Vascular mechanisms in hypertensive cerebrovascular disease.

Hypertension causes vascular changes of essentially three types: structurally adaptative changes, degenerative alterations unrelated to atherosclerosis, and atherosclerosis. Structural changes result in an increased peripheral resistance, even in the relaxed vascular bed, and a reduced collateral capacity, thus predisposing to ischemia distal to an arterial stenosis/occlusion and to "watershed" infarcts in connection with a drop in blood pressure. Degenerative changes in the small intracerebral arteries can lead to plasma extravasation and focal brain edema, lacunar infarcts, and intracerebral hemorrhages. Hypertension also predisposes to saccular aneurysms and subarachnoid hemorrhages. Finally, atherosclerotic changes including stenoses or occlusions of predominantly extracranial and pial arteries give rise to transitory ischemic attacks and brain infarcts by artery-to-artery embolism or distal hemodynamic perfusion insufficiency.