Are aneurysms treated with balloon-assisted coiling and stent-assisted coiling different? Morphological analysis of 113 unruptured wide-necked aneurysms treated with adjunctive devices.

RESEARCH—HUMAN—CLINICAL STUDIES RESEARCH—HUMAN—CLINICAL STUDIES

Are Aneurysms Treated With Balloon-Assisted Coiling and Stent-Assisted Coiling Different? Morphological Analysis of 113 Unruptured Wide-Necked Aneurysms Treated With Adjunctive Devices Eric Peterson, MD, MS* Brian Hanak, MD‡ Ryan Morton, MD‡ Joshua W. Osbun, MD‡ Michael R. Levitt, MD‡ Louis J. Kim, MD‡ *Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, Florida; ‡Department of Neurological Surgery, University of Washington School of Medicine, Harborview Medical Center, Seattle, Washington Correspondence: Louis J. Kim, MD, 325 9th Ave, Box 359924, Seattle WA 98104. E-mail: [email protected] Received, September 27, 2013. Accepted, March 27, 2014. Published Online, April 15, 2014. Copyright © 2014 by the Congress of Neurological Surgeons.

BACKGROUND: In the endovascular treatment of wide-necked unruptured aneurysms, there is controversy over which adjunctive device (stent vs balloon) is appropriate. At the payer level it has been posited that stents and balloons treat the same aneurysms, and, as such, the more expensive stents should not be reimbursed. OBJECTIVE: We challenge this assertion, and instead hypothesize that aneurysms treated with stent assistance are morphologically different than those selected for balloon assistance. METHODS: Retrospective review of unruptured aneurysms treated with an adjunctive device between 2008 and 2010. Morphological analysis was performed on the pretreatment 2-D catheter angiogram. The immediate posttreatment Raymond score was compared with that seen on the 12-month follow-up angiogram. RESULTS: One hundred six unruptured aneurysms were treated with an adjunctive device and followed for a mean of 24.5 months. Morphological analysis revealed a lower dome-to-neck ratio (1.5 vs 1.2) and aspect ratio (1.44 vs 1.16) in the aneurysms treated with stent assistance vs balloon assistance. Of the 15.3% that were worse on follow-up angiography, there was no statistical difference between those treated with a stent vs a balloon (17.1% vs 14.2%). The overall re-treatment rate was 10.2% and was not statistically different between the 2 groups (12.7% vs 5.7%). CONCLUSION: We found that unruptured aneurysms selected for treatment with stent-assisted coiling are morphologically different from those selected for treatment with balloon assistance. Despite the more challenging morphology, Raymond scores and re-treatment rates at 1 year were not statistically different between the 2 groups, suggesting an important role for stents in the treatment of unruptured aneurysms. KEY WORDS: Balloon assistance, Endovascular, Morphological analysis, Stent assistance, Unruptured aneurysm Neurosurgery 75:145–151, 2014

DOI: 10.1227/NEU.0000000000000366

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ince its introduction over 30 years ago, coil embolization has made remarkable technological progress as a treatment modality for intracranial aneurysms. The first major advance was complex coil shapes that allowed for better filling of aneurysms.1 The second major advance was the development of adjunctive devices to help ABBREVIATIONS: DSA, digital subtraction angiography; TE, thromboembolic

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keep the coil mass in the dome of the aneurysm. While extensively used in the cardiac literature, the small caliber and tortuous nature of the intracranial vasculature precluded simple translation of cardiac balloons and stents for intracranial use. The development of specialized neurovascular devices in recent years has dramatically expanded the types of aneurysms that can be treated with endovascular means. Large series of balloon remodeling and stent-assisted coiling have validated the safety and efficacy of both techniques.2-4

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Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.

PETERSON ET AL

Rather than occupying the same niche in the treatment of aneurysms, stent assistance allows for the treatment of aneurysms that would be difficult if not impossible to treat with simple balloon remodeling. We hypothesized that the aneurysms selected for balloon remodeling are morphologically different from those selected for stent-assisted coiling. We sought to quantify this “gestalt” of whether to select balloon remodeling or stent assistance by comparing the morphological characteristics of aneurysms selected for each treatment modality in a high-volume modern endovascular center.

