Ischemic and Hemorrhagic

Strokes can be caused either by blockage or rupture of an artery

About 87% of strokes are ischemic – due to arterial occlusion. The resulting inadequate blood flow (ischemia) deprives the brain of oxygen and glucose, and slows the removal of metabolic wastes. The parts of the brain that the occluded artery can no longer adequately supply very rapidly begin to function abnormally or cease to function. If ischemia persists, brain cells die. The term “infarct” is commonly used to describe such a region of dead tissue. The brain is at special risk for ischemia because there is often not enough redundancy in its arterial supply to maintain adequate blood flow if one artery is suddenly occluded. 

About 13% of strokes are hemorrhagic – due to arterial rupture. Bleeding can initially occur within the brain (intraparenchymal hemorrhage accounts for about 10% of strokes), or around the brain in the subarachnoid space (subarachnoid hemorrhage accounts for about 3% of strokes). A hemorrhage can produce injury by distorting, compressing, and tearing the surrounding brain tissue (including its blood vessels), by the toxic effects of the blood itself, or by increasing intracranial pressure.