An epidural hematoma (EDH) is found in approximately 3% of patients suffering from TBI. Nine percent of those in a coma have EDH. EDH is a collection of blood which occurs below the skull but above the thick leathery cover of the brain itself known as the Dura. This area of the brain is basically fluid and is a shock absorber for the brain. However, there are veins that feed and drain the brain which move through this area and when they are torn an epidural bleed can occur. These patients are often ones who have symptoms including a "lucid interval" which means they are struck in the head and have a short period of initial unconsciousness, wake up and seem better then seem to deteriorate. This is because of the gradual accumulation of blood in this area which presses on the brain over time.
The surgical indication for this condition depends of the neurological condition of the patient. On a patient in a coma, surgery will be done to relieve the pressure. In patients not in a coma, surgeons look at the thickness of the blood in the brain and its volume. Usually with a thickness more than 15mm and a Glasgow Coma Scale of 9 or lower, surgery will be recommended. Of course, surgical evacuation should be done as soon as possible. When the blood is pushing the brain away from its normal position, and possibly damaging the brain in doing so, it is read on an MRI as a condition known as "mass effect."
SDH is diagnosed when there is a collection of blood inside the skull, but also inside the covering of the brain called the Dura. The collection is therefore between the dura and the outer most brain tissue itself. The source of the bleed can be from damage to the brain itself (a focal lesion or tear of tissues), damage to a vein or damage to delicate tissue inside the dura. Between 10% and 30% of patients admitted with severe TBI suffer from SDH. They can be caused by motor vehicle accident, falls and assaults. They are more common with an older patient resulting from a fall. It is generally felt that a patient with a clot thickness greater than 10mm should undergo surgical evacuation, regardless of their level of consciousness. Non-comatose patients with a clot thickness less than 10mm may not need surgery.
The presence of blood directly under the brain tissue is thought to be an irritant to the brain, and can lead to an increased risk of developing a seizure condition.