Understanding Brain Injury Pathology
Brain Injury Pathology – Beyond Simply Hitting Your Head
Brain injury pathology happens for more many other reasons than you just hitting your head. While severe injuries often do involve a blow to the head, significant injury can occur just from rapid acceleration/deceleration forces. An example of an acceleration/deceleration force is whiplash. Thus, in order to understand brain injury pathology, it is key to grasp the forces at work inside the skull.
The terms brain injury and traumatic brain injury mean the same thing. The terms concussion and mild traumatic brain injury mean the same thing. Brain injury is often shortened to TBI; mild brain injury to MTBI.
Brain Injury Pathology Biomechanics
The forces inside the skull which cause brain injury pathology comprise both impact and/or rotational forces. Impact forces result from the direct force against brain tissue as a result of the collision between the hard inside of the skull and the soft brain. The term shearing is used to describe the result of these rotational forces because when the layers within the brain move across each other at different speeds, a twisting injury can occur. This twisting shears the long parts of these cells, like a paper cutter would shear a piece of paper. Both impact damage and rotational injury can occur from any time substantial forces are directed against the head.
For example, when the head hits a windshield, there is damage occurring to the brain surface from the direct transference of force to the head. Yet, the rotational forces will also be severe to the internal parts of the brain because of the rapid stopping of the movement of the head and the brain. Rotational forces involve movements in an arc. Rotation within the brain can occur whether the head is the object moving in the arc or whether it is the internal structures of the brain moving which are moving in the arc.
Impact brain damage tends to be focal – largely concentrated in a particular part of the brain. Shear damages tends to be diffuse – distributed throughout widespread parts of the brain. The term Diffuse Axonal Injury means distributed damage over a large area of the axons, which is the long, thin portion of the neuron. The neuron is the main thinking cell in the brain which communicates with other brain cells through its wire like protrusion, the axon. Damaged axons will continue to die over the first days after injury. If an axon is not able to communicate correctly anymore with other neurons, the neighboring neurons will have difficulty doing their job as well.
Primary versus Secondary Brain Injury Pathology
The other significant issue in brain injury pathology is that both instant damage can happen at the time of the trauma and secondary damage as a result of processes which go on inside the brain and the skull. In severe brain injury, the secondary damage can cause even more serious brain injury pathology.
It is the delayed effects of secondary damage, even in MTBI, which often prove diagnosis. For this reason, Emergency Room evaluations often overlook the disabling potential of MTBI.
Moderate brain injury, involves loss of consciousness or other significant neurological deficits, yet does not involve extended coma. Moderate brain injury often presents with a mixture of pathology somewhere between MTBI and severe brain injury. Some disability should be expected after moderate brain injury. Yet a significant number of people have good recoveries after such injuries. It is important to understand in all brain injury, but especially in moderate brain injury, that an apparent full recovery does not mean frontal lobe issues, which are difficult to assess in a doctor’s office or through neuropsychological evaluation, are not issues. They may be causing major disruptions in day to day function. Mood and behavioral problems are the key areas that often go under-diagnosed.