抄録
Both the Moyamoya Phenomenon and complete or incomplete occlusion of the internal carotid fork are essential neuroradiological findings of the true Moyamoya Disease of unknown etiology. However, the Moyamoya Phenomenon often is observed in occlusive diseases of the internal carotid fork whose etiologies are known, i. e., arteriosclerosis, tuberculous meningitis, sickle cell anemia, etc. Recently the authors observed the rather acute development of unilateral Moyamoya Phenomenon following severe vasospasm of the bilateral anterior cerebral and left middle cerebral arteries due to the rupture of an anterior communicating aneurysm. An autopsy of this case revealed the marked development of anastomotic small arteries and arteriolae in the basal part of the brain, and only on the left side. Such exteraordinarily dilated arteries mainly are branches of the posterior communicating, anterior choroidal and perforating arteries, and well correspond to the Moyamoya Phenomenon observed angiographically. There were no occlusive changes in the main intracranial arteries except for moderate stenosis of the A2 portion of the bilateral anterior cerebral arteries. Histologically, arteriosclerotic change generally was, very slight, and a slight thickening of the intima and edematous change of the media were observed only at the stenotic site. There was no histological change in the markedly dilated Moyamoya vessels. The following 4 factors have been suspected of contributing to development of the Moyamoya Phenomenon : 1. The chronology of arterial occlusion. 2. Location and extent of occlusion. 3. The cause of occlusion. 4. Anatomical and functional disposition of the basal circulation. As regards the chronology, chronic or slowly progressive arterial stenosis has been thought a mandatory factor in development of a Moyamoya network which plays an important role in the form of collateral channels. However, based on the findings outlined above, the congenital factor may be the most important of the 4 factors listed.
