Poster D46, Friday, August 17, 4:45 – 6:30 pm, Room 2000AB

Anatomical connectivity and conversational impairments in patients who suffered from a moderate to severe traumatic brain injury

Karine Marcotte1,2, Simona Maria Brambati2,3, Erlan Sanchez-Gonzalez1,2, Caroline Arbour1,2, Christophe Bedetti3, Nadia Gosselin1,3;1Centre de recherche du CIUSSS du Nord-de-l'île-de-Montréal (Hôpital du Sacré-Cœur de Montréal) Montréal, Quebec, Canada., 2Université de Montréal, 3Centre de recherche de l’Institut Universitaire de Gériatrie de Montréal, Montréal, Québec, Canada.

Background Patients who suffered from a moderate to severe traumatic brain injury (TBI) often present significant long-term cognitive impairments in multiple domains including communication skills. Given the diffuse nature of the pathology, attributing communication deficits to a specific area in the brain can be difficult. Initial structural imaging is considered a good clinical tool for detecting focal lesions, that are mostly localized in the ventral and polar frontal regions and in the anterior temporal lobes. However, diffuse axonal injury may not be apparent on conventional imaging techniques and thereby, may limit its prognostic value. Despite the functional significance of the communication impairments following traumatic brain injury (TBI), language related fiber bundles have not been investigated with regards to communication skills. The aim of this study was to determine the role of the major white matter fiber bundles reconstructed using anatomically-constrained probabilistic high angular resolution diffusion imaging (HARDI)-based tractography in patients presenting chronic communication impairments following TBI. Methods In the present study, 15 moderate to severe TBI patients were compared to 15 healthy controls. Diffusion magnetic resonance imaging (dMRI) was conducted on a 3T Siemens Trio scanner using the following parameters: eight-channel coil, 65 noncollinear directions with a b=1000 and one unweighted image (TR=9500 ms, TE=93 ms, 120 X 120 matrix, 240 mm FOV, 2 mm slice thickness). Diffusion tensor estimation and corresponding fractional anisotropy (FA) map generation were done using MRtrix3. Fiber orientation distribution function was computed using the spherical deconvolution of the single fiber response. Then, we used a whole brain tractography algorithm that was randomly seeded in a FA mask. Based on the FreeSurfer parcellation, the Tract-Querier, a novel open-source tool, was used to extract fiber bundles known for their role in language (left arcuate fasciculus, inferior longitudinal fasciculus, uncinate fasciculus) as well as the genu and splenium of the corpus callosum, known to be particularly vulnerable to TBI. Fractional anisotropy (FA), radial diffusivity (RD), number of fiber orientation (NuFO) and volume were extracted from each tract. Conversational skills were evaluated using the Protocole Montreal Evaluation de la Communication. Results Chronic TBI patients present with persistent conversational impairments. TBI patients showed lower FA and NuFO than the control group in the language-related fiber bundles and both subparts of the corpus callosum as well as higher RD in the language-related bundles. Most importantly we found a negative correlations between conversational scores and RD in the left arcuate fasciculus whereas significant correlations were found between the Glascow score in the emergency room and FA in the left inferior longitudinal fasciculus. Conclusion These results provide evidence that conversational impairments in TBI patients are associated with structural lesions to the left arcuate fasciculus, which suggest that the measures extracted from this bundle could predict long-term conversational outcome in TBI patients. Further research regarding the longitudinal evolution between acute, subacute and chronic changes in white matter structural changes and recovery of communication skills could help defining a more specific prognostic of communication impairments for moderate to severe TBI patients.

Topic Area: Meaning: Discourse and Pragmatics