Stroke is defined as an acute neurologic deficit lasting more than 24 hours and caused by cerebrovascular etiology. It is subdivided into ischemic stroke (caused by vascular occlusion or stenosis) and hemorrhagic stroke (caused by vascular rupture, resulting in intraparenchymal and/or subarachnoid hemorrhage). Ischemic stroke accounts for about 85% of cases and hemorrhagic stroke about 15%. 
Regardless of the specific etiology, ischemic stroke occurs when blood supply in a cerebral vascular territory is critically reduced due to occlusion or critical stenosis of a cerebral artery. A minority of ischemic strokes are caused by cerebral sinus or cortical vein thrombosis. Risk factors strongly associated with ischemic stroke include smoking,  diabetes,  atrial fibrillation,  comorbid cardiac conditions,  carotid artery stenosis,    and sickle cell disease. 
Cause of a minority of ischemic strokes. Carotid revascularization of high-grade asymptomatic, and moderate or high-grade symptomatic, carotid artery stenosis helps to prevent future stroke.
Cerebral ischemia should be suspected when a patient presents with typical symptoms of rapidly resolving unilateral weakness or numbness, but also with less classic symptoms such as unilateral vision loss, transient aphasia, or vertigo. TIAs have considerable risk of early recurrent cerebral ischemic events. Evaluation and initiation of secondary prevention should occur rapidly.
Intracerebral hemorrhage is caused by vascular rupture with bleeding into the brain parenchyma. Three-quarters of hemorrhagic strokes are due to intracerebral hemorrhage, with the rest being due to subarachnoid hemorrhage. Strong risk factors include anticoagulation,   use of illicit sympathomimetic drugs,  and vascular malformations. 
Typically asymptomatic until ruptured, resulting in a subarachnoid hemorrhage. Screening with noninvasive neuroangiography is recommended for at-risk populations.
A medical emergency where there is bleeding into the subarachnoid space. The most common cause of nontraumatic subarachnoid hemorrhage is intracranial aneurysm. Strong risk factors include hypertension, smoking, family history, and autosomal dominant polycystic kidney disease. 
BMJ Publishing Group
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