Anal Fistulas

What is an anal fistula?

An anal fistula is an abnormal tunnel that forms between the inside of the anal canal and the skin near the anus. It usually develops after an infection in an anal gland leads to an abscess (a pocket of pus). When the abscess drains or bursts, a small tract may remain, connecting the infected gland to the skin surface.

Anal fistulas vary in depth and complexity. Some are simple and involve only one straight channel, while others may branch or extend deeper into surrounding tissues. They can cause symptoms such as persistent discharge, irritation or pain around the anus, and may reopen repeatedly if not treated properly.

This condition is more common in people who have had an anal abscess, but it can also occur in those with inflammatory bowel disease (particularly Crohn’s disease), tuberculosis or after surgery or trauma to the area.

Because anal fistulas rarely heal on their own and tend to recur, medical or surgical treatment is usually required to close the tract and prevent reinfection.

What are the different types of anal fistulas?

Anal fistulas are classified based on how the tract passes through or around the anal sphincter muscles — the circular muscles that control bowel movements. Understanding the type of fistula helps the surgeon choose the safest and most effective treatment while protecting continence.

The main types include:

• Intersphincteric fistula — the most common type. The tract runs between the internal and external sphincter muscles and opens onto the skin near the anus.

• Transsphincteric fistula — the tract passes through both sphincter muscles and exits further from the anal opening. It may form an abscess in the ischiorectal fossa (a fat-filled space beside the rectum).

• Suprasphincteric fistula — the tract starts above the internal sphincter, loops over the top of the external sphincter and then extends down to the skin.

• Extrasphincteric fistula — a rare and complex form that runs from the rectum to the skin without passing through the sphincter muscles. It is often associated with trauma, surgery, Crohn’s disease or infection.

• Superficial fistula — a short tract lying beneath the skin that does not cross any sphincter muscle. These are usually simple and easier to treat.

Each type differs in depth, direction and relation to the anal sphincters. Accurate classification through examination and imaging, such as MRI or endoanal ultrasound, is essential for planning the appropriate surgical approach and ensuring the best outcome.

What causes an anal fistula?

An anal fistula most commonly develops as a complication of an anal abscess, which is an infection in one of the small glands located just inside the anus. When an abscess forms, it fills with pus and creates pressure in the surrounding tissue. Even after the abscess drains or is surgically opened, a small tunnel can remain between the infected gland and the skin surface — this persistent channel is the fistula.

Other possible causes and risk factors include:

• Inflammatory bowel disease (IBD) — Crohn’s disease, in particular, is strongly associated with recurrent or complex fistulas due to chronic inflammation around the anal region.

• Tuberculosis or sexually transmitted infections (STIs) — rarely, certain infections such as tuberculosis or HIV can cause or complicate fistula formation.

• Trauma or surgery — injury to the anal area or previous operations, e.g., for haemorrhoids or fissures can occasionally lead to fistula formation.

• Radiation therapy or cancer — prior radiation or malignancy in the pelvic region may damage tissue and promote abnormal tracts.

• Chronic inflammation — long-standing local irritation or inflammation increases the likelihood of fistula development.

In most cases, the process begins with an infected anal gland that fails to heal completely, allowing a persistent tract to form. Treating both the fistula and any underlying disease is essential for lasting recovery.

What are the symptoms of an anal fistula?

The symptoms of an anal fistula can vary depending on its size, depth and whether it is actively infected. In most cases, people experience a combination of discomfort, discharge and irritation around the anus.

Common symptoms include:

• Persistent discharge — pus or blood-stained fluid leaking from an opening near the anus, which may soil clothing.

• Pain or swelling — discomfort around the anus that may worsen during sitting, bowel movements or prolonged walking.

• Recurring abscesses — repeated episodes of painful swelling or infection in the same area.

• Skin irritation — itching, redness or soreness around the anal opening due to constant moisture or discharge.

• Fever or general unwellness — if an infection is present or the abscess re-forms.

• A small external opening or lump — often visible or palpable on the skin near the anus, sometimes with intermittent drainage.

