Strokes can either be ischemic (88% of all strokes) or hemorrhagic (12% of all strokes). Figure 11-1 provides a classification of stroke by mechanism. Ischemic stroke is the abrupt development of a focal neurologic deficit that occurs due to inadequate blood supply to an area of the brain. Most often, this is due to a thrombotic or embolic arterial occlusion leading to cerebral infarction. A thrombotic occlusion occurs when a thrombus forms inside an artery in the brain. An embolism refers to a clot originating either inside or outside of the cerebral vessels in which a piece of the clot breaks loose and is carried either further through or into the cerebral vessels until it lodges causing occlusion. An outside source of emboli is often the heart causing cardioembolic stroke.

Hemorrhagic stroke is a result of bleeding into the brain and other spaces within the CNS and includes subarachnoid hemorrhage (SAH), intracerebral hemorrhage (ICH), and subdural hematomas. SAH results from sudden bleeding into the space between the inner layer and middle layer of the meninges, most often due to trauma or rupture of a cerebral aneurysm or arteriovenous malformation (AVM). ICH is bleeding directly into the brain parenchyma, often as a result of chronic, uncontrolled hypertension. Subdural hematomas result from bleeding under the dura which covers the brain and most often occur as a result of head trauma.

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