破裂動脈瘤と未破裂動脈瘤を合併する多発性脳動脈瘤―破裂部位とsizeから破裂率の検討

Study of Multiple Cerebral Aneurysms Comprised of both Ruptured and Unruptured Aneurysm : An Analysis of Incidence Rate with Respect to Site and Size

　Ⅰ．はじめに

未破裂動脈瘤を合併する破裂動脈瘤症例では，しばしば破裂部位の特定が困難な場合がある．動脈瘤は，一般にsizeの大きなもの，blebをもつもの，前交通動脈に存在するものが破裂しやすいと言われ⁵⁾，多発性動脈瘤では，くも膜下出血の所見や合併する脳内出血の部位を考慮して破裂部位を推測している．しかし，くも膜下出血が脳槽に広範にある場合や発症から時間が経過し，くも膜下出血が薄くなっているもの，動脈瘤が近接して複数存在しているものは必ずしも破裂動脈瘤の特定が容易でなく，手術中の所見から破裂した動脈瘤が診断されている．多発性動脈瘤では，術前に破裂動脈瘤部位を推定することによって，手術の安全性の向上と手術時間の短縮につながると考えられ，破裂部位を術前に診断することは非常に重要なことと考えられる．

　今回，われわれは，未破裂動脈瘤と破裂動脈瘤を合併する多発性動脈瘤症例について破裂部位とsizeについて検討した．さらに，これらの動脈瘤では同じ脳内の環境下にあって破裂するものと破裂しないものがあることから，動脈瘤の部位あるいはsizeによって破裂率が異なる可能性が推測された．そこで，破裂動脈瘤と未破裂動脈瘤のsizeと破裂部位に注目し，それぞれを比較することによって，動脈瘤の部位とsizeによる破裂率を検討した．

　The purpose of this investigation was to study the incidence rate of rupture with respect to the site and size of multiple cerebral aneurysms that include both ruptured and unruptured aneurysms. Site and size were investigated in 58 cases of this type of multiple cerebral aneurysm. All cerebral aneurysms were examined with MR angiography,3D-CT angiography and digital subtraction angiography,as well as seeing measured using 3D-CT or digital subtraction angiography. As regards the site of the 58 ruptured cerebral aneurysms under study,18 were internal carotid aneurysms (C2 or C3 : 4 cases,IC-PC : 12 cases,IC-ancho. : 1 case,IC terminal : 1 case),25 were anterior communicating aneurysms,10 were middle cerebral aneurysms,4 were anterior cerebral aneurysms and 1 case was a VA-PICA aneurysm. The ruptured internal carotid aneurysms were 4.0-21.0 mm in size,the anterior communicating aneurysms were 1.8-13 mm,the middle cerebral aneurysms were 2.0-21.3 mm,the anterior cerebral aneurysms were 3.2-9.1 mm,and the VA-PICA aneurysm was 4.4 mm. The sites of the 89 unruptured cerebral aneurysms break down as follows : 29 were internal carotid aneurysms (C2 or C3 : 4 cases,IC-PC : 10 cases,IC-ancho. : 10 cases,IC terminal : 5 cases),18 were anterior communicating aneurysms,34 were middle cerebral aneurysms,and there were 5 cases of posterior circulation aneurysm. In size,the unruptured internal carotid aneurysms were 1.0-18.3 mm,the anterior communicating aneurysms were 1.0-6.5 mm,the middle cerebral aneurysms were 1.0-10.3 mm,the anterior cerebral aneurysms were 1.0-3.3 mm,and the posterior circulation aneurysms were 2.2-17.3 mm. Out of 58 ruptured cerebral aneurysms,44 were of the largest size category,and 53 (91.4%) were in the largest size category and/or anterior communicating aneurysms. The accumulated incidence rate of rupture of anterior communicating aneurysms rose suddenly upon reaching 2 mm in size,and after reaching 3 mm,these aneurysms accounted for a nearly uniform 55%-60% of the incidence rate of rupture. The accumulated incidence rate of rupture of IC-PC aneurysms rose drastically at 4 mm in size with the data describing a parabolic slope when graphed. IC-PC aneurysms represented a uniform 55% of the incidence rate of rupture after reaching 8 mm in size. The accumulated incidence rate of rupture of middle cerebral aneurysms rose in a gently sloping parabola beginning at 4 mm,and stabilized at 20% upon reaching 10 mm. These results suggest that each site is associated with a characteristic size and rate of aneurismal rupture. Special attention should thus be paid to large and anterior communicating aneurysms when operating on multiple cerebral aneurysms.