In atherosclerosis, cholesterol and other fatty substances collect in arteries, causing narrowing or blockages. The carotid arteries are blood vessels in the neck that bring blood to the brain. Carotid artery stenosis (CAS) is a condition in which atherosclerosis-related blockages in the carotid arteries may not allow ample blood flow to the brain. Low blood flow to the brain can cause transient ischemic attacks or stroke. When a transient ischemic attack occurs, blockage of blood flow to the brain is temporary and the brain suffers no permanent damage; however, when a stroke occurs, blockage of the blood flow lasts long enough that a section of brain tissue dies.