Hemodynamic Differences Observed between Growing and Stable Symmetric MCA Bifurcation Aneurysms

Introduction: The analysis of symmetric aneurysms can control for genetic differences in studies of aneurysm growth. This study aims to evaluate the differences in hemodynamic flow between growing and stable aneurysms symmetrically located at the middle cerebral artery (MCA) bifurcation. Hypothesis: Differences in the hemodynamic flow exist between growing and stable symmetric aneurysms at the MCA bifurcation. Methods: 6 patients with symmetric pairs of MCA bifurcation aneurysms were followed with CTA imaging for a mean of 19.82 ± 7.68 months, across 2.67 ± 0.52 imaging scans. In three patients both aneurysms were stable, while in three others one of the aneurysms exhibited growth. 16 computational flow simulations of the complete Circle of Willis, each including a pair of symmetric aneurysms, were run based on the CTA imaging studies. Blood flow at the neck, body, and dome of each aneurysm was analyzed. Welch’s t-test was used to compare growing and stable groups. Results: The mean diameters were 4.46±2.29 mm for the growing aneurysms and 4.24±1.99 mm for the stable aneurysms (p=0.8). No significant difference in wall shear stress (WSS) was found between growing and stable aneurysms (p=0.14). However, the growing aneurysms exhibited a significantly higher neck pulsatility index (PI) (1.33±0.27 vs 1.02±0.52, p=0.05) and a lower body PI (1.04±0.41 vs 1.69±0.76, p<0.01). Stable aneurysms in patients with a growing symmetric aneurysm had significantly lower dome PI (1.61±0.32 vs. 2.56±1.26, p=0.01) and overall higher WSS (p=0.02) (5.49±4.42 vs. 3.16±3.54) than bilaterally stable aneurysms. Conclusion: Stable aneurysms with symmetric growing aneurysms share similar hemodynamic characteristics and may be at risk for future growth. In general, interpatient aneurysm hemodynamic differences were more significant than intrapatient differences. Such patient-specific differences may arise from the tortuosity of the cerebral vascular tree.