A longitudinal study of diffusion tensor imaging after severe traumatic brain injury

Introduction: Diffusion Tensor Imaging (DTI) is able to detect damage of subcortical tract systems by measuring changes in fractional anisotropy (FA). Previous studies indicate that the extent of early diffuse axonal injury (DAI) correlates with the severity of the functional neurological deficits following traumatic brain injury. The present study investigates the FA change over time in patients with severe traumatic brain injury and the correlation with outcome using voxel and ROI-based approaches.

Patients and Method: Ten patients (2 females, 8 males) with severe traumatic brain injury were examined longitudinally using conventional MRI and DTI (Philips Gyroscan 1.5 Tesla) while they were hospitalised in the Neurological Early Rehabilitation department of Kliniken Schmieder. The first examination (E1) was 52 (±18) days, the second examination (E2) 108 (±24) days after trauma. The functional deficits of the patients were assessed by evaluating the Coma Remission Scale, Early Rehabilitation Barthel Index, Functional Independence Measure and Glasgow Outcome Score. Nine age and sex-matched subjects served as a control group. Regions of interest (ROI) were defined in the centrum semiovale (CS), corpus callosum (CC) and brain stem. The SPM5 software (FIL, University College of London) was used for the voxelwise statistical analysis.

Results: In the voxel-based analysis, patients showed significantly reduced FA values in the pyramidal tract, in the crus posterior of the cerebrum and in the splenium of the CC when compared to the control group. No change in voxel-based FA values was found between E1 and E2. In the ROI-based analysis, the FA decreased in the genu and splenium of the corpus callosum of the patients between E1 and E2. The whole white matter FA was significantly lower in patients at both examinations compared to control subjects. There was no significant correlation of clinical parameters with changes in FA values in the current analysis.

Conclusion: In line with previous studies, patients after severe traumatic brain injury showed axonal damage especially in the peduncle of the cerebrum, pyramidal tract and the corpus callosum. In the ROI-based analysis, fractional anisotropy values decreased in the corpus callosum between two and approximately four months after the trauma despite functional improvement in most patients. Studies with longer follow-up are needed to resolve the question if axonal damage can recover over time.