脳血管写による脳動脈瘤の形態学的研究

ANGIOGRAPHICAL STUDY OF INTRACRANIAL SACCULAR ANEURYSM, PARTICULARLY REFERING TO ITS SIZE AND SHAPE

I．はじめに

　脳動脈瘤の発生機序に関しては，先天説^{1,3,10,13,22,29）}，後天説^{15,21,23,25,26,31）}，両者合併説^4,5）があり，いまだ定説をみない。またその成長増大あるいは破裂の機序に関しても，壁の退行変性^7），血行動態の変化^12,18）等様々な因子が考えられているが結論が出ていない。しかし一般的には動脈瘤は成長増大し，ある臨界値（critical size）に達した時に破裂すると考えられており，この考えを示唆するような動脈瘤の形態的研究は数多く報告^6,7,14,20）されている。しかし，これらの報告は殆ど剖検例を中心としており，脳血管写から調べた報告は，これまで例をみないと思われる。

　今回，我々は脳動脈瘤直接手術症例における脳動脈瘤の形態，特にその大きさと形について脳血管写より検討を行い，動脈瘤破裂のcritical size，成長増大に関与する因子等について，若干の知見を得たので文献的考察を加え報告する。

We have investigated on the morphology of cerebral aneurysm, particularly its size and shape. Subjects were 655 cases, 655 aneurysms excluding the cases of multiple aneurysm and the cases of single aneurysm with incomplete data among 1,000 cases of direct surgery of saccular cerebral aneurysm we encountered during a period from June 1961 to Sept. 1975. Of them, 636 cases were ruptured aneurysms and 19 cases non-ruptured aneurysms.With the scale of enlargement of preoperative cerebral angiogram corrected, cerebral aneurysm was measured each in the A-P view, lateral view and oblique view at the accuracy of 0.5 mm. The largest major diameter and the smallest minor diameter among them were respectively made the maximum diameter and the minimum diameter of the cerebral aneurysm concerned.

According to the studies on the size of 636 ruptured aneurysms, the diameter of aneurysms varied from 2. 5 mm to 28 mm, and the frequency distribution showed that the frequency increased sharply from the diameter of 4 mm or more, reached its peak at 7 mm and decreased gradually from the diameter of 7 mm or more. From this distribution, it was surmised that the critical size for the rupturing of aneurysm would be in the vicinity of 4 mm.

In non-ruptured aneurysms, the diameter varied between 2 mm and 27 mm and one showing the maximum diameter of 9 mm was found most frequently.

As to the sex difference in the size of ruptured aneurysms, the size tended to be slightly larger in female ; regarding the age difference, however, there was no distinctive difference.

As to the site difference in the size of ruptured aneurysms, internal carotid artery aneurysm was shown to be the largest, followed by middle cere-bral artery aneurysm and anterior communicating artery aneurysm in this order. Regarding the shape, internal carotid artery aneurysm tended to be slender compared with aneurysms in other sites.

There also was a tendency for cerebral aneurysm to be enlarged and slender by repetition of ruptur-ing, and a similar tendency was observed when the period from SAH attack to angiography taken become longer.