A stroke is loss of blood flow to part of the brain. It happens when a blood clot blocks an artery in the brain or when a bleed from a blood vessel in the head creates pressure in the brain.
In either case, brain cells die, and the brain is damaged temporarily or permanently. Depending on the area of brain deprived of oxygen, a person may experience loss of memory, movement, speech or other disabilities. If blood flow is restored or pressure is relieved quickly through medical treatment, the brain may fully recover.
Two Types of Stroke: Ischemic and Hemorrhagic:
Ischemic stroke. This type of stroke occurs when a blood clot blocks the flow of blood to the brain. The clot may have traveled from another part of the body (called an embolus) or formed inside an artery that supplies blood to the brain (called a thrombus).
Strokes that result from a blood clot make up about 87 percent of all strokes, according to the American Stroke Association. Medications that dissolve a clot can prevent severe damage if given quickly after stroke symptoms appear.
Hemorrhagic stroke. When a blood vessel in the brain breaks or leaks due to weakness in the vessel wall, blood flows into or around the brain and creates swelling and pressure. This bleeding (or hemorrhage) damages brain cells and tissue.
“What generally all strokes have in common is that brain cells die,” Dr. Huang says. There are different types of brain cells, but the most critical ones are the neurons, which act like wires that transmit signals from cell to cell. There are other cells in the brain that can be affected, such as the cells that insulate neurons, like plastic coating around a wire.
Because each part of the brain controls certain functions, the results of a stroke will differ depending on which part of the brain is damaged. “When the average person experiences a stroke, they will develop some sort of weakness or a deficit,” Dr. Huang says. That deficit could be:
Speech problems (slurred speech, inability to understand or produce language)
Weakness or numbness on one side of the body
Vision issues (double vision, inability to see or process what you’re seeing)
Impairment of a motor activity
Confusion
“Depending on the cell that dies and in what part of the brain damage occurs, you get certain degrees of damage. If you kill neurons, the damage is pretty much as permanent as it gets,” Dr. Huang says. “You might have other neurons that can recover some function, but it’s not going to be great function. But if you injure the insulating cells, there is some level of recovery with that.”
This is one of the biggest differences between strokes and heart attacks. “Unlike heart attacks, where you damage heart tissue but your heart hopefully keeps pumping, in the brain, stroke can present in varying different ways: Your left side might be weak, your right side might be weak, you might not be able to speak or you could have blurry vision, and that function might not be recovered,” Dr. Huang says. “It’s more complex, which can make it hard to diagnose a stroke.”
To make matters more complicated, most brain cells don’t have nerves, which means they can’t sense pain. “When you have a stroke, more often than not, you’re not going to feel pain,” Dr. Huang says. “So again, unlike heart attack, where you might have pain that signals people to go to the emergency room, with a stroke, you probably won’t feel anything.