A hematoma is a collection of blood outside of a blood vessel. It occurs when an injury causes blood to collect and pool under the skin, giving the skin a spongy, rubbery, lumpy feel. Hematomas are similar to bruises, but the damage that causes them occurs in larger blood vessels. They can occur in any blood vessel, including veins, arteries, and capillaries, and their location may change their nature. Hematomas can be seen under the skin or nails as purplish bruises of different sizes, and they can also happen deep inside the body where they may not be visible. Hematomas may sometimes form a mass or lump that can be felt. Some examples of hematomas include subdural, spinal, subungual (under the finger or toenail bed), hepatic (liver), and ear or aural hematoma. Most hematomas resolve spontaneously over time as the blood debris is removed and the blood vessel wall is repaired by the bodys repair mechanisms. However, other times, surgically removing or evacuating the blood in a hematoma becomes necessary based on its symptoms or location.