Koyanagi I, Iwasaki Y, Isu T, Abe H, Akino M, Kuroda S
Department of Neurosurgery, Hokkaido University School of Medicine, Sapporo, Japan.
Neurosurgery. 1993 Sep;33(3):451-9; discussion 459-60. doi: 10.1227/00006123-199309000-00015.
Spinal cord evoked potentials (SCEPs) after spinal cord stimulation were used as a method of spinal cord monitoring during surgery of 6 extramedullary and 14 intramedullary spinal cord tumors. SCEPs were recorded from an epidural electrode placed rostral to the level of the tumor. Electrical stimulation was applied on the dorsal spinal cord from a caudally placed epidural electrode. The wave forms of SCEPs consisted of a sharp negative peak (N1) in 15 cases and two negative peaks (N1 and N2) in 5 cases. The N2 wave was markedly attenuated by posterior midline myelotomy, whereas the N1 activity showed less-remarkable changes by myelotomy. An increase in N1 amplitude was observed after the removal of the tumor in four extramedullary and three intramedullary cases. Of six patients that showed decreased N1 amplitude after the removal of the tumor, five patients developed postoperative motor deficits. However, there were four false-negative cases and one false-positive case in regard to changes of N1 amplitude and postoperative motor deficits. Four false results occurred in intramedullary cases. In two of them, postoperative symptoms indicated intraoperative unilateral damage to the spinal cord. The position of the stimulating electrode, the difference in thresholds of the axons for electrical stimulation between the right and left side of the spinal cord, or the change of the distance between the electrode and the spinal cord surface may account for these false results. Thus, our analysis of the changes of SCEP wave forms and early postoperative symptoms indicates that the sensitivity of this monitoring method to detect intraoperative insults to the spinal cord is unsatisfactory in spite of the reproducible wave forms. We conclude that SCEP monitoring can be used as an alternative method or in combination with other types of evoked potentials in patients with severe spinal cord lesions who show abnormal somatosensory evoked potentials preoperatively.
脊髓刺激后的脊髓诱发电位（SCEPs）被用作6例髓外和14例髓内脊髓肿瘤手术期间脊髓监测的一种方法。SCEPs从置于肿瘤水平上方的硬膜外电极记录。电刺激通过置于尾侧的硬膜外电极施加于脊髓背侧。SCEPs的波形在15例中由一个尖锐的负峰（N1）组成，在5例中由两个负峰（N1和N2）组成。N2波在经后正中脊髓切开术后明显衰减，而N1活动在脊髓切开术后变化不太明显。在4例髓外和3例髓内病例中，肿瘤切除后观察到N1波幅增加。在6例肿瘤切除后N1波幅降低的患者中，5例出现术后运动功能障碍。然而，在N1波幅变化和术后运动功能障碍方面有4例假阴性病例和1例假阳性病例。4例假性结果发生在髓内病例中。其中2例术后症状表明术中脊髓单侧损伤。刺激电极的位置、脊髓左右两侧轴突对电刺激的阈值差异或电极与脊髓表面距离的变化可能是这些假结果的原因。因此，我们对SCEP波形变化和术后早期症状的分析表明，尽管波形可重复，但这种监测方法检测术中脊髓损伤的敏感性并不理想。我们得出结论，对于术前体感诱发电位异常的严重脊髓病变患者，SCEP监测可作为一种替代方法或与其他类型的诱发电位联合使用。
