Axonal Shear Injury
In the event of a traumatic accident that causes the brain to impact violently against the skull, most commonly caused by injuries sustained during an auto accident, the brain can suffer axonal shearing, or what is known as a diffuse axonal injury. Axonal shear injuries are a result of the nuerons within the brain having their connection twisted and or torn from trauma resulting in either damage to the normal health of the brain cells or in the permanent death of the cells. The neurons of the brain being the vital cell of the brain and nervous system, their being damaged interrupts the healthy interconnectedness of the brain and can lead to a number of disabilities and cognitive damage.
Diffuse Axonal Injury - Severe Brain Injuries
During a high velocity acceleration - deceleration event research has shown that the brain undergoes rotational movement that can cause massive neurological damage and loss of neuron function in areas of the brain not directly traumatized by impact with the skull. The key to understanding diffuse injuries is in the differing tissue densities of the grey matter of the cerebral hemisphere and the white matter of the brainstem and central brain structures. Essentially, the varying densities cause the areas of the brain to pick up speed and slow down at different velocities, causing a rotation of the various tissues in the brain to rotate and ultimately shearing of neuronal axons. In laymans terms, the axonal region of the neuron gets twisted by the trauma caused rotation. The severity of injury is a function of the degree of ratotation caused by the trauma, the violence of the occurence and the duration of the force that caused the injury.
The areas of the brain found to be especially susceptible to diffuse axonal injury include the brainstem, the corpus callosum (the cerebral hemispheres fubridge), and the temporal and frontal lobe white matter regions. These regions do not control basic life functioning operations and therefore those who suffer from DAI typically survive.
Diffuse axonal injuries typically occur in two phases, the primary injury and then a delayed phase. The initial injury phase involved the event that causes the axons within the brain to undergo the shear forces from the trauma. The delayed phase of diffuse injuries is recognized by the swelling of the damaged axons and ultimately their rupturing, which is experienced for up to several weeks after the initial trauma is experienced.
Symptoms of Diffuse Brain Injuries
Due to the incredible complexity of the neurological communication center in the brain typically affected by a traumatic brain injury or DAI, there exist a number of neurological effects to the sufferer of a shear injury. In severe damage cases, the sufferer can experience a loss of consciousness and remain in a vegetative state. Due to the regions of the brain most susceptible to shear damage, cardiac and respiratory brain functions typically remain unaffected.
For those that regain consciousness following a traumatic event, improvements in brain functioning can occur. Typically, after injury, the first 12 months are vital in regaining cognitive functionality. Symptoms of cognitive damage can consist of any number of neurological delibilitation. The injured party can suffer memory loss, loss of decisiveness, judgement impairment, speech problems, motor skill impairment, and other processing impairments.
Sufferers of traumatic brain injury commonly experience confusion, high levels of distraction and a loss of ability to concentrate. Problem solving, reasoning, organizational, and judgement deficiencies are also to be expected following a DAI or brain shear injury. In addition to cognitive and reasoning deficiencies, injured typically experience a variety of physical impairments, including a loss of hand eye coordination, loss of balance, and vision alterations and other changes in the perception of their senses.
Determining the Severity of DAI Injuries
Nearly everyone who experiences a traumatic acceleration-deceleration accident and loses consciousness will have suffered some degree of diffuse axonal shear injury. The severity of the axonal injury is determined by the degree of damage and the region area of the brain most directly impacted. A neurophysician should be consulted to determine the full extent of the neurological damage incurred in the injury. A medical professional will likely recommend a CT scan, or MRI performed post injury to check for hemorrhaging and identify the extent of the brain damage incurred. An MRI is the more sensitive imaging technique currently used to examine the brain tissue for damage.
Over 90% of people who suffer Diffuse Axonal Injury remain in vegetative state indefinitely. The injuries to the brain can have far reaching functional ramifications and only a lucky few will recover pre-injury neurological function. Improvements, if at all, following injury, should be expected in the 1 year period following the traumatic event, as improvement in DAI injury cases is not common.