Background: DFNA9 is a form of autosomal progressive sensorineural hearing loss, caused by more than 30 variants in the COCH gene. p.Pro51Ser (p.P51S) variant is characterized by late-onset functional deterioration toward bilateral severe hearing loss and vestibulopathy. Focal sclerosis on computed tomography (CT) and T2-weighted magnetic resonance imaging (MRI) signal loss of semicircular canals are presumably radiologic biomarkers of advanced otovestibular deterioration. Objectives: The aim of this study was to investigate whether these biomarkers are more frequent in cochlear implant candidates carrying the p.P51S mutation versus noncarriers. Second, the correlation between the hearing and vestibular function and carrier status was studied. Finally, the relationship between the presence of these radiologic features and the degree of hearing and vestibular deterioration was investigated. Methods: A prospective cohort study was performed on 38 candidates for cochlear implantation in a tertiary referral center. Patients underwent pure tone audiometry, videonystagmography, video head impulse tests and vestibular-evoked myogenic potentials. In addition, three dizziness questionnaires were used. All subjects were administered CT, MRI, and molecular genetic analysis. Results: Sixteen of 38 patients were carriers of the p.P51S COCH mutation. Radiologic lesions were almost exclusively observed in carriers. MRI was more sensitive in showing lesions than CT. Furthermore, p.P51S carriers showed significantly lower function on most vestibular tests, including questionnaires, than noncarriers. Patients with imaging abnormalities showed more pronounced vestibulopathy. Conclusion:The present study supplements previous data that endorse the hypothesis that focal sclerosis of semicircular canals are biomarkers of advanced vestibular deterioration, especially in DFNA9.