Haematoma is a discrete internal collection of blood which has leaked from damaged blood vessels. At some sites blood can seep away between layers of tissue, but where there are tighter compartments it remains a circumscribed mass which can cause problems by putting pressure on its surroundings. A small one, for example, appears under a fingernail which has been hit with a hammer. At the other extreme a life-threatening one can occur on the surface of the brain (subdural haematoma) following a head injury. Bruises are a type of haematoma.
hematomas (collections of blood that have escaped from the vessels)
Some call it a blood-blister. It is a mass of usually clotted blood that forms in a tissue, organ, or body space as a result of a broken blood vessel.
Hematomas are masses of blood (or clotted blood) that accumulate in tissues and may result from trauma.
According to general linguistic rules, ann intermuscular haemotoma is a bruise between muscles whereas an intramuscular haemotoma is a bruise within a muscle. JAB
Usually - no.
It is dangerous anywhere in the body. If small (a "blood blister") it should go away naturally. If large enough to put pressure on the surrounding tissue, it can cut off circulation and make the injury worse.