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Diffusion Tensor Imaging Detects White Matter Abnormalities and Associated Cognitive Deficits in Chronic Adolescent TBI

Researchers in Australia and Cincinnati utilized diffusion tensor imaging (DTI) to examine the long‑term alterations in white matter microstructure following traumatic brain injury in adolescents.  The researchers utilized DTI in this study, noting that rotational and shearing forces associated with traumatic brain injury often result in multi‑focal and diffuse axonal injuries which are not evident on CT scans or conventional T1 or T2 weighted MRI. 

The researchers used adolescents between the ages of 12‑17 who had been hospitalized overnight with confirmed TBI.  The injury classifications were defined by values of the Glasgow Coma Scale.  All participants were at least twelve months post‑injury to ensure that acute recovery was complete.  A comparison group of typically‑developing adolescents with no history of TBI or other neurological insults were recruited from the community.  Groups were matched by age, gender, and maternal education.  Subjects with significant development delay, significant psychiatric or behavioral disturbance prior to injury and extreme vision or hearing impairments were excluded.  Study neuropsychological data and MR imaging were acquired in the chronic phase. 

Seventeen adolescents with traumatic brain injury and thirteen controls consented and produced usable imaging data.  The TBI control group did not differ on measures of general intellectual ability, although there was a trend for poor performance for word reading (Wrat‑4) in the TBI group.  Adolescents with TBI had significantly higher behavioral ratings of executive dysfunction. 

There were also group differences in DTI variables.  Group comparison of the DTI variables identified several regions of elevated axial diffusivity (AD) in the TBI group across white matter.  All clusters were lateralized to the right hemisphere.  To “more fully understand the genesis of the right lateralized findings, the study examined the pattern of white and gray matter injuries found in the imaging review.  Of the eight participants that had identifiable parenchymal damage, each had at least one site of damage in the right hemisphere at either the sub‑acute or late state of TBI. 

The researchers also investigated the association between white matter microstructure and neuropsychological performance. 

The researchers found that consistent with their hypothesis, regions of elevated white matter diffusivity were found in adolescents with TBI more than twelve months after the initial injury.  The finding of increased pain diffusivity in the TBI group was suggestive of demyelination and axonal death that occurs with traumatic brain injury.  The increase of axonal diffusivity for adolescents with chronic TBI agrees with cross‑sectional studies of chronic injury that reported increased axial diffusivity in patients compared to controls. 

The researchers concluded “this study augments the existing literature of DTI study of TBI by reporting abnormal white matter microstructure determined by DTI matrices as well as their association with cognitive functioning in a cohort of adolescents who sustained mostly complicated mild or minor TBI...  This study also presented evidence for the association between the elevated axial diffusivity, and the processing speed and executive function in the TBI group providing a snapshot of white matter track recovery and its relationship with neuropsychological variables in chronic TBI.”  Brain Injury, April 2013; 27(4):454-463.

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