Treatment outcome of flow-diversion with Surpass Evolve stent for unruptured intracranial aneurysms: Predictors of poor occlusion

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J Cerebrovasc Endovasc Neurosurg. 2026;28(1):24-34

Publication date (electronic) : 2025 October 16

doi : https://doi.org/10.7461/jcen.2025.E2025.08.004

Jiyeong Kim, Jai Ho Choi, Yong Sam Shin, Woo Cheul Cho

Department of Neurosurgery, Seoul St. Mary’s Hospital, The Catholic University of Korea

Correspondence to Woo Cheul Cho Department of Neurosurgery, Seoul St. Mary’s Hospital, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul, 06591, South Korea Tel +82-2-2258-6129 Fax +82-2-594-4248 E-mail woobari@gmail.com

Received 2025 August 19; Revised 2025 September 16; Accepted 2025 September 18.

Abstract

INTRODUCTION

Flow diverting stent (FDS) is one of the main devices to treat unruptured intracranial aneurysm (UIA). From the first use of FDS, numerous kinds of FDS have been developed over the past two decades. The Surpass Evolve (SE) stent is new-generation consisting of 48 to 64 wires, which was approved in March 2019 [1,24]. Many studies demonstrated the efficacy and safety of previous FDS for UIA [3,13,19,23,25,31]. However, there were few studies about risk factors for poor occlusion rate using SE stent. In this study, we aimed to investigate which factors were associated with poor occlusion after flow diversion for UIA using SE stent.

MATERIAL AND METHODS

RESULTS

Baseline characteristics

The baseline characteristics of the patients and aneurysms are presented in (Table 1). A total of 52 procedures were performed on 68 aneurysms. The mean age of patients was 57.3±13.4 years, and 38 patients (73.1%) were female. Fourteen patients (20.6%) had multiple aneurysms. A history of previous SAH was present in 3 patients (5.8%), and prior ischemic infarction was noted in 2 patients (3.8%). Previous endovascular or surgical treatment had been performed in 9 cases (17.3%). Of these, seven aneurysms were previously treated with any stent. Fifty-seven aneurysms (83.8%) were in the anterior circulation. Cavernous to ophthalmic segment of internal carotid artery (ICA) aneurysms were the most common (n=52, 76.5%), and vertebral fusiform or dissecting aneurysms were 8 cases (11.8%). The mean maximum aneurysm diameter was 12.2±8.0 mm. Among them, giant aneurysm (≥25 mm) and large aneurysm (≥10 mm) were 5 (7.4%) and 35 cases (51.5%), respectively. There were 6 cases (8.8%) which used concurrent coil embolization.

Table 1.

Baseline characteristics

Clinical and radiological outcome

Clinical outcomes were evaluated in 52 procedures, with a mean clinical follow-up duration of 17.9±9.8 months (Table 2). One major complication (1.9%) occurred, consisting of the progression of brainstem compression following treatment. No cases of major hemorrhage or major ischemic stroke were reported. Minor complications occurred in 5 procedures (9.6%), all of which were ischemic strokes. Among these, 4 cases (7.7%) were silent infarction, and 1 case (1.9%) was symptomatic. No minor hemorrhagic events were observed. There was no delayed rupture or delayed remote intraparenchymal hemorrhage. A procedure-related mortality was 0%. Aneurysm recurrence occurred in 2 cases (3.8%), and 1 case (1.9%) underwent retreatment during the follow-up period.

Table 2.

Clinical outcome of procedures

Table 3 showed radiological outcomes were assessed for 68 aneurysms, with a mean DSA follow-up duration of 12.0±7.8 months. At final imaging follow-up, no aneurysms remained in total filling (OKM A, 0.0%), while 14 aneurysms (20.6%) showed subtotal filling (OKM B), 18 (26.5%) in entry remnant (<5%) (OKM C), and 36 (52.9%) in complete occlusion (OKM D). A favorable radiological outcome, defined as OKM grade C or D, was observed in 54 of 68 aneurysms (79.4%). One case (1.9%) of in-stent stenosis (>50% stenosis) and one case (1.9%) of distal stent migration with ICA occlusion had occurred (Figs. 1 and 2).

Table 3.

Radiological outcomes

Fig. 1.

80-year-old female patient with an unruptured aneurysm involving the right posterior communicating artery and anterior choroidal artery presenting with ptosis. (A) Preoperative angiography of a large aneurysm (15.8 mm). (B) The patient underwent flow diversion with a Surpass Evolve flow diverter stent (4.0×30 mm). (C) and (D) 6-month follow-up angiography reveals in-stent stenosis with subtotal aneurysm filling.

Fig. 2.

71-year-old male patient with an unruptured cavernous segment of left internal carotid artery (ICA) aneurysm treated with a flow diverter. (A) Preoperative angiography of a large aneurysm (19.7 mm). (B) and (C) Surpass Evolve flow diverter (4.5×40 mm) was deployed. (D) At 18-month follow-up angiography, distal stent was migrated to proximally with left ICA occlusion. (E) Collateral circulation was maintained via the anterior communicating artery and the ophthalmic artery collaterals.

