Focal Ischemia: Atherosclerosis represents the most common mechanism producing focal ischemia. Atherosclerotic plaques line the artery walls and build up over the course of many years. These may eventually reduce arterial flow, completely block the artery, or produce an embolus that flows in the arterial stream to block an artery downstream. Other sources include infection emboli and emboli produced by cardiac disease. Once an artery is occluded, neurons perfused by the artery no longer receive necessary nutrients and oxygen. These cells eventually die and this results in a focal infarct. The area appears hypodense on neuroimaging and autopsy reveals a fluid filled cavity.