Southwestern Neuroscience Center

Stroke, also called a brain attack, occurs when blood flow to the brain is disrupted. Disruption in blood flow is caused when either a blood clot blocks one of the vital blood vessels in the brain (ischemic stroke) or when a blood vessel in the brain bursts, spilling blood into surrounding tissues (hemorrhagic stroke).

The brain needs a constant supply of oxygen and nutrients in order to function. Even a brief interruption in blood supply can cause problems. Brain cells begin to die after just a few minutes without blood or oxygen. The area of dead cells in tissues is called an infarct. Due to both the physical and chemical changes that occur in the brain with a stroke, damage can continue to occur for several days. This is called a stroke-in-evolution.

A loss of brain function occurs with brain cell death. This may include impaired ability with movement, speech, thinking, and memory, bowel and bladder, eating, emotional control, and other vital body functions. Recovery from stroke and the specific ability affected depend on the size and location of the stroke. A small stroke may result in problems such as weakness in an arm or leg. Larger strokes may cause paralysis (inability to move part of the body), loss of speech, or even death.

The following are the most common symptoms of stroke. However, each individual may experience symptoms differently. If any of these symptoms are present, call 911 (or your local ambulance service) immediately. Treatment is most effective when started immediately.

Symptoms may be sudden and include:

• Weakness or numbness of the face, arm, or leg, especially on one side of the body
• Confusion or difficulty speaking or understanding
• Problems with vision, such as dimness or loss of vision in one or both eyes
• Dizziness or problems with balance or coordination
• Problems with movement or walking
• Severe headaches with no other known cause

All of the above warning signs may not occur with each stroke. Do not ignore any of the warning signs, even if they go away--take action immediately. The symptoms of stroke may resemble other medical conditions or problems. Always consult your doctor for a diagnosis.

Other, less common, symptoms of stroke may include the following:

• Sudden nausea, vomiting, or fever not caused by a viral illness
• Brief loss or change of consciousness such as fainting, confusion, seizures, or coma
• Transient ischemic attack (TIA), or "mini-stroke"
  • A TIA can cause many of the same symptoms as a stroke, but TIA symptoms are transient and last for a few minutes or up to 24 hours. Call for medical help immediately if you suspect a person is having a TIA, as it may be a warning sign that a stroke is about to occur. Not all strokes, however, are preceded by TIAs.

Strokes can be classified into two main categories:

• 87 percent are ischemic strokes. These strokes are caused by blockage of an artery.
• 13 percent are hemorrhagic strokes. These strokes caused by bleeding.

An ischemic stroke occurs when a blood vessel that supplies the brain becomes blocked or "clogged" and impairs blood flow to part of the brain. The brain cells and tissues begin to die within minutes from lack of oxygen and nutrients. The area of tissue death is called an infarct. About 87 percent of strokes fall into this category. Ischemic strokes are further divided into two groups, including the following:

• Thrombotic strokes. These strokes are caused by a blood clot that develops in the blood vessels inside the brain.
• Embolic strokes. These strokes are caused by a blood clot or plaque debris that develops elsewhere in the body and then travels to one of the blood vessels in the brain via the bloodstream.

Thrombotic strokes are strokes caused by a thrombus (blood clot) that develops in the arteries supplying blood to the brain. This type of stroke is usually seen in older persons, especially those with high cholesterol levels and atherosclerosis (a buildup of fat and lipids inside the walls of blood vessels).

Sometimes, symptoms of a thrombotic stroke can occur suddenly and often during sleep or in the early morning. At other times, it may occur gradually over a period of hours or even days. This is called a stroke-in-evolution.

Thrombotic strokes may be preceded by one or more "mini-strokes," called transient ischemic attacks, or TIAs. TIAs may last from a few minutes to a few days and are often a warning sign that a stroke may occur. Although usually mild and transient, the symptoms caused by a TIA are similar to those caused by a stroke.

Another type of stroke that occurs in the small blood vessels in the brain is called a lacunar infarct. The word lacunar comes from the Latin word meaning "hole" or "cavity." Lacunar infarctions are often found in people who have diabetes or hypertension (high blood pressure).

Embolic strokes are usually caused by an embolus (a blood clot that forms elsewhere in the body and travels through the bloodstream to the brain). Embolic strokes often result from heart disease or heart surgery and occur rapidly and without any warning signs. About 15 percent of embolic strokes occur in people with atrial fibrillation, a type of abnormal heart rhythm in which the upper chambers of the heart do not beat effectively.

Hemorrhagic strokes occur when a blood vessel that supplies the brain ruptures and bleeds. When an artery bleeds into the brain, brain cells and tissues do not receive oxygen and nutrients. In addition, pressure builds up in surrounding tissues and irritation and swelling occur. About 13 percent of strokes are caused by hemorrhage. Hemorrhagic strokes are divided into two main categories, including the following:

• Intracerebral hemorrhage. This is bleeding from the blood vessels within the brain.
• Subarachnoid hemorrhage. This is bleeding in the subarachnoid space (the space between the brain and the membranes that cover the brain).

Intracerebral hemorrhage is usually caused by hypertension (high blood pressure), and bleeding occurs suddenly and rapidly. There are usually no warning signs and bleeding can be severe enough to cause coma or death.

Subarachnoid hemorrhage results when bleeding occurs between the brain and the meninges (the membrane that covers the brain) in the subarachnoid space. This type of hemorrhage is often due to an aneurysm or an arteriovenous malformation (AVM).

• An aneurysm is a weakened, ballooned area on an artery wall and has a risk for rupturing.
• Aneurysms may be congenital (present at birth), or may develop later in life due to such factors as hypertension or atherosclerosis.
• An AVM is a congenital disorder that consists of a disorderly tangled web of arteries and veins. The cause of AVM is unknown.