***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background and Purpose — Contrast-enhanced magnetic resonance angiography ( CEMRA ) is among the newer noninvasive tests used for the evaluation of patients with carotid artery disease . Evidence supporting its utility in routine clinical practice is lacking . Methods — The results of CEMRA were compared with those of catheter angiography in 50 consecutive patients being evaluated for carotid endarterectomy ( CEA ) at a community hospital . Using indications for CEA based on published guidelines , we determined the rate of misclassification for surgery , sensitivity , specificity , and positive and negative predictive values . In addition , the interrater agreement ( & kgr ; score ) of CEMRA was compared with that of catheter angiography in the studied population and with interpretations provided by 2 blinded radiologists . Results — Compared with catheter angiography , 24 % ( 95 % CI , 12 % to 36 % ) of patients would have been misclassified for CEA on the basis of CEMRA results alone . CEMRA was associated with sensitivity of 92 % , specificity of 62 % , positive predictive value of 78 % , and negative predictive value of 89 % . When both CEMRA and duplex Doppler ultrasound were performed and the results were concordant , the misclassification rate decreased to 17 % ( 95 % CI , 2 % to 32 % ) . & kgr ; scores were similar for CEMRA and catheter angiography ( 0.72 and 0.75 , respectively ) . Conclusions — CEMRA was found to be highly sensitive for detection of surgically amenable carotid stenosis . & kgr ; scores for the interpretation of CEMRA and catheter angiography were similar . However , clinicians should be cautious when using CEMRA alone for surgical decision making in CEA c and i date s because a significant number of patients may be misclassified . The rate of misclassification is reduced when the results of CEMRA and duplex Doppler ultrasound are concordant BACKGROUND AND PURPOSE The estimated prevalence of intracranial atherosclerotic disease ( IAD ) in patients with stenosis of the extracranial internal carotid artery ( ICA ) varies between 20 % and 50 % . The benefits of carotid endarterectomy ( CE ) in patients with both IAD and symptomatic extracranial ICA stenosis are uncertain . METHODS The association between IAD and other vascular risk factors and with the risk of stroke at 3 years were studied in patients with symptomatic extracranial ICA stenosis who participated in the North American Symptomatic Carotid Endarterectomy Trial ( NASCET ) . Since the NASCET protocol excluded severe IAD , only a modest number of patients in this category could be studied . RESULTS IAD was observed in one third of the patients . In medically treated patients , the relative risk of stroke associated with IAD varied from 1.3 ( 95 % CI , 0.9 to 1.9 ) with extracranial ICA stenosis of < 50 % to 1.8 ( 95 % CI , 1.1 to 3.2 ) with 85 % to 99 % ICA stenosis . In contrast , IAD did not affect the risk of stroke among surgically treated patients . To prevent 1 stroke ipsilateral to the symptomatic ICA stenosis over 3 years in patients who have also IAD , 12 patients with 50 % to 69 % , 5 patients with 70 % to 84 % , and 3 patients with 85 % to 99 % ICA stenosis have to undergo CE . In patients without IAD these numbers are 26 , 7 , and 6 , respectively . CONCLUSIONS IAD is an independent risk factor for subsequent stroke in medically treated patients with symptomatic ICA stenosis . CE reduces this risk . The additional risk imposed by IAD in medically treated patients enhances the value of CE in patients with moderate symptomatic extracranial ICA stenosis . Detection of IAD , requiring angiography , is an important prelude to planning CE in symptomatic patients with moderate extracranial ICA stenosis BACKGROUND AND PURPOSE The risk of ischemic stroke distal to an atherothrombotic carotid stenosis increases with the degree of stenosis . The main mechanism of stroke is thought to be embolism from fissured or ruptured plaque , but there are few published data on the relationship between plaque morphology and severity of stenosis and their independent effects on the risk of ischemic stroke . We sought to determine the interrelation between plaque surface morphology , degree of carotid stenosis , and the risk of ipsilateral ischemic stroke . METHODS Severity of stenosis and plaque