Changes in brain morphology over the first year in adult mixed-mechanism mild traumatic brain injury: the role of injury severity factors.

OBJECTIVE

Assess changes in brain morphology after mild traumatic brain injury (mTBI).

METHODS

In the community-based Trondheim mTBI study, 194 patients with mixed-mechanism mTBI (age 32.5y, 63.4% men) were scanned with 3T brain MRI within 72 h, at 3- and 12 months post-injury. Eighty-three age-, sex-, and education-matched community controls were scanned at the same intervals. MRIs were analyzed using the longitudinal FreeSurfer-pipeline. Linear mixed models were conducted to assess changes in cortical thickness and area and subcortical volumes over time, with gray matter/white matter (GM/WM) intensity ratio - reflecting changes in underlaying tissue contrast - as a covariate. Sub-group analyses were performed in patients with: complicated mTBI (intracranial traumatic lesions on MRI) vs. uncomplicated mTBI; loss of consciousness (LOC) vs. no LOC; Glasgow Coma Scale score 13-14 vs 15; post-traumatic amnesia duration 1-24 h vs < 1 h.

RESULTS

Patients with mTBI had larger ventricular volumes compared to controls at all timepoints and significant ventricular dilation over 12 months. The ventricular dilation was most pronounced in complicated mTBI. Additionally, patients with complicated mTBI showed a decrease in cortical area, cerebral white matter, thalamic and hippocampal volumes over time. Cortical thickness remained stable over the 12 months when GM/WM intensity ratio was adjusted for.

CONCLUSION

Increased ventricular volume during the first year following the injury characterized mTBI. Greater ventricular dilation and decreases in cortical area and subcortical volumes were present in complicated mTBI. Changes in GM/WM intensity ratio affected cortical measures and should, together with injury severity factors, be accounted for in future studies.