METHODS Clinical and angiographic outcomes of 116 aneurysms treated endovascularly with an adjunctive device between 2008 and 2011 were retrospectively analyzed from a prospectively collected database. All aneurysms were unruptured, and all were treated with either balloon remodeling or stent-assisted coiling. The choice of adjunctive device was left to the discretion of the treating physician. All patients were followed up with 6- and 12-month catheter angiograms. The morphological characteristics were measured on the pretreatment angiogram. Each parent vessel was protected with a single stent. If there were 2 parent vessels at risk (anterior communicating artery aneurysm, middle cerebral artery aneurysm), then a single stent was used for each vessel. We did not doublecover aneurysms.

Measurement Technique All aneurysm measurements were performed on a PACS workstation, and included aneurysm size, neck size, aspect ratio, and dome-to-neck ratio. Measurements were made by using electronic calipers and performed on a single midarterial phase image from the 2-dimensional (2-D) digital subtraction angiography (DSA) (Figure 1 and Figure 2). After a recent publication reported that the 2-D DSA native runs were better suited to aneurysm morphology measurement than 3-D rotational angiography,5 we used the 2-D DSA whenever possible, particularly the working view runs used for aneurysm treatment. When we felt that the 2-D runs did not adequately visualize the morphology, the 3-D rotational angiography was used. Two separate readers performed measurements on 2 separate occasions, and the readers were blinded to the adjunctive device used. We cropped each image to only include the parent vessel directly underneath the coil mass, thus excluding the distal and proximal stent tines if a stent was used. The middle of the stent is usually not visible. There was excellent agreement between the 2 readers (Κ = 0.99), and averages of the 2 measurements were used for analysis. Aneurysm size was defined as the largest distance between any 2 points on the aneurysm surface, and the aneurysm height was defined as the largest distance between the neck center and the aneurysm surface. Statistical analysis was performed using SAS software, using a paired t test for the analysis of the measurement differences between aneurysms treated with balloon remodeling and aneurysms treated with stent assistance. A Fisher exact test was used for analyzing the different retreatment rates for the stent vs balloon groups.

Outcome Measures Angiographic outcomes were recorded immediately posttreatment and at the 12-month follow-up angiogram, and documented as Raymond class

146 | VOLUME 75 | NUMBER 2 | AUGUST 2014

FIGURE 1. Anterior-posterior angiogram demonstrating the measurement technique for dome-to-neck ratio.

I (complete aneurysmal occlusion), class II (residual neck), or class III (residual aneurysm dome filling). Complications were recorded as minor (groin complications, asymptomatic vessel dissections not requiring intervention) or major (symptomatic thromboembolic complications, vessel perforations, or permanent neurological deficit). Technical difficulties were defined as asymptomatic difficulties in treating the aneurysm (inability to catheterize the aneurysm through the tines of a stent, asymptomatic herniation of a coil loop into the parent vessel, inability to navigate the stent into position, etc) Re-treatment was defined as any procedure performed for residual aneurysm found on follow-up angiography. The decision to re-treat or not was at the discretion of the treating physician. Every effort was made to obliterate Raymond 3 aneurysms (residual/recanalized dome) to at least a Raymond 2, whether the aneurysm was initially only coiled to a Raymond 3 or if it worsened on follow-up to a Raymond 3. The latter was presumed to be secondary to inadequate packing at the time of the initial treatment.

Endovascular Procedure Treatment was performed under general anesthesia in all cases. Patients treated with stent-assisted coiling were pretreated with 5 days of Plavix 75 mg and aspirin 325 mg per day. All procedures were performed under full heparinization with a goal activated clotting time of 250 to 300. In stented patients, aspirin and Plavix were continued postoperatively for 6 months after which the Plavix was discontinued and the aspirin continued indefinitely. Stenting was performed with either the Neuroform stent (Boston Scientific, Natick, Massachusetts) or Enterprise stent (Cordis, Miami Lakes, Florida) according to operator preference. Our institutional preference is to place the stent first and then access the aneurysm through the stent rather than jailing the catheter. If there was difficulty accessing



