脳梁近傍の末梢性前大脳動脈瘤に対するbasal interhemispheric approachの有用性

Basal Interhemispheric Approach for Distal Anterior Cerebral Aneurysms

Ⅰ．はじめに

　末梢性前大脳動脈瘤（distal anterior cerebral artery aneurysm：DACAA）は比較的稀な脳動脈瘤で，全脳動脈瘤の2.5～9.1％と報告されている^{1,2,4-6,8-10,13-15,17,19,22)}．この部位の脳動脈瘤の手術手技は，①狭いくも膜下腔に存在するために周囲との癒着が強いことが多い，②生理的にくも膜下腔ではない大脳縦裂の剝離操作においては手術の指標になるものが少ない，③架橋静脈の温存，④動脈瘤の発育方向がアプローチと一致することが多く術中破裂に遭遇しやすい^{2-4,7,8,11,15,21,22)}，などが挙げられ比較的困難とされている．これらの動脈瘤は一般的に脳梁膝部を境界にして，①前交通動脈から前頭極動脈分岐部まで（infracallosal portion group：IPG），②脳梁周囲動脈分岐部（genu portion group：GPG），さらに③末梢（supracallosal portion group：SPG），の3つに区別されている^3,7,8,13)．SPG動脈瘤については片側傍矢状開頭による経大脳縦列間アプローチ^{1-3,8,10,13,17,19,25)}が一般的であるが，IPG，GPG動脈瘤についてはanterior interhemispheric approach（AIHA）^{1-4,6,8,10,18,19)}の報告が多い．

　われわれの施設では脳梁膝部近傍のIPG,GPG動脈瘤に対し両側前頭開頭によるbasal interhemispheric approach（BIHA）を行い比較的良好な結果を得ている．脳梁膝部近傍のDACAAに対する同アプローチの有用性を検討した．

Purpose　To investigate retrospectively the usefulness of basal interhemispheric approach for neck clipping of aneurysms located on genu or infracallosal portion of anterior cerebral artery.

Clinical materials and methods　Seventeen aneurysms in 17 patietns treated by clipping with basal interhemispheric approach in our department for past 8 years were reviewed. Of them,12 were ruptured aneurysm and 5 were unruptured one. The distance between frontal base and most frontally located bridging vein and the shortest distance from cranium to aneurysm were measured from angiograms of lateral view,and the point on cranium of the shortest distance was identified in each cases. Bridging vein damage suffered during surgical approach and the duration of brain retractor use were examined from operative videotapes. The clinical outcome was rated at discharge by Modified Rankin Scale.

　Results　The distance between frontal base and most frontally located bridging vein was ranged as 15～69 mm (mean,32 mm). The shortest distance between cranium and aneurysm in each case was ranged as 25～48 mm (mean,33 mm),and the point on cranium of the shortest distance was these within 20 mm from frontal base in 11 cases. Any damage or cut of bridging vein were not seen in all cases. The duration of brain retractor for unilateral frontal lobe and for bifrontal lobe in recent 14 cases was ranged 0～46 minutes 41 seconds (mean,8 minutes 55 seconds) and 0～16minutes (mean,2minutes 24 seconds),respectively. No brain damage caused by operative procedure was detected on postoperative CT scan. All five patients of unruptured one and 8 patients of ruptured one were rated as 0 by Modified Rankin scale,2 patients of ruptured one as 3 and 5,and 2 patients of ruptured one died.

　Conclusion　The basal interhemispheric approach for neck clipping of aneurysm located on genu or infracallosal portion of anterior cerebral artery would provide wide view of aneurysm and its surrounding structures with minimum retraction of frontal lobe,short distance to the aneurysm,and low risk of bridging vein damage.