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.

Blood that escapes from the blood stream is very irritating 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.

>causes :
Trauma is the most common cause of a hematoma. When people think of trauma, they generally think of car accidents, falls, head injuries, broken bones, and gunshot wounds, etc.. Trauma to tissue may also be caused by an aggressive sneeze or an unexpected twist of a limb. When a blood vessel is damaged blood leaks into the surrounding tissue; this blood tends to coagulate or clot. The greater the amount of bleeding that occurs, the larger the amount of clot formation.
Blood vessels that are fragile may contribute to hematoma formation.