Overview
This lecture explains the main types of ischemic strokes, their causes, and how they affect brain tissue due to interrupted blood flow.
Types of Stroke
- Stroke occurs when brain tissue dies from lack of blood and oxygen.
- Two main types: ischemic stroke (due to blockage, 75% of cases) and hemorrhagic stroke (due to burst vessel).
Causes of Ischemic Stroke
- Ischemic strokes result from obstruction of a cerebral blood vessel.
- Three main causes: embolism, thrombosis, and hypoperfusion (watershed stroke).
Embolic Stroke
- Caused by an embolus, a traveling mass (usually a blood clot) lodging in a cerebral artery.
- Emboli often originate from the heart (valves, left atrium/ventricle) or from cholesterol plaques in arteries (atherosclerosis).
- Blockage causes death of brain tissue supplied by affected artery (e.g., middle or anterior cerebral arteries).
Thrombotic Stroke
- Caused by local formation of a blood clot (thrombus) due to rupture of a cholesterol plaque in a brain artery.
- Most common in larger arteries: basilar, middle cerebral, or internal carotid arteries.
- Thrombotic strokes block blood flow at the site of the atherosclerosis.
Lacunar Stroke (Small Vessel Thrombosis)
- Occurs in small brain vessels, commonly due to chronic hypertension.
- High blood pressure thickens vessel walls, narrowing the lumen and limiting blood flow.
- Leads to localized death of brain tissue in small, deep regions.
Watershed (Hypoperfusion) Stroke
- Caused by reduced overall brain blood flow (hypoperfusion), often from severe blockage in major arteries.
- Affects "watershed areas"—regions between territories supplied by major cerebral arteries.
- These regions are most vulnerable when blood flow is globally decreased.
Key Terms & Definitions
- Ischemic stroke — Brain cell death due to blocked blood supply.
- Embolism — Obstruction from a traveling mass, usually a blood clot.
- Thrombosis — Local vessel blockage by a blood clot at a cholesterol plaque site.
- Atherosclerosis — Buildup of fatty deposits in artery walls.
- Lacunar stroke — Stroke from blockage of a small, deep brain vessel.
- Hypoperfusion — Reduced blood flow to the brain.
- Watershed area — Brain region at the border of two arterial supplies, susceptible during low blood flow.
Action Items / Next Steps
- Review diagrams of cerebral arteries and their territories.
- Study the differences between causes of embolic, thrombotic, lacunar, and watershed strokes.