Perianal Abscess & Fistula: Symptoms, Causes & Surgical Treatment

What Is a Perianal Abscess?

A perianal abscess is a localized collection of pus (infected fluid) that forms in the tissues surrounding the anal opening. It results from a bacterial infection, usually originating in the small glands just inside the anus. The condition causes severe pain, swelling, and sometimes fever, requiring urgent surgical drainage in most cases.

The term "perianal" refers to the area immediately surrounding the anus. When bacteria infect the tissues in this region, the body's immune response creates a pocket of pus as it tries to fight off the infection. This pocket is the abscess. The condition is distinct from hemorrhoids, though both cause pain and swelling in the same general area.

Perianal abscesses are more common than many people realize, affecting approximately 2-3 per 10,000 people each year. Men are affected two to three times more often than women, and the condition most commonly occurs in people between ages 30 and 50. While anyone can develop a perianal abscess, certain factors increase the risk, including diabetes, inflammatory bowel disease (particularly Crohn's disease), and conditions that weaken the immune system.

The medical terminology can be confusing, as these abscesses are sometimes called "anorectal abscesses" or classified by their specific location (such as "ischiorectal abscess" or "intersphincteric abscess"). The location matters for surgical planning but doesn't change the fundamental nature of the condition – a bacterial infection requiring drainage.

How Perianal Abscesses Form

Inside the anal canal, there are small glands that produce mucus to help with bowel movements. These glands are located in the area where the anal canal meets the rectum. When the opening of one of these glands becomes blocked, bacteria that normally live harmlessly in the intestines can become trapped inside. The blocked gland provides an ideal environment for these bacteria to multiply.

As the bacteria multiply, the body's immune system responds by sending white blood cells to fight the infection. This battle between bacteria and immune cells produces pus – a thick, yellowish fluid consisting of dead bacteria, dead white blood cells, and tissue debris. The pus accumulates and forms a pocket, which is the abscess.

The abscess can remain superficial, just beneath the skin near the anal opening, or it can track deeper into the tissues surrounding the rectum. Deeper abscesses may be harder to detect on physical examination but can cause more severe illness. Without treatment, the pressure within the abscess increases as more pus forms, eventually causing the abscess to rupture either to the skin surface or back into the rectum – this is how fistulas begin to form.

Types of Perianal Abscesses by Location

Colorectal surgeons classify abscesses based on their anatomical location, which influences both the symptoms and the surgical approach needed for treatment. Understanding these classifications helps patients make sense of their diagnosis and treatment plan.

• Perianal abscess (most common, ~60%): Located just beneath the skin at the anal margin. Usually visible as a tender, red swelling and can often be drained under local anesthesia.
• Ischiorectal abscess (~20%): Located in the ischiorectal fossa, a fat-filled space on either side of the rectum. These are deeper and larger, causing significant buttock swelling and pain.
• Intersphincteric abscess (~5%): Located between the internal and external anal sphincter muscles. May not cause visible external swelling but causes severe deep pain.
• Supralevator abscess (rare): Located above the levator ani muscle, deep in the pelvis. These are the most dangerous and may present with pelvic pain and fever without obvious anal symptoms.

What Is an Anal Fistula?

An anal fistula (fistula-in-ano) is an abnormal tunnel that forms between the inside of the anal canal and the skin outside the anus. It typically develops as a complication of a perianal abscess when the infection drains but leaves behind a persistent tract. Fistulas cause ongoing discharge, recurring infections, and usually require surgical treatment to heal.

While a perianal abscess is an acute infection, an anal fistula represents a chronic condition. Think of the fistula as the "scar" or remnant of an abscess – a tube-like channel that connects two body surfaces that shouldn't normally be connected. In most cases, one opening (the internal opening) is inside the anal canal, usually at the site of the original infected gland, while the other opening (the external opening) is on the skin near the anus.

Approximately 30-50% of perianal abscesses will develop into fistulas, even after proper surgical drainage. This high rate occurs because the underlying problem – the blocked or diseased anal gland – often persists even after the acute infection is drained. The fistula tract becomes lined with tissue that prevents it from closing on its own, which is why surgical intervention is typically necessary.

Fistulas vary considerably in their complexity. Simple fistulas take a direct path from the internal to external opening without involving much of the sphincter muscle. Complex fistulas may branch into multiple tracts, involve significant portions of the sphincter muscles, or be associated with underlying conditions like Crohn's disease. This complexity is important because it determines what surgical approach will be most effective while preserving continence.

