Patients who suffer a major ischemic stroke—the narrowing or blocking of arteries that chokes off blood flow to the brain—often experience prior symptoms that do not result in injury. In most cases, these transient ischemic attacks preceded major strokes by no more than a week, according to a recent study of 2,416 patients. Physicians should begin preventive treatment within hours of a mini stroke rather than taking weeks to assess a patient, as some studies have found.

Percent of strokes that are ischemic: 80

Typical length of a mini stroke: 5 minutes

Percent of ischemic stroke patients who experience a prior mini stroke: 15 to 30

Annual number of strokes in the U.S.: 700,000

Number resulting in death: 168,000

Total number of survivors: 4.7 million

Amount spent every year on stroke-related medical costs and disability: $51 billion

SOURCES: Neurology, March 8; Society for Neuroscience