Traumatically induced axonal injury: pathogenesis and pathobiological implications.

This work reviews the pathobiology of traumatically induced axonal injury. Drawing upon literature gleaned from the experimental and clinical setting, this review attempts to emphasize that, other than the most destructive insults, traumatic brain injury does not typically cause direct mechanical disruption of the axon. Rather, this review documents that with traumatic injury focal, subtle axonal change occurs, and that over time, such change leads to impaired axoplasmic transport, continued axonal swelling, and ultimate disconnection. The initial intra-axonal events that trigger the above described sequence of reactive axonal change are considered with focus on the possibility of either traumatically altered axolemmal permeability, direct cytoskeletal damage/perturbation, or more overt metabolic/functional disturbances. Not only does this review focus on the sequence of traumatically induced axonal change, but also, it considers its attendant consequences in terms of Wallerian degeneration and subsequent deafferentation. The concept that traumatically induced diffuse axonal injury leads to diffuse deafferentation is emphasized together with its pathobiological implications for morbidity and recovery. The potential for either adaptive or maladaptive neuroplasticity subsequent to such diffuse deafferentation is considered in the context of mild, moderate and severe traumatic brain injury.