The Difference Between Abscess and Fistula

Understanding the difference between these two conditions is crucial for patients, as the symptoms, urgency, and treatment approaches differ significantly. The abscess is the acute phase – a sudden, painful infection that requires urgent treatment. The fistula is the chronic phase – an ongoing abnormal channel that causes persistent symptoms but is not usually an emergency.

What Are the Symptoms of Perianal Abscess and Fistula?

Perianal abscess symptoms include severe constant anal pain that worsens with sitting or bowel movements, a visible swollen lump near the anus, redness, and often fever. Anal fistula symptoms are typically less severe but more persistent: ongoing discharge (pus or blood-tinged), skin irritation, and intermittent pain that improves when discharge occurs.

The symptoms of these two related conditions differ significantly in their character and urgency. Recognizing these symptoms is important for seeking appropriate care at the right time. Many people feel embarrassed about anal symptoms and delay seeking help, but early treatment leads to better outcomes and faster recovery.

Perianal Abscess Symptoms

The hallmark symptom of a perianal abscess is severe, constant pain in the anal region. This pain is often described as throbbing or pulsating and tends to worsen progressively over hours to days. Unlike hemorrhoid pain, which often improves between bowel movements, abscess pain is persistent and may actually worsen when sitting, coughing, or having a bowel movement due to increased pressure on the infected area.

Physical signs depend partly on how superficial or deep the abscess is located. Superficial perianal abscesses typically cause visible swelling near the anal opening – a tender, red, warm lump that is clearly abnormal. The overlying skin may appear stretched and shiny. Deeper abscesses may cause significant pain without obvious external swelling, making them more challenging to diagnose. In these cases, the pain seems to come from inside, and the only visible sign might be subtle asymmetry in the buttock or perineum.

• Severe constant pain: Throbbing pain around the anus that doesn't go away and worsens over time
• Visible swelling: A tender lump or bulge near the anal opening that may be red and warm to touch
• Fever and chills: Present in many cases, indicating the body is fighting infection
• Difficulty sitting: Pressure on the abscess causes increased pain
• Pain with bowel movements: May also cause difficulty passing stool due to pain
• General malaise: Feeling unwell, tired, or ill beyond just local symptoms

Anal Fistula Symptoms

Unlike the acute, severe symptoms of an abscess, fistula symptoms tend to be chronic and intermittent. The most characteristic symptom is persistent drainage from an opening near the anus. This discharge is usually purulent (containing pus) and may be blood-tinged. It stains underwear and can cause significant skin irritation and discomfort around the anal area.

Many patients with fistulas notice a cyclical pattern to their symptoms. The external opening of the fistula may temporarily close, causing fluid to accumulate in the tract. This causes increasing pain and swelling – essentially a small abscess forming. Eventually, the opening reopens or a new opening forms, the accumulated fluid drains, and the pain improves. This cycle can repeat indefinitely until the fistula is properly treated.

Some patients may notice passage of air or even fecal material through the fistula opening, depending on where the internal opening is located. A specific type of fistula, called a rectovaginal fistula in women, creates a connection between the rectum and vagina, causing gas and stool to pass through the vagina – an extremely distressing symptom that requires specialized treatment.

Pilonidal Cyst – A Related but Different Condition

A pilonidal cyst is sometimes confused with a perianal abscess because both occur in the general buttock region. However, a pilonidal cyst develops in the cleft between the buttocks (natal cleft) near the tailbone, not at the anal opening itself. It typically results from hair follicles becoming ingrown and infected in this area, which is why it's more common in young men with significant body hair.

The key distinguishing feature is location: pilonidal disease occurs at the top of the gluteal cleft near the sacrum, while perianal disease occurs around the anal opening. Treatment principles are similar (surgical drainage for acute abscesses, definitive surgery for chronic disease), but the surgical approaches differ significantly due to the different anatomical locations.

When Should You See a Doctor for Anal Pain?

You should see a doctor promptly if you have persistent anal pain with swelling or discharge that lasts more than a day or two. Seek emergency care immediately if you have severe anal pain combined with fever, difficulty urinating, or feeling very unwell. Early treatment of abscesses prevents complications and speeds recovery.

Many people delay seeking care for anal symptoms due to embarrassment or hoping the problem will resolve on its own. While some minor anal conditions do improve without treatment, perianal abscesses almost never heal without medical intervention. Delaying treatment allows the infection to spread, increases the risk of complications, and often results in a more extensive surgery being needed.

