A stroke which is also called Cerebrovascular accident (CVA) or a brain attack.
There are two main types of stroke. An Ischemic stroke – which is when there is a blocked artery that reduces blood flow to the brain and A Hemorrhagic stroke – which is when an artery in the brain breaks, creating a pool of blood that damage the brain.
Ischemic Stroke:-
Of the two of these strokes, Ischemic stroke are much more common and the amount of damage they cause is related to the parts of the brain that are affected and how long the brain suffers from reduced blood flow. If symptoms self-resolve within 24 hours, it’s called a Transient Ischemic attack and there are usually minimal long-term problems.
Brain Anatomy:-
Let’s discuss some basic brain anatomy. The brain has a few regions – the most obvious is the cerebrum, which is divided into two cerebral hemispheres, each of which has a cortex – an outer region – divided into four lobes including the frontal lobe, Parietal lobe, Temporal lobe and Occipital lobe. There are also a number of additional structures including the Cerebellum which is down below as well as the Brainstem which connects to the spinal cord.
The right cerebrum controls muscles on the left left side of your body and vice Verda. The frontal lobe controls movement and executive function, which is our ability to make decisions. The parietal lobe processes sensory information, which lets us locate exactly where are physically and guides movements in a three dimensional space. The temporal lobe plays a role in hearing, smell, memory as well as visual recognition of faces and languages. The occipital lobe which is primarily responsible for vision. The cerebellum helps with muscle coordination and balance. The brainstem plays a vital role in functions like heart rate, Blood pressure, Breathing, gastrointestinal function and Consciousness.
The brain receives blood from the left and right internal carotid arteries as well as the left and right vertebral arteries, which come together to form the Basilar Artery. The internal carotid arteries turn into the left and right middle cerebral arteries which serve the lateral portion of the frontal, parietal and temporal lobes of the brain. Each of the internal carotid arteries also give off branches called the anterior cerebral arteries which serve the middle portion of the frontal and patient lobes and connect with one another with a short little connecting blood vessel called the anterior communicating artery. The vertebral arteries and basilar artery gives off branches to supply the cerebellum and the brainstem. The basilar artery divides to become the right and left posterior cerebral artery which mainly serve the occipital lobe and some of temporal lobe as well as the thalamus. Finally, the internal carotid arteries each give offa branch called the posterior communicating artery which attaches to the posterior arteries on each side. So together, the main arteries and the communicating arteries complete what is called the Circle of of Willis – a ring where blood can circulate from one side to the other in case of blockage. The circle of Willis offers alternative ways for blood to get around an obstructed vessel.
In general, the brain can get by on diminished blood flow – especially when it happens gradually because that allows enough time for collateral circulation to develop, which is where a nearby blood vessel starts sending out branches of blood vessels to serve an area that’s in need. But once the supply of blood flow is reduced to below the needs of the tissue – it causes tissue damage, which we call an Ischemic Stroke.
How Ischemic Stroke Happens?
There are two main ways that an ischemic stroke happens:-
1) Endothelial cell dysfunction:-
It is when something irritates or inflames the slippery inner lining of the artery – the tunica intima. One classic irritant is the toxins found in tabacco which float around in the blood damaging the endothelium. That damage becomes a site for atherosclerosis, which is where a plaque forms which is when a buildup of fat, cholesterol, protein, calcium and immune cells forms and starts to obstruct arterial blood flow.
The Plaque has two parts – the soft chessy -textured interior and the hard outer shell which is called the fibrous cap.
Branch points in arteries and particularly the internal carotid and middle cerebral arteries are the most common spot of atherosclerotic. Usually it takes years for plaque to build up and this slow blockage only partially blocks the arteries and so even through less blood makes it to brain tissue, there’s still some blood. So stroke happens when there’s a sudden and complete or near-complete blockage of an artery.
2) Embolism:-
An embolic stroke typically happens when a blood clot breaks off from one location and travel through the blood and gets lodged in an artery downstream, typically an artery, arteriole or capillary with a smaller diameter. These blood clots typically emerge from atherosclerosis but they can also form in the heart. If a clot forms in the left atrium and then moves into the left ventricle and from there it has a direct route to the brain. On the other hand, if a clot forms in the low-pressure veins or right atrium, then it goes into the right ventricle and gets lodged in the pulmonary capillaries with no way of getting to the brain.
Lacunar Stroke:-
One specific type of ischemic stroke is called a Lacunar Stroke and it typically involve the deep branches of the middle cerebral artery that feed the basal ganglia. Lacunar refers to “lake” and is called that since after a lacunar stroke damaged brain tissue develops fluid filled pockets called cysts that look like little lakes under a microscope. This stroke develop as a result of hyaline atherosclerosis which is when the arteriole wall gets filled with protein. This can be happen as a result of hypertension or diabetes and can make the artery wall quite thick and reduces the size of the lumen.
Symptoms of Stroke:-
Stroke symptoms depends on the exact part of the brain that is affected.
An anterior or middle cerebral artery stroke can cause Numbness and sudden muscle weakness. If a stroke affects the Broca’s area, which is usually in the left frontal lobe or Wernicke’s area, which is usually in the left temporal lobe then it can cause Slurred Speech or Difficulty in understanding speech.
If there’s a posterior cerebral artery stroke then it can affect Vision.
An acronym to remember some common stroke symptoms is BE FAST:-
B – Balance appropriate
E – Eyes shaky
F – Facial drooping
A – Arm weakness
S – Speech Difficulty
T – Time (Emergency)
Time is obviously not a symptom but just a reminder to get help as quickly as possible to minimise cell injury and maximise the chance of a fell recovery.
Diagnosis:-
To diagnose and confirm the location and size of an ischemic stroke, medical imaging with a CT or MRI can be used. Also, Angiography which uses contract injected into the blood can help to visualise the exact location wher blood flow is blocked within an artery. In addition, using FLAIR sequence MRIs, it’s possible to distinguish a new stroke injury with an old one.
Treatment:-
In an ischemic stroke the ultimate treatment goal is to re-establish blood flow as quick as possible to prevent further cell death, particularly in the penumbra – every minute counts. So thrombolytic enzymes like Tissue Plasminogen Activator or TPA are used to activate the body’s natural clot busting mechanism. Aspirin is also used to prevent platelets from forming additional clots. If TPA is unsuccessful then Surgical procedures can be used to push a wire through the artery and physically remove the clot.
Minimise Risk Factors:-
After a stroke has occurred, there is an elevated risk of having additional strokes so it’s important to minimise risk factors.
1) Quit Smoking
2) Having healthy blood pressure
3) Normal LDL cholesterol levels
4) Controlling disease like Diabetes