Relationship between diameter asymmetry of the anterior cerebral arteries of the Circle of Willis and asymmetry in diameters and blood flow of the upstream vasculature: preliminary results

Abstract

Both internal carotid arteries (ICA) distribute blood via the anterior (ACA) and middle (MCA) cerebral arteries to the anterior part of the brain. Asymmetry of the pre-communicating part (A1-segment) of the ACA is common and is related to intracranial aneurysm formation. It is unknown if A1 asymmetry is also related to blood flow changes in the dominant A1 segment and the ipsilateral ICA and MCA. This study aims to relate artery diameters of both ICAs, M1- segments MCA and A1-segments ACA to blood-flow distribution in 10 subjects with symmetric A1s versus 10 with asymmetric A1s. Diameter measurements of the ICA (C3 and C7 segments), M1 and A1-segments were performed manually on the time-of flight magnetic resonance angiography (TOF-MRA) using an in-house developed tool. 4D phase-contrast MR imaging (PC-MRI)datasets were analyzed using CAAS software. The asymmetric group had on average 43% (range 26–84) asymmetry of the A1-segments and this asymmetry was directly related to the right-left flow difference (R²=0.890). The asymmetric group also had increased diameters and blood-flow for all ICA, M1 and A1 segments on the dominant A1 side. In conclusion, this preliminary study showed that asymmetry in A1 diameter is directly associated with increased blood-flow in the ICA, MCA and ACA on the dominant side. Our findings should be confirmed in a larger population which will also help to find an ideal cut-off in asymmetry diameter measurement that reflects a statistically significant difference in blood flow and velocity.