Understanding Brain Injury Pathology
Brain Injury Pathology – More than Simply Hitting Your Head
Brain injury pathology occurs for more complicated reasons than you hit your head. While many of the most severe injuries do involve a blow to the head, significant injury can occur from rapid acceleration/decelerations forces, such as whiplash. Regardless, it is most important in understanding brain injury pathology to understand the internal forces at work inside the skull.
The terms traumatic brain injury and brain injury are synonymous. The terms mild traumatic brain injury and concussion are synonymous. Brain injury is often shortened to the term TBI; mild brain injury to MTBI.
Biomechanics of Brain Injury Pathology
The internal forces which can cause brain injury pathology may include both impact or rotational (shear forces.) The term shearing is used because what is happening is that layers within the brain are moving at different speeds, causing a cutting or twisting injury to cells, much like you might shear a piece of paper in a paper cutter. While it is the common conception that impact damage comes from blows to the head and shear damage from whiplash forces, 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 in a car, there is damage occurring to the brain from the direct transference of force to the head. Yet, the rotational forces will also be severe because of the rapid stopping of the movement of the head and the brain, when the windshield stopped the arc of the movement of the head. Rotational forces involve movement in an arc, whether the head is the object moving in the arc or whether it is the internal structures of the brain moving.
Impact brain damage tends to be focal – concentrated in a specific part of the brain. Shear damages tends to be diffuse – occurring in widespread portions of the brain. The term Diffuse Axonal Injury means widespread damage to the axons, the long thin portion of the neuron. The neuron is the principal thinking cell in the brain and it communicates with other brain cells through its wirelike protrusion, the axon.
Axons can be compared to an electrical system where each wire has to be connected properly for the system to work. Once torn or damaged, an axon cannot work properly. Injured axons often die over the first few days after injury. If an axon can no longer communicate properly with other neurons, the other neurons will have difficulty doing their job too.
Primary versus Secondary Brain Injury Pathology
The other principal issue to understand in grasping brain injury pathology is that both immediate damage may occur at the time of the blow and secondary damage as a result of processes going on inside the brain and the skull. In severe brain injury cases, the secondary damage can cause severe brain injury pathology. While the secondary damage in a mild traumatic brain injury is rarely catastrophic, it is the delayed effects of mild traumatic brain injury which often confound diagnosis. For this reason, ER evaluations often miss the disabling potential of mild traumatic brain injury. In between mild brain injury and severe brain injury, is moderate brain injury, which involves loss of consciousness or other significant neurological deficits, yet does not involve extended coma. Moderate brain injury typically involves a mixture of pathology somewhere between mild traumatic brain injury and severe traumatic brain injury.