Subdural hematoma

A subdural hematoma (SDH) is a type of bleeding in which a collection of blood usually caused from a traumatic brain injury—gathers in the inner layer of the dura mater and the arachnoid mater of the meninges surrounding the brain. It usually results from tears in bridging veins that cross the subdural space.
The symptoms of a subdural hematoma are slow to notice because the lower-pressure veins involved bleed more slowly than arteries. Signs and symptoms of acute hematomas may appear in minutes, if not immediately, but can also be delayed as much as two weeks.