The Gateway Balloon-Wingspan stent system has shown good recent results in the clinical use of symptomatic intracranial artery stenosis in North America and Europe, and this has been confirmed in clinical use in China since its introduction in 2007. However, recent long-term follow-up of this stent has shown a high risk of in-stent restenosis after implantation, with half of the luminal stenoses being more severe than the original stenosis, which calls into question its clinical application. Although in-stent restenosis can be treated by targeted stenosis revascularization, the technique is relatively difficult to perform and the results are not durable. Therefore, caution should be exercised when applying this stent for symptomatic intracranial artery stenosis. 1. Introduction The prevalence of symptomatic intracranial artery stenosis is high in China and is an important cause of stroke in the young and middle-aged population [1]. Although antiplatelet or anticoagulation therapy with warfarin-aspirin is effective, the cumulative incidence of ipsilateral stroke in severe stenosis is still as high as 25% within 2 years, and there is a risk of intracranial hemorrhage due to long-term application of these drugs. Extracranial-intracranial bypass has long been rejected by a large multicenter clinical study. In recent years, with the advancement of endovascular treatment techniques and the emergence of new stent materials, endovascular stenting has become a breakthrough point in the treatment of symptomatic intracranial arterial stenosis, but in-stent restenosis has become a new problem to be solved [2]. 2. Wingspan stent and its recent efficacy The Gateway balloon-Wingspan stent system, developed by Boston, USA, was marketed in August 2005 after FDA approval and is the first self-expanding stent made of nickel-titanium alloy designed specifically for the treatment of intracranial artery stenosis. In 2005, Henkes et al [3] first reported 15 cases of symptomatic intracranial arterial stenosis treated with the Wingspan stent system, and the mean stenosis rate decreased from 72% to 38%, with only one case of complication due to balloon expansion of the M1 segment of the penetrating artery. complications due to occlusion of the M1 segment. Subsequently, a multicenter study by Bose et al [4] on 45 cases of atherosclerotic intracranial artery stenoses that had failed pharmacological treatment showed that the mean stenosis rate decreased from 74,9% ± 9,8% to 31,9% ± 13,6% after Wingspan stent placement, with only 2% of patients experiencing an ischemic event within 30 days after the procedure (1/45 cases). study also found that the stent was effective in improving the degree of stenosis of intracranial arteries (74,6% ± 13,9% preoperatively vs. 27,2% ± 16,7% postoperatively), with an operation-related neurological complication rate of 6,1% (5/82). In addition, clinical reports of the Wingspan stent system for the treatment of symptomatic intracranial artery stenosis in Chinese patients since its introduction in 2007 have confirmed its good recent safety and efficacy [6-10]. 3. Techniques of Wingspan stent use and prevention of complications Studies have shown that the combination of a semi-compliant pre-expandable Gateway balloon and a self-expanding slow-release Wingspan stent can effectively reduce the surgical risks of arterial entrapment, arterial wall elastic retraction, penetrating stroke, and intracranial hemorrhage, in which the selection of the appropriate type of balloon and stent is crucial to the success of the operation. Some authors recommend that the diameter of the pre-expansion Gateway balloon should not exceed 80% of the diameter of the normal reference vessel at both ends of the stenotic segment [6], and the length should cover a range of 3 mm at each end of the lesion [9], but the diameter of the balloon after filling should not exceed the diameter of the diseased vessel to reduce the risk of rupture and bleeding of the sclerotic vessel during balloon expansion [7].Wingspan stents should be selected slightly larger than the normal vessel 0.5 mm in diameter to prevent elastic retraction of the vessel by its continuous outward vertical tension, thus consolidating the initial angioplasty effect [7]; however, some authors recommend the use of stents 0.8-1.0 mm larger than the normal vessel diameter to prevent elastic retraction of the vessel wall and to provide sufficient time for effective collateral circulation through “space for time” [8]. The use of stents with a larger than normal vessel diameter of 0.8-1.0 mm is recommended by authors to prevent the elastic retraction of the vessel wall and to provide sufficient time for effective collateral circulation through “space for time”, thus better preventing ischemic events [8]. Although these techniques can significantly reduce perioperative complications, long-term follow-up suggests that postoperative in-stent restenosis (ISR) is still a concern. 4. definition and staging of ISR It is well known that ISR after percutaneous transluminal angioplasty and stenting is a long-standing problem. albuquerque et al [11] defined it as a stenosis of more than 50% within 5 mm of the stent and its ends or an absolute narrowing of the lumen of more than 20% and proposed four modified staging types of ISR after intracranial artery stenting: type I ( Type I (limited type) lesion involvement is less than half of the stent length, among which only one end of the stent is involved as type IA, the body of the stent is involved as type IB, and multifocal involvement is type IC; type II (diffuse type within the stent) lesion involvement is more than half of the stent length, but confined within the stent; type III (hyperplasia type) lesion involvement exceeds the stent length; type IV stent is completely occluded. 5. Incidence of ISR The incidence of ISR after Wingspan stent implantation has been reported inconsistently. Initially, Bose et al [4] found only 7,5% of ISR in 40 cases treated with Wingspan stents at 6-month follow-up, whereas Levy et al [12] showed 29,7% of ISR in 78 cases with 84 lesions at a mean follow-up of 5,9 months, which is about 4 times more than that reported by Bose et al [4]. More recently, the US NIH multicenter Wingspan stenting for symptomatic intracranial artery stenosis (70% to 99%) was followed by ISR in up to 25%, resulting in 14% of ischemic or hemorrhagic strokes and even death [13]. A large sample, multicenter, prospective study showed that the incidence of ISR at a mean follow-up of 8,5 months was 32,3%; of these, 61,0% were limited (type I), 26,8% were diffuse and proliferative (types II and III), and 12,2% were completely occluded (type IV) [11]. Domestic observations by Gao Feng [6] and Deng Jianping [10], who performed a 30-d perioperative period after stent implantation, showed that the incidence of ischemic complications was divided into 10% and 14, 8%. This shows that ISR after Wingspan stent placement should not be neglected. 6. Mechanisms and influencing factors of ISR Current considerations on the mechanisms and influencing factors of ISR are: (1) Anatomical site ISR is more likely to occur in the anterior circulation, especially in the superior segment of the internal carotid bed and middle cerebral artery, which is about 3 times more likely to occur in the posterior circulation. Some people believe that the occurrence of ISR is related to the relatively weak support of the Wingspan stent, so it is recommended to use a stent slightly larger than the diameter of the distal normal artery in order to fully expand the arterial stenosis and minimize postoperative stenosis through “space for time” [8]; others believe that the Wingspan stent has some shortening after release. It has been suggested that the stent length should cover 3 mm at each end of the lesion to avoid residual lesion [9]; others believe that ISR is due to endothelial proliferation induced after stenting [14]. (3) Smoking Levy et al. found a positive correlation between smoking and the occurrence of restenosis [12]. (4) Age Turk et al [15] followed up 155 lesions in 144 patients and showed that young patients were prone to ISR, especially those with lesions located in the superior segment of the internal carotid artery bed protrusion had a high incidence of ISR of 88,9%, and 60% of them had clinical symptoms due to restenosis. The current endovascular treatment for ISR is targeted lesion revascularization (TLR), which includes balloon dilation angioplasty alone or balloon dilation combined with stent reimplantation. 26 cases of balloon dilation and 3 cases of balloon dilation combined with stent reimplantation. The results showed that TLR was safer in the treatment of ISR, and the incidence of bleeding due to postoperative reperfusion