Collateral circulation of the brain

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Abstract
Collateral circulation of the brain was studied in 400 autopsied subjects aged 60 and over, selected at random, with special reference to atherosclerosis of the cervical and cerebral arteries. Of the arteries branching off from the aortic arch, the lumen of the subclavian and the common carotid were more narrowed on the left side of the body than on the right. Fifteen to 25% of 400 cases examined showed stenosis of more than 50% in one or more of the internal carotid and vertebral arteries. Complete occlusion of the carotid arteries was observed in 9 subjects (2%) and of the vertebral artery in 24 subjects (6%); however, in only 2 of the former and in 4 of the latter was cerebral infarction confirmed at autopsy. The incidence of cerebral infarction was not paralleled by the degree of stenosis of the internal carotid, but was significantly correlated to the severity of cerebral atherosclerosis. It was concluded that the cerebral infarction was due more to stenotic changes of the cerebral arteries than of the cervical arteries. This fact may be important in interpreting angiographic findings. The grade of stenosis of the internal carotid was significantly correlated with that of the vertebral and external carotid arteries. Anastomoses between the external carotid, the internal carotid, and the vertebral arteries were demonstrated by anatomic or radiographic methods. The function of collateral circulation of these anastomoses, however, might not be sufficiently expected in the aged subjects, with already advanced sclerotic changes in these arterial parts. The variations of the basal cerebral arteries were observed in 65% of 400 cases. In the cases with cerebral infarction, the incidence of the right and left caliber-difference of the anterior and of the vertebral arteries was significantly higher than in the cases without gross findings in the brain. The embryonic derivation of the posterior cerebral artery from the internal carotid was also found more commonly in the cases with cerebral infarction. The latter type of variation was 2 or 3 times more frequent in the Japanese than in Americans and Europeans. An existence of some hereditary factors was suggested in the formation of this variation. Clinicopathologic significance of the variations of the basal cerebral arteries was discussed with emphasis on collateral circulation. Of 67 cases with severe stenosis in the cervical arteries, 38 showed recurrent episodes of cerebral vascular insufficiency along with a drop of the blood pressure; on an average, there was a drop of 76 [plus or minus] 24 mm. Hg, systolic. Cerebral vascular insufficiency was frequently observed in febrile conditions with various causes.

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