Cerebral aneurysms (ANs) are a potentially life-threatening condition that requires prompt and effective treatment. Consequently, the increased frequency of neuroimaging during health check-up for minor symptoms has led to a steady rise in the incidence of unruptured intracranial aneurysms (IAs) [24]. Over the years, various methods have been used to treat the cerebral AN, and endovascular therapy has become popular and has been developed to treat wide neck ruptured and unruptured IAs [13,14].

To avoid coil protrusion into the parent vessel and insufficient occlusion of the aneurysm, various endovascular techniques have been developed. Previously balloon-assisted coil embolization (BAC) was one of the treatment options to treat wide neck aneurysms. BAC intermittently occluded the parent artery, potentially resulting in unanticipated flow disruption to regional area of the brain. In addition, unexpected overinflation and vessel rupture can lead to catastrophic events.

Stent-assisted coil embolization (SAC) is the widely acceptable technique for treating wide neck IAs [8]. SAC is a minimally invasive procedure that uses a stent to support the coils to occlude the AN. The goal of this procedure is to prevent the AN from rupturing and potentially causing stroke without procedural complications. A variety of factors influence the success of SAC, including the size and location of the AN, the features of the patient’s blood vessels, and the experience and ability of the medical team executing the procedure. Several reports have highlighted the effectiveness of SAC over other techniques in addressing these risks. Over time, several studies reported that the AN with a wider neck was more likely to use SAC technique [1,23].

Among SAC, there have been various techniques including dual-stent techniques (Y- and X-stenting), trans-circulation stenting, and antegrade horizontal stenting [3,15,25]. In addition to these techniques, Hong et al. first introduced the semi-jailing technique (SJT), in which the stent was partially deployed across the aneurysm neck to secure the coils in place while also enabling blood flow to be maintained [6]. They concluded that SJT was a safe and effective SAC technique that facilitates the treatment of complex, wide-necked aneurysms. The SJT was typically performed with a resheathable closed-cell stent but may encounter issues with tortuous blood vessels including stent migration and malapposition [4,5,6]. On the other hand, our previous study indicated that although the open-cell stent carries the disadvantage of an unresheathable design, coil placement with a shorter stent deployment length may be advantageous during SJT for internal carotid artery aneurysm embolization with favourable consequences for excellent vessel wall apposition [18].

To date, the definite impact of the SJT on outcomes in patients with unruptured IAs remains unknown. We aimed to evaluate the efficacy and safety of SJT using open- or closed-cell stents in the treatment of patients with unruptured IA.

This study was based on the Strengthening the Reporting of Observational Study in Epidemiology statement [22]. A single-center, hospital-based observational study was conducted with a retrospective approach. The study protocol was approved by the institutional ethics committee at Hyogo Medical University (No. 4552), and the need for informed consent was waived. Patients with unruptured IAs who were treated with SAC in our hospital between December 2013 and May 2022 were retrospectively evaluated.

Patient characteristics (age, sex, past medical history, and previous treatment of IA) were obtained through a review of the patient’s medical records. Aneurysm characteristics (side, size, shape, morphology, whether IA was growing or not, side-wall type, branch from the aneurysm sac, aneurysm shape, and previous treatment for the same aneurysm) were also obtained.

SAC was performed using open and closed cell stents (Neuroform and Neuroform Atlas: Stryker, Freemont, San Francisco, California, USA, Enterprise: Cordis Neurovascular, Miami, FL, USA, LVIS: MicroVention, Tustin, CA, USA). Details of SAC and SJT were described in the previously published study [12]. The non-SJT group consisted of jailing and trans-cell techniques.

A total of 320 patients were included and 220 patients undertook SJT (68.8%) (Fig. 1). Demographic and aneurysm characteristics are shown in Table 1. The median age of patients was 61.0 years (interquartile range, 50.3-71.0 years) and 73 were male (22.8%). Patients with SJT were significantly younger (59.0 vs. 66.0 years, p=0.01) and less likely to have hypertension (35.9% vs. 57.0%, p<0.01). Other demographic characteristics showed no significant difference between the two groups. Right side IA location was more frequently observed in patients with SJT (46.8% vs. 36.0%, p<0.05 by residual analysis). Maximum diameter and neck size were significantly smaller in patients with SJT (5.3 vs. 7.2 mm, p<0.01; 4.2 vs. 5.3 mm, p<0.01, respectively). Proportion of sidewall IA was significantly smaller in patients with SJT (57.3% vs. 69.0%, p=0.046). Patients with SJT were more likely to have internal carotid artery aneurysms and less likely to have basilar artery aneurysms (46.4% vs. 33.0%, p<0.05; 5.0% vs. 20.0%, p<0.05 by residual analysis, respectively). Other aneurysm characteristics showed no significant differences between the two groups.

