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Background and Purpose— Complex vascular anatomy might increase the risk of procedural stroke during carotid artery stenting (CAS). Randomized controlled trial evidence that vascular anatomy should inform the choice between CAS and carotid endarterectomy (CEA) has been lacking. Methods— One-hundred eighty-four patients with symptomatic internal carotid artery stenosis who were randomly assigned to CAS or CEA in the ICSS (International Carotid Stenting Study) underwent magnetic resonance (n=126) or computed tomographic angiography (n=58) at baseline and brain magnetic resonance imaging before and after treatment. We investigated the association between aortic arch configuration, angles of supra-aortic arteries, degree, length of stenosis, and plaque ulceration with the presence of ≥1 new ischemic brain lesion on diffusion-weighted magnetic resonance imaging (DWI+) after treatment. Results— Forty-nine of 97 patients in the CAS group (51%) and 14 of 87 in the CEA group (16%) were DWI+ (odds ratio [OR], 6.0; 95% confidence interval [CI], 2.9–12.4; P P =0.027) and the degree of the largest internal carotid artery angle (≥60° versus P =0.002) were both associated with DWI+, also after correction for age. No predictors for DWI+ were identified in the CEA group. The DWI+ risk in CAS increased further over CEA if the largest internal carotid artery angle was ≥60° (OR, 11.8; 95% CI, 4.1–34.1) than if it was P =0.035). Conclusions— Complex configuration of the aortic arch and internal carotid artery tortuosity increase the risk of cerebral ischemia during CAS, but not during CEA. Vascular anatomy should be taken into account when selecting patients for stenting. Clinical Trial Registration— URL: http://www.isrctn.com/ISRCTN25337470 . Unique identifier: ISRCTN25337470.

Background and Purpose— Stenting for symptomatic carotid stenosis (carotid artery stenting [CAS]) carries a higher risk of procedural stroke or death than carotid endarterectomy (CEA). It is unclear whether this extra risk is present both on the day of procedure and within 1 to 30 days thereafter and whether clinical risk factors differ between these periods. Methods— We analyzed the risk of stroke or death occurring on the day of procedure (immediate procedural events) and within 1 to 30 days thereafter (delayed procedural events) in 4597 individual patients with symptomatic carotid stenosis who underwent CAS (n=2326) or CEA (n=2271) in 4 randomized trials. Results— Compared with CEA, patients treated with CAS were at greater risk for immediate procedural events (110 versus 42; 4.7% versus 1.9%; odds ratio, 2.6; 95% CI, 1.9–3.8) but not for delayed procedural events (59 versus 46; 2.5% versus 2.0%; odds ratio, 1.3; 95% CI, 0.9–1.9; interaction P =0.006). In patients treated with CAS, age increased the risk for both immediate and delayed events while qualifying event severity only increased the risk of delayed events. In patients treated with CEA, we found no risk factors for immediate events while a higher level of disability at baseline and known history of hypertension were associated with delayed procedural events. Conclusions— The increased procedural stroke or death risk associated with CAS compared with CEA was caused by an excess of events occurring on the day of procedure. This finding demonstrates the need to enhance the procedural safety of CAS by technical improvements of the procedure and increased operator skill. Higher age increased the risk for both immediate and delayed procedural events in CAS, mechanisms of which remain to be elucidated. Clinical Trial Registration— URL: https://clinicaltrials.gov . Unique identifier: NCT00190398. URL: http://www.isrctn.com . Unique identifier: ISRCTN57874028. URL: http://www.isrctn.com . Unique identifier: ISRCTN25337470. URL: https://clinicaltrials.gov . Unique identifier: NCT00004732.