Does otosclerosis affect the dimensions of the facial canal and cochlear aquaduct?

Purpose Our aim was to evaluate the relationship of the dimensions of the facial canal (FC) and cochlear aqueduct (CA) in otosclerosis (OS) with the type and severity of OS. Methods Two radiologists retrospectively evaluated temporal bone high-resolution computed tomography (HRCT) images obtained from 48 healthy individuals and 94 OS patients between January 2015 and July 2020. In the study group, the CA width, funnel base width, and funnel length, in addition to the FC transverse length, were measured in the axial plane. The CA length was measured in the coronal plane on HRCT images. The FC craniocaudal length was measured in the same plane as the fissula ante fenestram (FAF) in coronal reformatted HRCT images. Grading of OS was based on otosclerotic plaque density and new bone formation extending toward the tympanic cavity at the FAF level. Results In the OS patients, the CA width and FC craniocaudal and FC transverse diameters were significantly decreased on both sides compared to those in the control group (p < 0.001). In fenestral OS, the FC craniocaudal and transverse widths on both sides were statistically significantly lower than the FC widths in the control group (p < 0.0001). A statistically negative correlation was found in the FC craniocaudal (r = - 0.831/- 0.818) and transverse (r = - 0.742/- 0.750) measurements on both sides in accordance with an increase in the otosclerotic plaque density (p < 0.0001). Conclusion The presence of narrowing in the FC and CA adjacent to the FAF supports the role of autoimmunity theory in the etiology of OS.