Cerebral Strokes The two major mechanisms that cause brain damage in stroke are, ischemia and hemorrhage. In ischemic stroke there is decreased or absent circulating blood deprives neurons of essential substrates. Ischemic stroke represents about 80% of all strokes. I- Ischemic stroke The three main mechanisms causing ischemic strokes are (1) thrombosis, (2) embolism and (3) global ischemia (hypotensive) stroke. Thrombosis Atherosclerosis is the most common pathological feature of vascular obstruction resulting in thrombotic stroke. Atherosclerotic plaques can undergo pathological changes such as ulcerations, thrombosis, calcifications, and intra-plaque hemorrhage. Endothelium disruption occur due to any of these pathological changes initiates a complex process that activates many destructive vasoactive enzymes. Platelet adhere and aggregate to the vascular wall flow. Leucocytes present at the site mediate an inflammatory response within 1 hour. Embolism Embolic strokes (ES) result from embolization of an artery in the central circulation from a variety of sources. Clot, fibrin, pieces of atheromatous plaque, fat, air, tumor bacterial clumps and foreign bodies are known to embolize into central circulation. Global stroke Profound reduction in systemic blood pressure due to any reason is responsible for hypotensive stroke. Pyramidal cell layer of the hippocampus, Purkinje cell layer of the cerebellar cortex, cerebral grey matter neurons are more susceptible to ischemia than other brain neurons. Abundance of glutamate in these neurons makes them more susceptible to global ischemia. II- Hemorrhagic strokes Hemorrhagic strokes are either subarachnoid or intracerebral. A hemorrhagic stroke originates from deep penetrating vessels and cause brain tissue injury by disrupting biochemical substances released from multiple sources play an important role in tissue destruction. It accounts for approximately 10% to 15% of all strokes. Subarachnoid hemorrhage is due to bleeding into the subarachnoid space – the area between arachnoid membrane and pia mater surrounding brain. This occurs either from a ruptured cerebral aneurysm or due to head injury.
Posted on: Sat, 18 Jan 2014 16:42:49 +0000
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