HISTOPATHOLOGY OF THE PERIPHERAL VESTIBULAR SYSTEM IN SMALL VESTIBULAR SCHWANNOMAS

Gadolinium-enhanced magnetic resonance imaging can be used to detect s mall vestibular schwannomas/acoustic neuromas. Early detection raises the question of the necessity of their surgical removal. Do small tumo rs induce lesions in the vestibule and to what extent? We thus investi gated the ultrastructure of peripheral Vestibular systems in grades I and II schwannomas. Vestibular tissues were fixed as soon as they were removed during the resection of tumors, by the translabyrinthine appr oach, and then processed for transmission electron microscope observat ions. In neurosensory epithelia, hair cells lost stereocilia, whereas cuticular plates disaggregated. The cytoplasm of hair cells degenerate d in either a dense or vacuolated manner, and cytoplasmic blisters ext ended into the endolymph. In some cases, supporting cells extended pro cesses covering the apical surface of hair cells. Nerve fibers massive ly disappeared from epithelia, only few nerve fibers contacted type I and type II hair cells, and both afferent and efferent terminals were abnormal. In vestibular nerves, axons degenerated, and myelin sheaths disaggregated, Glycogen was present in both intracellular and extracel lular spaces. Luse bodies associated with collagen bundles were found between fibers. Scarpa ganglion neurons contained lysosomes/lipofuscin granules and vacuoles. Tumor cells were found in both the ganglion an d the vestibular nerve. Thus small tumors induce extensive degeneratio n of vestibular tissues. The various hallmarks of schwannomas are alre ady present in small acoustic neuromas. Moreover, different types of d egeneration of hair cells and neurons were observed, together with the covering of hair cells by supporting cells and the accumulation of gl ycogen in the vestibular nerve.