Stent-assisted coiling (SAC) is a well-established option for the treatment of intracranial complex and broad-necked aneurysms, yielding higher rates of complete occlusion [1,2]. Various types of stents with different properties have been developed, including laser-cut stents with open- or closed-cell designs as well as braided stents [3]. Among these, low-profile self-expandable stents are relatively safe and allow easier delivery manipulation and deployment through tortuous vessels [4,5].

Treatment with SAC may occasionally show intra-procedural difficulties due to restriction in the swift navigation of the coil delivery microcatheter through the stent lumen and the entry of aneurysmal sac; this may increase the procedural difficulty and subsequently increase the procedure risk. Although the incidence of procedural abortion due to this mechanism is decreasing, intra-procedural technical difficulties may still be encountered as a result.

We hypothesized that such navigation difficulties would be minimized if the stent was covered with a neo-intima layer and fixed into the vessel wall after a certain time. Thus, the purpose of this study was to evaluate the feasibility of staged coiling in cases involving initial failure of intra-saccular aneurysm catheterization during SAC.

The patients’ mean age was 57.2 years (range, 49–76 years); there were 5 females and 2 males (female-to-male ratio, 5:2). The clinical presentations at the time of presentation included headache (n=5) and right-side weakness (n=1), while 1 patient was asymptomatic (n=1).

The aneurysms were located in the paraclinoid ICA (n=3), ophthalmic origin ICA (n=1), superior cerebellar artery (SCA) origin basilar artery (n=2), basilar tip (n=2), and middle cerebral artery (MCA) bifurcation (n=1) (Table 1). The location of the aneurysms can be classified as a side aneurysm (n=6; paraclinoid ICA, ophthalmic ICA origin, superior cerebellar artery origin basilar artery aneurysms) or a bifurcation aneurysm (n=3; basilar tip and MCA bifurcation aneurysms). Furthermore, the aneurysms were located in the greater curvature side of a parent artery curve (n=6; ophthalmic ICA origin, basilar tip X2, paraclinoid ICA X2, superior cerebellar artery origin basilar artery aneurysms) and located in the lesser curvature of the parent artery (n=3; paraclinoid ICA, SCA origin basilar artery aneurysm and MCA bifurcation aneurysms).

We utilized self-expandable intracranial stents, including an open stent such as the Neuroform Atlas (n=4) and Neuroform EZ (n=2), and a closed stent such as the LVIS blue (n=1). One patient with a LIVS blue stent showed total aneurysm resolution due to the flow diverter effect.

The mean interval between stent staging and the complete coiling procedure was 15 weeks (range, 12–21 weeks). In our study, successful stent deployment in the target artery was achieved in all cases involving staged stent procedures with complete flow patency (7/7, 100%). We used Excelsior SL-10 (Stryker, Kalamazoo, MI, USA) as the primary microcatheter. As per the location of each aneurysm in relation to the parent artery, the microcatheter’s shape was used as primary curves (straight, 45, 90, and J shapes), or modified microcatheter tip curves by steaming to conform to the shape of the aneurysm sac opening. We used primary curved 45 (n= 2), primary curved 90 (n=1), primary curved J shaped (n=1), and straight tip (n=1), and the rest used a steam complex microcatheter tip curve (n=4).

We observed smooth navigation and great stability of the coil delivery microcatheter into the aneurysmal sac in the coiling stage, and that less time was required compared to that required for stent staging. Moreover, the mean estimated time between the first roadmap of the target vessel to the delivered microcatheter within the aneurysmal sac, crossing the stent mesh, was 14 minutes (range, 8–20 minutes) compared to a mean time of 34 minutes (range, 28–41 minutes) for the stenting procedure to access the stent mesh before procedure termination (P=0.017). No periprocedural thromboembolic events or intracranial hemorrhage were observed during intraoperative assessments or immediate postoperative MRI.

The remaining aneurysms showed complete coiling without any technical difficulties and no long-term complications. No residual or recanalized aneurysms were identified during magnetic resonance angiography follow-up. All patients had a favorable mRS (0–2) at discharge and at follow-up.

SAC is considered to be an effective method for endovascular treatment of intracranial aneurysms, with low rates of intraoperative and clinical complications. SAC of intracranial aneurysms is performed as a single- or multistage procedure based on the intraoperative circumstances or personal preference [7]. However, only a few studies have described a multistage approach [1,7-9].