Univariate and multivariate analyses for favorable occlusion

Table 4 summarizes the results of both univariate and multivariate analyses evaluating factors associated with favorable radiological outcome. In univariate analysis, aneurysms without an incorporated branch showed significantly higher rates of favorable occlusion compared to those with a branch (84.6% vs. 50.0%, p=0.008). A history of previous treatment was more likely to have poor occlusion (31.3% vs. 9.6%, p=0.047). The favorable occlusion group was younger on average (54.5±12.9 vs. 62.2±12.3 years, p=0.039), and aneurysm size was smaller (10.4±6.4 vs. 18.2±10.1 mm, p=0.002). In multivariate logistic regression, smaller aneurysm size remained significantly associated with favorable occlusion, with an odds ratio (OR) of 0.89 (95% CI, 0.81–0.98; p=0.011). The absence of an incorporated branch was also independently associated with favorable occlusion (OR, 8.26; 95% CI, 1.78–38.28; p=0.007). Age and previous treatment history did not reach statistical significance in the adjusted model (age: OR 0.95; p=0.123; previous treatment: OR 2.55; p=0.293, respectively).

Table 4.

Univariate and multivariate analysis of risk factors for poor occlusion

DISCUSSION

Our study demonstrates treatment outcomes for UIAs with Surpass Evolve stent. Within our cohort, the larger size of an aneurysm and a branch-incorporated aneurysm were independent risk factors for poor occlusion following flow-diversion using the SE stent.

Several papers have established that the placement of flow-diverting stent (FDS) for UIA is effective [2,10,28]. Hanel et al. and Meyers et al. also described the treatment outcome using the Surpass Streamline (SS) stent [10,21]. The SS stent was designed with 64 to 96 braided wires, which is higher than previous other FDS, to achieve more effective occlusion. However, the increased number of braided wires was associated with greater stiffness, making deployment of the SS stent technically more difficult. Furthermore, the SS stent was associated with a higher incidence of thromboembolic (TE) complications. Consequently, the Surpass Evolve stent was introduced to the market as a next-generation stent consisting of fewer wires (48-64) to reduce both stiffness and device-related TE complications [6,26,29]. A recent meta-analysis study demonstrated the efficacy of SE stent, with complete and adequate occlusion (OKM C-D or Raymond-Roy Occlusion Classification 1-2) rates of 72.4% and 86.6%, respectively [12]. In the present study, the complete and adequate occlusion rates were 52.9% and 79.4%. In the recently published SEASE multicenter registry, the complete occlusion rate at a mean follow-up of 10.2 months was 73%, with only 18.4% of large or giant aneurysms. In comparison, our study demonstrated a lower complete occlusion rate, likely attributable to the relatively high proportion of large and giant aneurysms (58.9%) in our cohort. Larger aneurysm size has consistently been identified as a negative predictor of complete occlusion after flow diversion, and thus, the size distribution in our population may have contributed to the reduced overall success rate observed.

On the other hand, prior studies demonstrated the safety of FDS for aneurysm treatment [4,5,15,16,18]. According to these studies, ischemic complications occurred in 4.1-6.1% of cases, intraparenchymal hemorrhage in 2.4-3.0%, and SAH in 0.6-4.0%. The neurological morbidity and mortality were 3.5-7.4 and 1.6-4.0%, respectively. In the present study, there was one case of delayed symptomatic ischemic infarction (1.9%). No hemorrhagic complication or mortality was observed. One patient had delayed distal stent migration which led to distal ICA occlusion (Fig. 1). In this case, collateral flows from the anterior and posterior communicating arteries compensated for the ipsilateral ICA occlusion without causing any neurological symptom. Additionally, one case of in-stent stenosis (>50% of stenosis) was observed (Fig. 2).

Previous studies suggested that diverse factors were associated with aneurysm occlusion following flow-diversion, such as larger aneurysm size, incorporated branch, younger age, location, previous treatment, and follow-up duration [9,20,22,24]. Meyers et al. suggested that aneurysm size highly affects the aneurysm occlusion after flow-diversion [20]. Other studies showed that larger aneurysm size has been identified as a risk factor for residual aneurysm following FDS treatment [9,24]. Hemodynamically, large aneurysms typically develop slow but persistent vortical flow patterns [17] which delay thrombus stabilization and endothelialization across the aneurysm neck [14]. Thereby prolonging the time to complete occlusion and increasing the likelihood of residual filling. On the other hand, although the SEASE (Safety and Effectiveness Assessment of the Surpass Evolve) trial did not reach statistical significance (p=0.06) between larger aneurysm (≥10 mm) and aneurysm occlusion, they demonstrated a negative trend toward lower complete occlusion rates [31]. Nevertheless, an increase in aneurysm size was associated with a poor occlusion rate following FDS using SE stent in our study. In SEASE trial, only 18.4% of aneurysms were ≥10 mm. In contrast, the aneurysms in our study were larger, which may have influenced the different results.

