Generally, they result from an obstruction, typically a blood clot. These clots are called cerebral thrombi or a cerebral emboli.
Cerebral thrombus is a blood clot that develops at the site of the clogged portion of the vessel.
Cerebral embolism refers to a blood clot that forms at another location in the circulatory system. A portion of the blood clot dislodges, enters the bloodstream and travels through the blood vessels of the brain. The clot enters a vessel that is smaller than the clot, causing it to lodge in this small vessel. This obstructs the flow of blood to a specific part of the brain, leading to a stroke. An important cause of these types of clots is an irregular heartbeat called atrial fibrillation.