Morphometric changes in the cochlear nucleus in patients who had undergone cochlear implantation for bilateral profound deafness

Abstract

We have investigated the morphometric changes in the cochlear nucleus of patients who had undergone cochlear implantation following profound deafness. The brain stems of 11 adult patients who had undergone implantation and four non-implanted control cases with varying degrees of hearing loss were studied. The volumes of the ventral cochlear nucleus (VCN) and dorsal cochlear nucleus (DCN), and the maximal cross-sectional area and densities of cell bodies in the anterior ventral cochlear nucleus (AVCN) were measured bilaterally by light microscopy assisted by the Neurolucida 2000 image analysis system. In addition, the density of synapses on cells of the AVCN were estimated using immunostaining for the synaptosome-associated protein (SNAP-25) by light microscopy. There was no significant difference in volumes of VCN and DCN, maximal cross-sectional area and density of cell bodies of the AVCN, and SNAP-25 immunostaining between the cochlear nucleus ipsilateral and contralateral to cochlear implantation. In addition, there was no significant correlation between these morphometric parameters and clinical performance. Peripheral deafness seems to reduce the size of neurons in the AVCN in that the maximum diameter of cell bodies was greater in the ear with better hearing preoperatively (chi-square test P<0.05). However, electrical stimulation provided by the cochlear implantation did not alter these morphometric changes in adult cochlear implant patients.