Cerebrovascular disease

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Abstract
Four large groups of possible factors were surveyed intracranial and extracranial artery narrowing, impaired collateral circulation, dis -turbances in systemic circulation, and vascular spasm. An analysis was made of 1,120 autopsy cases for which information was available regarding the extent and degree of atherosclerosis of the intracranial arteries, dis -turbances of systemic circulation, and changes within the brain. In these 1,120 cases, there were 290 separate areas of infarction. Of these, 145 or half had severe narrowing of arteries of the circle of Willis that closely correlated with these areas of softening. In 79 instances, the narrowing implicated the middle cerebral arteries. Since the extracranial arteries were not studied, the role played by these vessels in the lesions could not be evaluated. In 267 cases, 1 or more intracranial arteries where severely narrowed or occluded without producing any tissue changes. This emphasizes the importance of collateral circulation which, in many cases, can compensate for reduced circulation through the cerebral arteries. There are 3 main sources of collateral circulation to the brain, any or all of which may play a role in protecting the brain in the presence of vascular occlusion: the large superficial arteries of the brain stem and cerebral cortex, the circle of Willis, and anastomoses between the various parts of the extracranial circulation. In 95 cases, cerebral infarction occurred in the absence of any involvement of the intracranial arteries. In these cases, the lesions may have been due to involvement of the extracranial vessels or perhaps to disturbances in the systemic blood flow. In many cases, localized narrowing of a cerebral artery or even deficient collateral circulation may still allow for adequate, though reduced, cerebral blood supply. The addition of systemic circulatory factors may be the chief precipitating factor in the cerebral infarction. The disturbances in systemic circulation most often implicated in cerebrovascular disease consist of: severe anemia, congestive heart failure, hypotension secondary to surgical shock and hypotensive drugs, myocardial infarction, and loss of vascular tone with venous stasis. Considering the marked decrease of contractile tissue within the cerebral arteries of the older age group, vascular spasm probably plays little role in the genesis of cerebral ischemia.