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Ⅰ.緒 言
未破裂脳動脈瘤の開頭クリッピング術において,クリッピング後に生じ得る虚血性合併症をいかに予測し,回避できるかはこの手術の課題の1つといえる.これまでにドップラー血流計による血流評価や,indocyanine green(ICG)などを用いた蛍光血管造影による血流評価が試みられてきた11,13).しかし,いずれの評価法も対象血管の血流の有無を評価しているのみで,その血流が実際に灌流する脳組織にとって必要量たり得るかは評価できない.こうした脳血流の機能的側面での評価方法として用いられているのが,運動誘発電位(motor evoked potential:MEP)による術中モニタリングである.これまでにも開頭クリッピング術においてMEPを用いた報告は多く,いずれもその有用性を指摘するものであった.その一方,MEPで血流を評価していたにもかかわらず,術後に虚血性合併症を引き起こしていた例も少なくない4,8,12).本報告では,当院で行われた未破裂脳動脈瘤に対する開頭クリッピング術におけるMEPの経験を報告し,その有用性と問題点を考察する.
It has been pointed out that the motor evoked potential(MEP)with a subdural electrode is useful in the intraoperative monitoring for unruptured aneurysm surgery. However, in some cases, we experienced postoperative ischemic complications despite evaluating the motor function via MEP monitoring. Herein, we have reported the usefulness and problems of intraoperative monitoring with MEP to evaluate brain dysfunction caused by insufficiency of cerebral blood flow.
Out of 279 aneurysm surgery procedures, we performed MEP monitoring in 142 cases and successfully recorded in 126 cases. We compared the ischemic complication rate of the group for which MEP was monitored with that of the group for which MEP was not monitored. The whole ischemic complication rate was decreased in the group that underwent MEP monitoring. Thus, it was suggested that MEP monitoring was useful for avoiding ischemic complications.
In internal carotid artery aneurysms, the amplitude of MEP changed and recovered in 2 cases and disappeared in one case. In anterior cerebral artery aneurysms, the amplitude of MEP changed and recovered in 2 cases. In middle cerebral artery aneurysms, the amplitude of MEP changed and recovered in 5 cases.
We could avoid ischemic complications by intraoperative MEP monitoring in many cases. However, in some cases, we found ischemic complications that were not detected by MEP monitoring with a subdural electrode. In these cases, transcranial stimulation in combination with subdural electrode might be effective in avoiding ischemic complications that might occur after dural closure.
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