Survival and regeneration of spiral ganglion neuron (SGN) following deafening carries critical implication for cochlear implantation as well as reinnervation of restored hair cells. Survival and development of SGN depend on neurotrophic factors supplied by hair cells glial cells and other targets. The membrane electrical activity of spiral ganglion neurons also support their survival. Cell death inhibitors can also preserve spiral ganglion neurons. Recent studies of spiral ganglion survival including stem cell transplantation have identified several neurotrophic factors which protect neurons from death following hair cell loss. Although these experimental results are still preliminary, progression in study of strategy for SGN survival should be an important part of future neurobiology.
Cell Death ; Cochlear Implantation ; Cochlear Implants ; Hair ; Membranes ; Nerve Growth Factors ; Neurobiology ; Neuroglia ; Neurons ; Regeneration ; Spiral Ganglion ; Stem Cell Transplantation

The endolymph and perilymph of the inner ear have unique ionic composition and electrical potential. It is widely accepted that normal auditory function depends on them and Na/K-ATPase plays a central role in production and maintenance of them. The distribution of five Na/K-ATPase subunit isoform (alpha1, alpha2, alpha3, beta1, and beta2) in rat inner ear was determined by immunohistochemistry after decalcifying the temporal bone with Gooding and Stewart's solution. In the cochlear regions, Na/K-ATPase alpha1beta1 isozyme was abundantly expressed in the infrastrial fibrocytes, suprastrial fibrocytes, spiral prominence, outer sulcus cells and spiral ganglion, and also detected in cochlear nerve and interdental cells. alpha1beta2 isozyme was abundantly expressed in all layers of stria vascularis and alpha3beta1 isozyme was detected in cochlear nerve and spiral ganglion. alpha3beta2 isozyme was expressed in spiral ganglion. In vestibular regions, Na/K-ATPase alpha1b1 isozyme was expressed in macular sacculi hair cell, transitional cells of ampulla, and vestibular ganglion, and alpha1b2 isozyme was abundantly expressed in ampullary dark cells and transitional cells and vestibular ganglion. a3b1 isozyme was abundantly expressed in crista ampularis, macula utriculi, and macula sacculi hair cells, and also moderately detected in ampullary, utricular, and saccular nerves, and vestibular ganglion. alpha3beta2 isozyme also detected in ampullary, utricular, and saccular nerves, and vestibular ganglion. But, alpha2beta1 and alpha2beta2 isozymes were not detected in any regions of inner ear. These findings suggest the possibility of four unique Na/K-ATPase isozymes deferentially expressed among the various cell types of the inner ear. This structural diversity imparts considerable biological versatility to the Na/K-ATPase and would be provided the explanations for the differences in fluid and ion transport and its regulation among the inner ear regions.
Animals ; Cochlear Nerve ; Ear, Inner* ; Endolymph ; Ganglion Cysts ; Hair ; Immunohistochemistry ; Ion Transport ; Isoenzymes ; Perilymph ; Protein Isoforms* ; Rats* ; Spiral Ganglion ; Stria Vascularis ; Temporal Bone

BACKGROUND AND OBJECTIVES: Auditory neuropathy is a hearing disorder characterized by the absence or the marked impairment of the auditory brainstem responses with the preservation of the cochlear microphonics (CMs) and otoacoustic emissions. This suggests that outer hair cell (OHC) function is normal but proximal auditory function to OHCs is impaired. It is assumed that the lesion is localized at the level of the inner hair cells (IHCs), auditory nerve fibers, or the synapse between them. This study was aimed to observe the change of hearing threshold and pathology of spiral ganglion cell induced by ouabain application, and present basic data to explain the auditory neuropathy. MATERIALS AND METHOD: Twenty ears of twenty normal hearing cats were used in this study. Cats were treated with 100 microL ouabain (1 mM) applied on the round window. After three days, compound action potential (CAP) and CM were measured and the cochlea was obtained. Pathologic change of spiral ganglion cell was evaluated under light microscope after H&E stain. Normal saline was injected for the control group. RESULTS: In the ouabain group, CAP threshold was increased in all tested frequencies (p<0.001) and the difference of CM threshold was not significant in all frequencies (p>0.05). There was significant difference between CAP and CM threshold shift (p<0.001). In the control group, there was no significant difference in CAP and CM thresholds. Light microscopic findings show that the condensed chromatin and nuclear fragments of spiral ganglion cells of an ear was exposed to ouabain, and outer hair cell and inner hair cell were not damaged. CONCLUSION: This study shows that the CAP threshold was significantly increased but the CM threshold was not changed in the ouabain group. Ouabain induced damage of spiral ganglion cells. This study is not sufficient to explain auditory neuropathy because threshold shift of CAP is not obvious, but it would be helpful to explain that selective damage of spiral ganglion cell would be the mechanism of auditory neuropathy.
Action Potentials ; Animals ; Cats* ; Chromatin ; Cochlea ; Cochlear Nerve ; Ear ; Evoked Potentials, Auditory, Brain Stem ; Hair ; Hearing ; Hearing Disorders ; Ouabain* ; Pathology ; Spiral Ganglion* ; Synapses

