Hemodynamic Parameters in the Parent Arteries of Unruptured Intracranial Aneurysms Depend on Aneurysm Size and Are Different Compared to Contralateral Arteries: A 7 Tesla 4D Flow MRI Study

Background Different Circle of Willis (CoW) variants have variable prevalences of aneurysm development, but the hemodynamic variation along the CoW and its relation to presence and size of unruptured intracranial aneurysms (UIAs) are not well known. Purpose Gain insight into hemodynamic imaging markers of the CoW for UIA development by comparing these outcomes to the corresponding contralateral artery without an UIA using 4D flow magnetic resonance imaging (MRI). Study Type Retrospective, cross‐sectional study. Subjects Thirty‐eight patients with an UIA, whereby 27 were women and a mean age of 62 years old. Field Strength/Sequence Four‐dimensional phase‐contrast (PC) MRI with a 3D time‐resolved velocity encoded gradient echo sequence at 7 T. Assessment Hemodynamic parameters (blood flow, velocity pulsatility index [vPI], mean velocity, distensibility, and wall shear stress [peak systolic (WSS MAX ), and time‐averaged (WSS MEAN )]) in the parent artery of the UIA were compared to the corresponding contralateral artery without an UIA and were related to UIA size. Statistical Tests Paired t ‐tests and Pearson Correlation tests. The threshold for statistical significance was P < 0.05 (two‐tailed). Results Blood flow, mean velocity, WSS MAX , and WSS MEAN were significantly higher, while vPI was lower, in the parent artery relative to contralateral artery. The WSS MAX of the parent artery significantly increased linearly while the WSS MEAN decreased linearly with increasing UIA size. Conclusions Hemodynamic parameters and WSS differ between parent vessels of UIAs and corresponding contralateral vessels. WSS correlates with UIA size, supporting a potential hemodynamic role in aneurysm pathology. Level of Evidence 2 Technical Efficacy Stage 2