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Hematomas are usually caused by trauma, whether it is the result of a car accident, a minor bump, a cough, or an unknown event. The blood within blood vessels is continually flowing and therefore does not clot or coagulate. When blood leaves the circulatory system and becomes stagnant, there is almost immediate clotting unless the individual is taking anticoagulation medication to prevent blood clots (these may include aspirin, warfarin [Coumadin], clopidogrel [Plavix) and dipyridamole [Persantine]). The greater the amount of bleeding that occurs, the larger the hematoma.
Blood vessels that are fragile may contribute to hematoma formation. For example, an aneurysm or weakening in a blood vessel wall may gradually cause blood vessel cell walls to come apart from constant exposure to the blood flowing and spontaneously leak.
There are many people who take blood thinners or anti-coagulation medications. Examples include warfarin (Coumadin), aspirin, clopidogrel and prasugrel (Effient). These medications increase the potential for spontaneous bleeding and for allowing hematomas to expand because the body cannot efficiently repair blood vessels and blood continues to leak through the damaged areas.
Occasionally, diseases (for example, autoimmune diseases and bacterial infections) may occur that decrease the number of platelets in the blood stream or their ability to function. The platelets are the cells that help initiate blood clot and fibrin formation. If platelets are inhibited, bleeding can continue and hematomas can develop and expand. Examples of bacterial infections and autoimmune diseases include:
All these situations may exist independently to cause a hematoma or two or more may occur together.
Medically Reviewed by a Doctor on 6/5/2014
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