Evaluation of the relationship between otosclerotic focus and audiometry values detected in HİGH-resolution temporal bone computerized tomography in patients with otosclerosis

In this study, we aimed to evaluate the relationship between the parameters of the fenestral otosclerotic focus and audiometric data and types of hearing loss, to predict the course and severity of the disease in the clinical and preoperative stages, to better understand the etiopathogenesis of the disease and to assist the surgeon in the selection of patients to be operated. After obtaining local ethics committee approval, retrospective evaluation of high-resolution computed tomography (HRCT) scans of the temporal bone was performed on 188 patients (271 ears) diagnosed with otosclerosis clinically and radiologically between May 2014 and August 2022. 81 patients (113 ears) with conditions such as myringosclerosis, separation of the incudomalleolar joint, superior semicircular canal dehiscence, posterior semicircular canal dehiscence, history of previous surgery and cochlear implant, retrofenestral focus, chronic otitis media, cystic dilatation in the vestibular canal, and mastoiditis were excluded from the study. A total of 107 patients (158 ears) with audiograms taken within a maximum of 1.5 months before the HRCT examination were included in the study. No control group was available. The temporal bone HRCT scans of the patients in the study group were obtained using a 128-detector row multi-slice computed tomography (Ingenuity 128, Philips Healthcare, State, USA) and a 16-detector row multi-slice computed tomography (Brilliance 16, Philips Medical Systems, Best, The Netherlands). The images were evaluated by two radiologists with 18 years and 4.5 years of experience, using OsiriX software and Philips workstations. The boundaries of the otosclerotic focus were manually drawn on all discernible slices, and the volume was calculated using the OsiriX software. Additionally, the distance of the focus from the apical and middle turns of the cochlea and the length of contact with the vestibule were measured manually, and the vestibular contact area was calculated based on these measurements. Since the distance measurement of the focus from the basal turn could not be accurately and reliably obtained, the focus was examined for contact with the basal turn and categorized as present or absent. The odyometric air-bone gap values were calculated based on the evaluation of the audiograms of the patients included in the study group, considering the air and bone conduction thresholds. Patients were divided into two groups: conductıve hearing loss and mixed hearing loss according to these thresholds. Among the patients in the mixed hearing loss group, those with a mean bone conduction threshold of 20-30 decibels were classified as mild mixed hearing loss, while those with a threshold exceeding 30 decibels were classified as severe mixed hearing loss. There was no significant difference (p > 0.05) observed in terms of fenestral focus volume, distance of the focus from the middle and apical turns of the cochlea, axial and coronal contact length with the vestibule, and contact area between the groups of patients with conductive hearing loss and mixed hearing loss, as well as between the groups with mild and moderate-to-severe mixed hearing loss. There was no significant difference (p > 0.05) in fenestral focus volume, distance of the focus from the middle turn of the cochlea, axial and coronal contact length with the vestibule, and contact area between the age groups of 0-40 years and 41-80 years. However, the odyometric air-bone gap values in the 41-80 years age group were found to be higher than those in the 0-40 years age group (p < 0.05). Additionally, the distance of the otosclerotic focus from the apical turn of the cochlea was found to be lower in the 41-80 years age group compared to the 0-40 years age group (p < 0.05). The average fenestral focus volume, contact length with the vestibule, and contact area were found to be higher in patients with a focus in the round window and basal turn of the cochlea compared to those without a focus in these areas (p < 0.05). Additionally, the distances of the fenestral foci from the middle and apical turns of the cochlea were found to be lower in patients with a focus in the round window and basal turn compared to those without a focus in these areas (p < 0.05). In conclusion, our study did not find a significant and consistent relationship between the types and severity of hearing loss and the parameters associated with the focus. This suggests that the disease has a highly complex etiopathogenesis, and factors other than the parameters of the investigated focus, whose mechanism has not yet been fully elucidated, may play a role in the type and severity of hearing loss. Keywords: Otosclerosis, High-resolution temporal bone computed tomography, Conductive hearing loss, Mixed hearing loss