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Background: The features of intracranial arteries in patients with Moyamoya disease (MMD) have been widely investigated. However, the MR characteristics of extracranial internal carotid artery (EICA) and their effect on outcomes of revascularization treatment are not fully understood. Purpose: To investigate the characteristics of EICA and their relationship with outcomes of revascularization treatment in adult patients with MMD based on higher‐resolution MRI (HRMRI). Study Type: Prospective interventional outcomes. Subjects: Two hundred eighty‐eight consecutive patients with MMD (mean age: 43.7 ± 11.2 years; 140 male). Field Strength/Sequence: Turbo inversion recovery magnitude T1‐weighted imaging and turbo spin echo (TSE) T2‐weighted imaging, three‐dimensional time‐of‐flight MR angiography, T2‐fluid attenuated inversion recovery, and 3D T1‐SPACE vessel wall imaging at 3.0 T. Assessment: The HRMRI characteristics of EICA were determined. The relationship between the characteristics of EICA (proximal stenosis, diffuse wall thickening, carotid plaques, and luminal thrombosis) and stroke outcomes of revascularization treatment in patients with MMD was analyzed. The discriminative ability of EICA characteristics in combination with intracranial carotid artery features (involvement of vessel segments, bilateral involvement, and Suzuki stage) to determine stroke outcomes was compared with that of intracranial artery features alone during a mean 8.0 months follow‐up period. Statistical Tests: Cox proportional hazards models and Kaplan–Meier curves to calculate the hazard ratios (HRs) for stroke with 95% confidence intervals (CIs). Area under the receiver operating characteristic curve (AUC) for assessing discriminative performance. A P value <0.05 was considered statistically significant. Results: During a mean 8.0 ± 2.2 months follow‐up, of the 288 participants, 137 had proximal stenosis (47.6%), 106 had diffuse wall thickening (36.8%), 60 had carotid plaques (20.8%), and 27 had luminal thrombosis (9.4%) of EICA. Of these features, proximal stenosis (HR = 2.86; 95% CI = 1.13–7.29) and diffuse wall thickening (HR = 2.62; 95% CI = 1.16–5.94) of EICA were significantly associated with stroke after surgery, before and after adjusting for confounding factors. In discriminating the stroke outcomes after surgery, combining characteristics of EICA with features of intracranial arteries resulted in a significant incremental improvement (DeLong test, P < 0.05) in the AUC over that obtained with features of intracranial arteries alone (AUC: 0.73 vs. 0.60–0.64). Conclusion: Proximal stenosis and diffuse wall thickening of EICA were significantly associated with stroke outcomes after surgery in patients with MMD. Our findings suggest that understanding the characteristics of EICA has added value for intracranial vessels in predicting future events after surgery in patients with MMD. Evidence Level: 2 Technical Efficacy: Stage 4 [ABSTRACT FROM AUTHOR]

Background: Little is known about the association between stroke and imaging and clinical features in conservatively treated patients with moyamoya disease (MMD). Purpose: To investigate independent risk factors for stroke in conservatively treated patients with MMD during a long‐term follow‐up. Study Type: Prospective study. Subjects: One hundred sixty conservatively managed patients with MMD (median age 46 years, 89 male). Field Strength/Sequence: Time of flight, turbo inversion recovery magnitude T1WI, turbo spin echo (TSE) T2WI, echo‐planar imaging DWI, T2‐fluid attenuated inversion recovery, dynamic susceptibility contrast‐magnetic resonance imaging, and pre‐ and post‐contrast 3D TSE T1WI sequences at 3.0 Tesla. Assessment: Patients were assessed at baseline and followed yearly. Ischemic and hemorrhagic stroke incidence rates were determined. Multiple demographic, clinical (modified Rankin score [mRS]), and cerebral imaging (cerebral blood volume [CBV] and concentric enhancement of arterial wall) factors at baseline were considered as potential predictors of stroke during the follow‐up period. Statistical Tests: Univariable and multivariable Cox proportional hazards models to calculate the hazard ratios (HRs) and corresponding 95% confidence interval (CI) for stroke. Cumulative risk of stroke was estimated by the Kaplan–Meier product‐limit method. A P value <0.05 was considered statistically significant. Results: The median follow‐up duration was 47 months. During the follow‐up period, 18 (11.25%) patients experienced stroke events (13 [8.13%] ischemic, 5 [3.12%] hemorrhagic). Univariable analysis showed that 11 factors were significantly associated with stroke. After adjustment for clinical characteristics, multivariable analysis showed that mRS score ≥3 (HR, 1.99; 95% CI, 1.26–3.14), decreased CBV (HR, 5.31; 95% CI, 2.32–12.13), and concentric enhancement of the arterial wall (HR, 4.16; 95% CI, 1.55–11.15) were significantly associated with stroke. Data Conclusion: Decreased CBV, mRS score ≥ 3, and concentric enhancement of the arterial wall were significantly associated with increased incidence of stroke in conservatively treated MMD. Evidence Level: 2 Technical Efficacy: Stage 4 [ABSTRACT FROM AUTHOR]