In staged procedures, the stent is first deployed across the aneurysm neck and left to endothelialize for up to 12 weeks before the patient can undergo coil embolization. This staging ensures greater stability and less movement of the stent during coil packing. Moreover, the choice of intracranial stenting was mostly based on operator preference, compatibility with the delivered microcatheter, and the status of the vascular anatomy, which can improve navigability and ease of stent deployment [9]. The results of our study revealed that multistage procedures were applicable to intracranial aneurysms that may present difficulties in establishing microcatheter stability, either for a cross stent or while creating a position for coil packing or for stent movement when struggling to pass the microcatheter through the stent struts. We did not observe any complications associated with this approach and achieved good clinical and radiological outcomes. We believe that the time between the staged stenting and completion of the coiling procedure allowed the stent to be in a stable position to prevent unavoidable movement by enhancing endothelialization and platelet activation. This enhancement may further stabilize the stent mesh against the wall, providing safer microcatheter manipulation and reduced incidence of thromboembolic events. A large cohort study is needed to verify this theory as well as our finding that the multistage approach resulted in fewer periprocedural complications than a single-stage procedure, which may be attributed to the interval between stenting and coiling that may provide a sufficient stent insulation time to avoid complications [7].

Advancing a microcatheter into an aneurysm in SAC embolization using the cell-through technique does not always feel secure. The closed-cell stent design at the proximal end with a flaring end provides good trackability and enhances the cell-through technique by smoothly passing a microwire in the stent lumen. When a microwire cannot be advanced through the stent or is stuck in the struts, a microwire looping technique provides easy navigation through the inside of the stent lumen. In contrast, an open-cell stent design, with both ends flared, provides excellent stability to the vessel wall and wall apposition. Microcatheters and microwires can easily pass through the inside of the stent without irritating the struts. Nevertheless, once the aneurysm selection is made using the cell-through technique, the microcatheter is stuck within a cell of the stent, becoming very stable while inserting coils. Thus, patients with small-caliber, stenotic, or very tortuous parent arteries may be good candidates for this technique [10].

Self-expanding stents provide more support in aneurysm packing, with an increased neck coverage ratio, in addition to improved treatment durability through a combination of flow diversion, parent vessel straightening, and fibroelastic tissue formation along the neck of the aneurysm. This helps prevent aneurysm recanalization by redirecting flow and facilitating endothelialization at the aneurysm neck [1,9]. Another study suggested that hemodynamic changes after stent crossing of the aneurysmal sac play a role in changing the parent vascular configuration [11].

In our study, we identified anatomical and technical factors that may influence the ability of a microcatheter to pass the stent mesh and cause difficulties in aneurysmal sac catheterization. The anatomical factors were closely and independently associated with the aneurysm location, which was further influenced by regional vascular flow and may have a complex geometry as seen in the communicating artery or MCA branching aneurysms. We believe that for aneurysms located in the greater curvature side of a curved parent artery, it is more often than not easier to catheterize them than locate the lesser curvature side, unless they are not in the direction of flow impacted (Table 1). Technical factors play an important role in microcatheter navigation through the stent, including the stability of the guiding catheter and the proximity to the aneurysm, which are important for achieving optimal control for microcatheter stabilization. Furthermore, steady guidance of the catheter over a great distance is necessary for sufficient sustenance of the devices, especially in tortuous vessels. The precise shaping of microcatheter tips to conform to the aneurysm’s configuration is also a key factor for safe aneurysm embolization after crossing the stent. Proper shaping can reduce microcatheter resistance during its navigation. Moreover, the selection of an appropriate microcatheter size and tip flexibility are crucial, as different properties affect the navigation strategy to cross the stent mesh and the stabilization within the aneurysmal sac. Finally, stent selection also plays a role in the feasibility of microcatheter navigation through the pores of the stent mesh and conformation against the vessel wall. In comparison with laser-cut stents, braided stents caused difficulties while re-crossing the stent after deployment.

Stent deployment plays a role in modifying mechanical, hemodynamic, and biological properties. With respect to the biological properties, the reaction of the stent to the parent artery wall is influenced by multiple factors, including vascular intimal injury, vascular remodeling, inflammation, and the healing process. After stent implantation, the adventitia and medium layers respond to stent-induced alterations, leading to vessel wall remodeling and resulting in significant changes to its mechanical properties. Muscle fibroblasts in the media layer can shrink, migrate, and secrete extracellular matrix, leading to further fibrosis and subsequent decreased vascular compliance [12].

The disadvantages of this approach include the long time required to complete aneurysm embolization, which is not favorable for the patient, and the requirement of unexpected staged stenting under general anesthesia. Nevertheless, we advise that since the operator is not in a rush to complete the procedure, he or she can stop before an unexpected event occurs and consider multi-staged SAC embolization.

This retrospective study included a small case series; thus, the effects of possible selection bias cannot be excluded. The results reflect the experience of a single neurovascular center with a specific technique and hospital medication protocol, all of which may differ from other centers.

In cases showing difficulty in intra-saccular catheterization, intentional staged coiling may be a viable procedural option for SAC of cerebral aneurysms.