This constitutes a special type of infarction that follows cardiac arrest and other forms of prolonged hypotension or hypoxia. The most typical configuration, seen with imaging, is of widespread cortical infarction affecting also the deep nuclei, that is, the most metabolically active regions of the cerebral hemispheres. An important distinction is drawn between the concept of end-arterial distribution, the site of distal embolization, and the area of lowest flow between two or more end territories, which is compromised in any form of globally returned blood flow. In extreme cases of hypotension, there is global infarction of the brain accompanied by the clinical syndrome of brain death. In the case of reduced blood flow to the cerebral hemispheres, there is a tendency for regional infarctions to occur in the areas of lowest blood flow that lie between the major surface arteries, referred to metaphorically as a watershed infarction (which may not be apt as a watershed is a region of water collection).
Pure hypoxia-anoxia without hypotension produces another type of damage in areas susceptible to reduced oxygen delivery, mainly affecting the hippocampi; a
Korsakoff syndrome results. Most often, ischemic and hypoxic states coexist and produce complex patterns of cerebral damage. This topic is discussed fully in Chap. 39. The special problem of cerebral ischemia during cardiac surgery with the use of a bypass pump is discussed further on in the section “Stroke with Cardiac Surgery.”
This is a segmental, nonatheromatous, noninflammatory arterial disease of unknown etiology, largely occurring in middle-aged women. It is uncommon (0.5 percent of 61,000 arteriograms in the series of So et al) but is being reported with increasing frequency because of improved arteriographic techniques. In our experience, it has often been an incidental finding in asymptomatic individuals undergoing vascular imaging for other reasons. Approximately 10 percent of cases have been reported to be familial and a connection to a variant in the phosphatase and actin regulator 1 gene (PHACTR1) has been found in some patients.
First described in the renal artery by Leadbetter and Burkland in 1938, fibromuscular dysplasia is now known to affect other vessels including cervicocerebral ones. The internal carotid artery is involved most frequently, followed by the vertebral and cerebral arteries. The radiologic picture is of a series of transverse constrictions, giving the appearance of an irregular string of beads or a smooth tubular narrowing; it is observed bilaterally in the carotid arteries in up to75 percent of cases. Usually only the extracranial part of the artery is involved. A single transverse web that occupies a portion of the carotid lumen is probably a variant of the fibromuscular condition or could conceivably represent an entirely different static congenital process. In the series of Houser and colleagues, 42 of 44 patients were women and most were older than 50 years of age. All of the patients reported by So and coworkers were women, ranging in age from 41 to 70 years. Cerebral ischemia may be associated with the process but the rate of this complication has not been established; our impression is that it is low. In the study by Corrin and colleagues, among 79 untreated asymptomatic patients followed for an average of 5 years, 3 had a cerebral infarct 4 to 18 years after the initial diagnosis. Also, between 7 and 20 percent of affected individuals are found to have intracranial saccular aneurysms (rarely a giant aneurysm), which may be sources of subarachnoid hemorrhage, and up to 12 percent develop arterial dissections, as described below.