Predicting the outcome of cochlear implantation in adults with postlingual deafness via tractography of auditory and language pathway

In recent years, cochlear implantation has revolutionized post-lingual deafness treatment, but predicting their outcomes still remains challenging. While many studies have focused on prelingual deaf children, this study aims to provide new perspectives in the field of cochlear implantation in postlingual deaf adults by correlating multiple diffusion measurements with different objective auditory tests, such as AWRS and DEWA. This study involves a cohort of 53 adult patients with postlingual deafness who underwent preoperative diffusion MRI scans. The DTI metrics of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and streamline count of eight brains areas related to audition and language - the left arcuate fasciculus, the genu, body, and splenium of the corpus callosum, the right and left uncinate fasciculus, and the right and left inferior fronto-occipital fasciculus - were measured. The goal of this thesis was to use tractography to investigate white matter pathways related to audition and language in order to identify pre-operative DTI metrics that would influence post-cochlear implant outcomes. Two strategies were used to achieve it. For the first one, patients with an average postoperative word recognition score (AWRS) of 0.5 or more were classified in the "good outcome" group and those with a score of 0 in the "bad outcome" group. A two-sample t-test evaluation was performed to determine the significant variables between these two groups. The second consisted of a correlation analysis between post-cochlear implantation audiometric test results and pre-operative DTI measurements. The post-operative audiometric tests performed were the AWRS, the DEWA - an audio-visual integration test - and the categories of auditory performance (CAP). Results from the two strategies performed show a significantly better recovery audition (better AWRS and DEWA results) in patients with a better conservation of white matter integrity (lower MD and RD values, as well as higher FA values and streamline count) in the brain areas related to audition and language (left arcuate and uncinate fasciculus, corpus callosum, and left and right IFOF) before the cochlear implantation. Maintaining the microstructural integrity of these specific brain areas would therefore play a crucial role in the success of cochlear implantation in adults with postlingual deafness, offering new prospects for improving personalized hearing care.