Leptomeningeal collateral volume flow assessed by quantitative magnetic resonance angiography in large-vessel cerebrovascular disease

BACKGROUND/PURPOSE: Leptomeningeal collateral volume flow has not been previously quantified. Quantitative magnetic resonance angiography (QMRA) can determine flow in the large vessels of the intracranial circulation. METHODOLOGY: We reviewed consecutive QMRA studies performed between December 1, 2004 and August 30, 2005, for cases showing asymmetrically higher flow in a posterior cerebral artery (PCA) just distal to the origin of the posterior communicating artery ipsilateral to a hemodynamic middle cerebral artery (MCA) or internal carotid artery lesion. The mean, range, and standard deviation (SD) of the flow rate in the PCAs, MCAs, and PCA ipsilateral-contralateral difference were calculated. Ipsilateral and contralateral PCA flow rates were compared using the Student's t-test. RESULT: Sixteen studies met selection criteria. Mean age was 52 years (range 21-79) and 9 were female. MCA flow was below QMRA detection limits in 6 studies. Mean measurable ipsilateral MCA flow reduction was 84 mL/min (range 9-147, SD 51.4). Mean ipsilateral PCA flow was 118 mL/min (range 72-206, SD 38.5) and mean contralateral PCA flow was 68 mL/min (range 35-144, SD 30.5, P <.001); mean difference was 50 mL/min (range 10-93, SD 24.3). CONCLUSION: Leptomeningeal collateral flow can be assessed with QMRA and may be substantial.