Pattern of Thalamic Connectivity Loss Following Moderate-Severe Traumatic Brain Injury

283 

Abstract Submission 

Daniel Brennan¹, Catherine Lyons², Junghoon Kim¹

¹The City University of New York, New York, NY, ²The Graduate Center, City University of New York, New York, NY

Daniel Brennan  
The City University of New York
New York, NY

Catherine Lyons  
The Graduate Center, City University of New York
New York, NY

Junghoon Kim  
The City University of New York
New York, NY

Regional cortical and subcortical atrophy have been identified in the months-to-years following moderate-severe traumatic brain injury (msTBI).1,2 Recently, we identified a pattern of cortical atrophy prior to 3 months in frontal and temporal cortices, while atrophy between 3-12 months was observed in the posterior cortical regions of the parietal and occipital lobes.3 In this cohort, atrophy of the bilateral thalamus was observed within both of these time windows; this unique temporal pattern and the interconnected nature of the thalamus prompted us to hypothesize that thalamic white matter may show a similar spatial distribution of damage.

Thirty-nine (39) msTBI patients were evaluated at 3, 6 and 12 months post injury. Thirty-five (35) age-matched controls were evaluated once. The diffusion data were reconstructed in the MNI space using q-space diffeomorphic reconstruction4 available in DSI studio. Voxel-wise quantitative anisotropy (QA) was extracted as the local connectome fingerprint.5 To estimate white-matter changes in patients present at 3 months post injury, a cross-sectional connectomic analysis6 between patients' 3-month diffusion data (N=38) and controls (N=34) was performed. A nonparametric Spearman partial correlation was used to derive the effect of group identity, and the effect of age was removed using a multiple regression model. A T-score threshold of 2.5 was assigned and tracked using a deterministic fiber tracking algorithm7 to obtain correlational tractography. To estimate longitudinal changes, diffusion data from patients' 3-month and follow-up scan (6 or 12 months post injury; N=34) were compared using the same procedure. An FDR threshold of 0.05 was used to select tracks. To estimate the false discovery rate, a total of 4000 randomized permutations were applied to the independent variable in each analysis to obtain the null distribution of the track length.

Divergent tract profiles originating from the thalamus were observed between 3 months and 3-12 months post injury. In TBI patients at 3 months post-injury, thalamic tracts with decreased QA relative to uninjured controls were identified in frontal and temporal cortices. Mean QA of these tracts was correlated with thalamic volume at 3 months within the patient group (t=3.247, p=0.00273). In contract, significant decreases in QA were observed between 3 months post injury and follow-up timepoints in tracts projecting to the temporal cortex in addition to tracts projecting dorsally to occipital, superior parietal and superior frontal cortices. Mean QA of these tracts were also significantly correlated with thalamic volume at 3 months post injury (t=2.117, p=0.0424), and approached significance at follow-up (t=1.900, p=0.0668).

White-matter microstructural integrity in thalamic fibers shows a regionally selective distribution of damage following msTBI. Qualitatively, this pattern reflects the overall spatiotemporal distribution of cortical atrophy previously observed within this cohort. The degree of microstructural integrity, measured by mean QA across all identified fibers, generally correlated with thalamic volume. These results suggest a unique spatiotemporal distribution of concomitant damage between the cortex, thalamocortical fibers, and the thalamus itself during the first year following msTBI. Future work is necessary to clarify the relationship of cortical, thalamic, or thalamocortical damage in this identified profile and the clinical implications of damage to these tracts.

Neurodegenerative/ Late Life (eg. Parkinson’s, Alzheimer’s) ¹

White Matter Anatomy, Fiber Pathways and Connectivity ²

Trauma

WHITE MATTER IMAGING - DTI, HARDI, DSI, ETC

Other - Traumatic Brain Injury