Perianal abscess

What is perianal abscess?

A perianal abscess is a collection of pus in the tissue next to the anus, usually caused by an infected anal gland. It appears as a painful, red, swollen lump, sometimes with fever. It grows quickly and needs prompt drainage, because antibiotics alone do not clear it.

When a gland just inside the anus becomes blocked and infected, pus builds up in the nearby tissue to form an abscess. It can enlarge quickly, so early drainage is important and prevents the infection spreading.

What causes perianal abscess?

A perianal abscess starts when a gland just inside the anus becomes blocked and infected, and pus collects in the nearby tissue. Crohn's disease, a weakened immune system, bacteria entering a small crack, hard stools and local injury also contribute.

• Blocked and infected anal glands
• Bacteria entering a small crack or gland
• A weakened immune system
• Crohn's disease
• Hard stools or local trauma

What are the symptoms?

The main symptom of a perianal abscess is a throbbing, painful lump beside the anus with red, hot, swollen skin. Pain is worse when sitting, walking or passing stool. Some people also have pus discharge, fever and chills, and feel generally unwell.

• A throbbing, painful lump near the anus
• Red, hot, swollen skin
• Fever and feeling unwell
• Pus or discharge
• Pain worse when sitting

When should I see a colorectal surgeon?

A painful, swollen lump near the anus, a possible perianal abscess, needs assessment the same day, because it enlarges quickly and needs drainage. Go to an emergency department for high fever or chills, rapidly spreading redness, confusion or severe illness, especially with diabetes or a weakened immune system.

The warning signs below need prompt attention.

• High fever or chills
• Rapidly spreading redness
• Diabetes or a weakened immune system
• Confusion or severe illness

How is it diagnosed?

A perianal abscess is usually diagnosed by examining the painful swelling. Drainage is done under anaesthesia, when the surgeon also checks for an underlying fistula and sends pus for testing if the infection is unusual. Diabetes and immune conditions are reviewed, as they affect treatment.

• Examination of the swelling
• Drainage under anaesthesia
• A sample of pus if infection is unusual
• Check for an underlying fistula
• Review of diabetes or immune conditions

How is perianal abscess treated?

A perianal abscess is treated by incision and drainage, a small procedure that releases the pus and relieves pain quickly. Antibiotics alone do not clear a collection of pus. They are added for spreading skin infection, diabetes, a weakened immune system or sepsis. Warm baths, wound care and follow-up for a fistula come next.

• Incision and drainage of the pus
• Antibiotics only when infection extends or in special cases
• Wound care and warm baths
• Pain relief
• Follow-up to watch for a fistula

What are the risks and complications?

The risks of draining a perianal abscess are a fistula forming afterwards, the infection returning, delayed healing, and spread of infection if drainage is delayed. Follow-up a few weeks later checks for a fistula so it is found and treated early.

• A fistula forming later
• Infection coming back
• Delayed healing
• Spread of infection if drainage is delayed