Current work has focused on the evaluation of cochlear implant electrode arrays and the use of temporal bone microanatomy to study those cochleae in which electrodes have been partially inserted. Microdissection techniques are an effective way to study human cochlea and vestibular anatomy and are suitable for the evaluation of insertion performance of cochlear implant electrodes. The membrane vagus tissue with osmium staining thins the cochlear shell and allows direct opening and direct observation of the three-dimensional anatomy of the cochlea. The preservation of residual hearing has become an important goal. Despite, advances in surgical techniques and continuous improvement in electrode design, patients with a residual hearing loss of 10-20% are the best candidates for cochlear implantation. A variety of factors may contribute to implantation-related hearing loss; however, mechanical damage to various intracochlear structures may play a major role. Some structures that are particularly susceptible to implant-related injury include damage to the cochlear shaft, basilar membrane, soft-tissue lateral cochlear wall, and blood vessels associated with the tympanic cavity. In recent years various “perimodiolar” electrode arrays have come into clinical use. These arrays are designed to be conveniently placed as close as possible to the cochlear shaft in order to provide more targeted contact with the spiral ganglion cells and to stimulate them. While they offer the potential for efficient electrical stimulation, perimodiolar arrays also pose a risk of injury to the spiral ganglia and associated nerve fibers. In previous studies, vascular injury occurring during cochlear implantation surgery may impair inner ear function and thus have exacerbated residual hearing loss. In addition, implantation of electrodes can sometimes tear or compress the basilar membrane beneath the spiral ligament and the delicate tissue attached to it. Scanning electron microscopy studies have shown that an open connective tissue trabecula comprising part of the spiral ligament can undergo mechanical fragmentation due to the sensitive electrode array. This injury would inevitably damage the veins passing through the spiral ligament. The bony cochlear wall is very fragile, with many gaps and open spaces in its structure. The cochlear aqueduct vein is thought to provide almost 100% venous drainage, and in most human cochleae, the possibility of collateral venous circulation exists. It has been shown that even in laboratory animals, a few microliters of blood entering the tympanic class can result in significant, permanent changes in hearing thresholds. If there is a relatively small amount of bleeding during cochlear implantation, this may also have a negative impact on auditory function, i.e., a post-implant hearing loss.