Anal Fistula: Symptoms, Causes, Types, and Treatment Options

Dr. Chok Aik Yong

Colorectal Surgeon & General Surgeon

MBBS | MRCS (UK) | MMed (Surgery) | FRCS (UK)

Symptoms causes types diagnosis treatments prevention FAQ

What is an Anal Fistula?

An anal fistula is an abnormal tunnel that connects the anal canal (the internal anus) to the skin around the anus. This condition develops when an anal abscess, a pus-filled infection, fails to heal properly. The fistula creates a passage for bacteria and faecal matter to move to the skin’s surface, causing chronic drainage, discomfort, and recurring infections that require medical treatment.

Symptoms of Anal Fistula

Recognising the symptoms of an anal fistula is crucial for early diagnosis and effective treatment. Common signs include:

Persistent Drainage: A continuous discharge of pus or blood-stained fluid from an opening near the anus, which may stain undergarments.
Pain or Discomfort: Throbbing pain that worsens when sitting or during bowel movements, often accompanied by general discomfort in the anal area.
Skin Irritation: Redness, soreness, and itching of the skin around the external fistula opening due to constant moisture and irritation.
Swelling: Periodic episodes of painful swelling around the anus, often indicating possible abscess formation.
Difficulty with Hygiene: Ongoing drainage can make proper hygiene challenging and may cause an unpleasant odour.

Causes and Risk Factors

Several factors can increase the likelihood of developing an anal fistula or contribute to its formation. These include:

Previous Anal Abscess

Approximately 50% of patients who develop an anal abscess will subsequently develop a fistula.
Inflammatory Bowel Disease

Crohn’s disease and ulcerative colitis increase the risk of fistula formation.
Previous Anal Surgery

Healing complications from past surgeries in the anal area might lead to the development of anal fistula.
Trauma or Injury

Physical damage to the anal area can create conditions favourable for fistula development.
Sexually Transmitted Infections

Certain STIs affecting the anal region may increase the risk of fistula formation.

Types of Anal Fistula

Anal fistulas are classified based on their location and the way they interact with or pass through the anal sphincter muscles.

Intersphincteric Fistula

Passes through the internal sphincter, exiting near the anus. It is the most common type and more straightforward to treat surgically.

Transsphincteric Fistula

Crosses through the internal and external sphincter muscles before reaching the skin. Their treatment requires careful consideration of sphincter muscle preservation to maintain proper bowel control.

Suprasphincteric Fistula

Travels above the anal sphincter structure before crossing back down to the skin. They follow a more complex path and often require specialised surgical techniques.

Extrasphincteric Fistula

Bypasses sphincter muscles entirely, connecting directly to the rectum or anal canal. They are rare and often associated with underlying conditions such as Crohn’s disease or rectal cancer, presenting considerable challenges in treatment.

Diagnostic Methods

Physical Examination

The doctor examines the anal area to locate the external opening and checks for signs of drainage or inflammation. Digital rectal examination helps assess sphincter tone and locate the internal opening. This initial assessment provides basic information about fistula location and complexity.
Fistula Mapping

A thin, flexible probe is carefully used to explore the fistula tract, identifying its path and any branches. The procedure is performed under local anaesthetic if necessary. While effective for mapping straightforward fistulas, it may not provide a complete assessment of more complex cases.
MRI Scan

Magnetic Resonance Imaging provides detailed images of the anal canal, sphincter muscles, and fistula tract. The scan shows the complete path of complex fistulas and identifies hidden branches or abscesses. This information guides surgical planning.
Endoanal Ultrasound

A small ultrasound probe inserted into the anal canal creates detailed images of the sphincter muscles and fistula tract. This technique helps assess the fistula’s relationship to the sphincter muscles and guides treatment decisions.

Treatment Options

Treatment options are divided into non-surgical and surgical approaches, depending on the fistula’s location, complexity, and the patient’s overall health.

Non-Surgical Treatments

Antibiotics

These medications help treat active infections and reduce inflammation. A typical course lasts 7–14 days. While antibiotics alone do not heal fistulas, they can temporarily control symptoms.

