Abstract TP130: Age-Adjusted Normative Blood Flow in Major Cerebral Vessels: Implications for Assessment of Cerebrovascular Occlusive Disease

Abstract

Objective: We have previously demonstrated an effect of age and Circle of Willis anatomic variants on individual major cerebral vessel flow rates, using quantitative magnetic resonance angiography (QMRA). We have now sought to establish normative flow ranges which could serve as clinically useful benchmarks for evaluating the hemodynamics of large vessel cerebrovascular occlusive disease. Methods: 326 healthy adult volunteers with no history of cerebrovascular disease underwent QMRA of cerebral vessels. Flows were measured bilaterally in the internal carotid artery (ICA), middle cerebral artery (MCA), anterior cerebral artery (ACA) A1 and A2 segments, posterior cerebral artery (PCA), basilar artery (BA), and vertebral artery (VA). Both individual vessel flow in ml/min, and indexed to total cerebral flow (TCBF=ICAs + VAs) was examined in relation to age and vascular anatomy, and percentile thresholds for normative flow were determined. Results: The volunteers ranged from 18 to 84 (mean 48) years old, with 48% female. All individual vessel flows declined with age (P<0.01), with TCBF on average 3ml/min/year lower. When individual vessel flow was indexed to TCBF, the age effect was neutralized (as demonstrated for left MCA flow in figure). Although anatomic variations, such as fetal PCA or hypoplastic A1 continued to have a significant impact on indexed flow in vessels proximal to the circle of Willis (ICA and BA), distal vessels revealed less variability, allowing percentile distributions of normative flow to be created. Conclusions: Indexing individual flows to TCBF allows age-adjusted normative ranges to be defined by percentile categories. Definition of these ranges may allow examination of the hemodynamic effect of cerebrovascular occlusive disease, although it remains to be examined if specific percentile thresholds for individual distal vessel flow will be a useful predictor of increased hemodynamic stroke risk.