Etiology of hearing loss and cochlear computed tomography: findings in preimplant assessment

Patients being considered for cochlear implantation undergo, of necessity, a wide-ranging selection process, of which imaging of the temporal bone to assess cochlear patency is an important part. We have studied the correlation between the results of computed tomography (CT) imaging of the cochlea and the cause of hearing loss in this group of patients. The CT scans of 105 patients were reviewed. Of these, 74 (70%) were normal, with the commonest abnormalities being labyrinthitis ossificans in 14 (13.3%) cases and capsular rarefaction in 10 (9.5%) cases. A congenital abnormality was seen in 4 (3.8%) cases and temporal bone fractures in 2 (1.9%) cases; 1 patient had previously undergone a labyrinthectomy. In 25 patients the cause of the hearing loss was known to be meningitis. Of these patients, 15 had normal scans and 10 showed labyrinthitis ossificans. Of note is that none of the 6 patients with tuberculous meningitis had abnormal scans. There was a high correlation between a rarefied capsule on CT imaging and a diagnosis of otosclerosis, with 6 out of 7 otosclerosis patients demonstrating this abnormality. Evidence of a previous temporal bone fracture was seen on the scans of only 2 out of 6 patients in whom the cause of deafness was thought to be severe head injury.