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the accumulation of blood that has flowed out of the blood vessels into the body cavities or surrounding tissues.
Extravasation may occur when the walls of the vessels are destroyed by a mechanical injury or a pathological process (for example, tumor). It may also occur through an uninjured wall, when the permeability of the wall is increased (for example, under the influence of certain chemical substances). The discharged blood may either permeate the tissues affected by the extravasation or form a circumscribed accumulation, called a hematoma. The significance of extravasation is determined by dimensions, rapidity of development, and site of formation. When the process is minor it is resorbed without treatment. If encapsulated or suppurative, it often requires special treatment. Because extravasation may lead to the destruction of tissue, it is especially dangerous in the brain (insult).