Evaluating the integrity of white matter after traumatic brain injury and the utility of diffusion tensor imaging

Pathophysiological processes after traumatic brain injury (TBI) are multifaceted and complex. Their ultimate fate, however, converges into one common consequence, i.e. more preferential damage to the white rather than to the gray matter. The injured or dysfunctional white matter tracts lead to diverse clinical abnormalities such as disordered consciousness, cognitive deficits, oculomotor abnormalities, and postural imbalance. The bedside examination and instrumental assessment provide, however, partly objective evidence for the injury because they require the patient’s cooperation. Therefore, there is a need for an objective and highly sensitive brain imaging technique that can evaluate the presence and extent of damage to the whole brain white matter. Diffusion tensor imaging (DTI) has been widely used in the study of patients with TBIs in that it can assess brain white matter integrity as a whole. Group-comparison DTI studies in patients with moderate-to-severe TBI show clear differences; however, studies in patients with mild TBI or blast-induced TBI show somewhat inconsistent results. Overall, DTI has contributed significantly to understanding the pathophysiology of TBI, but still has considerable limitations for clinical diagnostic purposes in patients with TBI, especially those with milder injuries.