What is a stroke?
A stroke, also called a “brain attack”, occurs when a blood vessel in the brain is blocked or ruptures and therefore interrupts the blood supply to parts of the brain. Being denied the oxygen carried by the blood the brain starts to die and loss of brain functions develop rapidly.
Strokes are normally grouped together into one of two main categories reflecting the causes of the stroke:
- Ischemic
- Hemorrhagic
Ischemic strokes are the more common of the two, representing about 80% of all strokes, and it is caused by something blocking the blood flow to the brain. The reminders, hemorrhagic strokes, are due to break of a blood vessel resulting in blood leaking into the brain.
ISCHEMIC STROKE
Ischemic stroke is the most common stroke type and usually results from a blood clot developing in clogged arteries (around plaques). Plaque, which is formed by fatty deposits on the wall of the arteries, often results in abnormal blood flow which in turn can cause a blood clot. We normally separate between blood clots that develop locally in the brain (cerebral thrombus) and blood clots brought to the brain with the blood stream (cerebral embolism). Embolic strokes can also result from other substances such as fat, air, cancer cells or bacteria clumps. Other causes of ischemic strokes are systemic hypoperfusion (general reduction in blood flow) and cerebral venous sinus thrombosis (rare form of thrombosis (blood clot) affecting the dural venous sinuses which drain blood from the brain, and it is causing strokes as locally increased venous pressure exceeds the pressure generated by arteries). Strokes without obvious explanations are often named “cryptogenic”.
HEMORRHAGIC STROKES
The second main type of strokes, hemorrhagic stroke, is caused by blood vessels in the skull rupturing. We separate between the cases where the bleeding happens inside the brain (intra-axial hemorrhage or intracerebral hemorrhage) and where the bleeding happens outside the brain (extra-axial hemorrhage). The flow of blood after the burst of a vessel causes the brain cells to die. Hemorrhagic strokes are the more deadly of the two main types of strokes.