There are two main categories of stroke - ischemic and hemorrhagic .
Most strokes are ischemic meaning they are caused by a lack of blood supply to part of the brain.
They are most commonly caused by atherosclerosis, a buildup of plaque inside the arteries. A blood clot can form on the plaque and block blood flow to the brain. This is a thrombotic stroke . Less frequently, a tiny blood clot or other material breaks loose from an artery outside the brain or from within the heart and is swept through larger arteries into smaller vessels in the brain. When the clot lodges in a brain artery, blocking blood flow, an embolic stroke occurs.