Symptoms of these so-called mild TBI’s typically involve problems with the memory, mood changes and personality changes. Most of these injuries go undiagnosed because the symptoms are only detectable by those who knew the person well. Before the injury occurred. Frequently diagnosis of a mild TBI is dependent upon history and clinical presentation, because physical evidence of injury often does not exist.
There may be no evidence of a direct blow to the head or any other type of direct head trauma immediately following an incident that results in a mild TBI. Such evidence may be absent because the injury can occur with little or no impact to the head, the TBI itself results from the soft friable brain impacting on the hard-sharp ridges on the inside of the skull, during a sudden acceleration or deceleration event.
There may be absolutely no head impact involved, or the head impact may be against a cushioned surface such as an airbag or headrest leaving little or no evidence of impact on the face or head. Traditional imaging studies like CT and MRI most often show no evidence of mild TBI’s, because they are not sensitive enough to detect the widespread microscopic axonal injuries, that can collectively result in devastating neuropsychological and cognitive deficits.
TBI’s can occur as the result of impacts at varying speeds and from multiple directions. The severity of the TBI does not necessarily correlate with the speed of a vehicle during a collision, but with the unique combination of deceleration and rotational forces that affect the brain during the collision. The car-crash animation sequences (see video below) show how a sudden deceleration injury typically occurs. For purposes of demonstration and impact at a speed of 15 to 35 miles per hour into a sturdy barrier was used. Frontal impact was selected because frontal impacts are one of the most commonly occurring causes of TBI’s.
The crash depicted in the animation was based on video studies of crashes performed by several crash-test engineers. The first animation sequence shows the impact and sudden deceleration at a speed that is slightly slower than real time, to help demonstrate the violence of the motion. The collision is then repeated in slow motion to highlight the detailed movements of the upper body and head. Prior to the impact of the vehicle the body and head are traveling forward at the same rate of speed, at the moment of impact the vehicle suddenly stops but the body and head continue to travel forward.
Next, the body’s forward motion is halted by the seatbelt, but the head continues to travel forward, the left shoulders forward motion is halted by the shoulder harness before the rest of the body. So, rotation is added to the upper body and head in addition to the continuing forward motion. The head then comes to a sudden halt as it impacts with the airbag at the moment of impact the head violently rotates and begins an immediate reversal of movement. This back-and-forth motion is sometimes referred to as the contra cool effect. The head then rebounds into the headrest experiencing yet another immediate and violent impact and change of direction. To understand how TBI’s, occur one must have a detailed understanding of some areas of the brain, as well as a basic understanding of the relationships of various significant structures of the brain, to the head and skull.
In this animation sequence, the head and brain are sectioned through the left eye. The brain is surrounded in the skull by cerebrospinal fluid this fluid helps protect the soft friable brain from impacts with the hard-jagged edges of the inner skull. The brain is composed of gray matter and white matter. Grey matter consists of cell bodies. White matter consists of myelinated extensions of the cell bodies that communicate with other cell bodies. These extensions are called axons, the arteries that supply the brain penetrate the external surface of the brain and divide into smaller and smaller branches.
Upon microscopic examination of the brain one can appreciate the relationship between the fragile axons as compared to the much larger and more resilient blood vessels. Axons typically measure from 1/4 of one micron to 10 microns in diameter, while the blood vessels in this area typically measure from 30 to 240 microns in diameter. During a sudden deceleration as shown in the beginning of the animation sequences, the brain violently impacts against the inner surface of the skull at two times.
First when the head impacts with the airbag or otherwise stops its forward motion and begins its immediate rapid violent reversal of motion, and second when the head impacts against the headrest and repeats the immediate rapid violent reversal of motion. By observing the collision from a view that follows the motion of the head, one can appreciate the deformation of the brain as it violently impacts against the front and back of the skull. When the impacts of the brain against the skull are viewed in slow motion the shock waves that travel through the brain during the impacts can be observed.
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