I know in some cases it can be even more confusing because you don’t have any bruises, cuts, or scrapes to show for it. Yet you still feel like absolute garbage. So whats the deal?
Well first I should note there is a lot of variation. However, TBI refers to damage to the brain caused by an external physical force and is not caused by something internal, such as a stroke or tumor. Moreover, you should remember that it is possible to have a TBI and never lose consciousness.
In a closed head injury, the skull and brain contents has not been penetrated (broken into or through). An example of this could be whiplash from a motor vehicle accident. The mechanism behind closed head injury is due to the forces of acceleration, linear translation, as well as rotational and angular acceleration. These forces cause brain matter to undergo acceleration followed by rapid deceleration and collision against the skull. It is this jarring movement that bruises brain tissue, damages axons, and tears blood vessels. This type of injury can occur in specific brain areas (localized injury) or throughout the brain (diffuse axonal injury).
In an open head injury, the skull and other protective layers are penetrated and exposed to air. An example of this could be a gunshot wound to the head. Due to the nature of the injury the damage that follows tends to be localized and therefore limited to a specific area of the brain. That being said, this does not mean that these injuries cannot be severe. In fact, these injuries can be as destructive as closed head injuries depending on the area of brain affected.
However, there is more to it than that. TBI is also broken down into the primary injury and the secondary injury. I will briefly touch on these two definitions but a complete blog post will be coming up on both aspects. The primary injury represents the diffuse and focal mechanical damage inflicted on the brain at the time of impact. It is what happens as the injury is occurring and is the injury that occurs as a result of the mechanical forces of TBI. On the other hand, the secondary injury refers to the changes that occur after the initial trauma and plays a large role in the brain damage or death that can result from TBI. Secondary injury occurs hours and days following the injury and therefore has potential for pharmacological intervention and treatment. There are many compounding factors that interact to create the secondary injuries such as ischema (insufficient blood flow), cerebral hypoxia (insufficient oxygen in the brain), cerebral edema (swelling of the brain) and many more.
Besenski, N. (2002) Traumatic injuries: imaging of head injuries. European Radiology. 12(6): 1237-1252
Mustafa, A. G., Al-Shboul, O. A. (2013) Pathophysiology of traumatic brain injury. Neurosciences. 18(3): 222-234