In some people, especially those with Crohn’s disease or complex fistulas, symptoms can be more persistent and difficult to manage. Because untreated fistulas rarely heal on their own, medical evaluation is important to prevent chronic infection or further complications.

How can I tell the difference between an anal fissure and an anal fistula?

Anal fissures and anal fistulas are two distinct conditions that affect the anal region but differ in cause, depth and treatment approach. Both can cause discomfort, pain and bleeding, but they arise from very different problems within the anal canal.

An anal fissure is a small tear in the skin lining of the anus, often caused by constipation, hard stools or excessive straining. It results in sharp pain during or after bowel movements and may produce a small amount of bright red bleeding. Anal fissures are usually superficial and heal with conservative measures such as stool softeners, high-fibre diets and topical medication.

An anal fistula, by contrast, is a small tunnel that develops between the inside of the anal canal and the skin near the anus. It usually follows an infection or abscess and causes persistent discharge, irritation, or swelling. Fistulas are deeper and more complex than fissures, and they generally require surgical treatment to heal completely.

Both conditions can be painful and distressing, but the key difference is that fissures affect the surface lining, whereas fistulas involve a deeper tunnel caused by infection. Consulting a colorectal specialist ensures the right diagnosis and a targeted treatment plan for complete healing.

What are the complications of an anal fistula?

If left untreated, an anal fistula can lead to a number of complications due to ongoing infection and inflammation. These problems may become chronic and significantly affect comfort and quality of life.

• Recurrent infection and abscess formation — the fistula can repeatedly trap bacteria, leading to new abscesses that cause pain, swelling and fever.

• Persistent discharge and irritation — continuous leakage of pus or stool through the fistula opening can cause skin breakdown, itching and local discomfort.

• Complex or branching tracts — over time, untreated fistulas can form multiple channels, making surgical repair more difficult.

• Anal sphincter damage — chronic infection or repeated surgery may weaken the anal muscles, potentially affecting bowel control.

• Fistula recurrence — even after treatment, some fistulas may return, particularly in patients with Crohn’s disease or complex tracts.

• Rare complications — in long-standing cases, chronic inflammation can cause scar tissue, strictures, or, in extremely rare instances, cancerous changes within the fistula tract.

Early diagnosis and appropriate management are essential to prevent these complications and ensure proper healing.

Who is at risk of developing an anal fistula in Singapore?

Anal fistulas can occur in anyone, but certain factors increase the likelihood of developing one,  especially in people with a history of anal infection or inflammation.

• Previous anal abscess — the most significant risk factor; about half of all anal abscesses eventually lead to a fistula.

• Inflammatory bowel disease (IBD) — Crohn’s disease, in particular, increases the risk of complex or recurrent fistulas due to chronic inflammation of the intestinal and anal tissues.

• Chronic diarrhoea or constipation — both can irritate the anal glands and increase susceptibility to infection.

• Trauma or surgery near the anus — injury or procedures affecting the anal canal can disrupt tissue healing and form abnormal tracts.

• Tuberculosis or HIV infection — these conditions can weaken the immune system and impair healing, allowing persistent infection.

• Male gender — men are affected more often than women, possibly due to anatomical differences and higher incidence of anal gland infections.

• Previous pelvic radiation or cancer — radiation therapy and certain cancers can damage tissues, increasing the risk of fistula formation.

Recognising these risk factors helps identify individuals who may benefit from early evaluation and treatment, preventing chronic or recurrent infections.

How is an anal fistula diagnosed?

Diagnosis of an anal fistula is usually straightforward, based on medical history, physical examination, and imaging tests if needed to define the tract’s extent.

• Clinical assessment — the doctor will begin by asking about symptoms such as pain, discharge, swelling or a history of abscesses. During examination, one or more small openings may be seen near the anus, sometimes with pus or fluid discharge. Gentle probing can help determine the direction of the tract, although this is done carefully to avoid creating false passages.

• Digital rectal examination — a gloved finger is used to assess tenderness, the position of the internal opening, and any signs of infection or associated conditions such as Crohn’s disease.

• Imaging studies — in complex or recurrent cases, further tests are often recommended:

• MRI of the pelvis — the most accurate method for mapping fistula tracts and detecting secondary channels.

