The LVIS device is a novel, self-expanding, braided stent that provides approximately 23% surface metal coverage. The smaller cell structure and higher metal coverage might result in better flow diversion compared with other currently available coil-assist stents. In this study, our experience with the LVIS stent demonstrated that the technology can be safely used to treat vertebral and basilar artery aneurysms, with good clinical outcomes and follow-up occlusion rates.
Angiographic results at follow-up
In this study, the immediate angiographic results demonstrated relatively lower rates of complete occlusion (50%); however, the progression to complete occlusion was quite satisfactory, with a high rate of 90.7% at the midterm follow-up. King et al.  reported the results of a literature review comparing the most widely-used intracranial stents (Neuroform and Enterprise) and found that initial and final complete occlusion was seen in 52.7% and 61.1%, respectively, of the patients treated with Neuroform stents. The final complete occlusion rate for the Enterprise stent was higher at follow-up (74.7%). In a recent prospective multicenter study of cerebral aneurysms treated with LVIS stents, the authors reported a total aneurysm occlusion rate of 91% on immediate postprocedure angiograms, and 92.4% at follow-up.  Cho et al.  reported that the complete obliteration rate of aneurysms undergoing LVIS-assisted coil embolization was 92.6% at the 6-month follow-up. However, these studies did not analyze the complete occlusion rate of vertebral and basilar artery aneurysms, separately. Wang et al. [8, 13] reported a series of patients treated with the LVIS device in vertebral and basilar artery aneurysms, with a complete occlusion rate in basilar artery aneurysms of 65% at 6.9 months of follow-up, and a complete occlusion rate in vertebral artery dissecting aneurysms of 76.7% at 8.3 months of follow-up. However, the follow-up periods might have been too short to identify a higher complete occlusion rate. In our study, the follow-up period was 12.5 months, which might explain why the complete occlusion rate at follow-up in our patients with vertebral and basilar artery aneurysms was higher than in previous studies. However, our patient cohort was relatively small, and the follow-up was still short.
Flow diversion has emerged as a treatment option for vertebral and basilar artery aneurysms, although this is currently an off-label use. Flow diversion stents are mechanistically unique in that they have low porosity with obvious hemodynamic effects on aneurysms, which results in parent vessel reconstruction and intra-aneurysmal thrombosis, resolving the aneurysm. Several studies reported that flow diversion is a feasible and effective treatment for aneurysms in the vertebral and basilar artery. However, flow diversion in vertebral and basilar artery aneurysms carries a high risk of periprocedural stroke, and might be associated with high overall mortality.[14–16] Numerous studies showed that LVIS stents also have flow diverting effects to minimize aneurysmal hemodynamics.[7, 17] Wang et al. quantified the flow diverting effects of the LVIS device, and compared the effect with the Pipeline device (Chestnut Medical Technologies, Menlo Park, CA) and the Enterprise stent. The authors found that the flow diverting effect of a single LVIS stent caused more flow reductions than the double-Enterprise stent but less than with a Pipeline device, and that double-LVIS stenting resulted in better flow diversion than a Pipeline device. However, the findings in that study were based on virtual models, and were not compared with clinical outcomes. Li et al.  selected two consecutive clinical cases to compare the hemodynamic aneurysmal changes after stent-assisted coiling between patients with the LVIS vs an Enterprise stent. The authors found that aneurysms treated with the LVIS device had greater reductions in blood flow velocity at the neck plane and within the aneurysm, and that such hemodynamic changes might explain the higher complete occlusion rate and lower recanalization rate in intracranial aneurysms treated with the LVIS device. The clinical results in our study also supported this potential mechanism. In immediate postprocedural angiography images, the complete and near-complete occlusion rate was 93.2% in patients treated with LVIS-assisted coiling, and the contrast residual time in the aneurysm was increased in all patients treated with LVIS stenting, alone. Importantly, 90.7% of the patients with follow-up images had stable or improved aneurysms.
Aneurysms in the vertebral and basilar artery are rare but are associated with substantial morbidity and mortality. The risk of rupture in vertebral and basilar artery aneurysms is also higher compared with aneurysms in the anterior circulation, and managing vertebral and basilar artery aneurysms is particularly challenging. In the International Study on Unruptured Intracranial Aneurysms guidelines, aneurysm location in the vertebral and basilar artery was a predictor of poor outcomes with endovascular treatment. The LVIS device is a novel, self-expanding stent, and limited data provide evidence supporting the use of the LVIS stent in the reconstructive treatment of vertebral and basilar artery aneurysms. In our study, the overall procedure-related complication rate was 9.6%, which is comparable to other studies evaluating LVIS stents in vertebral and basilar artery aneurysms.[8, 13] The risk of thromboembolic complications is relatively higher in vertebral and basilar artery aneurysms compared with anterior circulation aneurysms because the vertebral and basilar artery arteries have a rich collateral system, and a stent might disrupt the flow in collateral arteries. Incomplete stent expansion is a common cause of thromboembolic complications, especially when using wire-braided stents. In our study, the use of the LVIS device was feasible, with a high technical success rate of 98.4%. The stent failed to expand adequately in only one patient. Cho et al.  suggested that the LVIS stent might fold or twist in the tortuous anatomy and acute curve of the parent artery because of incomplete flaring of the braided closed-cell structure. In the study, the rate of thromboembolic complications following LVIS stenting was 4.8%, which is comparable to the rate of thromboembolic events of 4.9%, in a previous systematic review. However, the rate of thromboembolic complications is higher with flow diverter stents (11.0%).  The possible reason for the lower rate of thromboembolic complications with the LVIS stent might be that this stent offers better visualization, improved wall apposition, and less stent bending compared with other devices. Importantly, one patient in our study died of distal arterial hemorrhage. Previous studies have strongly suggested that excessive platelet inhibition was associated with an increased risk of hemorrhagic complications. [21, 22] However, platelet function testing was not performed in this study, and this testing might be helpful in the clinical determination of hemorrhagic risks before endovascular procedures. In our center, for the complex aneurysms located at vertebral and basilar artery (such as giant dissecting aneurysm, aneurysm involved vertebral-basilar junction, etc.), internal trapping technique was the initial treatment of choice for the lower recanalization rate. However, internal trapping might be not an appropriate treatment with several anatomic factors of the parent artery, including the involved important arterial branches, the dominance of the affected vertebral artery, and the insufficiency of the collateral blood supply. Flow diverter is an alternative treatment for the patients who were not suitable to internal trapping, for which treatment with flow diverter had a higher complete occlusion rate and better clinical outcome compared with conventional endovascular treatment. However, flow diverter applied in the vertebral and basilar artery was off-label for high risk of thromboembolic events. The clinicians should be cautious in the decision-making process regarding whether or when a flow diverter should be applied in the vertebral and basilar artery. Apart from the above treatments, stent-assisted coiling might be considered for the aneurysm of classic dissecting aneurysm and segmental ectasia, and had a favorable angiographic outcome. 
This study has several limitations. First, this was a single-center retrospective study, and might include an inherent bias in patient selection. Second, the small sample size and mid-term follow-up may have influenced our findings, and a prospective study with a larger sample size is needed for validation. Third, other techniques such as internal trapping or flow diverters should be compared in future studies to evaluate the safety and efficacy of the LVIS device in vertebral and basilar artery aneurysms. Fourth, platelet function monitoring during dual-antiplatelet therapy was not standard procedure in this study, and a multicenter prospective trial may best evaluate the clinical usefulness of platelet function testing.