Stroke is a medical emergency that occurs when there is a sudden interruption to the flow of blood to the brain, with the resulting loss of neurological function to the area of the brain affected. Stroke is a very common disease. One in six people will have a stroke over the course of their lifetime. It is the number one cause of disability, and the second cause of mortality worldwide, and therefore, involves a significant health care cost. There are two types of stroke. Ischemic stroke is the most common, comprising 80 percent of all strokes. It is due to an abstraction of a cerebellar artery by a thrombus or embolus, causing part of the brain to stop receiving blood. The cells of the brain do not receive the necessary nutrients, oxygen, and glucose. So, initially they stop working properly. If this lack of blood flow continues, a cerebral infarct occurs. Hemorrhagic stroke is less common, accounting for about 20 percent of all strokes. It occurs due to a rupture of a cerebral artery, and bleeding into the brain parenchyma, which affects the function of the part of the brain. In both cases, the symptoms can be similar and depend on the part of the brain that is affected. In ischemic stroke, there are multiple risk factors that predispose towards clot formation, including hypertension, diabetes, high cholesterol, smoking, sedentary lifestyle, and high alcohol intake. The most common causes of ischemic stroke are atherosclerosis, which affects the arterial wall forming plaques and clots, and cardiac embolism which involves thrombus formation inside the heart in patients with arrhythmias such as atrial fibrillation or valvular heart disease. Thrombus then embolize, and moves towards the brain. There are other less common causes such as clotting abnormalities, vasculitis or inflammation of the cerebellar arteries, and arterial dissection. Hemorrhagic strokes are caused mainly by hypertension, aneurysm or vascular malformations of the brain that may rupture, anticoagulant medication or even amyloid angiopathy that damages the arterial wall. We refer to a hemispheric stroke when the damaged area of the brain affects all or part of one of the hemispheres. The symptoms always manifest on the opposite side of the body from the brain region. So, if the right hemisphere is affected, the patient will have left-sided weakness affecting the face, arms and legs, altered sensation on the left side of the body, hemianopia or loss of the right visual field. The patient may also have agnosia or the inability to recognize half of their body and the impairment. Agnosia occurs when the non-dominant hemisphere is affected, which for most people is the right hemisphere. So, agnosia is usually associated with left-sided weakness. In contrast, if the stroke affects the left hemisphere, the patient will have reduced strength, sensation and vision on the right side. They usually have aphasia, which is the inability to say the correct words or to understand language. Aphasia occurs when the dominant hemisphere is affected, which in most people it's the left, but it can differ, especially in left-handed people. Meaning that aphasia is usually associated with right-sided weakness. These symptoms are often associated with gays or head deviation toward the side of the brain lesion. That is towards the opposite side from the affected side of the body. It is important to note that hemispheric strokes are often due to an occlusion in one of main cerebral arteries. In these cases, it cause the largest stroke with more severe neurological impairment. When a stroke is due to obstruction of a smaller arteries in the deeper part of the brain, this causes a lacunar stroke. In this situation, there may be weakness and altered sensation on one side of the body as well as dysarthria, or difficulty pronouncing words correctly, as if the patient had a numb tongue, or something in their mouth that prevented them from pronouncing correctly. But, unlike aphasia, they can say the appropriate word, and understand language. It is important to remember that a lacunar stroke affects the deep parts of the brain, where the neural tracts carry information related to movement and sensation. So, it never produces cortical syndromes, such as aphasia, agnosia, hemianopsia and gaze or head deviation, which are due to hemispheric strokes. When the stroke affects the posterior region of the brain, brainstem or cerebellum, the typical symptoms are sudden vertigo, double vision, diplopia, hemianopia, ataxia, or unstable walking, dysmetria or lack of coordination of an extremity, and even drowsiness, and reduced level of consciousness. Posterior strokes if extensive, have a high mortality, because the brain stem is a structure that controls vital functions such as heart rate, breathing, and conscious level. Lastly, there's an entity within stroke known as transient ischemic attack, or TIA. TIA refers to the onset of symptoms typically of a stroke, but which resolves spontaneously within 24 hours, usually in less than one hour. Up to 15 percent of patients who have an ischemic stroke have had a TIA in the days prior. But, often people do not think it is serious, and do not seek medical attention because the symptoms are transient, and they recover quickly. Although the symptom resolve, the situation is a medical emergency, and the patient needs urgent medical assessment as the risk of a stroke in the subsequent hours and days is high between five and 10 percent. This patient should be referred to the closest Stroke Center to have an urgent neurovascular study within the first 24 hours and start preventative measures
