NEJM: MRI differentiates between blast-related and civilian brain injuries
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| Brain Regions of Interest for Diffusion Tensor Imaging Image source: N Engl J Med 2011;364:2091-2100 |
The number of blast-related TBIs among Iraq and Afghanistan military personnel has reached 320,000, yet little is known about the nature of “mild” TBI, according to senior author David L. Brody, MD, PhD, assistant professor of neurology at Washington University School of Medicine in St. Louis.
The researchers examined the hypothesis that traumatic axonal injury is a primary feature of blast-related TBI by employing diffusion tensor imaging (DTI). They enrolled 63 subjects with mild TBI and 21 controls over five non-consecutive months between November 2008 and October 2009. In many cases, clinical histories were unavailable, but those that were indicated a change in the level of consciousness for a few minutes and post-traumatic amnesia for less than 24 hours.
Subjects were initially scanned at Landstuhl Regional Medical Center in Germany and re-scanned at Washington University six to 12 months later.
The initial scans of TBI patients indicated abnormalities consistent with traumatic axonal injury, reported Brody and colleagues, with scans showing reductions in relative anisotropy in several brain regions. Furthermore, quantitative analysis showed significant reductions in relative anisotropy in the TBI cohort compared with the control group. The authors also noted that abnormalities were detected more often in regions predicted to be most vulnerable to primary blast injury: the middle cerebellar peduncles and orbitofrontal white matter.
However, at the individual level, 18 of the 63 scans of individuals diagnosed with TBI revealed abnormalities consistent with multifocal traumatic axonal injury, indicating that diffusion tensor imaging cannot be employed as a diagnostic measure.
The study indicated changes over time in TBI subjects, with this cohort presenting with higher mean diffusivity and radial diffusivity on initial scans. The differences normalized on follow-up scans. Meanwhile, axial diffusivity, comparable on initial scans, was lower in the TBI patients on the follow-up scans.
“Substantial numbers of abnormalities were found in regions of the brain not known to be commonly injured in civilian cases of mild TBI but predicted to be vulnerable to blast on the basis of computational simulations,” wrote Brody et al. The scans also showed abnormalities in areas of the brain impacted in civilian TBI. The researchers suggested that the abnormalities might be explained by a combination of traumatic axonal injuries in regions vulnerable to blast and in regions vulnerable to other mechanisms of injury.
The authors acknowledged that the exact contributions of primary blast exposure and other types of injury could not be determined with certainty. The findings, continued Brody et al, are limited by several factors, including the lack of direct comparison with subjects with non-blast-related TBI.
“DTI-based assessments may be useful in the diagnosis, triage and treatment planning in clinical practice,” wrote the authors, who emphasized that only 29 percent of TBI subjects had definitively abnormal scans, which means that a normal diffusion tensor imaging result does not rule out TBI nor do diffusion tensor imaging findings suffice for a certain diagnosis. Mild TBI remains a clinical diagnosis.
“Our hope is that these advanced MR-based methods will one day help make more accurate diagnoses, assist with triage and allow treatment interventions to start early for people with TBIs,” offered Brody.