A stroke happens when blood flow to a part of the brain is interrupted because a blood vessel in the brain is blocked or bursts open. If blood flow is stopped for longer than a few seconds, the brain cannot get blood and oxygen. Brain cells can die, causing permanent damage.
The two main types of stroke include ischemic stroke and hemorrhagic stroke.
- Ischemic stroke accounts for about three-quarters of all strokes and occurs when a blood clot, or thrombus, forms that blocks blood flow to part of the brain. If a blood clot forms somewhere in the body and breaks off to become free-floating, it is called an embolus. This wandering clot may be carried through the bloodstream to the brain where it can cause ischemic stroke.
- A hemorrhagic stroke occurs when a blood vessel on the brain’s surface ruptures and fills the space between the brain and skull with blood (subarachnoid hemorrhage) or when a defective artery in the brain bursts and fills the surrounding tissue with blood (cerebral hemorrhage).
Ischemic strokes are ultimately caused by a thrombus or embolus that blocks blood flow to the brain. Blood clots (thrombus clots) usually occur in areas of the arteries that have been damaged by atherosclerosis from a buildup of plaques. Embolus type blood clots are often caused by atrial fibrillation – an irregular pattern of heart beat that leads to blood clot formation and poor blood flow.
Hemorrhage strokes can be caused by uncontrolled high blood pressure, a head injury, or aneurysms. High blood pressure is the most common cause of cerebral hemorrhage, as it causes small arteries inside the brain to burst. This deprives brain cells of blood and dangerously increases pressure on the brain.
Aneurysms – abnormal blood-filled pouches that balloon out from weak spots in the wall of an artery – are the most common cause of subarachnoid hemorrhage. If an aneurysm ruptures, blood spills into the space between the surfaces of the brain and skull, and blood vessels in the brain may spasm. Aneurysms are often caused or made worse by high blood pressure.
A less common from of hemorrhage stroke is when an arteriovenous malformation (AVM) ruptures. AVM is an abnormal tangle of thin-walled blood vessels that is present at birth.
The primary goal in treating ischemic stroke is to restore blood flow to the brain. This will be attempted using blood clot-busting drugs such as aspirin, heparin, or tissue plasminogen activators that must be administered within three hours of the stroke. In addition, surgical procedures may be performed that can open up or widen arteries. These include carotid endarterectomy (removal of plaque and widening of the carotid artery) and angioplasty (a balloon that widens the cartoid artery and is held open with a metallic mesh tube called a stent).
Hemorrhagic stroke is treated differently than ischmic stroke. Surgical methods used to treat this stroke variant include aneurysm clipping, aneurysm embolisation, and arteriovenous malformation (AVM) removal. Aneurysm clipping consists of a small clamp placed at the base of the aneurysm that isolates it from the circulation of it’s attached artery and keeps the aneurysm from bursting or re-bleeding. Aneurysm embolisation (coiling) uses a catheter inserted into the aneurysm to deposit a tiny coil that coil fills the aneurysm, causing clotting and sealing off the aneurysm off from arteries. AVM removal is a surgical procedure to remove usually smaller AVMs or AMVs that are in more accessible portion of the brain in order to eliminate the risk of