脳動脈瘤手術における経頭蓋運動誘発電位モニタリング

Transcranial Motor Evoked Potentials Monitoring for Cerebral Aneurysm Surgery

Ⅰ．はじめに

　脳神経外科手術における種々の術中モニタリングのうち，特に四肢や顔面運動機能の監視を行う目的で運動誘発電位（motor evoked potential：MEP）モニタリングが用いられ，これまで大動脈，脊椎脊髄手術^8,10)や頭蓋底手術^3,4)におけるMEPモニタリング法が報告されてきた．脳血管疾患についても同様であり，特に脳動脈瘤クリッピング術におけるMEPモニタリングの有用性については，錐体路に関与する穿通枝や皮質領域の血流不全を検知するという観点から最近広く認められてきている^{5,7,14-16,18)}．しかしながら，術中MEP波形変化とwarning criteriaの設定や術後の運動麻痺の関連など，未だ不明な点が多い^1,7,16-18)．また，MEPモニタリングの刺激は，経頭蓋，皮質のどちらで行うのか，記録は四肢の筋肉からか，頚部硬膜外からD-waveを得るのか，などの点も議論のあるところである^2,12,14)．

　今回われわれは，これまで当科で施行してきた脳動脈瘤クリッピング術における術中経頭蓋MEPモニタリングの方法と結果を提示し，その有用性について検討した．

　Objective:To evaluate the usefulness of transcranial motor evoked potential（MEP）monitoring for aneurysm surgery.

　Methods:Sixty-four patients undergoing aneurysm surgery were included in the study. We recorded MEP responses at craniotomy, when dissecting the aneurysm and surrounding tissue, after clipping, and during temporary clipping of the parent artery. We examined the relations between MEP wave pattern change and postoperative motor function.

　Results:In all of the patients MEPs were recordable for continuous neurophysiological monitoring of the vascular territory of interest throughout the surgery. In 16 patients, significant intraoperative MEP changes occurred. Of these patients, three patients presented with postoperative transient motor deficit. From the changes in MEP wave recording after aneurismal clipping and temporary occlusion of the parent artery. We speculated that the maximal time allowed for occlusion of the perforating arteries without ischemic damage is five minutes. Intraoperative MEP changes had a sensitivity of 100%（3/3）and specificity of 78.7%（48/61). The positive predictive value of postoperative motor deficit was 18.8%（3/16), and the negative predictive value was 100%（48/48). It was important to carry out MEP monitoring, so as not to produce false-negatives.

　Conclusions:Intraoperative transcranial MEP monitoring is useful for predicting motor function after aneurysm surgery.