Types of In-stent Stenosis After Flow-diversion: A Proposed Classification. (16th November 2020) - Monteiro, Andre
Abstract: INTRODUCTION: Flow diversion for treatment of intracranial aneurysms have gained wide acceptance. Clinical trials and retrospective series have observed different rates (0.3% to 18%) of in-stent stenosis (ISS) during follow-up of patients treated with flow-diverters (FD). In most cases, ISS has no clinical relevance and sometimes can be reversible overtime. Different patterns of stenosis seen on angiographic follow-up could represent distinct underlying mechanisms, which may impact aneurysm occlusion in different ways. There are no studies clarifying different ISS types. METHODS: We analyzed angiographies of patients treated with FDs. Any degree of stenosis between lumen and device strus was evaluated. Three main patterns were observed and described. RESULTS: In Negative Remodeling, device mesh is constrained symmetrically in its circumferential aspect, as the vessel loses both its inner and outer diameter. There is no gap between strut and lumen, observed by contrast filling adjacently to the FD. Possibly, it occurs secondary to vessel response to injury, when overstretching triggers inflammation and tissue remodeling. Neointimal Hyperplasia presents mild stenosis, without distortion of the mesh. There is thin gap between struts and lumen. Neointima development is described in cardiology as foreign-body reaction to metal struts, but it is not completely understood in flow-diverters yet. Endothelized Thrombus is a new concept proposed after studies with optimal coherence tomography (OCT) and histological correlation. The device mesh is in its original place, but a gap causing more significant stenosis is seen between struts and lumen. It's a plausible mechanism for most cases where this pattern is seen along with reversibility overtime, given that when thrombus resolves, the stenosis disappear. CONCLUSION: ISS after flow diversion likely occur secondary to a variety of mechanisms. Different patterns can have distinct mechanisms behind them, with more or less impact in aneurysm occlusion. It is also possible that these types of ISS occur simultaneously and share common points in pathophysiology. Further studies with sophisticated imaging, such as OCT, and consistent follow-up would be necessary to understand the origin these phenomena and define its role in aneurysm occlusion.