Anal Abscesses & Fistulas

Pain, swelling, and discharge around the anus may point to an abscess or fistula.

Persistent symptoms should be assessed with a colonoscopy to rule out deeper causes.

20+ years of experience

5000+ scopes performed

Fellowship-trained colorectal surgeon

Medisave & Insurance Claimable

What Are Anal Abscesses and Fistulas?

Anal abscesses, and fistulas are relatively common, yet often misunderstood, conditions that affect the anal, and perianal region. If these conditions are not properly treated, they can cause ongoing pain, recurrent infections, and complications such as chronic fistula formation. In fact in worse cases, surgical treatment is required for complete healing, and to prevent recurrence.

An anal abscess occurs when a small gland near the anus or rectum becomes infected, leading to the collection of pus in the surrounding tissue. This results in a swollen, painful lump near the anus, often accompanied by redness, fever, and pain when sitting or passing stools.

Additionally, anal abscess can be categorised into the following categories:

Perianal Abscess – the most common type, located just beneath the skin around the anus.
Ischiorectal Abscess – extends deeper into the ischiorectal space, causing swelling, and pain on one or both sides of the anus.
Intersphincteric Abscess – lies between the internal, and external sphincter muscles.
Supralevator Abscess – a rare and deep abscess that may originate from pelvic infections or spread from other compartments.

An anal fistula, on the other hand, is a small tunnel that forms between the anal canal, and the skin around the anus. It typically develops after an abscess has burst or been drained but has not healed fully. Some fistulas are silent, but many cause persistent discharge, skin irritation, and recurrent infections.

Anal fistulas are categorised based on their location, and relationship to the anal sphincter muscles. The main types include:

Intersphincteric fistula – runs between the internal, and external sphincter muscles.
Transsphincteric fistula – passes through both the internal, and external sphincters.
Suprasphincteric fistula – starts above the internal sphincter, and loops over the puborectalis muscle.
Extrasphincteric fistula – extends from the rectum to the skin, bypassing the sphincter muscles.
Submucosal fistula – lies just beneath the anal lining, often less complex.

Comparison Table Between Anal Abscess and Anal Fistula

FEATURE	ANAL ABSCESS	ANAL FISTULA
Definition	A collection of pus caused by infection.	A tunnel between the anal canal, and skin surface.
Cause	Infection of anal glands.	Often a complication of a previously drained abscess.
Onset	Sudden (acute infection).	Gradual (following unresolved abscess).
Visible Signs	Swollen lump near the anus.	Small external opening or persistent drainage.

What causes Anal Abscesses and Fistulas?

Anal abscesses typically begin with an infection of the small glands located inside the anal canal. These glands, known as anal crypt glands, normally secrete mucus to aid in stool passage. However, when these glands become blocked or damaged, bacteria can multiply within the trapped secretions, leading to the formation of an abscess, which is a painful pocket of pus.

Beyond that, several factors may similarly contribute to the development of an anal abscess, including:

Blocked anal crypt glands – the most common cause, where glandular secretions become trapped, and infected.
Inflammatory bowel disease (IBD) – conditions like Crohn’s disease can cause chronic inflammation, and ulceration in the anal region, increasing susceptibility to abscess formation.
Sexually transmitted infections (STIs) – infections such as gonorrhoea or chlamydia can involve the anal area, and lead to localised abscesses.
Trauma to the anal region – injury from anal intercourse, surgery or hard stools can damage the delicate tissues, allowing bacteria to invade.
Immunosuppression – conditions such as diabetes or HIV can impair the body’s ability to fight infections, increasing the risk of abscess formation, and recurrence.

From Abscess to Fistula

If the abscess is not completely treated or recurs, a chronic tract may develop between the infected gland, and the skin near the anus. This persistent tunnel is known as an anal fistula.

A fistula forms when the body attempts to drain the infection through an alternative route, often externally through the skin. Unfortunately, this tract rarely closes on its own, and ongoing inflammation can cause persistent pain, discharge, and recurrent infections. In some cases, the fistula may remain silent for a period but can flare up unexpectedly.

Without appropriate surgical intervention, an anal fistula can persist for months or even years, significantly impacting quality of life.

