Strokes KEITH MILLS, Meds '56
INTRODUCTION Th e term "s troke" refers, in its broadest sense, to any neurological event in the brai n of vasc ul ar origin, whether short-lived or prolonged, mild or serious . Strokes may be produced by a number of causes, but the pathogenes is may be reso lved into one of three fundam ental vascular processes - hemorrhage, embo lis m and thrombosis. Th e relative fr equ ency of each is still somewhat contr oversial. Thrombosis, however, is beli eved to be the commones t - producing 50-70 % of strokes. H emorrhage is said to be res ponsible for 15-20% of cases ; and embolism, while formerly th ought to occur uncommonly, is now being recogni zed wi th increasing frequency and some impl icate it in as many as 35 % of cases. Cerebrovascular lesi ons are a very important cause of illness, dis ability, and dea th . As a cause of death they are exceeded only by heart disease and malignancy. In the United States in 1952, for exampl e, 170,000 people died and 1,800,000 persons w ere disabled by th ese lesions. Briti sh fi gures for th e same yea r impli ca te th em in 14 % of all deaths. The therapy of conditions predisposing to cerebrovascular lesions and th e manage ment of stroke vi ctims thu s is of importance to every prac titi oner.
ANATOMY A brief review of the cerebral circulation may be useful at this point. Arterial blood reaches the brain through four main vessels, the paired vertebral and internal carotid arteries. In general, the vertebrals supply the posterior half and the internal carotids the anterior half of the brain . The two vertebral arteries, after entering the cranial cavity through the foramen magnum, unite to form the basilar artery at the point of junction of medulla and pons. The basilar, which gives off supplying branches to the cerebellum, bifurcates into the posterior cerebral arteries where pons and midbrain meet. These latter vessels supply the inferior surfaces of the temporal lobes and the entire occipital lobes. Each internal carotid artery, after entering the skull via the carotid canal, runs forward within the cavernous sinus and enters the subarachnoid space medial to MAY,
1956
the anterior clinoid process. Then, at the medial end of the lateral cerebral fissure, it divides into its terminal branches, the anterior and middle cerebral arteries, which supply blood to the medial and lateral portions of the hemispheres. The Circle of Willis, at the base of the brain, joins the vertebral and carotid systems and provides for anastomatic blood flow between them . In addition, anterior, middle, and posterior cerebral arteries are joined by many small, but potentially anastom:atic, channels over the cortex. From the above mentioned larger vessels, smaller, but important, penetrating arteries arise which supply all areas of cerebral tissue. Functionally, these penetrating vessels are "end arteries" so that stoppage of the blood flow in them results in infarction in the particular area supplied. In a location where tracts and functions are highly concentrated such an occurrence produces marked findings . The venous return from the brain is via the external and internal cerebral
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