Cerebral Ischemia
CVA
The Common Vein Copyright 2010
Definition
Cerebrovascular accident refers to ischemia of a part of the brain. It is the third most common cause of death in the United States, being also the leading cause of neurologic disability.
Also termed stroke, it can be ischemic or hemorrhagic. Depending on its duration (small time window for reversibility), it can be classified as transient ischemic attack (when lasting less than 24 hours) or completed stroke (all the sequelae not reverted after 72 hours).
It is caused by blockage of a cerebral artery. The most common causes of this blockage are embolism of thrombotic material, atherosclerosis in a large or medium artery, causing stenosis and hypertrophy resulting in luminal compromise of small penetrating vessels.
A TIA is usually embolic. Transient hypotension in the presence of severe carotid stenosis (>75% occlusion) can also lead to a TIA.
It results in rapidly developing loss of brain functions, depending on the area affected.
Two major vascular systems can be involved: the carotid and vertebrobasilar systems.
Because the areas irrigated by these systems are different, presentation due to ischemia in these systems vary. Classically, deficits in the carotid systems present with aphasia, contralateral paralysis/paresthesias, apraxia, amaurosis fugax. When there is a failure in the vertebro-basilar system, then symptoms such as diplopia, vertigo, ataxia, dysarthria and dysphagia occur.
According to the specific vessel affected, different stroke syndromes are described. Ischemia in the anterior cerebral artery region produces contralateral lower extremity and face motor deficits. When in the middle cerebral artery, aphasia, contralateral hemiparesis and sensory loss are predominant. As described above, vertebral/basilar artery deficits result in ipsilateral ataxia, diplopia, dysphagia, dysarthria and vertigo. If the posterior cerebral artery is also affected, then homonymous hemianopsia is also present.
Lacunar infarcts, that is, those resultant from occlusion of the small penetrating vessels affect the internal capsule, thus originating a pure motor hemiparesis.
The goals of neuroimaging are to localize the site the infarct and the extent of ischemia. A site of acute vascular occlusion should also be sought; and hemorrhage must be looked for, as well as unexpected lesions that could imitate acute cerebral infarction.
Noncontrast CT is able to show acute hemorrhagic strokes in most cases. However, it is insensitive for hyperacute infarction. For early infarction, MRI is more sensitive than CT, best seen in DWI sequences. Contrast should not be used in the initial CT study, because of the possibility of an hemorrhagic stroke.