A subdural hematoma results in blood gathering between the inner layer of the dura mater and the arachnoid mater. Usually resulting from tears in bridging veins which cross the subdural space. As blood builds up, it causes an increase in intracranial pressure which may cause compression and damage to the brain tissue. After performing a craniotomy the surgeon pulls back the top of the head to reveal the bloodied dura mater. The dura mater is cut and beneath lies the thick pool of blood, the subdural hematoma. Photo by @jadkassem98