Polo Gustavo, Fischer Catherine, Sindou Marc P, Marneffe Vincent
Department of Neurosurgery, Hôpital Neurologique Pierre Wertheimer, Lyon, France.
Neurosurgery. 2004 Jan;54(1):97-104; discussion 104-6. doi: 10.1227/01.neu.0000097268.90620.07.
The nerve function of Cranial Nerve VIII is at risk during microvascular decompression for hemifacial spasm. Intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) can be a useful tool to decrease the danger of hearing loss. The aim of this study was 1) to assess the side effects of surgery on hearing and describe the main intraoperative BAEP changes observed in the authors' series, and 2) to define warning values beyond which the probability of hearing impairment rises significantly. These values were calculated by correlating the (possible) postoperative hearing disturbances evaluated in terms of pure tone average with intraoperative BAEP changes (especially delay in Wave V latency).
This series included 84 consecutive patients affected with hemifacial spasm who underwent microvascular decompression during which BAEPs were monitored. During surgery, Wave I, I to V interpeak interval, latency, and amplitude of Wave V were recorded and measured. Auditory function was studied before and after surgery and expressed as a pure tone average in all patients. Then, correlations were made between hearing impairment after surgery and intraoperative BAEP changes in an attempt to define warning values.
Seventy-four patients (88%) had no hearing loss after surgery (Group 1). Eight patients (9.5%) had hearing impairment with a decrease in pure tone average of more than 20 dB (Group 2). Two patients (2.3%) experienced a definitive and complete hearing loss on the side operated on (Group 3). Among intraoperative BAEP changes, latency of Peak V was the most frequently observed and the most significant phenomenon, especially during cerebellar retraction and the decompression step of the microvascular decompression procedure. In the group of patients without hearing loss (Group 1), the mean delay in latency of Peak V was 0.61 millisecond (standard deviation, +/-0.36 ms); in the group with hearing decrease (Group 2), the mean delay was 1.05 milliseconds (standard deviation, +/-0.64 ms); and in the group with deafness (Group 3), Wave V was abolished.
From a practical standpoint, three warning values, based on delay in latency of Peak V, were established for use during surgery: an initial one at 0.4 millisecond ("watching" signal) at the safety limit; a second one at 0.6 millisecond (risk "warning" signal), which is the mean value corresponding to the group of patients without postoperative hearing loss; and an ultimate one at 1 millisecond ("critical" warning), before irreversibility. These warnings should help the surgeon to avoid or correct maneuvers that are dangerous for hearing function, which is mandatory in functional surgery.
在微血管减压治疗面肌痉挛过程中，第八颅神经的神经功能面临风险。术中监测脑干听觉诱发电位（BAEP）可能是降低听力丧失风险的有用工具。本研究的目的是：1）评估手术对听力的副作用，并描述作者系列中观察到的主要术中BAEP变化；2）确定听力损害概率显著上升的预警值。通过将根据纯音平均水平评估的（可能的）术后听力障碍与术中BAEP变化（尤其是V波潜伏期延迟）相关联来计算这些值。
本系列包括84例连续的面肌痉挛患者，他们接受了微血管减压手术，术中监测了BAEP。手术过程中，记录并测量I波、I至V峰间间期、V波潜伏期和振幅。在所有患者中，术前和术后研究听觉功能，并以纯音平均水平表示。然后，对术后听力损害与术中BAEP变化进行相关性分析，以确定预警值。
74例患者（88%）术后无听力损失（第1组）。8例患者（9.5%）有听力损害，纯音平均水平下降超过20dB（第2组）。2例患者（2.3%）在手术侧出现明确且完全的听力丧失（第3组）。在术中BAEP变化中，V峰潜伏期是最常观察到且最显著的现象，尤其是在小脑牵拉和微血管减压手术的减压步骤期间。在无听力损失的患者组（第1组）中，V峰潜伏期的平均延迟为0.61毫秒（标准差，±0.36毫秒）；在听力下降组（第2组）中，平均延迟为1.05毫秒（标准差，±0.64毫秒）；在耳聋组（第3组）中，V波消失。
从实际角度出发，根据V峰潜伏期延迟确定了三个术中使用的预警值：第一个在0.4毫秒（“观察”信号），处于安全极限；第二个在0.6毫秒（风险“警告”信号），这是无术后听力损失患者组的平均值；最后一个在1毫秒（“关键”警告），在出现不可逆情况之前。这些警告应有助于外科医生避免或纠正对听力功能有危险的操作，这在功能性手术中是必不可少的。
