surrounding areas of severe ischemia, which may still be salvageable due to collateral flow. hemorrhagic hemorrhagic strokes are classified based on their underlying pathology. some causes of hemorrhagic stroke are hypertensive hemorrhage, ruptured aneurysm, ruptured av fistula, transformation of prior ischemic infarction, and drug-induced bleeding. they result in tissue injury by causing compression of tissue from an expanding hematoma or hematomas. in addition, the pressure may lead to a loss of blood supply to affected tissue with resulting infarction, and the blood released by brain hemorrhage appears to have direct toxic effects on brain tissue and vasculature. inflammation contributes to the secondary brain injury after hemorrhage. diagnosis a ct showing early signs of a middle cerebral artery stroke with loss of definition of the gyri and grey white boundary dense artery sign in a patient with middle cerebral artery infarction shown on the left. right image after 7 hours. stroke is diagnosed through several techniques: a neurological examination (such as the nihss), ct scans (most often without contrast enhancements) or mri scans, doppler ultrasound, and arteriography. the diagnosis of stroke itself is clinical, with assistance from the imaging techniques. imaging techniques also assist in determining the subtypes and cause of stroke. there is yet no commonly used blood test for the stroke diagnosis itself, though blood tests may be of help in finding out the likely cause of stroke. in deceased people, an autopsy of stroke may help establishing the time between stroke onset and death. physical examination a physical examination, including taking a medical history of the symptoms and a neurological status, helps giving an evaluation of the location and severity of a stroke. it can give a standard score on e.g., the nih stroke scale. imaging for diagnosing ischemic (blockage) stroke in the emergency setting: ct scans (without contrast enhancements) sensitivity= 16% (less than 10% within first 3 hours of symptom onset) specificity= 96% mri scan sensitivity= 83% specificity= 98% for diagnosing hemorrhagic stroke in the emergency setting: ct scans (without contrast enhancements) sensitivity= 89% specificity= 100% mri scan sensitivity= 81% specificity= 100% for detecting chronic hemorrhages, an mri scan is more sensitive. for the assessment of stable stroke, nuclear medicine scans such as single-photon emission computed tomography (spect) and positron emission tomography–computed tomography (pet/ct) may be helpful. spect documents cerebral blood flow, whereas pet with an fdg isotope shows cerebral glucose metabolism. ct scans may not detect an ischemic stroke, especially if it is small, of recent onset, or in the brainstem or cerebellum areas (posterior circulation infarct). mri is better at detecting a posterior circulation infarct with diffusion-weighted imaging. a ct scan is used more to rule out certain stroke mimics and detect bleeding. the presence of leptomeningeal collateral circulation in the brain is associated with better clinical outcomes after recanalization treatment. cerebrovascular reserve capacity is another factor that affects stroke outcome – it is the amount of increase in cerebral blood flow after a purposeful stimulation of blood flow by the physician, such as by giving inhaled carbon dioxide or intravenous acetazolamide. the increase in blood flow can be measured by pet scan or transcranial doppler sonography. however, in people with obstruction of the internal carotid artery of one side, the presence of leptomeningeal collateral circulation is associated with reduced cerebral reserve capacity. underlying cause 12-lead ecg of a patient with a stroke, showing large deeply inverted t-waves. various ecg changes may occur in people with strokes and other brain disorders. when a stroke has been diagnosed, various other studies may be performed to determine the underlying cause. with the current treatment and diagnosis options available, it is of particular importance to determine whether there is a peripheral source of emboli. test selection may vary since the cause of stroke varies with age, comorbidity and the clinical presentation. the following are commonly used techniques: an ultrasound/doppler study of the carotid arteries (to detect carotid stenosis) or dissection of the precerebral arteries; an electrocardiogram (ecg) and echocardiogram (to identify arrhythmias and resultant clots in the heart which may spread to the brain vessels through the bloodstream); a holter monitor study to identify intermittent abnormal heart rhythms; an angiogram of the cerebral vasculature (if a bleed is thought to have originated from an aneurysm or arteriovenous malformation); blood tests to determine if blood cholesterol is high, if there is an abnormal tendency to bleed, and if some rarer processes such as homocystinuria might be involved. for hemorrhagic strokes, a ct or mri scan with intravascular contrast may be able to identify abnormalities in the brain arteries (such as aneurysms) or other sources of bleeding, and structural mri if this shows no cause. if this too does not identify an underlying reason for the bleeding, invasive cerebral angiography could be performed but this requires access to the bloodstream with an intravascular catheter and can cause further strokes as well as complications at the insertion site and this investigation is therefore reserved for specific situations. if there are symptoms suggesting that the hemorrhage might have occurred as a result of venous thrombosis, ct or mri venography can be used to examine the cerebral veins. misdiagnosis among people with ischemic strokes, misdiagnosis occurs 2 to 26% of the time. a "stroke chameleon" (sc) is stroke which is diagnosed as something else. people not having a stroke may also be misdiagnosed as a stroke. giving thrombolytics (clot-busting) in such cases causes intracerebral bleeding 1 to 2% of the time, which is less than that of people with strokes. this unnecessary treatment adds to health care costs. even so, the aha/asa guidelines state that starting intravenous tpa in possible mimics is preferred to delaying treatment for additional testing. women, african-americans, hispanic-americans, asian and pacific islanders are more often misdiagnosed for a condition other than stroke when in fact having a stroke. in addition, adults under 44 years of age are seven times more likely to have a stroke missed than are adults over 75 years of age. this is especially the case for younger people with posterior circulation infarcts. some medical centers have used hyperacute mri in experimental studies for persons