An acute ischemic involves blood vessel blockage by an embolism or thrombus. In an embolism, blood flow from a larger blood vessel to a smaller one gets plugged, causing an embolic stroke. A thrombus is a localized blockage caused by a lack of blood movement, which creates a blood clot called thrombosis. 

Often, the thrombus is caused by an atrial fibrillation that interrupts the heart rhythm, producing an arrhythmia and consequent lack of blood flow. Likewise, atherosclerotic thickening of the artery wall by fatty material accumulation, such as cholesterol, can also result in artery stenosis or narrowing and severe blood flow restriction. 

If the blockage is removed and a steady blood supply restored within a few minutes, chances for a full recovery are good. If not, permanent neurological disorders, dysfunctional brain tissue and subsequent loss of brain function occur. 

It is generally known that strokes can cause paralysis and speech deficits, but specific ischemic symptoms depend on the actual arterial system affected. Carotid artery involvement usually produces one-sided symptoms, including partial Horner's syndrome (affecting eye appearance), same-sided blindness and opposite-sided hemiparesis (muscle weakness). Any symptom persisting after six months of treatment is ordinarily permanent.

In contrast, a transient ischemic attack results from a dysfunction in the internal carotid-middle cerebral or vertebral-basilar arterial systems. These attacks can range from two to three minutes to 30 minutes or more (rarely over one or two hours) without a loss of consciousness or lasting symptoms.

Moyamoya disease usually involves the constriction of the internal carotid artery, which, along with thromobosis, again restricts blood flow to the brain. In the body's attempt to compensate, collateral blood vessels grow, but tend to be weak. On an angiogram (X-ray), the collateral vessels appear as a "puff of smoke" or "moyamoya" in Japanese vernacular. An MRI scan is effective in detecting this disease.

Antiplatelet drugs such as aspirin can be administered to prevent thrombosis, but the ultimate recommended treatment is surgery, wherein other arteries are redirected to replace the internal carotid artery's blood circulation.

In a venous thrombosis, the thrombosis occurs within a vein.

A hemorraghic stroke is usually caused by a rupture resulting from longstanding arterial high blood pressure or hypertension. The initial symptom is an abrupt headache, often leading to steadily increasing nausea, delirium, vomiting and even unconsciousness. With large hemorrhages, there are over 50% fatalities within a few days. Where non-fatal, a reasonably functional recovery can be made.

Strokes share controllable and uncontrollable risk factors. The former are obesity, high blood pressure, alcohol consumption, high cholesterol levels, diabetes, atrial fibrillation, and physical inactivity. Uncontrollable factors include being male, being over 55, being an African-American, Hispanic or Asian-Pacific Islander, having fibromuscular dysplasia, having patent foramen ovale (hole in the heart) and having a family history of stroke or transient ischemic attack.