中大脳動脈瘤(M1-2分岐部)への最適接近法の選択  [in Japanese] The Preoperative Choice of the Optimal Approach for the Aneurysm of the Middle Cerebral Artery  [in Japanese]

中大脳動脈瘤(M1-2分岐部動脈瘤)は内頸動脈瘤と比較して深度が浅く,親動脈の血流が遅いため,たとえ術中に破裂してもcontrolが比較的容易であることが多い.このためsylvian fissureの剥離ができるようになった程度の経験の限られた術者が執刀することが多い,しかし,中大脳動脈瘤は,M1の長さ,動脈瘤の形状,M2に対する相対的位置などにより著しく難易度が異なり,さらにbroad neckであることが多く,容易なtypeばかりではけっしてない.これまでに多くの手術書があり,一様に,動脈瘤clippingの基本は動脈瘤を剥離する前に確実に親動脈をとらえることである,と強調している.しかし,この点を十分に理解しているはずの手術において,動脈瘤の一部が露出されると,親動脈の確保もそこそこにまるでそれに吸い寄せられるかのように動脈瘤に接近し,術中破裂に陥る場合が,時に散見される.これは,中大脳動脈瘤に対するapproach方法の十分な理解がなく,手術の設計図とでもいうべきclippingまでの具体的な手順が術前に確立されていないために起こるものと考えられる.今回,中大脳動脈瘤の連続自験90例を対象とし,中大脳動脈瘤へのapproach方法を整理検討し,より安全かつ適切なapproach方法への選択基準を試案したので報告する.

The surgical treatment of the middle cerebral artery (M1-2 bifurcation) aneurysm (MCA AN) employs the pterional approach and comprises much of aneurysm surgeries. But the surgical management of MCA AN remains a technically challenging problem especially for inexperienced neurosurgeons. This is largely caused by the difficulty of securing the M1 artery as the parent artery before exposing the whole aneurysm. In this study, we retrospectively analyzed the relationship between the approaches and operative difficulties in 90 MCA ANs in 86 of our patients operated on by the same neurosurgeon (K.U.). The variations of the MCA ANs were classified according to the following 3 points: the length of M1, M1 configuration on the angiogram (antero-posterior view), and the aneurysmal dome direction to M2. We subdivided the pterional approach into the following 4 groups: 1) the proximal approach (PA) to secure the proximal M1 after having controlled the internal carotid artery, 2) the distal approach (DA) to secure the distal M1 in the space between M2 arteries after having opened the distal sylvian fissure, 3) the superior approach (SA) to secure t.he dist,al M1 after having opened the distal sylvian fissure and followed the medial surface of M2 superior trunk, and 4) the inferior approach (IA) to secure the distal M1 after having opened the distal sylvian fissure and followed the lateral surface of M2 inferior trunk. The PA is effective in the cases of short M1 but in the cases of long Ml the DA is effective. The PA is safe for the cases in which the direction of the aneurysm is at the medial side of M2 arteries. On the other hand, in the cases in which the direction of the aneurysm is lateral to the M2 arteries, DA and SA are safe. In view of the results, we designed a scoring system to indicate the difficulties of securing M1 as the parent artery regarding the above-mentioned 3 points. Using these scores, we were able to decide the optimum approach preoperatively. To secure the parent artery is indispensable to safe aneurysm surgery. Comparing the points of each approach to the aneurysm with this scoring system, we were able to construct a better and safer micro-dissection plan with the goal of securing the parent M1 artery, and perform the operation by following the pre-operative plan. Surgical success or failure is determined by preoperative planning.