If we consider a blood vessel, blood flow to the brain tissue can be hampered in these ways:
1. the vessel clogs within (ischemic stroke) typically with a blood clot
2. the vessel ruptures, causing blood to leak into the brain (hemorrhagic stroke)
Ischemic stroke accounts for about 83 percent of all cases. Ischemic strokes occur as a result of an obstruction within a blood vessel supplying blood to the brain.
Hemorrhagic stroke accounts for about 17 percent of stroke cases.
It results from a weakened vessel that ruptures and bleeds into the surrounding brain. The blood accumulates and compresses the surrounding brain tissue.
TIAs (transient ischemic attacks)
TIAs are minor or warning strokes. In a TIA, conditions indicative of an ischemic stroke are present and the typical stroke warning signs develop. However, the obstruction (blood clot) occurs for a short time and tends to resolve itself through normal mechanisms.
Even though the symptoms disappear after a short time, TIAs are strong indicators of a possible major stroke. Steps should be taken immediately to prevent a stroke.
Information from the American Stroke Association web site (more)