Melanin in human vestibular organs: what do we know now? An ultrastructural study and review of the literature

Objective: Melanin is a pigment widely found in animals and plants. It has long been observed in the inner ear, but its function there is not even now entirely clear. The protective role of melanin against damage caused by ageing, ototoxicity and noise is still a matter of debate. Methods: The current study discusses ultrastructural findings in the vestibular organs removed via the translabyrinthine approach for the resection of a schwannoma of the 8th cranial nerve. Our aim was to shed more light on the role of melanocytes in the inner ear, analyzing their features in human subjects. Results: Melanin granules were present in all of the cases studied: in some samples they appeared scattered in the cytoplasm, whereas in others they accumulated in the reserve area. There was no correlation between the presence of pigment and schwannoma dimensions other than a greater frequency of accumulation in the reserve areas in the melanocytes of patients with small tumours. Conclusions: Our findings and literature data confirm that melanocytes are an integral part of the endolymph production system and appear essential for balance and hearing functions, having a protective effect. Thanks to its semiconducting properties, melanin could be involved in absorbing the mechanical energy arising from sensory stimulation.