The Connectomics Study Of Unilateral Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSNHL) is a frequently seen disease which is defined as a sensorineural hypoacusis of at least 30 dB within 72 hours and considered to be an otologic emergency. Population studies of SSHNL showed that the hearing loss is typically unilateral and can be associated with tinnitus and vertigo. The precise cause of SSNHL is still agnogenic in most cases, and no apparent significant pathological changes were detected by any routine clinical examination. The aim of this dissertation was systemic investigated the structural and functional brain alterations of the unilateral SSNHL patients from local to connectome level within the acute period by multimodal MRI data. The main results of this dissertation were as followings.The local level parameters of the brain properties based on the multimodal MRI data found that the structural (included gray and white matter) and functional brain alterations were already existed in unilateral SSNHL patients within the acute period. Compared with healthy control groups, the unilateral SSNHL patients showed significant decreased gray matter volume on the contralateral auditory cortex, and the gray matter volume of these areas significant negative correlation with the duration of the hearing loss which indicate a cumulative effect after the progress of the disease in unilateral SSNHL patients. Tract-based spatial statistics of the DTI images showed altered microstructural integrities of brain regions in a widely range of brain regions. The unilateral SSNHL patients showed a significant lower fractional anisotropy and a significant higher mean diffusivity, axial difrusivity and radial diffusivity compared with healthy control groups. A significant negative was also found between fractional anisotropy and PTA or THI in a range of brain areas in the right side unilateral SSNHL patients, suggesting potential imaging biomarkers the fractional anisotropy could serve as for SSNHL. Resting-state fMRI data analysise found that the SSNHL patients showed a significant increase of amplitude of low-frequency fluctuation, regional homogeneity, functional connectivity strength and homotopic functional connectivity compared with healthy controls, which indicated a brain ’hyperactivation’during resting state in SSNHL patients. The effect brain structures is beyond areas directly associated with auditory processing and perception, but also some brain areas involved several specific functional networks, such as the default mode networks, executive control networks, limbic and paralimbic networks.The connectome level topological properties study by graph theoretical analysis found that both the SSNHL and the healthy control group showed salient small-world property characteristic no matter gray matter volume structural covariance network, white matter structural network and functional connectivity network. Detectable alterations of network organization have already occurred in unilateral SSNHL patients at the global and regional level of each connectome networks within the acute period. Compared with healthy control group, the gray matter volume structural covariance network and white matter structural network showed a disrupted topologic organization and shift toward randomization while the functional connectome is characterized by a shift toward small-worldization, which may indicate a plastic reorganization procedure of the brain to compensate for the loss hearing in unilateral SSNHL within the acute period. Besides, the coupling strength of structural-functional connectome was decreased in SSNHL patients, which might reflect the different stress-response mechanism between the structural and functional brain connectome.It is hoped that this systemic investigated of the structural and functional brain alterations from local to connectome level could help to characterize unilateral SSNHL better through a new research perspective and provide insights for the potential pathophysiology of unilateral SSNHL. Furthermore, it is hoped that these results will alert audiologists to not only focus on the abnormal in the peripheral auditory system but also be aware of the alteration in the cerebral cortex that the unilateral SSNHL patients might have, which might ultimately assist in providing a better diagnosis and a more accurate and effective treatment for unilateral SSNHL.