RESUMO
Hearing preservation may be achieved initially in the majority of patients after cochlear implantation, however, a significant proportion of these patients experience delayed hearing loss months or years later. A prior histological report in a case of delayed hearing loss suggested a potential cochlear mechanical origin of this hearing loss due to tissue fibrosis, and older case series highlight the frequent findings of post-implantation fibrosis and neoosteogenesis though without a focus on the impact on residual hearing. Here we present the largest series (N = 20) of 3-dimensionally reconstructed cochleae based on digitally scanned histologic sections from patients who were implanted during their lifetime. All patients were implanted with multichannel electrodes via a cochleostomy or an extended round window insertion. A quantified analysis of intracochlear tissue formation was carried out via virtual re-sectioning orthogonal to the cochlear spiral. Intracochlear tissue formation was present in every case. On average 33% (SD 14%) of the total cochlear volume was occupied by new tissue formation, consisting of 26% (SD 12%) fibrous and 7% (SD 6%) bony tissue. The round window was completely covered by fibro-osseous tissue in 85% of cases and was associated with an obstruction of the cochlear aqueduct in 100%. The basal part of the basilar membrane was at least partially abutted by the electrode or new tissue formation in every case, while the apical region, corresponding with a characteristic frequency of < 500 Hz, appeared normal in 89%. This quantitative analysis shows that after cochlear implantation via extended round window or cochleostomy, intracochlear fibrosis and neoossification are present in all cases at anatomical locations that could impact normal inner ear mechanics.
Assuntos
Implante Coclear , Implantes Cocleares , Surdez , Perda Auditiva , Humanos , Implante Coclear/efeitos adversos , Implante Coclear/métodos , Osteogênese , Audição , Cóclea/diagnóstico por imagem , Cóclea/cirurgia , Cóclea/patologia , Perda Auditiva/patologia , Surdez/patologia , Janela da Cóclea/cirurgia , Fibrose , Eletrodos ImplantadosRESUMO
To further our knowledge of outer hair cell nonlinearities, we measured the dependence of the electrically-evoked otoacoustic emissions (EEOEs) on current level for a wide range of electrical frequencies. Alternating electrical current was delivered into the scala media of the gerbil cochlea while the EEOE was measured with a probe-tube microphone. While the EEOE scaled linearly with current level for many frequencies and current levels, notable exceptions occurred. For frequencies below 300 Hz and currents above 20-30 microA(peak), the gain (primary EEOE magnitude divided by the current level) increased abruptly. For higher frequencies, the gain often increased slightly with increasing current of up to 30-50 microA(peak), but decreased at even higher current levels. We also investigated the enhancement of the EEOE due to simultaneous acoustic stimulation. The enhancement of the EEOE was relatively insensitive to current level with little change in enhancement for current levels up to 20 microA(peak). For current levels above approximately 40 microA(peak), the enhancement decreased slightly.
Assuntos
Potenciais Evocados Auditivos do Tronco Encefálico/fisiologia , Células Ciliadas Auditivas Externas/fisiologia , Emissões Otoacústicas Espontâneas , Estimulação Acústica , Animais , Implantes Cocleares , Estimulação Elétrica , GerbillinaeRESUMO
INTRODUCTION: Superior semicircular canal dehiscence affects the auditory and vestibular systems due to a partial defect in the canal's bony wall. In most cases, sound- and pressure-induced vertigo are present, and are sometimes accompanied by pulse-synchronous tinnitus. CASE PRESENTATION: We describe a 50-year-old man with superior semicircular canal dehiscence whose only complaints were head rotation induced tinnitus and autophony. Head rotation in the plane of the right semicircular canal with an angular velocity exceeding 600 degrees/second repeatedly induced a 'cricket' sound in the patient's right ear. High resolution temporal bone computed tomography changes, and an elevated umbo velocity, supported the diagnosis of superior semicircular canal dehiscence. CONCLUSION: In addition to pulse-synchronous or continuous tinnitus, head rotation induced tinnitus can be the only presenting symptom of superior semicircular canal dehiscence without vestibular complaints. We suggest that, in our patient, the bony defect of the superior semicircular canal ('third window') might have enhanced the flow of inner ear fluid, possibly producing tinnitus.
Assuntos
Líquidos Labirínticos/fisiologia , Rotação/efeitos adversos , Canais Semicirculares/patologia , Zumbido/etiologia , Condução Óssea/fisiologia , Cabeça , Perda Auditiva Condutiva/diagnóstico , Perda Auditiva Neurossensorial/diagnóstico , Testes Auditivos , Humanos , Masculino , Pessoa de Meia-Idade , Canais Semicirculares/diagnóstico por imagem , Osso Temporal/diagnóstico por imagem , Tomografia Computadorizada por Raios XRESUMO
Moderate acoustic trauma results in decreased cochlear sensitivity and frequency selectivity. This decrease is believed to be caused by damage to the cochlear amplifier that is associated with outer hair cells (OHCs) and their nonlinear electromechanical characteristics. A consequence of OHC nonlinearity is the acoustic enhancement effect, in which low-frequency electrically evoked otoacoustic emissions are enhanced by a simultaneous tone. The present study found that acoustic trauma reduced the acoustic enhancement effect and this reduction is correlated with the N1 threshold at the electrode site. This result is consistent with the theory that trauma affects the mechanoelectric transduction process, thus affecting cochlear mechanical nonlinearity. Acoustic trauma also reduced the cochlear microphonic in a way that suggests that the number of functioning tension-gated channels and the stiffness of the gating springs were decreased. In some cases, the electromechanical transduction process was also found to be affected by acoustic trauma.
Assuntos
Cóclea/fisiopatologia , Perda Auditiva Provocada por Ruído/fisiopatologia , Emissões Otoacústicas Espontâneas/fisiologia , Animais , Estimulação Elétrica/métodos , GerbillinaeRESUMO
Electrically evoked otoacoustic emissions were measured with current delivered to the second and third turns of the gerbil cochlea. The emission magnitude and phase are dependent on the characteristic frequency (CF) of the stimulating microelectrode location. The death of the animal resulted in an initial increase in emission below the CF of the electrode location and a decrease in emission near the CF of the electrode location. The group delay of the electrically evoked emission phase data is twice as large as the acoustically evoked cochlear microphonic (CM) data obtained by Schmiedt and Zwislocki [J. Acoust. Soc. Am. 61, 133-149 (1977)]. This suggests the possibility of two separate propagation modes for the forward and reverse traveling waves.