Cerebrovascular disease refers to a group of conditions, diseases, and disorders that affect the blood vessels and blood supply to the brain. If a blockage, malformation, or hemorrhage prevents the brain cells from getting enough oxygen, brain damage can result. The word cerebrovascular is made up of two parts – "cerebro" which refers to the large part of the brain, and "vascular" which means arteries and veins. Together, the word cerebrovascular refers to blood flow in the brain. The term cerebrovascular disease includes all disorders in which an area of the brain is temporarily or permanently affected by ischemia or bleeding and one or more of the cerebral blood vessels are involved in the pathological process. Cerebrovascular disease includes stroke, carotid stenosis, vertebral stenosis and intracranial stenosis, aneurysms, and vascular malformations. Restrictions in blood flow may occur from vessel narrowing (stenosis), clot formation (thrombosis), blockage (embolism) or blood vessel rupture (hemorrhage). Lack of sufficient blood flow (ischemia) affects brain tissue and may cause a stroke. The vertebral arteries extend along side the spinal column and cannot be felt from the outside. The vertebral arteries join to form a single basilar artery near the brain stem, which is located near the base of the skull. The vertebrobasilar system sends many small branches into the brain stem and branches off to form the posterior cerebellar and posterior meningeal arteries, which supply the back third of the brain. The jugular and other veins carry blood out of the brain.Because the brain relies on only two sets of major arteries for its blood supply, it is very important that these arteries are healthy. Often, the underlying cause of an ischemic stroke is carotid arteries blocked with a fatty buildup, called plaque. During a hemorrhagic stroke, an artery in or on the surface of the brain has ruptured or leaks, causing bleeding and damage in or around the brain.