Stroke Pathophysiology, Etiology and Risk Factors

Stroke Pathophysiology, Etiology and Risk Factors


This presentation is on stroke, pathophysiology, etiology, and risk factors. At the end of this presentation, you should be able to define stroke and describe its underlying pathophysiology, understand the different etiological subtypes of stroke, and know the epidemiology and common modifiable risk factors for stroke. Stroke is classically defined as a sudden neurologic deficit of vascular etiology lasting more than 24 hours. However, with the advent of modern imaging studies, there are some modification to the definition. Patients with rapidly vanishing symptoms and imaging of an acute clinically relevant brain lesion are considered to have suffered from a stroke. A transient ischemic attack or TIA is a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia without acute infarction. There are two main types of stroke, ischemic stroke or cerebral infarction accounts for the majority of strokes, about 80% to 85%. This is caused by interruption of the blood supply to the brain or spinal cord, usually an occlusion by a thrombus or embolus. The cerebral arterial blood supply is usually involved. But uncommonly, the venous system is affected due to venous sinus thrombosis. Hemorrhagic stroke, or cerebral hemorrhage, accounts for about 10% to 15% of all strokes. This is caused by a rupture of a blood vessel. These may be related to hypertension, aneurysm, or arterial venous malformation. Hemorrhage may be inside a brain parenchyma, that is, intracerebral or outside the brain parenchyma, such as a subarachnoid hemorrhage. Both ischemic and hemorrhagic strokes can occur in the brain or the spinal cord. The etiology of ischemic stroke can be classified according to the pathologic mechanism involved. The pathology may be related to large vessel disease. This may be extracranial disease involving the common or internal carotid arteries or intracranial disease involving, for example, the middle cerebral and basilar arteries. Atherosclerosis is the usual underlying pathology causing plaque and thrombus formation, resulting in stenosis or narrowing of the blood vessel lumen. Another category of stroke is small vessel disease affecting arteries of small penetrating arterials supplying the deep subcortical and brain stem regions causing small areas of infarction sometimes referred as lacunar infarction. The underlying pathology is postulated to include microatheroma, lipohyalinosis, and fibrinoid necrosis. Cardioembolic stroke is due to a cardiac thrombus embolizing to cause cerebral arterial obstruction. Sources of cardioembolism include atrial fibrillation, mechanical prosthetic valves, poor cardiac ejection fraction, and valvular heart disease. Other known, but less common etiologies of ischemic stroke are autoimmune diseases, like systemic lupus erythematosus, hypercoagulable [INAUDIBLE] conditions, and arterial dissection. Next, we will discuss the etiology of hemorrhagic stroke. In primary hypertensive intracerebral hemorrhage, uncontrolled hypertension leads to weakening of arterial walls, causing Charcot-Bouchard aneurysms, which are prone to rupture causing intracerebral hemorrhage. The most common site is the basal ganglia due to involvement of the lenticulostriate branches of the middle cerebral artery. Abnormal dilatation of an arterial wall forming a secular aneurysm which can rupture causing subarachnoid, an intracerebral hemorrhage. Saccular aneurysms tend to occur along bifurcations of large cerebral arteries. Arterial venous malformations are abnormal connections between arteries and veins and are usually congenital. They can rupture causing cerebral hemorrhage, which is usually lobar and tends to affect younger individuals. Other etiologies of hemorrhagic stroke are vascular [INAUDIBLE], like amyloid angiopathy. These are more common among the elderly and the intracerebral hemorrhage seen in these cases are usually located more superficially in the lobar regions of the brain. We next move on to the epidemiology of stroke. This slide covers the non-modifiable risk factors of stroke. As one gets older, the risk of stroke increases. In demographically developed countries, the average age of stroke onset is 73 years, though it might be younger in less developed countries. Stroke risk doubles for each decade after age 55. Males have a slightly higher stroke incidence compared to females. Race is a non-modifiable risk factor with certain ethnicities predisposed to certain types of stroke. For example, small vessel arterial strokes are more common among Asians, and hypertensive bleeds are more common among Africans compared to Caucasians. A positive family history of stroke is also associated with increased risk of stroke. Some strokes subtypes are from genetic disorders, for example, CADASIL. There are a number of modifiable risk factors for ischemic stroke wherein hypertension is the most common and the most important one. Blood pressure of around 140 to 160 systolic and 90 to 94 diastolic increases the risk of stroke by 1.5 times while blood pressure of more than 160 systolic and 95 diastolic increases the risk by 3 to 4 times. Another common risk factor is diabetes mellitus. It increases risk of ischemic stroke by about two times independent of other associated risk. Dyslipidemia is another risk factor with one study showing for every 1 million mole per liter increase in total cholesterol, that is concurrent to a 5% increased risk of ischemic stroke. Atrial fibrillation, the most common cause of cardioembolic stroke, increases ischemic stroke risk by approximately 4 to 5 times. Acute myocardial infarction is also associated with 5% increased risk of ischemic stroke within the first two weeks of event with increased risk of 12% if complicated by presence of LV thrombus. Lifestyle factors are also very important as stroke risk factors. Cigarette smoking approximately doubles the risk of ischemic stroke compared to nonsmokers. Moderate alcohol consumption is also [INAUDIBLE] with lower incidence of ischemic stroke, but heavy drinkers have a higher chance of stroke. Obesity, which is increasing in prevalence, is also [INAUDIBLE] with coronary artery disease and ischemic stroke. Obese people tend to have a more sedentary lifestyle and eat a less healthy diet than non-obese people. Obesity increases risk of stroke with relative risk of 1.5 times. A sedentary lifestyle can also affect individual risk of stroke. Studies have shown that there are fewer strokes among more active patients compared to less active patients. Lastly, recreational use of drugs, such as cocaine and methamphetamine, is also associated with increased risk of stroke. Thank you for listening. We hope you have enjoyed learning about stroke through this presentation.

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