Causes of Stroke

Ischemic strokes may result from disorders in which arteries can become blocked by accumulation of material or by a blood clot (thrombus). For example, in atherosclerosis, fatty material, calcium, and other materials gradually accumulate in the walls of arteries, forming a plaque (atheroma). Eventually, the plaque may completely block an artery that carries blood to the brain, often the carotid artery (in the neck). Also, blood clots can develop on a plaque, blocking even more of the artery. Part of the blood clot may break off, travel through the bloodstream (becoming an embolus), and eventually block an artery that carries blood to the brain.

An ischemic stroke may result from heart disorders that can cause blood clots to form in the heart. The clots may break off and eventually block an artery that carries blood to the brain. These disorders include abnormal heart rhythms (arrhythmias) such as atrial fibrillation, heart valve disorders, heart attacks (due to coronary artery disease), and bulges (aneurysms) in the wall of the heart.

Hemorrhagic strokes may result from disorders that affect blood vessels in or around the brain. High blood pressure is an example. High blood pressure can cause tiny bulges (aneurysms) to form in small arteries within the brain. (Aneurysms form in areas where an artery's wall is weak.) These tiny aneurysms can break and cause bleeding within the brain (intracerebral hemorrhage). Other aneurysms affect arteries around the brain. These aneurysms may be present at birth, result from an injury, or develop over time. They can break and cause bleeding between two of the layers of tissue covering the brain (subarachnoid hemorrhage). The affected arteries may contract (constrict) several days later, cutting off the blood supply, and thus cause an ischemic stroke as well.

Some older people have amyloid angiopathy. It causes blood vessels to become more fragile and thus increases the risk of hemorrhagic stroke. Amyloid angiopathy is especially common among people with Alzheimer's disease.

Infrequently, a hemorrhagic stroke results from an abnormal connection between an artery and a vein (arteriovenous malformation) in or around the brain. The abnormal blood vessels can break, causing a subarachnoid or an intracerebral hemorrhage. Arteriovenous malformations may be present at birth or develop over time.

A hemorrhagic stroke may result from an ischemic stroke. The lack of blood and oxygen resulting from the ischemic stroke damages blood vessels, weakening their walls.

A high level of total cholesterol, low-density lipoprotein cholesterol (LDL, the "bad" cholesterol), or triglycerides (another fat in the blood) increases the risk of stroke. A low level of high-density lipoprotein cholesterol (HDL, the "good" cholesterol) also increases the risk.

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