I think one should apply an ice-pack to the hematoma and monitor his level of consciousness. Hematoma is an abnormal 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. Hematoma causes may include trauma, brain injury, diseases, infections, and more. Some types of hematomas can be a medical emergency and require immediate medical treatment or even surgery.