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Axon Morphology Changes in Peripheral Cochlear Nerve Axons Due to Vestibular Schwannoma

(2017) Eggink, M.C.

Sporadic vestibular schwannoma (VS) are the most common tumor within the cerebellopontine angle (CPA). VS patients present with sensorineural hearing loss in 95% of the cases, however the exact mechanism behind this is unknown. The theory of mechanical compression of the cochleovestibular nerve within the internal auditory canal (IAC) cannot fully account for this hearing loss. A recent theory postulates the secretion of molecules and extracellular vesicles by the tumor, shown to decrease the amount of spiral ganglion cell-bodies (SGCs) and hair cells in the cochlea. The morphology and therefore possible effect of these secretions on the peripheral nerve fibers in the osseous spiral lamina (OSL) has yet to be examined. A better understanding of the underlying pathology could lead to new therapies and treatment strategies for patients with VS. For this study, histopathologic slides from the human temporal bone archive of the Massachusetts Eye and Ear Infirmary (MEEI) were analyzed to quantify the density of the fibers in the OSL of 7 patients with sporadic and untreated VS, and 1 control. The density was found to be significantly lower on the side ipsilateral to the tumor than on the unaffected, contralateral side (p<0.01). A (p<0.01)larger tumor volume was correlated with a lower density , consistent with tumor compression of the cochlear nerve and/or a volume-related secretion of In conclusion, this study confirms the existence of cochlear pathology in neurotoxins.VS patients, with possible implications for cochlear implantation. This novel study required a method development, which posed clear limitations. Further studies should be done in a larger cohort, with specific staining of nerve fibers for more accurate quantification and analysis of the morphology.

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