Human vestibular nerve morphology and labyrinthectomy.

Surgical labyrinthectomy leads to extensive and degenerative changes in the membranous labyrinth and is often followed by fibrosis and ossification of the vestibule and neuroma formation. After labyrinthectomy the distal processes of the vestibular nerve degenerate, but the nerve trunk within the internal auditory canal, including Scarpa's ganglion, does not show an obvious loss of neurons. Electron microscopic examination of the cells of Scarpa's ganglion revealed many changes similar to those of chromatolysis, indicating increased cell metabolism and probable regenerative changes. Many nerve fibers appeared to be in the process of regeneration. Some ganglion cells were fibrotic and showed ultrastructural features similar to those of cells that had undergone atrophy but survived in a sublethal state.