Healthcare providers who treat these conditions – including family doctors, general surgeons, and colorectal specialists – examine patients with anal problems regularly and will not judge you for seeking help. Remember that your doctor's goal is to help you recover as quickly and completely as possible.

Situations Requiring Routine Medical Evaluation

Contact your doctor or schedule an appointment if you notice any of the following symptoms that persist for more than a day or two:

• A painful lump or swelling near the anal opening
• Persistent discharge (pus, blood, or mucus) from near the anus
• Recurring pain in the anal area that comes and goes
• A visible opening or hole in the skin near the anus that drains fluid
• Skin irritation or itching that doesn't respond to hygiene measures

Situations Requiring Urgent or Emergency Care

Certain symptoms suggest a more serious infection that needs immediate attention. If you experience severe anal pain combined with any of the following, you should go to an emergency department or urgent care center right away:

• Fever of 38°C (100.4°F) or higher, or shaking chills
• Difficulty urinating or complete inability to pass urine
• Redness and swelling that is spreading rapidly beyond the initial area
• Feeling very unwell – weak, dizzy, confused, or like you might faint
• Rapid heartbeat or fast, shallow breathing

These warning signs may indicate that the infection is spreading into the bloodstream (sepsis) or into surrounding tissues (Fournier's gangrene – a rare but life-threatening condition). These serious complications are uncommon but require immediate treatment with surgery and intravenous antibiotics.

How Are Perianal Abscesses and Fistulas Diagnosed?

Diagnosis typically begins with a physical examination, where the doctor inspects and gently palpates the anal area. For most perianal abscesses, physical examination is sufficient. Fistulas and complex cases may require additional testing including proctoscopy, MRI of the pelvis, or endoanal ultrasound to map the fistula tract and plan surgery.

When you see a doctor for suspected perianal abscess or fistula, they will first take a detailed history of your symptoms. They'll ask about the nature and duration of your pain, any discharge, fever, previous similar episodes, and relevant medical history including any inflammatory bowel disease or diabetes. This history provides important clues about the nature and severity of your condition.

Physical examination is the cornerstone of diagnosis. The doctor will visually inspect the area around the anus, looking for swelling, redness, discharge, or visible external fistula openings. They will gently palpate (feel) the area to assess for tenderness, fluctuance (the fluid feeling of an abscess), and to locate any abnormal tracts. A digital rectal examination – where the doctor inserts a gloved, lubricated finger into the rectum – helps assess for internal abscesses and may help identify internal fistula openings.

Additional Diagnostic Tests

While physical examination is often sufficient for diagnosing a straightforward perianal abscess, additional tests may be needed in certain situations. These include cases where the diagnosis is unclear, the abscess appears to be deep or complex, or when planning surgery for a fistula.

Proctoscopy or anoscopy involves inserting a small, lighted instrument into the anal canal to visualize the rectal lining. This helps identify internal fistula openings and can reveal signs of inflammatory bowel disease or other conditions that might be contributing to the problem.

MRI (Magnetic Resonance Imaging) of the pelvis is the gold standard imaging test for complex fistulas. MRI provides detailed images of the soft tissues, clearly showing the fistula tract, any branches, and the relationship to the sphincter muscles. This information is crucial for surgical planning in complex cases. MRI may also reveal abscesses that are not apparent on physical examination.

Endoanal ultrasound uses a small ultrasound probe inserted into the anal canal to image the sphincter muscles and surrounding tissues. It can identify fistula tracts and is particularly useful for assessing sphincter anatomy before surgery.

Fistulography involves injecting contrast dye into the external fistula opening and taking X-rays. While largely replaced by MRI, it may still be used in some settings.

How Are Perianal Abscesses and Fistulas Treated?

Both conditions are treated primarily with surgery. Perianal abscesses require incision and drainage – a procedure to release the pus. Anal fistulas require more specialized surgery to eliminate the tract while preserving sphincter function. Antibiotics are used as adjunct therapy when infection is spreading but cannot cure an established abscess or fistula on their own.

The fundamental principle in treating perianal abscesses is that "pus must be drained." Unlike some infections that respond to antibiotics alone, an abscess represents a walled-off collection of pus that antibiotics cannot effectively penetrate. Without surgical drainage, the infection will continue to grow, eventually rupturing spontaneously – often through an uncontrolled path that can damage surrounding tissues or lead to fistula formation.

Treatment approaches differ between the acute management of an abscess and the definitive treatment of a fistula. Some patients may need both – first, emergency drainage of an abscess, followed later by planned surgery to address an underlying or resulting fistula.

