Perianal Abscess

What is a perianal abscess?

A perianal abscess is a collection of pus caused by infection in the tissues around the anus.

Most arise when one of the small glands within the anal canal becomes blocked and infected. Infection can then spread into the surrounding tissues and form an abscess.

Abscesses vary considerably in depth and location. A superficial perianal abscess may produce an obvious painful swelling close to the anus, while deeper intersphincteric, ischioanal or supralevator abscesses may cause significant pain without a clearly visible external lump.

What symptoms can occur?

The commonest symptom is increasing pain around the anus.

The pain is often constant rather than occurring only during bowel movements. Sitting, walking or coughing may make it worse.

Other symptoms can include:

• a tender or swollen area near the anus;
• redness or warmth of the surrounding skin;
• fever or chills;
• pus or discharge;
• feeling generally unwell; and
• occasionally difficulty passing urine or stool because of pain and swelling.

Deep abscesses may cause less obvious external swelling and can present with pelvic, rectal, buttock or lower-back discomfort.

What causes a perianal abscess?

Most are cryptoglandular, meaning that infection begins in one of the normal anal glands.

A perianal abscess can also occur in association with other conditions such as Crohn's disease, immune suppression, diabetes or, less commonly, other local inflammatory or malignant conditions.

Having one uncomplicated perianal abscess does not by itself mean that a patient has Crohn's disease or another underlying disorder.

Recurrent, multiple or unusually located abscesses deserve more detailed evaluation.

How is a perianal abscess diagnosed?

Many superficial abscesses can be diagnosed from the history and physical examination.

The surgeon may examine the anal and perianal area and, when tolerable and clinically appropriate, perform a rectal examination.

Blood tests may be useful in patients who are systemically unwell or when the severity of infection needs assessment.

Imaging is not routinely required for every straightforward superficial abscess.

Ultrasound, CT or MRI may be appropriate when the abscess is deep or occult, the diagnosis is uncertain, there is recurrence, a complex fistula is suspected or Crohn's disease is being considered.

What is the treatment?

The main treatment for an established anorectal abscess is adequate drainage of the pus.

This is usually performed by incision and drainage. Depending on the size, depth, location and clinical condition, the procedure may be performed under local, regional or general anaesthesia.

The surgeon makes an opening large enough to drain the infected cavity adequately while avoiding unnecessary injury to the anal sphincter muscles.

Any loculations or connected pockets of pus are dealt with as appropriate.

The wound is usually left open rather than stitched closed so that residual infected material can continue to drain and the cavity can heal from inside outward.

Are antibiotics enough?

Usually not for an established abscess.

Once a true pus-filled cavity has formed, antibiotics may not penetrate the abscess sufficiently to replace drainage.

Antibiotics may nevertheless be used in addition to drainage when there is:

• significant surrounding cellulitis;
• fever, sepsis or systemic infection;
• impaired immunity;
• poorly controlled diabetes or other important comorbidity;
• extensive soft-tissue infection; or
• another specific clinical indication.

The need for antibiotics is therefore individualised rather than automatic.

Will the wound be packed?

Practice varies according to the cavity, bleeding and operative findings.

A temporary dressing or packing may sometimes be placed initially for haemostasis or cavity management.

However, repeated routine internal packing after drainage is not necessary for every uncomplicated perianal abscess.

A large multicentre randomized trial found that avoiding continued postoperative packing caused less pain without a significant increase in abscess recurrence or fistula formation.

Wound care should therefore follow the particular operative findings and the surgeon's instructions rather than assuming that every cavity requires repeated packing.

What is the relationship between an abscess and an anal fistula?

A fistula is an abnormal tract between the anal canal and the skin around the anus.

Some patients develop or already have a fistula associated with the abscess. The fistula may become apparent during the operation or only later, after the acute infection has settled.

Persistent or recurrent discharge, repeated swelling at the same site or failure of the wound to heal may suggest an underlying fistula.

Not every patient with a perianal abscess develops a fistula.

If a fistula is suspected, further examination and sometimes MRI or other imaging may be needed before planning definitive treatment.

Should a fistula be treated during the abscess operation?

Not necessarily.

The immediate priority in acute sepsis is safe and adequate drainage.

If a simple low fistula is clearly identified in a carefully selected patient, treatment may sometimes be considered during the same procedure.

In many situations, however, aggressive searching or division of tissue during acute inflammation can create unnecessary sphincter injury or false passages.

For suspected complex fistula, recurrent disease, Crohn's disease or uncertain anatomy, drainage first followed by later assessment is often safer.

What about diabetes?

Diabetes can increase susceptibility to infection and can affect wound healing.

Patients presenting with significant anorectal infection may sometimes be found to have previously unrecognized hyperglycaemia.

Good glycaemic control is particularly important during treatment and recovery.

What happens after drainage?

Pain usually improves significantly once the abscess has been adequately decompressed, although wound discomfort can continue for several days.

Some blood-stained or purulent discharge from an open drainage wound is expected initially.

The area should be kept clean, particularly after bowel movements. Showering or washing with clean water is generally adequate unless specific wound-care instructions have been given.

An absorbent pad may be useful to protect clothing while the wound drains.

Stool should be kept comfortably soft and constipation avoided.

The patient should follow the prescribed pain-relief and wound-care instructions.

Can the abscess come back?

Yes.

Recurrence can occur if part of the abscess cavity was difficult to drain, if there are deeper extensions, if an underlying fistula persists or if another predisposing condition is present.

Repeated abscesses at the same site should prompt evaluation for an anal fistula or other underlying cause.

When is urgent medical attention required?

Urgent medical assessment is appropriate for rapidly worsening pain or swelling, high fever, shaking chills, persistent fast heart rate, marked weakness, confusion or other signs of systemic illness.

Diabetic or immunocompromised patients require particular caution.

Rapidly spreading redness, severe pain out of proportion to the visible findings, skin discoloration, blistering, foul discharge or rapidly progressive swelling can rarely indicate a severe necrotising soft-tissue infection such as Fournier's gangrene and requires emergency treatment.

After drainage, increasing rather than improving pain, persistent high fever, worsening swelling, heavy bleeding or significant clinical deterioration should prompt reassessment.

This information is intended for general patient education and does not replace examination or individual medical advice.