Perianal hematomas or perianal thromboses occur when blood pools inside the tissues surrounding the anus, outside of the blood vessels. The hematomas vary in size depending on the cause and severity and can be very painful. A perianal hematoma forms when the small blood vessels in the anus break due to injury or excessive pressure on the anus. Some perianal hematomas resolve on their own, while others require specialist treatment.
Perianal hematomas present as a collection of blood, usually blue or deep purple, under the skin around the anus. A bump or bulge ranging from a tiny lump to a large swelling the size of a tennis ball. The growths are usually painful and can result in the passing of bloody stools if the hematoma is actively bleeding.