surface morphology were assessed on angiograms of the symptomatic carotid artery in 3007 patients in the European Carotid Surgery Trial and were related to baseline clinical characteristics , pathological characteristics of plaques examined at endarterectomy , and the risks of carotid territory ipsilateral ischemic stroke and other vascular events on follow-up . RESULTS The early risk of ipsilateral ischemic stroke on medical treatment was closely related to the degree of carotid stenosis . However , the initial degree of carotid stenosis was not predictive of strokes occurring > 2 years after r and omization . Angiographic plaque surface irregularity and plaque surface thrombus at endarterectomy increased in frequency as the degree of stenosis increased ( both P<0.0001 ) . However , the degree of stenosis was still predictive of the 2-year risk of stroke on medical treatment after correction for plaque surface irregularity . Angiographic plaque surface irregularity was an independent predictor of ipsilateral ischemic stroke on medical treatment at all degrees of stenosis ( hazard ratio=1.80 ; 95 % CI , 1 . 14 to 2.83 ; P=0.01 ) . This relationship was maintained when the analysis was confined to strokes occurring > 2 years after r and omization ( hazard ratio=2.75 ; 95 % CI , 1.30 to 5.80 ; P=0.01 ) . Neither the degree of stenosis nor plaque surface irregularity was predictive of the " background " stroke risk after endarterectomy or the risk of nonstroke vascular events . CONCLUSIONS Angiographic plaque surface irregularity is associated with an increased risk of ipsilateral ischemic stroke on medical treatment at all degrees of stenosis . The increase in stroke risk with degree of stenosis is partly accounted for by the parallel increase in plaque surface irregularity and thrombus formation , but the degree of narrowing of the vessel lumen is still an independent predictor of ischemic stroke within 2 years of presentation BACKGROUND AND PURPOSE Blood supply through collateral pathways improves regional cerebral blood flow and may protect against ischemic events . The effect of collaterals on the risk of stroke and transient ischemic attack ( TIA ) , in the presence of angiographic severe internal carotid artery ( ICA ) stenosis , was assessed . METHODS Angiographic collateral filling through anterior communicating and posterior communicating arteries and retro grade filling through ophthalmic arteries were determined in all patients at entry into the North American Symptomatic Carotid Endarterectomy Trial .  Kaplan-Meier event-free survival analyses were performed on 339 medically treated and 342 surgically treated patients . RESULTS The presence of collaterals supplying the symptomatic ICA increased with severity of stenosis . Two-year risk of hemispheric stroke in medically treated patients with severe ICA stenosis was reduced in the presence of collaterals : 27.8 % to 11.3 % ( P=0.005 ) . Similar reductions were observed for hemispheric TIA ( 36.1 % versus 19.1 % ; P=0.008 ) and disabling or fatal strokes ( 13.3 % versus 6.3 % ; P=0.11 ) . For surgically treated patients , the perioperative risk of hemispheric stroke was 1.1 % in the presence of collaterals versus 4 . 9 % when absent . The 2-year stroke risks for surgical patients with and without collaterals were 5.9 % versus 8.4 % , respectively . Neither comparison in the surgical group was statistically significant . The observed reductions were independent of the degree of ICA stenosis and other vascular risk factors . CONCLUSIONS Collaterals are associated with a lower risk of hemispheric stroke and TIA , both long term and perioperatively . Angiographic identification of collaterals assists in identifying patients with severe ICA stenosis at lower risk of stroke and TIA 
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A systematic review of prospect i ve studies of the risks of CAA in patients with cerebrovascular disease reported a 0.1 % risk of death and a 1.0 % risk of permanent neurological sequelae.3 More recent studies have reported lower risks in both academic centers and community hospitals,4 but many centers have already adopted a policy of operating on the basis of DU alone.5 The main advantage of DU over CAA is the absence of a procedural risk .
Given that the risk of stroke shortly after presentation with symptomatic carotid stenosis and