Indefinite future of complex intracranial aneurysm underwent extracranial-intracranial bypass without aneurysm trapping: a pilot reports of 15 cases and hemodynamic analysis of 4D flow MRI.

Although limited to case report, the role of extracranial-intracranial bypass without aneurysm trapping in resolving complex intracranial aneurysms (CIAs) remained unclear. The aim was to investigate clinical and hemodynamic features of CIAs underwent cerebral revascularization without aneurysm trapping. To the authors' knowledge, this was the first and largest series reported to date. The author prospectively recruited patients with CIAs not passing balloon occlusion test (BOT) or harboring important perforators from Jan. 2019 to Dec 2022. Cerebral revascularization without aneurysm trapping was performed, of which four-dimensional flow (4D-flow) MRI and computational fluid dynamics (CFD) based on CT angiography were utilized. The patients' demographic information and clinical course were obtained from reviewing medical records. Of 15 cases enrolled, CIAs disappeared, unchanged, and enlarged in 4, 8, and 3 cases. The 4D-flow results showed donor vessel had a trend of first increasing and then decreasing in flow and velocity after bypass, with a turning point (TP) that might occur one week after revascularization. The velocity and flow of parent artery (PA) after TP was discrepant with a decrease tendency for aneurysm disappeared, but an increase tendency for aneurysm enlarged. For cases with aneurysm disappeared, CFD analysis revealed postoperative streamline velocity and wall shear (WS) of aneurysm decreased significantly compared to preoperative values. Otherwise, streamline velocity and WS of aneurysm still existed or even increased. Cerebral revascularization without aneurysm trapping was not an ideal option for CIAs, achieving hemodynamic TP of postoperative one week and an uncertain future.