Effects of Extracranial Carotid Stenosis on Intracranial Blood Flow

Abstract

Background and Purpose— The hemodynamic effects of extracranial carotid stenosis on intracranial blood flow are not well characterized. We sought to determine the impact of degree of stenosis, stenosis length, and residual lumen on intracranial blood flow in patients with extracranial carotid stenosis. Methods— Carotid stenosis patients who had undergone both vessel flow rate measurements using quantitative magnetic resonance angiography and digital subtraction angiography were examined. The impact of the anatomic measurements of the stenosis relative to ipsilateral internal carotid artery (ICA) flow and ipsilateral-to-contralateral middle cerebral artery (MCA) flow ratio were assessed. Results— Forty-four patients (mean age, 67 years; 64% symptomatic) were included. Higher percentage stenosis and smaller residual lumen were associated with a significant decrease in ICA flow ( P <0.01 and 0.04, respectively). On multivariate analysis, percentage stenosis remained as the primary predictor of ICA flow ( P <0.001). MCA flow ratio was not significantly associated with percentage stenosis, stenosis length, or residual lumen. However, mean MCA flow ratio was significantly lower in symptomatic compared with asymptomatic patients (0.92 versus 1.22; P =0.001). In contrast, mean ICA flow ratio was similar among these 2 groups (0.55 versus 0.55; P =0.99). Conclusions— Percentage stenosis and residual lumen are significantly associated with ICA but not MCA flow, suggesting that local hemodynamic effects of carotid stenosis do not translate directly to distal vasculature, because intracranial flows can be maintained through collaterals. The lower MCA flow ratio in symptomatic patients highlights the potential importance of distal hemodynamics in symptomatic presentation.

Changes in Wall Shear Stress of Cerebral Arteriovenous Malformation Feeder Arteries After Embolization and Surgery

“…[6][7][8][13][14][15][16][17] Before any treatment, mean WSS among 48 feeder arteries in our study was significantly higher compared with the mean WSS in the contralateral vessel (29.7±12.0 dynes/cm 2 versus 23.3±11.0 dynes/ cm 2 ; P=0.007). This result reveals that cerebral AVMs are a high WSS pathology, which disputes Rossitti and Svendsen's hypothesis that WSS in arteries supplying AVMs is the same as in arteries within normal brain parenchyma.…”

Quantitative Assessment of Changes in Cerebral Arteriovenous Malformation Hemodynamics After Embolization

“…5,[8][9][10][11][12] We found that mean flow dropped on average by 29% after a single embolization session and by 75% at the end of all embolization sessions. Interestingly, the drop in flow per session did not correspond to occlusion of an intranidal fistula or the number of pedicles embolized in that single session, suggesting redistribution of flow through remaining compartments of the nidus in the setting of partial embolization, as posited by Kaspera et al 14 On the other hand, mean flow after completion of all embolization sessions correlated with both the total number of pedicles embolized and embolization of a high-flow fistula, with total pedicles embolized remaining predictive in the multivariate analysis.…”

“…This QMRA technique has been validated using in vitro and in vivo models and has demonstrated utility in the hemodynamic evaluation of cerebrovascular pathologies and interventions, including extracranial carotid artery stenosis, intracranial angioplasty/stenting, carotid endarterectomy, and extracranial-intracranial bypass. [8][9][10][11][12] Total AVM blood flow was derived based on the aggregate flow within the primary arterial feeders relative to flow in their contralateral counterparts, according to the following equation: …”

“…The mean number of pedicles embolized per session was 3 (range 1-8) and the mean total number of pedicles embolized was 8 (range [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] (Table 2). However, the total number of pedicles embolized (R 2 =0.64, P<0.001) and embolization of an intranidal fistula (R 2 =0.40, P=0.002) are each significantly associated with total decreased AVM flow after completion of all sessions of embolization.…”

Hemodynamic Features of Symptomatic Vertebrobasilar Disease

“…Similarly in subsequent analysis of patients with both anterior and posterior circulation intracranial stenosis from the WASID trial, angiographic collaterals had a marked influence on stroke risk, with good collaterals significantly reducing risk in those with severe stenosis 19 . Recent data from large vessel flow measurements in carotid disease further support the importance of regional flow by demonstrating that flow compromise in the distal territory measured in the middle cerebral artery territory was more frequently associated with symptomatic presentation, whereas flow decline in the internal carotid alone was not predictive 20 .…”