Other studies showed that the absence of a branch from an aneurysm was associated with higher complete occlusion [8,20,30]. A recent study on the SE stent, subgroup analyses from the SEASE registry, suggested that treatment with FDS for bifurcation aneurysm or dome-originated branch incorporated aneurysm resulted in poor occlusion [7]. The persistent flow demand and wall shear stress were known factors that delay thrombosis and neointimal coverage [8,11,22,26,27]. In our study, the presence of any incorporated branch, regardless of anatomical origin, was significantly associated with lower occlusion rates. Fig. 3 shows that an unruptured vertebrobasilar junction aneurysm was treated with SE stent and concurrent use of coils. One year later, an additional overlapping SE stent was deployed due to a remnant sac. Nevertheless, follow-up DSA revealed aneurysm growth with coil compaction, which was accompanied by persistent flow to the anterior inferior cerebellar artery.

Fig. 3.

65-year-old male with an unruptured vertebrobasilar junction (VBJ) aneurysm treated with a flow diverter. (A) Preoperative angiography of a giant aneurysm involving the VBJ (32.1 mm), with the right anterior inferior cerebellar artery arising from the top of the aneurysm. A Surpass Evolve flow diverter (4.0×20 mm) was deployed across the basilar artery to the left vertebral artery, and adjunctive coiling was performed. The parent artery occlusion on the right distal vertebral artery (VA) was followed. (B) At 3-month follow-up angiography, a remnant sac was observed, and an additional Surpass Evolve flow diverter was deployed for retreatment. (C) Ten months later, the patient presented with dysphagia. Follow-up angiography showed coil compaction with aneurysm growing.

The management of large aneurysms or those incorporating branch vessels has challenges in achieving a favorable occlusion. In our practice, these cases are followed more closely in the outpatient setting. During a certain period, if the follow-up image demonstrates limited occlusion, the additional interventions such as deployment of a second flow-diverter stent or adjunctive coil embolization are considered to augment treatment efficacy. In certain cases, additional destructive surgery such as parent artery occlusion with bypass surgery was considered. Nevertheless, these approaches are individualized and applied selectively. Larger, prospective, multicenter studies are needed to validate whether such stepwise strategies can reliably improve long-term occlusion rates in aneurysms with large size or branch incorporation.

There are several limitations to this study. First, while almost all aneurysms underwent follow-up catheter-based angiography (94.1%, n=64/68), the follow-up duration was heterogeneous. Consequently, we did not perform a time-stratified analysis. The limited sample size and the small number of patients with long-term radiological follow-up would have led to unstable statistical estimates with excessive censoring, precluding meaningful interpretation. Gupta et al. have reported that complete occlusion rates increase with longer follow-up after flow diversion [9]. One illustrative case in our series showed a similar pattern. A fusiform aneurysm involving cavernous segment of left ICA treated with SE stent (Fig. 4a, 4b). Six months follow-up DSA showed subtotal filling (OKM B, Fig. 4c). At 5-year follow-up, angiography confirmed complete occlusion (OKM D, Fig. 4d). This case reflects the potential for progressive aneurysm occlusion over extended follow-up. Therefore, a homogenous long-term study should be necessary. Second, although our study suggests that a larger size of aneurysm and branch-incorporated aneurysm are independent risk factors for poor occlusion after flow-diversion, no additional risk factors were identified compared to previous studies with other flow-diverters. However, to our best knowledge, there were a few studies about risk factors associated with poor occlusion using SE stent. At last, our study was a retrospective, single-center study with a relatively small cohort, which may have introduced bias. We acknowledge the potential risk of overfitting in the multivariate model due to the relatively small sample size. To minimize this concern, we limited the number of covariates and selected factors primarily based on those consistently reported in previous studies. Nevertheless, the limited cohort size could not fully eliminate this issue, and therefore, the estimates should be interpreted with caution, as exploratory findings rather than definitive conclusions.

Fig. 4.

53-year-old male with an unruptured fusiform-shaped aneurysm involving the cavernous segment of left internal carotid artery treated with a Surpass Evolve flow diverter. (A) Preoperative angiography of aneurysm (23.6 mm). (B) Deployment of a Surpass Evolve flow diverter with adjunctive balloon angioplasty was performed. Post-procedural angiography demonstrates contrast stagnation within the aneurysm sac. (C) 6-month follow-up angiography reveals persistent aneurysm filling (OKM grade B). (D) At the 5-year follow-up, complete aneurysm occlusion is achieved (OKM grade D) with preserved parent vessel patency. O’Kelly-Marotta, OKM

CONCLUSIONS

The Surpass Evolve stent might be feasible for the treatment of unruptured intracranial aneurysm with adequate occlusion and low complications. The presence of any incorporated branch and a larger size of aneurysm were identified as independent risk factors for poor occlusion following flow diversion using the Surpass Evolve stent.

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