The basal turn of the cochlea.

The coils of the cochlea are now readily demonstrated by thin-section high-resolution computed tomography (CT) in the axial plane. This assessment has become important in severely deaf patients who are candidates for cochlear implant surgery. The commonest abnormality shown in these cases is post-meningitic or tympanogenic labyrinthitis ossificans, which can obstruct the passage of the electrode. Severe otosclerosis can cause a similar problem. Congenital deformities of the labyrinth are rarely suitable for implantation, but the procedure may be indicated for the true Mondini deformity. Implantation is contraindicated for severe dysplasia of the cochlea and for the recently described variety of x-linked deafness with deficient bone at the fundus of the internal auditory meatus.