Research Reports - A review of magnetic resonance imaging and diffusion tensor imaging findings in mild traumatic brain injury

Shenton ME, Hamoda HM, Schneiderman JS, Bouix S, Pasternak O, Rathi Y, Vu MA,
Purohit MP, Helmer K, Koerte I, Lin AP, Westin CF, Kikinis R, Kubicki M, Stern
RA, Zafonte R.

Mild traumatic brain injury (mTBI), also referred to as concussion, remains a
controversial diagnosis because the brain often appears quite normal on
conventional computed tomography (CT) and magnetic resonance imaging (MRI) scans.
Such conventional tools, however, do not adequately depict brain injury in mTBI
because they are not sensitive to detecting diffuse axonal injuries (DAI), also
described as traumatic axonal injuries (TAI), the major brain injuries in mTBI.
Furthermore, for the 15 to 30 % of those diagnosed with mTBI on the basis of
cognitive and clinical symptoms, i.e., the "miserable minority," the cognitive
and physical symptoms do not resolve following the first 3 months post-injury.
Instead, they persist, and in some cases lead to long-term disability. The
explanation given for these chronic symptoms, i.e., postconcussive syndrome,
particularly in cases where there is no discernible radiological evidence for
brain injury, has led some to posit a psychogenic origin. Such attributions are
made all the easier since both posttraumatic stress disorder (PTSD) and
depression are frequently co-morbid with mTBI. The challenge is thus to use
neuroimaging tools that are sensitive to DAI/TAI, such as diffusion tensor
imaging (DTI), in order to detect brain injuries in mTBI. Of note here, recent
advances in neuroimaging techniques, such as DTI, make it possible to
characterize better extant brain abnormalities in mTBI. These advances may lead
to the development of biomarkers of injury, as well as to staging of
reorganization and reversal of white matter changes following injury, and to the
ability to track and to characterize changes in brain injury over time. Such
tools will likely be used in future research to evaluate treatment efficacy,
given their enhanced sensitivity to alterations in the brain. In this article we
review the incidence of mTBI and the importance of characterizing this patient
population using objective radiological measures. Evidence is presented for
detecting brain abnormalities in mTBI based on studies that use advanced
neuroimaging techniques. Taken together, these findings suggest that more
sensitive neuroimaging tools improve the detection of brain abnormalities (i.e.,
diagnosis) in mTBI. These tools will likely also provide important information
relevant to outcome (prognosis), as well as play an important role in
longitudinal studies that are needed to understand the dynamic nature of brain
injury in mTBI. Additionally, summary tables of MRI and DTI findings are
included. We believe that the enhanced sensitivity of newer and more advanced neuroimaging techniques for identifying areas of brain damage in mTBI will be
important for documenting the biological basis of postconcussive symptoms, which
are likely associated with subtle brain alterations, alterations that have
heretofore gone undetected due to the lack of sensitivity of earlier neuroimaging
techniques. Nonetheless, it is noteworthy to point out that detecting brain
abnormalities in mTBI does not mean that other disorders of a more psychogenic
origin are not co-morbid with mTBI and equally important to treat. They arguably
are. The controversy of psychogenic versus physiogenic, however, is not
productive because the psychogenic view does not carefully consider the
limitations of conventional neuroimaging techniques in detecting subtle brain
injuries in mTBI, and the physiogenic view does not carefully consider the fact
that PTSD and depression, and other co-morbid conditions, may be present in those
suffering from mTBI. Finally, we end with a discussion of future directions in
research that will lead to the improved care of patients diagnosed with mTBI.

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