Perianal/ischiorectal abscess

What is perianal abscess? 

A perianal abscess is a collection of pus that forms near the anus due to an infection, usually originating from blocked anal glands. These small glands, located within the anal canal, can become obstructed, allowing bacteria to multiply and cause a buildup of pus. The result is a painful, swollen lump near the anus that may be accompanied by redness, warmth, and sometimes fever or discharge.

Perianal abscesses are part of a broader group known as anorectal abscesses. If left untreated, the infection can worsen, spread to deeper tissue spaces, or form an abnormal tunnel between the anal canal and the skin (known as an anal fistula).

Types of Anorectal Abscesses

Anorectal abscesses are classified based on their depth and location in relation to the anus and rectum:

While superficial abscesses like perianal abscesses can often be drained under local anesthesia, deeper ones such as ischiorectal or supralevator abscesses usually require surgical drainage under general anesthesia. These deeper abscesses also carry a higher risk of complications, including the formation of anal fistulas.

What causes perianal abscess? 

A perianal abscess forms when one of the small glands inside the anal canal becomes blocked and infected. This leads to the buildup of pus and results in a painful swelling near the anus. The infection can stay localised or spread into deeper tissue planes, depending on the severity and location.

The main causes include:

• Obstruction of anal glands — the most common underlying cause; blockage leads to bacterial buildup and pus formation

• Cryptoglandular infection — infection that begins in the anal crypts and spreads into surrounding tissues

• Bacterial overgrowth — usually involves gut bacteria such as E. coli, Bacteroides, and Staphylococcus aureus

• Spread of infection from nearby tissues — including infected fissures or skin around the anus

• Extension of deeper anorectal infections — especially in more complex or recurrent abscesses

These infections develop rapidly and typically require prompt drainage to prevent complications like fistula formation or systemic spread.

What are the symptoms of perianal abscess? 

A perianal abscess usually presents with sudden and intense pain near the anus. The pain often becomes worse when sitting, walking, or passing stools. In many cases, the area appears red, swollen, and tender to touch. As the abscess grows, other symptoms may also develop.

Common symptoms include:

• Persistent pain near the anus — often throbbing and worsened by movement or bowel movements.

• Visible swelling or lump — usually red, warm, and tender to touch.

• Pus or discharge — spontaneous drainage may occur if the abscess bursts.

• Fever and chills — in cases where the infection spreads beyond the local area.

• Fatigue or general unwellness — particularly with deeper or more advanced infections.

• Difficulty sitting or walking — due to the location and tenderness of the abscess.

• Constipation or painful bowel movements — caused by discomfort in the anal region.

If untreated, the abscess may rupture on its own or lead to a more serious complication such as a fistula or systemic infection. Prompt medical attention is advised when these symptoms appear.

Who is at risk of perianal abscess in Singapore? 

While a perianal abscess can affect anyone, certain factors may increase the likelihood of developing one. These include underlying medical conditions, immune status, and specific local trends observed in clinical settings.

You may be at higher risk if you have:

• Male sex — men develop perianal abscesses significantly more often as compared to women. 

• Diabetes mellitus — poorly controlled blood sugar can impair immune response and promote infections.

• Immunocompromising conditions — conditions like inflammatory bowel disease (e.g., Crohn’s disease) impair immune response and raise risk

• History of anal fissures or trauma — tears or injury near the anus can allow bacteria to enter.

• Obesity — increased risk of skin breakdown and infection.

• Poor hygiene or local skin infections — can contribute to bacterial spread.

• Sedentary lifestyle — Prolonged sitting may contribute to gland blockage and poor circulation.

What are the possible complications of perianal abscess? 

If a perianal abscess is not promptly and properly treated, the infection may progress or recur, leading to more serious complications. Some complications may require further surgery or long-term management.

Common complications include:

• Anal fistula formation — an abnormal tunnel between the anal canal and the skin develops in up to 30–70% of patients after abscess drainage.

• Recurrent abscess — the infection may return, especially if the underlying source is not addressed.

• Systemic infection — in severe or untreated cases, bacteria can spread into the bloodstream, causing sepsis.

• Tissue damage — extensive infection can destroy surrounding tissues, leading to scarring or incontinence.

• Delayed wound healing — especially in patients with diabetes, poor nutrition, or immune suppression.

• Pain and discomfort — ongoing pain or swelling may persist due to chronic inflammation or secondary infections.

Early drainage and proper aftercare reduce the risk of these complications and support complete healing.

How is perianal abscess diagnosed? 

Diagnosing a perianal abscess usually begins with a physical examination. In most cases, the condition is identified based on the appearance of the area, along with the patient’s symptoms of pain, swelling, and possible discharge. However, for deeper or less obvious abscesses, imaging tests may be necessary to confirm the diagnosis and assess the extent of infection.

Diagnosis typically involves:

• Physical examination — a doctor will inspect the anal region for redness, swelling, warmth, tenderness, and any signs of drainage.

• Digital rectal examination (DRE) — used to detect deeper abscesses or assess tenderness inside the anal canal.

• Imaging tests (if needed):

• Ultrasound (transperineal or endoanal) — helps identify abscesses not visible on the surface.

• CT scan — useful for detecting deeper collections, such as ischiorectal or supralevator abscesses.

• MRI — often used in complex or recurrent cases to evaluate fistula formation or involvement of surrounding structures.

Most superficial perianal abscesses can be diagnosed and treated on the same day. However, deep-seated or recurrent infections may require more detailed imaging and surgical planning.

What are the treatment options for perianal abscess in Singapore? 

The primary treatment for a perianal abscess is to drain the accumulated pus and relieve pressure from the infected area. This helps prevent the infection from spreading and reduces the risk of long-term complications. Antibiotics may be used in certain cases, but they are not a substitute for drainage.

Treatment options include:

• Incision and drainage (I&D) — a small surgical cut is made to release the pus. Superficial abscesses may be drained under local anesthesia, while deeper or larger abscesses usually require general anesthesia in an operating theatre.

• Antibiotics — not routinely needed, but may be prescribed if there is surrounding cellulitis, systemic infection, delayed drainage, or if the patient is immunocompromised or diabetic.

• Wound care and aftercare — the wound is usually left open to heal naturally; patients are advised to take sitz baths, maintain hygiene, and use pain relief as needed. Dressing changes or wound packing may be required.

• Follow-up for fistula evaluation — if a fistula (link to service page) is suspected or develops later, additional surgical procedures like fistulotomy or seton placement may be necessary to prevent recurrence.

Prompt treatment and proper follow-up help reduce the risk of complications and support full recovery.

Summary 

A perianal abscess is a painful infection near the anus caused by a blockage in the anal glands, leading to the formation of pus. While it can happen to anyone, individuals with conditions like diabetes, inflammatory bowel disease, or a weakened immune system may be more prone to it. Symptoms often include swelling, redness, and intense pain that worsens with movement or bowel movements. 

Diagnosis is usually based on physical examination, but deeper abscesses may require imaging. The mainstay of treatment is timely incision and drainage, sometimes supported by antibiotics and wound care. Left untreated, perianal abscesses can lead to serious complications such as fistulas, recurrent infections, or sepsis. 

If you are experiencing symptoms of a perianal abscess, schedule a consultation with Tan Siong San Surgery for detailed evaluation and personalised treatment plan.