Definition of Terms

Definition: Traumatic Brain Injury
Traumatic brain injury is an insult to the brain, not of a degenerative or congenital nature but caused by an external physical force, that may produce a diminished or altered state of consciousness, which results in an impairment of cognitive abilities or physical functioning. It can also result in the disturbance of behavioral or emotional functioning. These impairments may be either temporary or permanent and cause partial or total functional disability or psychosocial maladjustment.
Adopted by the Brain Injury Association Board of Directors, February 22, 1986.

How the Brain Works
The brain controls the actions of the body and allows us to think, learn, and remember. The brain has three main sections: the cerebral hemispheres, cerebellum, and brain stem. There are left and right cerebral hemispheres. The cerebral hemispheres are divided into sections called lobes. Each section of the brain has special jobs to do and sections of the brain also work together. The left cerebral hemisphere controls the right side of the body and is usually responsible for speech. The right cerebral hemisphere controls the left side of the body and is usually responsible for creative thinking.

Protection and Oxygen for the Brain: The brain controls many important functions. It needs good protection and oxygen. The brain is protected and receives oxygen in the following ways:

• Skull: A hard bone that surrounds the brain tissue
  
• Dura: A tough covering around the brain tissue and the spinal cord
• Cerebrospinal Fluid (CSF) or Spinal Fluid: Fluid that flows through the ventricles and around the brain and spinal cord. The ventricles are spaces inside the brain.
• Blood: Provides oxygen and food for the brain

Bruising (Bleeding)
If a person is driving a car at 20 miles per hour and is struck head-on by another car traveling at the same rate of speed, the person's brain goes from 20 miles per hour to zero in an instant. The soft tissue of the brain is propelled against the very hard bone of the skull. The brain tissue is "squished" against the skull and blood vessels may tear. When blood vessels tear, they release blood into areas of the brain in an uncontrolled way.

Why do medical experts seem so concerned about bleeding in the brain? A major problem is that there is no room for this extra blood. The skull, being hard and brittle, does not expand. So the blood begins to press on softer things -- like brain tissue. Brain tissue is very delicate and will stop working properly or may even die off. With large amounts of bleeding in the brain, the pressure will make critical areas of the brain stop working. Areas that control breathing or heart rate could be affected, and a life or death situation could develop within hours of the accident. Some people have sustained a head injury from a car accident and seem "just fine" right after at the accident. Some have even gotten out of the car and directed traffic. Within a short period of time, they began to get more and more confused until they eventually lose the ability to perform simple activities of daily living. This is one reason Emergency Medical Technicians at the scene of the accident are so anxious to have people go to a hospital following a car accident.

Contra-Coup Injury
During a car accident, the brain, which is very soft, can be thrown against the front part of the skull, which is very hard, and bruising can happen. But the injury process is not over. The brain, and the rest of the body, then get thrown backwards. This bouncing of the brain, first against the front of the skull and then against the back of the skull, can produce bruises in the front and back of the brain. Thus people can have injury to the brain not only where their forehead hits the steering wheel, but other areas of the brain as well. Doctors call this a “contra-coup” injury.

Tearing
At some point in time, we've all played with the food "Jell-O". If you put a thin cut in a square of Jell-O with a knife and let it go, the Jell-O will come back to shape if you jiggle it. The Jell-O will look perfectly good up until the time you go to lift it up, and there will be the slice. The brain has a consistency slightly firmer than Jell-O, but the same effect applies. In the case of the car accident, the brain is thrown forward, then bounced backward (remember those car commercials where the crash dummy flies forward, then comes flying backward). In this forward/backward motion, the brain can be torn. The brain can also be torn by the effects of "energy". If you take a block of ice and hit it with a hammer (assuming you don't completely shatter the ice), you will see little cracks in the ice. Energy from the hammer has been transferred to the ice, producing the web-like cracks. Tearing in the brain is very serious. Tearing in the brain "cuts" the wires that make the brain work.

One of the problems with tearing is that it happens on a microscopic level (the brain has about 100 billion of these "wires"). This tearing may not show up on typical medical tests. Devices that take pictures of the brain will not see these small tears. Two common ways of viewing the brain are with a CT Scan (using X-rays) and an MRI (using magnetic fields) to create pictures of the brain. Both of these techniques are very good at seeing blood and tumors in the brain, but they are not good with tears (which are very small). In a number of medical studies with people who have brain injuries, only 10 to 15 percent had "positive" CT Scans or MRI findings.

New tests are being incorporated, including the next generation of high-resolution Single Photon Emission Computerized Tomography (SPECT), which provide a much more detailed image and assist in formulating a diagnosis of persons with brain injuries. This objective testing, may show neurological dysfunction and psychological disorders that may otherwise go undetected in MRI and CT scans. When correlated with other clinical testing and subjective data, the SPECT scan may help produce a more definitive evaluation of a person’s neuropsychological disability and prognosis.

Diffuse Axonal Injury
Damage to the pathways (axons) that connect the different areas of the brain. This occurs when there is twisting and turning of the brain tissue at the time of injury. The brain messages are slowed or lost. Treatment is aimed at managing swelling in the brain because torn axons cannot be repaired.

Anoxic Brain Injury
An injury that results from a lack of oxygen to the brain. This is most often from a lack of blood flow due to injury or bleeding.

Swelling
If you drop a bowling ball on your foot it will turn "black and blue" due to blood leaking under the skin. Your foot will also do something else -- it will swell up. The body realizes that the foot has been injured and sends agents to heal the injured area. The problem with the brain is that there is no extra room and the pressure begins to build up. This pressure pushes down on the brain and damages structures in the brain. If there is too much pressure, this can stop important structures that control breathing or the heart rate.

Open versus Closed Head Injury
Not too long ago, doctors made the distinction between open and closed head injuries. In an open head injury, the skull is fractured and doctors assumed this would produce a severe head injury. In a closed head injury, the skull is not broken and doctors mistakenly assumed that these produce less severe injuries. Doctors have now learned that this is not true. In a closed head injury, pressure builds up and damages brain tissue. If you fracture the skull, you may let off excess pressure thus saving the brain from further damage. Because of the wide variation in patients, these terms are no longer used.

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