A swelling composed of blood that has escaped from an injured, diseased, or abnormally fragile blood vessel into tissues--in other words, a bruise. The vast majority of hematomas subside in their own time, usually about a week, without need for treatment, changing color from purple to brown to green-yellow. Internal hematomas may follow severe injury; the effects depend on the site of the hematoma. After head injuries hematomas may occur over the surface of the brain or within its substance. Injury-induced hematoma of the lung or kidney can occur also.