Neurilemmoma is a benign neoplasm arising from the Schwann cell of the nerve sheath. Acoustic nerve is the most common site of neurilemmoma and mandible is the most frequently involved in intraosseous neurilemmoma. Extradurally located dumbbell type neurilemmoma was rarely reported. The histology of neurilemmoma was first described by Verocay in 1908 and elaborated upon by Stout in 1935. Characteristic histologic patterns of neurilemmoma were encapsulation and Verocay bodies, Antoni type A and B areas, palisading nuclei, and lack of malignant characteristics. We experienced such a rare case of neurilemmoma which probably arised from the left first lumbar spinal nerve root, and located extradurally and paravertebrally, and confirmed by radiologic and pathologic findings.
Cochlear Nerve ; Mandible ; Neurilemmoma ; Spinal Nerve Roots

Although cochlear implantation using posterior tympanotomy has been performed worldwide, other alternative approaches might be more beneficial and convenient in some selected cases. Of these, suprameatal approach was reported to be one of useful options in cases with narrow facial recess, anteriorly located facial nerve and an ossified cochlea. We describe a case of cochlear implantation using the modified suprameatal approach in a severely contracted mastoid cavity and suggest another indication of this approach.
Cochlea ; Cochlear Implantation* ; Cochlear Implants* ; Facial Nerve ; Mastoid*

Cochlear Implantation ; Cochlear Implants ; Humans ; Vestibulocochlear Nerve Diseases

Sensorineural hearing loss (SNHL) does not recover and only few exceptions exist. It is mostly due to the reason that hair cells in the cochlea cannot regenerate once damaged. Therefore, clinical approaches for SNHL mostly rely on the implantable or external device to deliver sound to brain. Despite the advance of technology, current strategy does not replicate the sound perception of naïve inner ear. To overcome this issue, novel trials to protect or rescue hair cells from the ototoxic insults are investigated. One of these is gene therapy. Protective gene therapy has been applied to several ototoxic insults, but some trials have shown negative effect. Gene therapy using neurotrophin, one of the growth factor, has been expected to show protective effect against acoustic overexposure. But unregulated and untargeted expression of Ntf3 revealed adverse effect showing deterioration of nerve ending and synapse. Meanwhile, gene therapies have been adopted and tried for cisplatin ototoxicity. Most of the studies has been shown promising outcome. Also several studies have shown protective effect of gene therapy for aminoglycoside ototoxicity. Recent publication showed that heat-shock protein 70 was effective in preventing aminoglycoside ototoxicity. Furthermore, use of gene therapy expands to the field of cochlear implant, in which it can be used as an enhancer of treatment outcome. Application of neurotrophins resulted in increase of spiral ganglion densities as well as migration of peripheral nervous fibers to the location which would be closer to the electrode when implanted.
Acoustics ; Brain ; Cisplatin ; Cochlea ; Cochlear Implants ; Ear, Inner ; Electrodes ; Genetic Therapy* ; Hair ; Hearing Loss, Sensorineural ; Hearing* ; HSP70 Heat-Shock Proteins ; Nerve Endings ; Nerve Growth Factors ; Publications ; Spiral Ganglion ; Synapses ; Treatment Outcome

