The term, “stroke” refers to a sudden stoppage of blood flow to a part of the brain. It can happen either due to a block to a supply route (artery) or a blast (rupture) in a supply route. Experts classify these into different types of stroke.
The block to a supply route occurs due to a blood clot that lodges within a blood-supplying vessel, an artery, or one of its smaller branches.
- In the medical field, “stroke” is called “cerebrovascular accident” (in short, CVA).
- A stroke due to blockage due to a blood clot is called “ischemic stroke”.
- A stroke due to a broken supply route is called “hemorrhagic stroke”.
Types of stroke
Of the two types, “ischaemic strokes” are much more commoner than “hemorrhagic strokes”. In the US, as much as 80 per cent of strokes are ischemic strokes according to the US government website.
There are common places where ischemic stroke occurs. One place is the junction where the main supply route (common carotid artery) divides into two smaller branches: internal and external. (Read the blood flow: Journeys to the brain-4.). These clots usually travel higher up and block a smaller artery. The extent of the damage depends on the size of the clot and the part of the brain it blocks. See Figure 1.
Sometimes, a clot can originate within the heart itself too.
In a hemorrhagic stroke, blood seeps through from an arterial branch either due to a leak or a rupture of that vessel. Brain damage occurs as a result of pressure due to blood collection (Figure 2).
Transient Ischemic Attack (TIA): “mini-stroke”
This term is used as its name implies a very brief attack due to a temporary blockage of a blood vessel. The block is caused by a very small blood clot that will dislodge by itself. This is considered a warning. However, it is a medical emergency meaning that we need to call 911 immediately.
The “mini-stroke” typically resolves within 24 hours; however, it can become a full-blown stroke if not attended.