The Vestibular Response Following Unilateral Vestibular Neurectomy

Abstract

15 patients suffering from unilateral Menière's disease were investigated before and at regular intervals for 3 years following vestibular neurectomy. The spontaneous vestibular signs as well as the caloric response of both labyrinths were recorded by electronystagmography. The process of vestibular compensation occurring after the excision of Scarpa's ganglion presented with two phases: (1) An acute phase (lasting for 4 weeks after surgery), and (2) a chronic phase (lasting from the first postoperative month to the third postoperative year).

The acute phase of compensation was characterized by the rapid but incomplete regeneration of the resting activity of the homolateral vestibular nuclei and by a strong central inhibition of the contralateral vestibular nuclei. During the chronic phase of compensation the reduction of the central inhibition was accompanied by an increased activity (recruitment) of the homolateral vestibular nuclei during caloric stimulation. Because of the different postoperative behaviour of the vestibular system at rest (spontaneous vestibular signs) and during caloric stimulation, the compensatory process occurring following vestibular neurectomy has to be considered under a static and a dynamic aspect. Only the evolution in time of the dynamic compensation-and not that of the static compensation-was found to correlate with the subjective postoperative complaints of the patients. The dynamic aspect of the vestibular compensation may, therefore, be used to objectivate the imbalance experienced by the patient following vestibular neurectomy.