Refinement of surgical techniques has allowed hearing preservation after tumor resection to be prioritized. Moreover, restoration of hearing after tumor removal can be attempted in patients with bilateral vestibular schwannomas or those with a schwannoma in the only-hearing ear. Cochlear implantation (CI) has emerged as a proper method of acoustic rehabilitation, provided that the cochlear nerve remains intact. Studies of electrical promontory stimulation in patients after vestibular schwannoma resection have demonstrated favorable results. We describe herein two cases of hearing rehabilitation via CI implemented at the time of vestibular schwannoma resection. Tumors were totally removed, and cochlear implant electrodes were successfully inserted in both cases. Also, post operative CI-aided hearing showed improved results.
Acoustics ; Cochlear Implantation* ; Cochlear Implants* ; Cochlear Nerve ; Ear ; Electrodes ; Hearing ; Humans ; Methods ; Neurilemmoma ; Neuroma, Acoustic* ; Rehabilitation

BACKGROUND AND OBJECTIVES: An essential part of the successful application of a cochlear implant is to adjust the stimulation levels to the patient's dynamic range. To test the subjective behavioral threshold (T-level) and the most comfortable loudness level (C-level), however, it may be troublesome or even impossible in very young children who are not able to perform such tasks appropriately. Therefore, utilization of objective measurements is important in children to estimate T- and C-levels. One of the objective measurements is the electrically evoked stapedial reflex (ESR) test. It has also been suggested that ESR may have applicability in confirming and quantifying electrical stimulation through a cochlear implant. The purpose of this study is to examine the feasibility of utilizing ESR to test device function during cochlear implant surgery and to predict ultimate behavioral T- & C-levels. MATERIALS AND METHODS: The ESR measurements were performed in 18 subjects during a cochlear implant surgery. Eight subjects received the Nucleus 22 multichannel cochlear implant (CI 22M) and 10 subjects received Nucleus 24 multichannel cochlear implant system (CI 24M). To test the ESRs, three electrodes, namely, apical electrode (E20), medial electrode (E12) and basal electrode (E5), were stimulated in each case. ESR thresholds were measured by visual observation of the stapedius muscle contraction in response to electrical stimulation delivered to the auditory nerve via a cochlear implant system. And the ESR thresholds were compared with the behavioral T- and C-levels in each electrode. RESULTS: ESRs were presented in 19/23 electrodes (82.6%) in subjects who received the CI 22M and 26/30 electrodes (86.7%) in subjects with CI 24M. The mean ESR threshold was the lowest in apical electrodes (E20) in both groups. In subjects with CI 22M, ESR thresholds were significantly correlated with behavioral T- and C-levels in apical electrodes (E20). In subjects with CI 24M, ESR thresholds were highly correlated with the C-levels in E5, E12, and E20. CONCLUSION: ESR provides an objective, accurate and rapid method to evaluate the device function during cochlear implant surgeries and in estimating T-/C- levels, which may be useful in the initial programming of younger children and the difficult-to-tests.
Child ; Cochlear Implantation* ; Cochlear Implants* ; Cochlear Nerve ; Electric Stimulation ; Electrodes ; Humans ; Muscle Contraction ; Reflex* ; Stapedius

Less traumatic electrode insertion along the basal turn of cochlea is essential to cochlear implantation. However, immoderate attempts to insert the electrode beyond the point of resistance can result in electrode kinking within the basal turn of cochlea. Electrode kinking tends to occur 1) in the use of contour or hugging type of electrode, 2) in the cochlear ossification or fibrosis, and 3) in wrong angle insertion in the approach of round window membrane or cochleostomy near the round window. Intra-operative radiologic evaluation and intra-operative measurement of the neural response telemetry or auditory nerve response telemetry during cochlear implantation is essential to check the status and proper insertion of electrode. Recently, we experienced two cases of electrode kinking in cochlear implantation and discovered that both patients showed abnormal impedances and crumpled electrode in X-ray. Based on these cases, we suggest routine impedance and radiologic measurement during the cochlear implantation.
Cochlea ; Cochlear Implantation* ; Cochlear Implants* ; Cochlear Nerve ; Electric Impedance ; Electrodes* ; Fibrosis ; Humans ; Membranes ; Telemetry