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What is a hematoma?
By definition, a hematoma is a collection of blood outside of a blood vessel. It occurs because the wall of a blood vessel wall, artery, vein or capillary, has been damaged and blood has leaked into tissues where it does not belong. The hematoma may be tiny, with just a dot of blood or it can be large and cause significant swelling.
The blood vessels in the body are under constant repair. Minor injuries occur routinely and the body is usually able to repair the damaged vessel wall by activating the blood clotting cascade and forming fibrin patches. Sometimes the repair fails if the damage is extensive and the large defect allows for continued bleeding. As well, if there is great pressure within the blood vessel, for example a major artery, the blood will continue to leak through the damaged wall and the hematoma will expand.
Blood that escapes from within a blood vessel is very irritating to the surrounding tissue and may cause symptoms of inflammation including pain, swelling, and redness. Symptoms of a hematoma depend upon their location, their size, and whether they cause associated swelling or edema.
Picture of a brain hematoma.
Bruises and contusions
The medical term ecchymosis is what most people would recognize as a bruise, or blood that has leaked out of an injured blood vessel beneath the skin.. Another word for this injury is a contusion. An ecchymosis tends to be flat while a hematoma has more of a three dimensional character to it. As well, hematomas may occur in any organ and not just under the skin.
Hemorrhage is the term used to describe active bleeding. The term hematoma describes blood that has already clotted.