A perianal haematoma is an acutely painful condition that often has an onset after straining at stool. The haematoma is caused by rupture of a blood vessel beneath the anal skin. On examination, there is a blue-black bulge in the skin near the margin of the anus. Sometimes this condition is described as a 'thrombosed external pile' but it is not related at all to haemorrhoids.
Generally the perianal haematoma resolves over a few days and the patient requires only oral analgesia. If the pain becomes intolerable then it is possible to excise and drain the haematoma under anaesthesia.
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