Vestibular findings in patients with schwannoma of the 8th cranial nerve: a survey of nine cases and review of the literature

Introduction: Some aspects of the natural history of vestibular schwannoma (VS) remain unsettled. A better understanding of the pathophysiology of the disease would improve its diagnostic workup and therapeutic management, as VS often requires surgery, which carries the risk of severe complications. This paper discusses the significance of ultrastructural findings in the vestibular organs removed during surgery. Material and methods: This study examined specimens from vestibular organs removed from patients who underwent VS resection through the translabyrinthine approach. The sample includes 9 patients, seven women and two men, with a mean age of 55 years (range 39–71 years). Results: The sensory epithelium showed a loss of stereocilia, numerous lipofuscin granules and vacuoles in the cytoplasm. The subepithelial myelinated nerve fibres showed signs of demyelination and sheath rearrangement. Some axons had markedly degenerative modifications, with neurofilament aggregation, more numerous mitochondria and vacuolization. As it lost its specialized structures, the epithelial covering of the semicircular canal walls progressively flattened out in the area farthest away from the sensorial area. Conclusions: There were no specific correlations between schwannoma size and instrumental or ultrastructural findings in the vestibular epithelium organs. The morphological features of the non-sensory epithelium suggest that the potassium circulation system is preserved in patients with VS even when they present prominent cochlear and/or vestibular symptoms. VS formation appears to be multifactorial; the vestibular nerve conduction block caused by tumour compression would not necessarily cause irreversible damage to the vestibular receptors at the outset.