A stroke is damage to the brain either due to blockage in blood flow or due to loss of blood from blood vessels in the brain. Blockage in blood flow or loss of blood causes the brain to lack sufficient oxygen and blood nutrients.

The brain needs a constant flow of blood to work properly. If the blood flow is disturbed and brain cells do not receive sufficient oxygen, resulting in cell death. The degree of damage that results from a stroke is based on where and how much blood flow to the brain is interrupted. Several different factors may result in stroke such as:

Hemorrhage

Hemorrhage results from the flow of blood from a ruptured blood vessel in the brain. Blood bursts at high pressure in the brain or in tissue surrounding the brain. Normal brain cells may be destroyed and the presence of blood often results in lethargy, severe headache or coma.

Embolus

Embolus is an obstruction of an artery due to material formed somewhere else in the body. The materials are usually produced in one part of the body and travels throughout the body until it trapped in a blood vessel.  The blood vessel then blocks and is unable to supply the brain with sufficient blood and nutrients.

Thrombosis:

Thrombosis is the formation or presence of a thrombus (a clot of coagulated blood attached at the site of its formation) in a blood vessel. If the clot is large enough, the obstructions may restrict or completely block blood flow through the artery. Blockage of arteries supplying the blood and nutrients to the brain causes stroke if alternative routes are not available to deliver an adequate blood supply.

Multiple Factors: Most strokes are associated with oxygen deficiency, atherosclerosis, high blood pressure, or a combination of the three.

Medication

Some medications used to treat certain diseases can increase the risk of developing a stroke.