Why do vestibular destructive procedures sometimes fail?

Vestibular nerve specimens and one temporal bone, from patients with vestibular symptoms after destructive surgery on the vestibular system, were studied by light microscopy. Surviving nerve axons in three specimens that followed retrolabyrinthine vestibular nerve section (RLVNS) were counted and compared to normative data. Results are consistent with persistence of the central processes of primary vestibular neurons in three specimens from patients who had persistent symptoms and ice-water caloric responses after RLVNS. Incomplete neurectomy probably results from anatomic variations in the plane of separation of the vestibular and cochlear portions of the eighth nerve in the posterior fossa. Regeneration neuromas were found in the vestibule after a complete transmastoid labyrinthectomy and a Fick sacculotomy; this indicates that wide degrees of injury to the labyrinth may provoke this response. Disabling unsteadiness after labyrinthectomy may or may not respond to revision surgery (translabyrinthine vestibular nerve section). The indications for revision surgery are discussed. The excision of Scarpa's ganglion by the translabyrinthine route offers the best chance to ensure complete removal of peripheral vestibular tissue, minimize postoperative unsteadiness, and prevent neuroma formation.