INTRODUCTION AND EPIDEMIOLOGY
In the United States, 795,000 people experience strokes annually (one stroke every 40 seconds and one death from stroke every 4 minutes).1 Of these events, 77% are primary strokes, whereas 23% represent recurrent strokes.1 In addition to the human costs, the financial implications of stroke are enormous—strokes accounted for an estimated $33.9 billion of total expenditures in the United States in 2012 to 2013.1 Despite these grim statistics, from 2004 to 2014, the age-adjusted stroke death rate fell 28.7%.1 With the growing use of stroke units, thrombolysis, mechanical retrieval, and the ever-expanding treatment time window, there is potential for improving patient outcomes.
PATHOPHYSIOLOGY AND ANATOMY
Stroke is generally defined as any disease process that interrupts blood flow to the brain. Injury is related to the loss of oxygen and glucose substrates necessary for high-energy phosphate production and the presence of mediators of secondary cellular injury. Subsequent factors, such as edema and mass effect, may exacerbate the initial insult.
An understanding of the diagnosis and treatment of stroke begins with a working knowledge of the relevant vascular supply and neuroanatomy of the brain. The arterial supply to the brain is illustrated in Figures 167-1 and 167-2.
Cerebral hemisphere, lateral aspect. Note the branches and distribution of the middle cerebral artery and the principal regions of cerebral localization. The middle cerebral artery bifurcates into a superior and inferior division. a. = artery; ant. = anterior; inf. = inferior; post. = posterior; sup. = superior. [Modified with permission from Fauci AS, Braunwald E, Kasper DL, et al: Harrison’s Principles of Internal Medicine, 17th ed. New York: McGraw-Hill Professional; 2008.]
Cerebral hemisphere, medial aspect. Note the branches and distribution of the anterior cerebral artery, posterior cerebral artery, and the principal regions of cerebral localization. a. = artery; ant. = anterior; post. = posterior. [Reproduced with permission from Fauci AS, Braunwald E, Kasper DL, et al: Harrison’s Principles of Internal Medicine, 17th ed. New York: McGraw-Hill Professional; 2008.]
The vascular supply is divided into anterior and posterior circulations. Clinical findings in stroke are determined by the location of the lesion(s) (Table 167-1), but the degree of collateral circulation may cause variations in the specific clinical symptoms and their severity.
TABLE 167-1Anterior and Posterior Circulation of the Brain ||Download (.pdf) TABLE 167-1 Anterior and Posterior Circulation of the Brain
|Circulation ||Major Arteries ||Major Regions of Brain Supplied |
|Anterior (internal carotid system) ||Ophthalmic ||Optic nerve and retina |
|Anterior cerebral ||Frontal pole |
|Anteromedial cerebral cortex |
|Anterior corpus callosum |
|Middle cerebral ||Frontoparietal lobe |
|Anterotemporal lobe |
|Posterior (vertebral system) ||Vertebral ||Brainstem |
|Posteroinferior cerebellar ||Cerebellum |
|Basilar ||Thalamus |