Temporal bone imaging for cochlear implantation.

Computerized tomography (CT) imaging of the inner ear structures is helpful when evaluating a patient for cochlear implantation. The accuracy of CT scan imaging in determining the presence of cochlear ossification was assessed. A retrospective study of 104 implant patient charts, operative reports, and CT scans was performed. The CT scan was in agreement with the operative findings in 78% of patients included in the study. Twenty-two percent were found to have ossification at surgery which was not detected radiographically. One patient with extensive otospongiosis and an obstructed cochlea on CT scan had a patent cochlea demonstrated by magnetic resonance imaging (MRI) which was corroborated at surgery. In 32 children with postmeningitic hearing loss, the CT scan had only a 53% accuracy in assessing cochlear ossification. Since 69% of these patients were found to have some degree of cochlear ossification, otologists should expect to encounter some degree of bony obstruction within the basal turn of the cochlea even when the CT scan is normal. Nevertheless, cochlear implantation can successfully be performed in these cases.