Fibrin Glue

The surgeon injects a specialised glue into the cleaned fistula tract to close it. This minimally invasive procedure, performed under local anaesthesia, typically takes about 30 minutes. While success rates vary, it is an effective option for preserving sphincter function.

Surgical Treatments

Fistulotomy

This technique involves opening the entire fistula tract. The surgeon cuts along the length of the fistula, removes infected tissue, and allows the wound to heal from the inside out. This method works best for simple, low fistulas that involve minimal sphincter muscle.

Seton Placement

A soft surgical thread (seton) is placed within the fistula and secured on the skin surface outside the anus. This technique facilitates drainage, reduces infection, and allows the fistula to heal gradually while minimising damage to surrounding tissue. The process typically takes several weeks and is particularly useful for preserving sphincter function in more complex cases.

LIFT (Ligation of Intersphincteric Fistula Tract)

This technique involves tying off and removing the fistula tract while preserving the sphincter muscles. This technique preserves the anal sphincter muscles and reduces healing time compared to traditional methods.

Rectal Advancement Flap

The surgeon creates a flap of healthy tissue from the rectum or anal canal. After removing the internal opening of a fistula, the flap is pulled down to cover the repair site. This method suits complex fistulas and helps maintain muscle integrity.

Video Assisted Anal Fistula Treatment (VAAFT)

VAAFT is a modern and advanced minimally invasive approach for managing complex anal fistulas. This technique uses a video scope to visually examine the entire fistula tract, from the external opening to its internal origin. Once the internal opening is located, it is sealed, and the fistula tract is thoroughly cleaned with specialised tools, such as a brush and probe, under direct visualisation. One of the key advantages of VAAFT is that it eliminates the need for a large incision on the skin, resulting in a less invasive procedure and potentially quicker recovery.

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Prevention and Management

Maintaining proper anal hygiene is key to preventing infections and fistula formation. Gently cleaning the area with warm water after bowel movements helps keep it clean. Consuming a high-fibre diet and staying hydrated can prevent constipation and reduce straining during bowel movements. Promptly treating anal abscesses lowers the risk of fistula development. For patients with inflammatory bowel disease, adhering to prescribed treatment plans can help minimise complications.

Frequently Asked Questions (FAQ)

Can anal fistulas heal naturally without surgery?

No, most anal fistulas do not heal on their own and typically require medical or surgical intervention. The constant presence of bacteria in the anal canal, combined with the regular movement of the area, prevents natural healing.

Does smoking affect fistula healing?

Yes, smoking significantly impacts wound healing. It reduces blood flow to tissues, slows the healing process, and increases the risk of complications. Smokers often face longer recovery times and higher chances of treatment failure.

What happens if a fistula remains untreated?

If left untreated, a fistula can lead to recurrent abscesses, the spread of infection to surrounding tissues, and the formation of additional fistula tracts. Chronic infection may also result in systemic health issues, increasing the potential for more severe complications.

Dr. Chok Aik Yong

Colorectal Surgeon & General Surgeon

MBBS|MRCS (UK)|MMed (Surgery)|FRCS (UK)

Expertise lies in managing colorectal diseases, particularly advanced colorectal cancer and inflammatory bowel disease.

Dr Chok graduated with degrees in Bachelor of Medicine and Surgery from the National University of Singapore. He was conferred the Master of Medicine (Surgery) in Edinburgh (UK) and a member of the Royal College of Surgeons, UK. He subsequently completed his specialist training in colorectal surgery and became a Fellow of the royal college of Surgeons in Edinburgh in 2016.
Dr Chok was awarded the Health Manpower Development Plan (HMDP) award in 2019 to further advance his colorectal training at Royal Marsden Hospital, one of the top 5 cancer centres in the world. While in London, Dr Chok trained with pioneers in the surgical management of advanced colorectal cancer and inflammatory bowel disease (IBD) and gained extensive experience while appraising the latest clinical and research evidence.

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