Pathologic features of the cochlear nerve in profound deafness.

Cochlear nerves transected in the internal meatus were studied in six totally deaf ears and in one ear with profound deafness. In five ears deafness had followed surgical procedures in the oval window, in one it was the result of a mumps infection, and one was probably due to a virus infection or a vascular lesion. In four cases there was no great reduction in the nerve fiber population and the ultrastructure appeared normal. In three nerves there was a reduction in the number of nerve fibers, interfibrillar fibrosis, and disorganized material or extensive degenerative changes in the myelin sheaths. In all specimens artificial myelin changes were seen that apparently resulted from manipulation of the specimens at removal. Analysis of these cochlear nerves suggests that retrograde degeneration after severe cochlear insults may not be as frequent as has been thought on the basis of animal studies.