A Study on the changes of latency and amplitude of brainstem auditory evoked potentials due to cochlear nerve injury: an analysis of their correlations

术中监测脑干听觉诱发电位（BAEP）已被广泛应用于减少术后脑桥小脑角操作引起的听力障碍。BAEP V波延长常作为提示外科医生调整手术操作的判据。然而，尚不清楚如果术中BAEP潜伏期恢复到基线水平是否可以避免所有的神经病理改变，或者即使BAEP正常化，一些神经病理改变也会“无声”地发生。本研究的目的是通过实验澄清这一点，这对患者听力的长期预后很重要。听神经的桥小脑角部分在大鼠中被定量压缩，再现了与人类手术过程中发生的一样的可逆的BAEP潜伏期延长。压迫24h后，取听神经进行β-APP免疫染色，观察轴突损伤程度。本研究的结果表明，即使在术中获得延长波IV（相当于人类波V）潜伏期正常化的情况下，也会发生轴突损伤。因此，仅根据BAEP潜伏期的延长来解释BAEP变化不足以阻止听神经发生形态学改变。作为听神经轴索损伤的术中指标，BAEP V波振幅的变化比其潜伏期的变化更为敏感。

Intraoperative monitoring of brainstem auditory evoked potentials (BAEP) has been widely utilized to reduce the incidence of postoperative hearing disturbance due to cerebellopontine angle manipulations. The prolongation of wave V of BAEP is usually used as a criterion to warn the surgeons to modify their surgical maneuvers. However, it is not known whether all neuropathological changes are avoided if BAEP latency intraoperatively returns to the baseline level or some neuropathological changes "silently" occur even if BAEP normalizes. The aim of this study was to experimentally clarify this point that would be important for the long-term prognosis of patients' hearing.The cerebellopontine angle portion of the auditory nerve was quantitatively compressed in the rats and reversible prolongation of BAEP latency was reproduced just as it occurs during surgery in humans. Twenty-four hours after the compression, the auditory nerve was removed for β-APP immunostaining to investigate the degree of axonal injury. The results of the present study disclosed that axonal injury occurred even in the cases where the intraoperative normalization of prolonged wave IV (equivalent to wave V in humans) latency had been obtained. Therefore, the interpretation of BAEP changes based only on the prolongation of the latency of BAEP was not enough to prevent the auditory nerve from developing morphological changes. Changes in the amplitude of wave V of BAEP appears to be more sensitive than its latency change as an intraoperative indicator for axonal injury in the auditory nerve.