Perianal Abscess

A thrombosed external haemorrhoid is acute thrombosis within the external haemorrhoidal venous plexus beneath the anoderm.

It produces sudden severe anal pain and a tense bluish perianal lump. Symptoms typically peak during the first 48 to 72 hours and gradually improve as the thrombus organises.

Pain is acute, constant and usually worsened by sitting or defaecation.

Examination shows a tender nonreducible blue or purple subcutaneous lump at the anal margin.

If skin necrosis develops, clot may become visible or begin to discharge.

Marked fever, spreading erythema, fluctuance or systemic illness suggests abscess or another diagnosis rather than uncomplicated thrombosis.

Diagnosis is clinical.

No routine imaging is required.

Digital examination may be deferred temporarily when pain is extreme and the diagnosis is already obvious externally.

Management is determined by severity, duration and whether symptoms are already improving.

For mild or improving disease:

• Oral analgesia
• Stool softening
• Fibre
• Warm water bathing
• Avoid straining

A practical analgesic regimen is:

Paracetamol 1 g orally every 6 to 8 hours as required, maximum 4 g daily in an adult without significant hepatic risk.

Add:

Ibuprofen 400 mg orally every 8 hours with food as required when renal function, gastrointestinal bleeding risk and other contraindications permit.

For severe pain early in the course, complete excision of the thrombosed external haemorrhoid under local anaesthesia provides faster symptom resolution and lower recurrence than simple incision and evacuation of clot.

Remove the entire thrombosed venous segment through an elliptical incision rather than simply incising the skin and expressing clot.

A patient presenting after several days with clearly improving pain usually gains little from late excision and can continue conservative treatment.