• Endoanal ultrasound — uses sound waves to visualise the fistula and its relation to the sphincter muscles.

• Fistulography — an X-ray technique where contrast dye is injected into the tract to outline its course (used less commonly today).

• Examination under anaesthesia (EUA) — in some cases, especially when the tract is deep or difficult to assess due to pain, the surgeon may examine the area under anaesthesia. This allows a complete evaluation and often treatment during the same procedure.

Accurate diagnosis is essential to plan the most effective treatment, minimise recurrence, and preserve sphincter function.

What are the treatment options for anal fistula in Singapore?

Anal fistulas rarely heal on their own and usually require surgical treatment to close the tract, drain infection, and prevent recurrence. The choice of procedure depends on the fistula’s complexity, location, and relationship to the anal sphincter muscles.

Initial management of an anal fistula 

If an abscess is still present, it must first be drained to control infection and relieve pain. Antibiotics may be prescribed if there are signs of spreading infection or if the patient has other health risks such as diabetes or immunosuppression.

Surgical treatment options for anal fistula

• Fistulotomy — the most common and effective treatment for simple fistulas. The tract is opened along its length, cleaned, and allowed to heal naturally from the inside out.

• Seton placement — a thin surgical thread is placed through the tract to keep it open and drain infection. It may be left for weeks or months and is particularly useful for fistulas passing through the sphincter muscles.

• Advancement flap repair — involves covering the internal opening of the fistula with a flap of healthy tissue to encourage healing and preserve muscle control.

• LIFT procedure (ligation of intersphincteric fistula tract) — the fistula tract is tied off and divided in a way that avoids cutting the sphincter muscle, reducing the risk of incontinence.

• Fibrin glue or plug therapy — in selected cases, the fistula tract may be sealed with special biological glue or a collagen plug. These methods are less invasive but have variable success rates.

Postoperative care after surgery for anal fistula 

After surgery, patients are advised to take warm sitz baths, keep the area clean and dry and use stool softeners to prevent strain. Pain relief and follow-up visits are important to ensure proper healing and to detect recurrence early.

With modern surgical techniques, most anal fistulas can be successfully treated with excellent long-term outcomes and minimal impact on bowel control.

Recovery and Outlook for Anal Fistula 

Recovery after anal fistula surgery depends on the type of procedure performed, the complexity of the fistula and the individual’s overall health. Most patients recover well with proper wound care and follow-up.

For simple fistulas treated with fistulotomy, healing usually takes 4 to 8 weeks. Mild pain, discharge or spotting of blood can occur initially but improves as the wound closes. Sitz baths, high-fibre diets and stool softeners help make recovery more comfortable.

For complex or high fistulas, healing may take longer, especially when setons, advancement flaps, or LIFT procedures are used. Regular dressing changes and good hygiene are essential to prevent infection. Patients are generally advised to avoid heavy lifting or strenuous exercise until cleared by their surgeon.

The long-term outlook is very good when the appropriate procedure is chosen. Success rates exceed 90% for simple fistulas, while more complex cases may require staged or repeated treatments. With expert management, most patients regain full comfort and function with minimal risk of recurrence or loss of continence.

Summary 

Anal fistulas occur when an infection near the anus creates a small channel between the anal canal and the surrounding skin. They often develop after an abscess and cause symptoms such as pain, swelling, persistent discharge and irritation. Diagnosis is usually made through physical examination and imaging, such as MRI or endoanal ultrasound, to assess the tract’s depth and complexity.

Because anal fistulas rarely heal on their own, surgery is usually required to remove or close the tract. Treatments may include fistulotomy, seton placement, advancement flap repair or the LIFT procedure, all aimed at eradicating infection while preserving normal bowel control. With modern techniques and proper postoperative care, healing is typically complete, and the risk of recurrence is low.

If you have ongoing discomfort, discharge or swelling near the anus, do not delay medical attention. Schedule a consultation with Tan Siong San Surgery for a thorough assessment and specialised treatment to ensure safe, effective healing and long-term relief.