in a few days. There may be some discharge from the external opening in the weeks following treatment while healing takes place.

5. LIFT — Ligation of the Intersphincteric Fistula Tract

The LIFT procedure is a sphincter-sparing technique in which the fistula tract is approached through the natural space between the internal and external sphincter muscles (the intersphincteric plane). The tract is tied off and divided in this space, away from the main sphincter bulk.

How it works: A small incision is made in the groove between the two sphincter muscles. The fistula tract is identified within this space, tied securely with sutures at both ends, and divided. The internal opening is closed, and the wound is left to heal. By working in the intersphincteric plane, the procedure avoids dividing any significant portion of the sphincter.

Published series report success rates of 60–80%. It is particularly well suited to transsphincteric fistulas — those that cross through the sphincter complex — where fistulotomy would carry a continence risk. If LIFT does not achieve full closure, other options remain available.

Recovery: Day case procedure under general or spinal anaesthetic. Most patients experience moderate discomfort for the first few days. Return to light activities is typically possible within 1–2 weeks, and the wound usually heals within 4–6 weeks.

The table below gives a brief overview of each treatment. Your surgeon will recommend the most appropriate option based on a careful assessment of your fistula.

Your surgeon will arrange the investigations needed to plan your surgery — most commonly an MRI scan and possibly an examination under anaesthetic. Please let the clinic know if you:

• Take blood-thinning medication (e.g. warfarin, apixaban, rivaroxaban, clopidogrel) — specific guidance will be given
• Take diabetes medication — the timing of doses may need to be adjusted on the day
• Have any allergies or previous reactions to anaesthetics
• Have any active infection near the back passage

You will be asked not to eat for 6 hours before a procedure under general anaesthetic, and not to drink for 2 hours beforehand. You can take most regular medications with a small sip of water unless told otherwise.

Pain and Discomfort

Some discomfort, aching, and throbbing around the back passage is expected after any fistula procedure. Regular paracetamol and ibuprofen (if suitable for you) are usually sufficient. Avoid constipation — keeping stools soft and easy to pass makes recovery more comfortable. Your surgeon will advise on laxatives if needed.

Wound Care

Keep the area clean by showering or bathing regularly. Pat the area dry gently afterwards. Loose, breathable underwear is more comfortable than tight or synthetic fabrics. A small pad or dressing can help manage any discharge.

Diet and Bowel Habits

Eat a balanced diet with plenty of fibre and fluid to keep your bowel movements soft and regular. This reduces straining, which is important for wound healing. Avoid heavy lifting or strenuous exercise until your surgeon advises it is safe to resume.

Follow-Up

You will be reviewed in the clinic after your procedure. Your surgeon will assess healing, check wound progress, and discuss next steps if further treatment is needed. Please do not skip this review even if you feel well.

Fistula surgery is generally safe, but as with all surgical procedures there are potential complications. The specific risks vary depending on which procedure you are having; your surgeon will discuss these with you individually.