Stroke

A stroke also known as a cerebrovascular accident occurs when blood flow to the brain is disrupted, resulting in tissue ischemia and death.

A stroke can be ischemic or hemorrhagic. An ischemic stroke is when there is an occlusion in an artery in the brain.

While a hemorrhagic stroke is when an artery in the brain ruptures and causes blood to leak into the brain tissue. Now, the brain is the communication and control center of the body and to maintain neurologic function.

All parts of the brain require a steady and consistent flow of oxygen and nutrient rich blood. The brain is supplied with blood through the internal carotid arteries and the vertebral arteries.

The internal carotid arteries branch off into the middle cerebral arteries and the anterior cerebral arteries. While the vertebral arteries come together to form the basilar artery, the basilar artery then leads to the posterior cerebral arteries.

The posterior cerebral arteries along with the anterior cerebral arteries, internal carotids and other small branched arteries form the circle of Willis.

The circle of Willis is a group of arteries arranged in a circle that allows for collateral blood flow, meaning blood can circulate from one side of the brain to the other if a blockage occurs.

Ok. So with ischemic strokes, blood flow is disrupted by obstruction from a thrombus or embolus.

A thrombus is a clot that forms within a vessel. Whereas an embolus is when a clot breaks off from one area and travels downstream, lodging in a smaller vessel.

For example, a thrombus can occur from atherosclerotic plaque or fat builds up within a vessel, supplying blood to the brain.

And an embolus can occur from a blood clot in the atria of the heart due to atrial fibrillation that makes its way into cerebral circulation.

Risk factors for ischemic strokes include hypertension, hyperlipidemia, increased age heart disease and sleep apnea. There's also an increased risk with smoking, oral contraceptive use and previous transient ischemic attacks or tia A s also called mini strokes or blockage is temporary, usually lasting minutes to hours and doesn't cause long term brain damage.

On the other hand, with a hemorrhagic stroke, blood flow is disrupted due to a rupture of a cerebral artery. This can occur due to conditions such as hypertension that cause weakening of the artery wall, making it more prone to rupture.

Risk factors include advanced age, obesity and the use of tobacco, alcohol or other illicit drugs like cocaine. Additionally, coagulation disorders such as disseminated intravascular coagulation, brain tumors and other brain abnormalities like aneurysms can increase risk.

All right. Now, when an ischemic stroke occurs, blood flow may be gradually or rapidly obstructed.

For example, gradual obstruction of blood flow can occur as plaque slowly builds up in an artery. Whereas if an embolus lodges in a small artery, it may cause an abrupt obstruction.

Now, the brain will usually be able to compensate for the reduced blood flow from one vessel by increasing blood flow to other vessels or through angiogenesis.

A process where collateral blood vessels are generated to go around the obstruction. However, as blood flow decreases, but there's an increased demand for oxygen and nutrient rich blood like during exercise, ti A s may occur.

This causes stroke like symptoms that resolve once demands aren't as high. If there's sudden complete or nearly complete obstruction of blood flow, brain tissue will be deprived of oxygen and nutrients and begin to die or infarct causing a stroke.

The longer the obstruction occurs, the more brain tissue is damaged and dies when a hemorrhagic stroke occurs, a cerebral artery ruptures interrupting blood flow and causing blood to pool within the skull.

Now, there isn't a lot of extra room within the skull. So as blood pools pressure within the skull increases, called increased intracranial pressure or ICP increased ICP puts direct pressure on brain tissue causing tissue injury.

The injury activates the immune system leading to more swelling which decreases cerebral perfusion even more. Eventually, blood runs out of space within the skull and there's no room left for brain tissue to swell.

As a result, brain herniation occurs or the parts of the brain like the brainstem cerebellum and cerebrum protrude through an opening such as the foramen magnum, a hole at the base of the skull where the spinal cord passes.

Clinical manifestations depend on the size of the affected artery, location of the brain, the affected artery supplies and how long the brain goes without blood flow.

In general, a stroke can present with sudden onset numbness or weakness in an arm leg or one side of the face, disorientation or confusion and difficulty speaking, there may be difficulty with walking or balance and visual disturbances such as double vision may occur.

If a smaller artery is affected, manifestations may be more subtle and can even evolve slowly over hours called an evolving stroke.

However, if a large artery is affected, there can be severe widespread effects that occur rapidly like a loss of consciousness or death.

A useful acronym to remember, common stroke symptoms is B fast, which stands for balance impairment, eye symptoms, facial drooping, arm weakness, speech difficulties and time to call emergency services.

All right. As a quick recap, a stroke occurs when blood flow to the brain is disrupted, resulting in tissue ischemia and death.

A stroke can be ischemic when there's an occlusion in an artery in the brain or hemorrhagic. When an artery in the brain ruptures and causes blood to leak into the brain tissue.

Clinical manifestations can include weakness in one arm leg or side of the face disorientation or confusion, difficulty speaking, balance or gait disturbances and vision changes.