Densitometry of the cochlear capsule and correlation between bone density loss and bone conduction hearing loss in otosclerosis.

Radiodensity of the bony cochlear capsule was investigated by CT-scanning in 134 ears with otosclerosis and 35 normal control ears. A technique of densitometry of the cochlea was developed comprising the measurement of maximum and minimum density together with mapping of the cochlea and measurement of the density at six predefined points in the cochlear capsule. Bone density in the normal cochlea showed very little interindividual variation. In the otosclerosis patients, minimum density was decreased in 58% of the ears, indicating the presence of a focus. At visual examination, foci were only detectable when density loss exceeded 200 Hounsfield. A positive correlation was found between bone density loss and bone conduction hearing loss with a maximum at 2,000 Hz and the medioventral point of the cochlear wall. The method appears to be useful for the follow-up during fluoride treatment, as is demonstrated by a case report.