If you are experiencing the symptoms,

consult a medical professional immediately.

Schedule an appointment with Dr Aaron Poh.

book an appointment

What are the symptoms of Anal Abscesses and Fistulas?

The symptoms of these conditions can overlap but vary in intensity, and duration:

Symptoms of an Anal Abscess

Fever, and chills.
Painful bowel movements.
Possible spontaneous drainage of pus.
Redness, and warmth in the anal area.
Severe, constant pain near the anus.
Swelling or a palpable lump.

Symptoms of an Anal Fistula

A visible opening or hole near the anus.
Foul-smelling drainage.
Painful swelling that comes, and goes.
Persistent or recurrent anal pain.
Pus or bloody discharge near the anus.
Skin irritation or itchiness.

Who Is at risk of developing Anal Abscesses and Fistulas?

Although anal abscesses, and fistulas can occur in anyone, several risk factors may increase the likelihood of developing these conditions. This may include:

Age – adults between 20, and 50 years old are more prone to developing anal abscesses, and fistulas. This age group tends to be more physically active, and may experience more exposure to minor trauma or infections in the anal area, which can trigger gland blockage or inflammation.
Gender – males are statistically more likely to develop these conditions. The exact reason is unclear, but it may relate to differences in gland size, hormone levels or behaviours that increase exposure to anal trauma or infection.
Medical conditions – chronic IBDs can cause long-term inflammation, and ulceration in the intestines, and around the anus. This ongoing irritation increases the chance of infection, and gland blockage, leading to abscesses and, subsequently, fistulas.
Infections – certain infections, especially sexually transmitted ones, can cause inflammation or direct damage to the anal tissues. This promotes bacterial invasion of the anal glands, and raises the risk of abscess formation, and fistula development if they are left untreated.

Weakened immune system – a compromised immune system reduces the body’s ability to fight off infections effectively. As a result, even minor infections can progress into larger abscesses and may not heal completely, increasing the likelihood of chronic fistula formation.

Schedule Your Appointment with Dr Aaron Poh.

What are the potential complications if treatment is delayed?

If both anal abscess, and anal fistula are left untreated, patients are exposing themselves to possible complications, such as:

Abscess rupture leading to sepsis
Chronic drainage
Complex fistula tracts involving the sphincter muscles
Faecal incontinence
Recurrent infections
Skin breakdown and irritation

How Anal Abscesses and Fistulas diagnosed in Singapore?

It is important to understand that early, and accurate diagnosis of anal abscesses, and fistulas is vital to prevent complications such as chronic infections, persistent pain, and delayed healing.

The diagnostic process typically involves:

Consultation

Clinical examination – a thorough inspection of the anal, and perianal area is carried out to identify visible swelling, redness, tenderness or discharge. Dr. Poh may also perform a digital rectal examination (DRE) to assess deeper abscesses or internal openings of a fistula.
Medical history review – this includes discussing symptoms such as pain, swelling, fever, discharge or bleeding. Dr. Poh also reviews any prior history of abscesses, fistulas or conditions like Crohn’s disease, which may influence diagnosis, and treatment planning.

Diagnostic Tests

Blood tests – a full blood count (FBC) may be done to check for raised white blood cell levels, which suggest active infection or inflammation.

Swab or culture tests – in cases with active discharge, a swab may be taken to identify the type of bacteria involved. This can help guide antibiotic therapy if required.

Imaging Tests

Endoanal or pelvic ultrasound – a non-invasive imaging method that uses sound waves to visualise fluid collections or fistulous tracts in the anal region.

Magnetic Resonance Imaging (MRI) of the pelvis – often considered the go-to diagnostic step for complex or recurrent fistulas, MRI provides detailed images of the soft tissues around the anal canal, helping to map the fistula’s course, and guide surgical planning.

Computed Tomography (CT) scan – CT scans are occasionally used for deeper or more extensive abscesses, especially when infection spreads to the pelvic or abdominal cavity.

How are Anal Abscesses and Fistulas treated?

