Ischemic strokes are classified by the underlying cause of the vascular occlusion. One of three main processes is usually operative: (i) atherosclerosis with superimposed thrombosis affecting large cerebral or extracerebral blood vessels, (ii) cerebral embolism, and (iii) occlusion of small cerebral vessels within the parenchyma of the brain. There are many other pathologic processes that lead to ischemic brain damage, not all associated with occlusion of cerebral vessels, including arterial dissection, inflammatory conditions such as vasculitis, thrombosis of cerebral veins and dural sinuses, in situ thrombosis of large or small cerebral vessels due to hypercoagulable conditions, vasospasm from any of several mechanisms, unusual types of embolic materials such as fat, tumor, cholesterol, and several unique diseases that involve the cerebral vasculature (see further on). Closely allied with ischemic strokes is the transient ischemic attack (TIA), a temporary neurologic deficit caused by a cerebrovascular disease that leaves no clinical or imaging trace. The causes of stroke are so numerous that the listing given in Table 33-1 offers only a guide to the remainder of this chapter. As helpful is knowledge of the major causes of stroke by each epoch of age, particularly in childhood and young adults, a subject taken up in a later section and summarized in Table 33-2.
The second broad category consists of hemorrhage, which occurs either within the substance of the brain, called intracerebral hemorrhage; or blood contained within the subarachnoid spaces, called subarachnoid hemorrhage. The causes of the first category are numerous and include chronic hypertension, coagulopathies that arise endogenously or because of anticoagulant medications, vascular malformations of the brain, cranial trauma, and hemorrhage that occurs within the area of an ischemic stroke. Subarachnoid hemorrhage has fewer fundamental causes, the most common being the rupture of a developmental aneurysm arising from the vessels of the circle of Willis, but also includes cerebral trauma and arteriovenous malformations, and rarer processes.
There are all gradations of severity, but in all forms of stroke the essential feature is abruptness with which the neurologic deficit develops—usually a matter of seconds that stamps the disorder as vascular. In its most severe form, the patient with a stroke becomes hemiplegic or even comatose—an event so dramatic that it had, in the past, been given vivid designations: apoplexy, cerebrovascular accident (CVA), or shock (colloquial). However, stroke is the preferred term. In its mildest form, a stroke may consist of a trivial and transient neurologic disorder insufficient for the patient even to seek medical attention. More often, there is an easily identifiable neurological deficit.