A subdural hematoma is most often the result of a severe head injury. This type of subdural hematoma is among the deadliest of all head injuries. The bleeding fills the brain area very rapidly, compressing brain tissue. This often results in brain injury and may lead to death.
Subdural hematomas can also occur after a minor head injury. The amount of bleeding is smaller and occurs more slowly. This type of subdural hematoma is often seen in older adults. These may go unnoticed for many days to weeks, and are called chronic subdural hematomas.
With any subdural hematoma, tiny veins between the surface of the brain and its outer covering (the dura) stretch and tear, allowing blood to collect. In older adults, the veins are often already stretched because of brain shrinkage (atrophy) and are more easily injured.