A subdural hematoma is one of the most serious brain injuries in terms of an acute injury that can occur. It arises when there is bleeding on the surface of the brain. It's very important that this be diagnosed right away because when the brain begins to bleed that blood has to accumulate or create a pocket somewhere and when it does that it begins to put pressure on the brain. Remember that the brain is encased within the skull and there is nowhere for the blood to go other than for it to start pressing on the brain tissue. Depending on where the bleeding has occurred, it's going to affect that area of the brain.
The bleeding has to be stopped and if it has already stopped and the blood has accumulated, in many situations it will need to be removed, or what a doctor would call evacuated. Sometimes the neurosurgeon will drill a hole in that part of the skull or in real serious cases they will actually go in and remove part of the skull to get access to the area that has been affected.
Subdural hematomas need to be evaluated quickly. They are clearly a life threatening emergency and when someone suffers the symptoms that indicate this type injury, like loss of consciousness, nausea, vomiting, loss of motor function and others, they need to be evaluated right away.