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White Matter Asymmetry: A Reflection of Pathology in Traumatic Brain Injury
Andrei A Vakhtin1,2, Yu Zhang1, Max Wintermark1,3
1War Related Illness and Injury Study Center, System of Care, Veterans Affairs Palo Alto, Palo Alto, California.
Abstract:
Comparisons of white matter (WM) fractional anisotropy (FA) values between mild traumatic brain injury (mTBI) patients and controls have revealed inconsistencies in the directions of the resulting FA changes. To address these discrepancies, we examined hemispheric FA symmetry levels across WM tracts in 150 mTBI patients relative to 96 military controls. Automated fiber quantification was used to extract 18 WM tracts with 100 FA values, which were used to compute correlation strengths between the nine bilateral tract pairs. The Fisher z-transformed Pearson's r values were entered into an analysis of covariance examining the effects of group (mTBI and controls) and age on symmetry levels within each tract pair. The mTBI group displayed lower symmetry levels in the corticospinal tract and the inferior longitudinal fasciculus. Interactions between age and group were detected in the inferior fronto-occipital (IFOF), uncinate (UF), and superior longitudinal fasciculi (SLF). A similar pattern emerged in the IFOF and the UF, revealing age-related symmetry decreases in the mTBI patients despite stable levels of symmetry across ages in controls. In contrast, although the control group's symmetry levels actually increased with age in the SLF, no age-related symmetry changes were detected across the mTBI participants. Here, we proposed WM symmetry measures as a potential means of circumventing directional inconsistencies of trauma-related FA changes, as well as capturing more within-tract and within-subject variances of diffusion tensor imaging (DTI) metrics. Further, we demonstrated the method's utility in detecting mTBI-specific effects and their associated interactions with age.
Insights
Mild traumatic brain injury (mTBI) alters white matter (WM) symmetry, particularly in specific tracts. This study introduces WM symmetry as a novel metric to better detect mTBI effects and age interactions.
Area of Science:
- Neuroimaging
- Traumatic Brain Injury Research
- White Matter Integrity
Background:
- Inconsistent findings in white matter (WM) fractional anisotropy (FA) changes in mild traumatic brain injury (mTBI) patients.
- Need for novel metrics to capture mTBI-related white matter alterations.
- Previous studies often focus on absolute FA values, overlooking symmetry.
Purpose of the Study:
- To investigate hemispheric white matter (WM) fractional anisotropy (FA) symmetry in mild traumatic brain injury (mTBI) patients compared to controls.
- To explore the utility of WM symmetry measures in detecting mTBI-specific effects and age-related interactions.
- To address discrepancies in previous FA change findings by examining symmetry.
Main Methods:
- Utilized automated fiber quantification to extract 18 white matter (WM) tracts from 150 mTBI patients and 96 military controls.
- Computed correlation strengths (Fisher z-transformed Pearson's r) between nine bilateral tract pairs to assess hemispheric FA symmetry.
- Employed analysis of covariance to examine the effects of group (mTBI vs. controls) and age on WM symmetry levels.
Main Results:
- Mild traumatic brain injury (mTBI) patients exhibited significantly lower white matter (WM) symmetry in the corticospinal tract and inferior longitudinal fasciculus.
- Detected significant interactions between age and group in the inferior fronto-occipital (IFOF), uncinate (UF), and superior longitudinal fasciculi (SLF).
- Observed age-related decreases in WM symmetry in mTBI patients for IFOF and UF, contrasting with stable symmetry in controls and age-related increases in SLF for controls.
Conclusions:
- White matter (WM) symmetry measures offer a promising approach to overcome directional inconsistencies in fractional anisotropy (FA) changes post-mild traumatic brain injury (mTBI).
- WM symmetry analysis effectively captures within-tract and within-subject variances, enhancing the detection of mTBI-specific effects.
- The findings highlight the utility of WM symmetry in revealing complex interactions between mTBI, age, and white matter integrity.