Surgical Treatment of Perianal Abscess

The standard treatment for a perianal abscess is incision and drainage, a surgical procedure to open the abscess and allow the pus to escape. For superficial abscesses, this can often be performed in an outpatient setting with local anesthesia. The surgeon makes an incision over the abscess, drains the pus, and may break up any internal chambers to ensure complete drainage.

Deeper or larger abscesses typically require drainage in an operating room under general or regional anesthesia. This allows the surgeon to adequately explore and drain the abscess cavity, which can be quite painful without proper anesthesia. The patient usually goes home the same day or the following day.

After drainage, the wound is usually left open rather than stitched closed. This "healing by secondary intention" allows the cavity to heal from the inside out, reducing the risk of recurrence. A drain (a small tube or piece of gauze) may be placed in the wound to keep it open and promote continued drainage during the early healing phase.

Surgical Treatment of Anal Fistula

Fistula surgery is more complex than abscess drainage because the surgeon must eliminate the fistula tract while preserving the anal sphincter muscles that control continence. The specific technique used depends on the location and complexity of the fistula, as well as the patient's anatomy and medical history.

Fistulotomy is the most common procedure for simple fistulas that involve minimal sphincter muscle. The surgeon cuts open the entire fistula tract, converting the tunnel into an open groove that heals from the base up. Healing rates exceed 90%, but this technique is only appropriate when the amount of sphincter muscle involved is small enough that cutting it won't cause incontinence.

Fistulectomy involves completely excising (cutting out) the fistula tract rather than simply opening it. This removes all diseased tissue and may be preferred in certain situations, though it creates a larger wound.

Seton placement involves threading a piece of suture material or rubber band (the seton) through the fistula tract and leaving it in place. The seton serves multiple purposes: it keeps the tract draining (preventing abscess recurrence), allows any acute infection to settle, and can gradually cut through sphincter muscle over weeks to months (cutting seton) or simply maintain drainage while the patient prepares for definitive surgery (draining seton).

LIFT procedure (Ligation of Intersphincteric Fistula Tract) is a sphincter-sparing technique where the surgeon approaches the fistula through the space between the sphincter muscles, ties off and divides the tract. Success rates of 60-80% are reported with low risk to continence.

Advancement flap repair involves covering the internal opening of the fistula with a flap of tissue moved from nearby. This is often used for complex fistulas or when other approaches have failed.

Recovery After Surgery

Recovery after perianal abscess drainage or fistula surgery requires attention to wound care and patience, as these wounds take time to heal. The surgical wound is typically left open and will heal gradually from the inside out over 2-6 weeks, depending on the size and depth of the original abscess or fistula.

Wound care involves keeping the area clean and allowing the wound to drain. After each bowel movement, gently clean the area with lukewarm water – using a hand-held shower head or a sitz bath (a shallow basin that fits over the toilet seat). Avoid scrubbing or using harsh soaps directly on the wound. Pat the area dry gently with a clean towel or let it air dry.

Sitz baths – sitting in a few inches of warm water – are highly recommended for comfort and healing. Most experts suggest taking sitz baths 2-3 times daily for 10-15 minutes each, plus after bowel movements. The warm water improves blood flow to the area and helps keep the wound clean.

Some drainage from the wound is normal and expected during healing. Many patients find it helpful to wear a pad or panty liner to protect clothing. The amount of drainage should gradually decrease over time. If drainage suddenly increases or becomes foul-smelling, contact your healthcare provider.

Pain is typically managed with over-the-counter medications like acetaminophen (paracetamol) or ibuprofen, though your doctor may prescribe stronger pain medication for the first few days. Stool softeners may be recommended to make bowel movements more comfortable.

What Causes Perianal Abscesses and Fistulas?

Most perianal abscesses arise from bacterial infection of the small anal glands located inside the anal canal. When a gland becomes blocked, bacteria normally present in the intestines multiply and cause infection. The resulting abscess can then develop into a fistula. Risk factors include Crohn's disease, diabetes, and immunosuppression.

Understanding the cause of these conditions helps explain why they occur and why certain people are more susceptible. The anal glands that give rise to most abscesses are a normal part of anatomy – small mucus-secreting glands located at the dentate line (the junction between the lower rectum and the anal canal). Everyone has these glands, but only some people develop infections in them.

The process typically begins when the duct (opening) of an anal gland becomes blocked. This may occur due to trauma, hard stool, foreign material, or for no identifiable reason. The bacteria that normally reside harmlessly in the intestines – including E. coli, Bacteroides, and other species – can then proliferate in the blocked gland. The body's immune response to this infection creates the characteristic collection of pus.

