Flow diverting stent for the treatment of cerebral aneurysms

Abstract

The use of flow diverters (FD) in treatment of cerebral aneurysm utilises the flow dynamics effect of stenting the parent blood vessel harbouring the aneurysm. It provides an alternative treatment for difficult aneurysms and relies on an entirely different mechanism compared to conventional treatment using detachable coils or open clipping. The underlying hemodynamic changes induced by FD stent, the clinical factors relevant to the treatment success or complication are incompletely understood. The objective of this candidate’s studies are to investigate the clinical, anatomical and hemodynamic factors that may affect the efficacy and safety of flow-diverting stent treatment in aneurysms. The literature was systemically reviewed for published studies describing the clinical outcomes of intracranial aneurysms treated with the first-generation FD, and that of the secondgeneration surface-modified FD. A retrospective case series in the candidate’s center was performed to study the early experience with FD in this candidate’s center was performed to explore risk factors of FD treatment failure. To understand the underlying flow dynamics before and after FD treatment in cases of treatment success and failure, computational fluid dynamics (CFD) and phantom aneurysm flow models were deployed. Using CFD and the flow model experiment, fetal and non-fetal configuration of posterior communicating artery aneurysms treated with FD was simulated, and compared with that of side-wall aneurysms. The long-term outcome of FD-treated aneurysms was reported, and the management strategies of FD treatment failures were discussed. The review of the literature and the single-center retrospective study identified that between 15-20% of aneurysms are refractory to FD treatment. The application of CFD technique on FD-treated aneurysm was validated with patient-specific phantom aneurysm models of various configuration and Doppler ultrasonography. This platform was further applied to identify flow parameters associated with FD success. It was found that the FD placement dramatically reduced the volume flow rate within the aneurysm sac, and increased the contrast turnover time in the aneurysm. These parameters appeared to correlate with the time to aneurysm obliteration observed clinically. Furthermore, by experimentally controlling the relative blood flow in the branches of a bifurcation aneurysm located in the posterior communicating segment of the ICA, it was demonstrated that the higher the flow rate of the jailed side-branch (i.e. fetal posterior communicating artery configuration), the lesser is the flow diversion effect observed in the aneurysm. Finally, the clinical outcome of these FD treatment failure was satisfactory despite conservative treatment, with a substantial portion progressing to obliteration after a prolonged period (up to 5 years) of observation. The candidate’s studies demonstrated that FD is an effective treatment for intracranial aneurysms. Clinical and anatomical factors, such as old age and fetal posterior communicating artery aneurysms are identified as risk factors of treatment failure. The underlying flow mechanisms of FD failures were explored with computational fluid dynamics simulation and aneurysm flow models. The ongoing development of second-generation FD, as well as the ability to do patient-specific treatment prediction based on individual flow parameters and aneurysm configuration may further improve the efficacy profile of FD in the future.