上向き前交通動脈瘤に対するpterional approach―A1-A2移行部が前方に位置する側からのアプローチにおける問題点と対処法

Clipping of Upward Projecting Anterior Communicating Aneurysms via Pterional Craniotomy : Approach from the Side of A2 of Anterior Displacement

Ⅰ．目　的

　脳動脈瘤は1つとして同じものがなく，手術中の問題点も1例ずつ異なる．手術には周辺血管との癒着など，術前には予想しにくい問題も多いが，術者が一定の指針に沿って自分の手術を標準化し，症例を重ねることによって，術野に一定のパターンが現れることがわかる．術前にそれらを予測して対策を考えておくことは，手術を円滑に進めるために有用と思われる．

　前交通動脈瘤をpterional approachで手術する際，術者が行う最初の作業は開頭側の決定である．このとき考慮すべき因子として，優位半球，A1の優位性，術者の利き腕，血腫の分布，前交通動脈の傾き，他の動脈瘤の存在などが挙げられるが，何を重視するかは術者によって異なる．例えば，利き腕や大脳半球の優位性を考えて右側の開頭のみを選ぶ術者^{2,12,13,15,22-24)}，術中破裂に備えて常にA1が優位な側の開頭を選ぶ術者もいる^3,16,18,20)．術者にとって最も安全確実と思われる接近法を選べばよいが，どの接近法を選ぶにせよ，手術経過全体を見通して，その術野ではどのような状況が生じうるかを予測しておくことは重要である．

The majority of anterior communicating artery(Acom) aneurysms can be approached via pterional craniotomy. When the fundus points superiorly,craniotomy in the side of A2 of posterior displacement may be advantageous for catching the aneurysm and both ACAs on the same plane. Sometimes,however,surgeons have to deliberately select a “contralateral” craniotomy to deal with other lesions in the same operative session. The first author has operated on 111 patients with Acom aneurysms during the last 8 years; 26 aneurysms projected superiorly,and 7 were approached via contralateral craniotomy because of the aneurysm multiplicity.

We reviewed surgical problems in the 7 upward projecting aneurysms approached from the “contralateral” side. All aneurysms were successfully secured without any surgery related complication. However,in each case,aneurysm and both ACAs formed a straight line in the narrow surgical field,and it was difficult to handle the aneurysm behind the ipsilateral A2,particularly when it tightly adhered to the A2.

Anticipating this prior to surgery allows the surgeon to know the possible problems in aneurysm dissection that may occur. Practically,wide separation of interhemispheric fissure with removal of the gyrus rectus,and dissection of the posterior aspect of the ipsilateral A2 facilitates the mobilization of A2 and exposure of the aneurysm neck. When the aneurysm is tightly adherent to the A2,however,isolation of the entire aneurysm risks tearing the aneurysm at its A2 junction. An aperture clip should be considered to avoid serious bleeding during dissection.