Pathophysiology of Ischemic Stroke
An ischemic stroke may be caused by a blood clot that occurs in the affected artery (thrombosis), a blood clot that traveled from another part of the body (embolism), or a blockage due to damage to the arterial wall (lacunar infarct). Blockage of a single artery can often be compensated for by other arteries in the blood vessel network, call collaterals. Artherosclerosis (hardening of the arteries), other damage to arteries, and natural variations in the collateral network can prevent the collateral system from compensating fully. The result is a loss of perfusion, or blood supply, to an area of the brain (ischemia).
Arteriovenous malformations (AVMs), abnormal tangles of blood vessels in which arteries flow directly into veins, are another possible cause of ischemic stroke. AVMs can press directly on brain tissue, blocking blood flow.
Pathophysiology of Hemorrhagic Stroke
The main type of hemorrhage that can lead to stroke is subarachnoid hemorrhage. In this type of bleed, which usually results from head trauma or a ruptured aneurysm, there is uncontrolled bleeding between the innermost two of the three meninges (membranes lining the brain), the pia mater and the arachnoid mater.
The blood that pools or collects in a subarachnoid bleed is called a hematoma. Ischemia (lack of blood flow) from the hematoma is a secondary problem. It is caused by constriction of the arteries (vasospasm) as a protective response to reduce bleeding. About 25% of patients with subarachnoid hemorrhages will experience stroke... [continues]
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