Acute epidural hematoma: A massive fresh blood clot is seen between the skull (black arrow) and dura (white arrow). Whereas most subdural hematomas arise from venous bleeding, epidural hemorrhage is almost always due to arterial bleeding as a result of a tear in the middle meningeal artery from fracture of the squamous portion of the temporal bone. A sizable blood clot may result within a matter of several hours producing compression of the underlying brain and the expected edema and herniation.