Treatment for Anal Abscesses

Anal abscesses are infections that require prompt attention. The main goal is to drain the accumulated pus, and eliminate the source of infection before it leads to complications such as fistula formation. This includes:

Incision and drainage – these are the primary, and most effective treatment for anal abscesses. Under local or general anaesthesia, a small incision is made over the abscess to release pus, and relieve pressure. This procedure is typically done on an outpatient basis, and offers quick relief from symptoms.
Antibiotic therapy – antibiotics may be prescribed alongside drainage, particularly for patients with surrounding cellulitis, diabetes, weakened immunity or systemic infection. However, antibiotics alone are generally not enough to treat an abscess definitively.
Follow-up care – after drainage, Dr. Poh monitors healing closely. If the wound does not fully resolve or shows signs of persistent discharge, further evaluation is done to check for a developing fistula.

Treatment for Anal Fistulas

Fistulas usually develop following an inadequately healed or recurrent abscess. These abnormal tracts do not resolve on their own, and typically require surgical correction, which are:

Fistulotomy – in simple, low-lying fistulas, a fistulotomy may be performed. This involves surgically opening the fistula tract to allow it to heal naturally from the inside out. It is a highly effective procedure with minimal risk of complications in suitable cases.
Seton placement – for complex or high fistulas that involve the anal sphincter, a seton (a thin surgical thread) may be inserted to allow drainage, and gradually cut through the tract while preserving sphincter control. This approach helps reduce the risk of incontinence.
Advancement flap repair – in selected cases where preserving sphincter function is critical, an advancement flap may be used. This technique involves covering the internal opening of the fistula with a flap of healthy tissue to promote healing without compromising continence.
Litigation of the Intersphincteric Fistula Tract (LIFT) Procedure – for deeper fistulas, this sphincter-sparing technique may be recommended. It involves accessing the tract between the sphincter muscles and tying it off to stop the abnormal communication, allowing natural healing.
Video-Assisted Anal Fistula Treatment – this procedure is a muscle-sparing procedure that involves navigating the fistula tract with an anoscope. The internal opening will then be located with the anoscope followed by obliteration of the fistula tract with diathermy treatment and injection of tissue glue.

Book An Appointment

Persistent anal pain, swelling or unusual discharge should not be dismissed as minor issues. These may be signs of a deeper problem such as an abscess or fistula that requires timely treatment.

At our clinic , Dr Aaron Poh and his clinical team provides compassionate, professional care to help you achieve complete healing, and prevent recurrence. We ensure a personalised treatment plan tailored to your condition and lifestyle. Schedule a consultation today, and take the first step toward long-term relief and recovery.

Frequently Asked Questions (FAQs)

Can an anal abscess go away on its own?

While small abscesses may temporarily drain, and seem to improve, most will not resolve completely without medical intervention. Without proper drainage, the infection often recurs or progresses into a chronic anal fistula.

How do I know if I have a fistula after an abscess?

Persistent discharge, pain or swelling at the site of a previous abscess may indicate a fistula. If symptoms are not fully resolved after abscess treatment, it is advisable to seek further evaluation from a colorectal surgeon.

Are anal abscesses and fistulas contagious?

No, these conditions are not contagious. They are caused by internal infections, often involving blocked glands or secondary inflammation due to underlying health issues, not by direct person-to-person transmission.

Do anal fistulas always require surgery?

Yes, in most cases. Unlike abscesses, fistulas do not heal on their own. Surgery is typically necessary to close the abnormal tract, and prevent further infection, although the type of procedure varies based on fistula complexity.

How long is the recovery after treatment?

Recovery time depends on the severity of the condition, and the type of procedure performed. Simple drainage of an abscess may heal in 1 to 2 weeks, while fistula surgery may require several weeks of recovery, and wound care.

Can lifestyle or diet changes help prevent recurrence?

While not a substitute for medical treatment, maintaining good hygiene, managing chronic health conditions (like diabetes or Crohn’s disease), and ensuring regular bowel movements may help reduce the risk of recurrence.

Is anal fistula surgery painful?

Discomfort is expected after surgery, but it is typically manageable with prescribed pain relief. Dr. Poh provides comprehensive aftercare, and instructions to ensure a smoother, more comfortable recovery.