Morphology of Human cochlear nerve after labyrinthectomy.

Five temporal bones and three surgical cochlear nerve specimens from patients who previously underwent labyrinthectomy were studied by light and electron microscopy. All cochleas had nearly total loss of sensory cells, extensive or total loss of both cochlear nerve fibers in the osseous spiral lamina, and spiral ganglion cells. In spite of this severe distal degeneration of the cochlear nerve, it processes within the internal auditory canal appeared normal in four of the five temporal bones, and the majority of the myelinated nerve fibers had survived in all three surgical specimens. Most of the central processes of the primary neurons of the cochlear nerve appear to have resisted retrograde degeneration when it was induced by a lesion primarily causing degeneration of the organ of Corti. This peculiar situation of a few nerve cell bodies and disproportionately large numbers of central axons is discussed.