A stroke result from an interruption of blood supply to the brain--either a lack of blood flowing to the brain or abnormal bleeding in the brain or skull cavity. Diseased arteries, blood clots and ruptured vessels in the brain are the most common causes of these disruptions in blood flow to the brain's cells.
Bleeding in the Skull Cavity or Brain
Some types of strokes--called hemorrhagic strokes--are caused by bleeding in the brain or the area between the surface of the brain and skull. This bleeding is the result of a rupture or leak in the blood vessels or arteries in or near the surface of the brain. According to the Mayo Clinic, hemorrhagic strokes may be caused by either an intracerebral hemorrhage or a subarachnoid hemorrhage. Intracerebral hemorrhages commonly occur as a result of high blood pressure, which causes the small arteries inside of the brain to become brittle and easily ruptured. When a blood vessel or artery bursts, it leaks blood into surrounding brain tissue, damaging or permanently affected brain cells. Subarachnoid hemorrhages typically are caused by a ruptured aneurysm--a ballooning of part of a blood vessel due to the weakening of its walls. This rupture may cause a sudden and severe headache. Blood from the rupture spills into the cavity between the brain and skull but not into the brain itself, according to the American Heart Association (AHA). This bleeding can cause other blood vessels in the brain to spasm erratically, interfering with blood flow to parts of the brain and causing further damage. Aging or genetic predisposition can increase the likelihood of subarachnoid hemorrhages.
Thrombus
A thrombus is a blood clot that forms and remains in a blood vessel. A thrombotic stroke is caused by the formation of a clot in an artery that sends blood to the brain. When the clot cuts off blood supply, it deprives the brain of oxygen, causing death to affected brain cells within minutes. According to the Mayo Clinic, thrombotic strokes are one of the most common types of ischemic strokes--strokes that occur as a result of narrowed or blocked blood flow to the brain. Thrombotic strokes often are caused by atherosclerosis--a condition in which blood vessel walls become thick and hardened due to fatty deposits called plaques in the lining of blood vessels. Atherosclerosis is a symptom of cardiovascular disease and commonly is associated with high cholesterol and high blood pressure, along with smoking and other dietary and lifestyle factors. According to the AHA, a thrombus usually forms in arteries damaged by the buildup of fatty deposits.
Embolus
An embolus is a blood clot that has become dislodged from its original blood vessel and travels through the bloodstream to another location in the body--commonly the heart, lungs or brain. And embolic stroke is a type of ischemic stroke that occurs when a clot travels from a distant vessel--commonly in the heart--and becomes lodged in a small artery that supplies blood to the brain. Atrial fibrillation, or irregular beating of the heart's two upper chambers, is commonly the cause of a brain embolus, the AHA reports. When the heart beats irregularly, it interferes with normal blood flow and can cause blood to pool and clot. As this blood enters circulation again, it can send the blood clot into a narrowed artery in the brain and cause a cardioembolic stroke--an ischemic stroke occurring as a consequence of a heart problem.