initially thought to have a low likelihood of stroke. and in some of these persons, strokes have been found which were then treated with thrombolytic medication. prevention given the disease burden of strokes, prevention is an important public health concern. primary prevention is less effective than secondary prevention (as judged by the number needed to treat to prevent one stroke per year). recent guidelines detail the evidence for primary prevention in stroke. in those who are otherwise healthy, aspirin does not appear beneficial and thus is not recommended. in people who have had a myocardial infarction or those with a high cardiovascular risk, it provides some protection against a first stroke. in those who have previously had a stroke, treatment with medications such as aspirin, clopidogrel, and dipyridamole may be beneficial. the u.s. preventive services task force (uspstf) recommends against screening for carotid artery stenosis in those without symptoms. risk factors the most important modifiable risk factors for stroke are high blood pressure and atrial fibrillation although the size of the effect is small; 833 people have to be treated for 1 year to prevent one stroke. other modifiable risk factors include high blood cholesterol levels, diabetes mellitus, end-stage kidney disease, cigarette smoking (active and passive), heavy alcohol use, drug use, lack of physical activity, obesity, processed red meat consumption, and unhealthy diet. smoking just one cigarette per day increases the risk more than 30%. alcohol use could predispose to ischemic stroke, as well as intracerebral and subarachnoid hemorrhage via multiple mechanisms (for example, via hypertension, atrial fibrillation, rebound thrombocytosis and platelet aggregation and clotting disturbances). drugs, most commonly amphetamines and cocaine, can induce stroke through damage to the blood vessels in the brain and acute hypertension. migraine with aura doubles a person's risk for ischemic stroke. untreated, celiac disease regardless of the presence of symptoms can be an underlying cause of stroke, both in children and adults. high levels of physical activity reduce the risk of stroke by about 26%. there is a lack of high quality studies looking at promotional efforts to improve lifestyle factors. nonetheless, given the large body of circumstantial evidence, best medical management for stroke includes advice on diet, exercise, smoking and alcohol use. medication is the most common method of stroke prevention; carotid endarterectomy can be a useful surgical method of preventing stroke. blood pressure high blood pressure accounts for 35–50% of stroke risk. blood pressure reduction of 10 mmhg systolic or 5 mmhg diastolic reduces the risk of stroke by ~40%. lowering blood pressure has been conclusively shown to prevent both ischemic and hemorrhagic strokes. it is equally important in secondary prevention. even people older than 80 years and those with isolated systolic hypertension benefit from antihypertensive therapy. the available evidence does not show large differences in stroke prevention between antihypertensive drugs—therefore, other factors such as protection against other forms of cardiovascular disease and cost should be considered. the routine use of beta-blockers following a stroke or tia has not been shown to result in benefits. blood lipids high cholesterol levels have been inconsistently associated with (ischemic) stroke. statins have been shown to reduce the risk of stroke by about 15%. since earlier meta-analyses of other lipid-lowering drugs did not show a decreased risk, statins might exert their effect through mechanisms other than their lipid-lowering effects. diabetes mellitus diabetes mellitus increases the risk of stroke by 2 to 3 times. while intensive blood sugar control has been shown to reduce small blood vessel complications such as kidney damage and damage to the retina of the eye it has not been shown to reduce large blood vessel complications such as stroke. anticoagulation drugs oral anticoagulants such as warfarin have been the mainstay of stroke prevention for over 50 years. however, several studies have shown that aspirin and other antiplatelets are highly effective in secondary prevention after a stroke or transient ischemic attack. low doses of aspirin (for example 75–150 mg) are as effective as high doses but have fewer side effects; the lowest effective dose remains unknown. thienopyridines (clopidogrel, ticlopidine) might be slightly more effective than aspirin and have a decreased risk of gastrointestinal bleeding, but are more expensive. both aspirin and clopidogrel may be useful in the first few weeks after a minor stroke or high risk tia. clopidogrel has less side effects than ticlopidine. dipyridamole can be added to aspirin therapy to provide a small additional benefit, even though headache is a common side effect. low-dose aspirin is also effective for stroke prevention after having a myocardial infarction. those with atrial fibrillation have a 5% a year risk of stroke, and this risk is higher in those with valvular atrial fibrillation. depending on the stroke risk, anticoagulation with medications such as warfarin or aspirin is useful for prevention. except in people with atrial fibrillation, oral anticoagulants are not advised for stroke prevention—any benefit is offset by bleeding risk. in primary prevention, however, antiplatelet drugs did not reduce the risk of ischemic stroke but increased the risk of major bleeding. further studies are needed to investigate a possible protective effect of aspirin against ischemic stroke in women. surgery carotid endarterectomy or carotid angioplasty can be used to remove atherosclerotic narrowing of the carotid artery. there is evidence supporting this procedure in selected cases. endarterectomy for a significant stenosis has been shown to be useful in preventing further strokes in those who have already had one. carotid artery stenting has not been shown to be equally useful. people are selected for surgery based on age, gender, degree of stenosis, time since symptoms and the person's preferences. surgery is most efficient when not delayed too long—the risk of recurrent stroke in a person who has a 50% or greater stenosis is up to 20% after 5 years, but endarterectomy reduces this risk to around 5%. the number of procedures needed to cure one person was 5 for early surgery (within two weeks after the initial stroke), but 125 if delayed longer than 12 weeks. screening for carotid artery narrowing has not been shown to be a useful test in the general population. studies of surgical intervention for carotid artery stenosis without symptoms have shown