Our study aimed to evaluate the clinical outcomes and efficacy of the SJT and non-SJT. The results of this study showed that obliteration rate of SJT was significantly higher than non-SJT and was related to 1-year complete and satisfactory occlusions in unruptured IA patients treated with SAC. Hong et al. introduced SJT and have described good result in occlusion rate [6]. This finding is consistent with earlier research that has shown efficacy of SJT approaches and align with the results of our study [9,18]. Subgroup analysis demonstrated that SJT for side-wall type IA was more related to 1-year complete occlusion.

The jailing technique restricts the movement of the coil delivery microcatheter, resulting in difficulties achieving paint-brushing or back-and-forth movement of the microcatheter [19]. In the trans-cell technique, although the microcatheter can move freely, it can easily be forced out of the aneurysm during coiling. In addition, the transcell technique is difficult because the microcatheter might become stuck in the struts of the open cell stent [7]. Besides, the transcell technique may be dangerous because the microcatheter can suddenly jump into the aneurysm sac, perforating the aneurysm [7]. Therefore, the jailing and transcell techniques could be evaluated as options on a case-by-case basis.

As stated above, repositioning of the microcatheter, enabling a compartmental approach, is often critical to safely achieving high coil packing densities in aneurysm necks, irregularly shaped multilobed aneurysms, and recurrent aneurysms. In this regard, Hong et al. introduced SJT, which could provide stent-assisted remodelling of the aneurysm neck during coil embolization without pinning the coil delivery microcatheter and has described good result in occlusion rate. The results of our previous and current study supported their results [6,18]. Additionally, the SJT can assist in maintaining blood flow to adjacent brain tissue, which can be essential in lowering the risk of stroke. It has good durability when manipulating the microcatheter and it can adjust the microcatheter during embolization. Furthermore, when deployed in difficult parent arteries, the open cell stent can provide adequate anchoring to the parent artery and reduce the chance of stent migration during microcatheter withdrawal. It can also improve inadequate expansion and apposition. This creates a sturdy framework for the coils to stick to and lowers the possibility of their becoming squeezed or dislodged over time. Closed cell stent has good efficacy with using the semi-jailing technique. However, the effectiveness of proper anchoring to the tortuous parent artery seemed to be less than using the open cell stent. Therefore, choosing the appropriate stent is one of the important factors which influencing clinical outcomes. There have been several reports regarding the effectiveness of the SJT, nevertheless, they didn’t compare the treatment results between two methods, SJT and non-SJT on using open-cell and closed-cell stents [9-11]. To our knowledge, this is the first report comparing the efficacy and safety of the open-cell and closed-cell stents in SAC.

Although no statistically significant differences were identified in perioperative complications of SJT and non-SJT, 1-year complete and satisfactory occlusion were significantly higher in SJT group. Shirakawa et al. described the effectiveness of SJT on open-cell stents, by comparing the outcomes of open and closed-cell stents where in SJT was applied. In which, the rate of immediate occlusion after the procedure tended to be higher in SJT with open cell stent group [18]. This may be because the open-cell stent gave good anchoring to the parent artery, and SJT allowed the microcatheter to get more free space while manipulating inside the aneurysm with proper expansion of the stent. In addition, SJT with dome-to-neck ratio ≥1.5 and with side-wall location were significantly and marginally related to higher 1-year complete occlusion in the subgroup analysis. Therefore, SJT may be a good option for treating IAs with these morphological characteristics. Furthermore, periprocedural hemorrhagic complications in non-SJT tended to increase (1.8% vs. 5.0%, p = 0.14) although the difference was not significant. This might be due to the limited mobility of the microcatheter and difficulty to reinsert the microcatheter into the aneurysm after being forced out of the aneurysm during embolization in the non-SJT [7]. On the contrary, SJT could offer more free space in manipulating the microcatheter during the coil embolization, therefore, the exceeded frictional force between the microcatheter and the wall of the vessel due to narrow space might be avoided. As a result, SJT ensures the proper manipulation of the microcatheter during embolization, leading to successful coil packing within the AN. Furthermore, it allows for adjustments to the stent during both embolization and deployment, particularly in challenging vessels, resulting in favourable obliteration of long-term technical outcomes.

SJT provided the noticeable good technical outcomes in achieving 1-year complete and satisfactory occlusions. In subgroup analysis for 1-year complete occlusion, SJT with sidewall type IA was more related to good outcomes. The satisfactory durability of SJT makes it a better choice as a technique in SAC in terms of technical effectiveness in clinical setting, especially in challenging vessels. Further prospective multicenter studies with larger sample sizes are necessary to improve the routine treatment regimens and outcomes.