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)已被广泛用于减少桥小脑角手术后听力障碍的发生率。脑干听觉诱发电位V波的延长常被作为警告外科医生调整手术方法的一个指标。然而，如果BAEP潜伏期在术中恢复到基线水平，或者即使BAEP恢复正常，一些神经病理变化是否也会发生，目前尚不清楚是否所有的神经病理变化都可以避免。这项研究的目的是从实验上阐明这一点，这对患者听力的长期预后很重要。在大鼠中，桥小脑角部分的听神经受到定量的挤压，BAEP潜伏期的可逆性延长在手术中重现，就像在人类手术中发生的那样。压迫后24小时取听神经进行β-APP免疫组织化学染色，观察轴突损伤程度。本研究的结果表明，即使在术中延长的IV波(相当于人类的V波)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的变化不足以阻止听神经发生形态变化。BAEP V波的波幅变化比潜伏期变化更敏感，是术中听神经轴索损伤的指标。

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.