Once formed, the abscess tends to track along the path of least resistance through the surrounding tissues. If it tracks to the skin surface and drains, the tract can become lined with epithelial tissue and persist as a fistula. This is why treating an abscess promptly and completely is important – though even with optimal treatment, a significant percentage will still develop fistulas.

Risk Factors for Perianal Abscess and Fistula

While anyone can develop a perianal abscess, certain factors increase the risk. Understanding these risk factors may help with prevention strategies and also explains why some patients need more specialized treatment.

Inflammatory bowel disease, particularly Crohn's disease, is one of the most significant risk factors. Crohn's disease can affect the entire digestive tract, including the anal region, causing chronic inflammation that predisposes to abscess and fistula formation. Patients with Crohn's disease often develop complex, difficult-to-treat fistulas and may require specialized management combining surgery with medical therapy.

Diabetes mellitus impairs immune function and wound healing, making infections more likely to occur and more difficult to treat. Diabetic patients may present with more severe abscesses and may need more aggressive treatment and monitoring.

Immunosuppression from any cause – including HIV/AIDS, chemotherapy, or immunosuppressive medications – increases infection risk. These patients may also have atypical presentations that make diagnosis more challenging.

Other risk factors include previous anal surgery or trauma, sexually transmitted infections, foreign bodies in the rectum, and a history of radiation therapy to the pelvic area. Smoking has been associated with increased risk of recurrence and complications.

Non-cryptoglandular Causes

While most abscesses arise from infected anal glands (cryptoglandular origin), other causes should be considered, especially in patients with unusual presentations or recurrent disease:

• Crohn's disease: Can cause abscesses and fistulas independent of anal gland infection
• Trauma: Including foreign body insertion, anal intercourse, or instrumentation
• Infection: Tuberculosis, actinomycosis, or sexually transmitted infections
• Malignancy: Rarely, anal or rectal cancer can present with fistula-like symptoms
• Radiation: Prior pelvic radiation can cause fistula formation

What Are the Possible Complications?

The main complications include fistula formation (30-50% of abscesses), recurrence of abscess or fistula, and rarely, fecal incontinence from sphincter damage. Untreated abscesses can lead to serious spreading infections. Most complications can be minimized with prompt, appropriate treatment and careful surgical technique.

While most perianal abscesses and fistulas can be successfully treated with modern surgical techniques, complications can occur. Understanding these potential complications helps patients make informed decisions about their care and recognize warning signs that require attention.

Fistula Formation

The most common complication of a perianal abscess is the development of an anal fistula. This occurs in approximately 30-50% of cases, even with appropriate initial drainage. The fistula forms when the original infected gland persists and creates a tract from inside the anal canal to the skin where the abscess drained. Patients who develop recurrent symptoms after abscess drainage – particularly ongoing discharge – should be evaluated for fistula.

Recurrence

Both abscesses and fistulas can recur after treatment. Abscess recurrence is often due to an underlying fistula that wasn't addressed at the initial surgery. Fistula recurrence after surgery occurs in approximately 10-25% of cases depending on the complexity of the original fistula and the surgical technique used. Patients with Crohn's disease have particularly high recurrence rates and often require multiple surgeries.

Fecal Incontinence

The anal sphincter muscles control bowel continence. Because fistulas often pass through or near these muscles, surgery carries some risk of causing incontinence – difficulty controlling gas or stool. Modern surgical techniques are designed to minimize this risk by preserving as much sphincter muscle as possible. The actual risk depends on the complexity of the fistula, the surgical technique, and patient factors. For simple fistulotomy, the risk of significant incontinence is less than 5%. More complex surgeries carry somewhat higher risks but remain relatively low in experienced hands.

Spreading Infection

Untreated or inadequately treated abscesses can lead to serious spreading infections. Cellulitis (infection of the surrounding skin and soft tissue), necrotizing fasciitis (a rare but life-threatening infection of the deep tissues, sometimes called Fournier's gangrene when it occurs in the genital area), and sepsis (systemic infection) are all possible if an abscess is not promptly drained. These complications emphasize the importance of seeking timely medical care.

Chronic Wound Problems

Some wounds fail to heal as expected after surgery, resulting in chronic non-healing wounds. This is more common in patients with diabetes, immunosuppression, or inflammatory bowel disease. Managing these wounds may require specialized wound care, hyperbaric oxygen therapy, or additional surgery.

Frequently Asked Questions