MORPHOLOGY OF BALLOON VS STENT

occlusion in 13/71 (18.3%). At 1 year, the balloon group’s results were as follows: 19/35 (59.4%) Raymond 1, 13/35 (40.6%) Raymond 2, and 0/35 (0%) Raymond 3. No patients were lost to follow-up. For the stent group, the 1-year angiographic outcomes were 34/63 (53.9%) Raymond 1, 26/ 63 (41.3%) Raymond 2, and 10/63 (15.9%) Raymond 3. Eight patients were lost to follow-up. The mean aspect ratio for the balloon-remodeling group was 1.44 vs 1.16 in the stent group (P , .009). The mean dome-toneck ratio was 1.5 for the aneurysms treated with balloon remodeling vs 1.18 for those treated with a stent (P , .01). Aneurysm location for the 2 groups is shown in Table 1.

FIGURE 2. Anterior-posterior angiogram demonstrating the measurement technique for aspect ratio.

the aneurysm through the stent tines or if the stent was seen to migrate during attempts at accessing the aneurysm, the procedure was aborted, and the patient brought back 6 weeks later for definitive coiling after the stent had stabilized. Balloon remodeling was performed with Hyperform or Hyperglide balloons (EV3, Irvine, California).

Re-treatment Rates One-year angiographic follow-up was available for 98 patients (Table 2). Raymond scores on follow-up for the entire group were stable or improved in 84/98 (85.7%) and worse in 15/98 (15.3%). Of the 15 that were worse on follow-up angiography, there was no statistical difference between those treated with stent-assisted coiling (6/29, 17.1%) vs balloon remodeling (9/63, 14.2%, P = .459). Overall, 10/98 (10.2%) aneurysms were re-treated, including 8/63 (12.7%) in the stent group and 2/35 (5.7%) in the balloon group. This difference was not statistically significant (P = .233). Complications The overall rate of complications was 12.1%. Major complications occurred in 5/116 (4.3%), all of which were in the stent group. Minor complications occurred in 9/116 (7.8%), 3 in the balloon group and 6 in the stent group. Technical failures occurred in 6/71 (8.5%) of the stent group. There were no technical complications precluding adequate treatment of the aneurysm in the balloon group.

RESULTS Overall, 106 aneurysms were included in the analysis: 71 treated with stent-assisted coiling and 35 treated with balloon remodeling (Figure 3). The locations of the aneurysms treated in each group were similar, with the notable exception of the anterior communicating and vertebrobasilar regions. Aneurysms of the anterior communicating artery were more likely to be treated with balloon assistance, while lesions of the vertebrobasilar junction all required a stent. Of the aneurysms treated with a stent, 11 were originally treated with stand-alone coiling but either recurred or were unable to be adequately coiled without a stent. Two patients were treated in a staged fashion because of operator preference. There were no complications in either of these 2 patients. For the balloon group, the immediate angiographic outcome was a Raymond 1 occlusion in 18/35 (51.4%), a Raymond 2 occlusion in 16/35 (45.7%), and a Raymond 3 occlusion in 1/35 (2.9%). For the stent group, the immediate angiographic outcome was a Raymond 1 occlusion in 29/71 (40.9%), a Raymond 2 occlusion in 28/71 (39.4%), and a Raymond 3

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DISCUSSION The primary finding of this study is that aneurysms that are selected for stent-assisted coiling are morphologically different than those selected for balloon-assisted coiling. We found less favorable aspect and dome-to-neck ratios in the patients selected for stent-assisted coiling. This difference in aneurysm morphology indicates that aneurysms clinically determined to need stent assistance over a balloon is based in part on angioarchitecture, not surgeon’s preference. The secondary finding is that, despite this more challenging morphology, the recurrence and retreatment rates were not statistically different, suggesting that stent technology allows for the effective obliteration of a challenging subset of aneurysms that traditionally have been associated with high recurrence and re-treatment rates. The use of adjunctive devices to assist in the coiling of aneurysms not anatomically suitable for stand-alone coil embolization has expanded dramatically in recent years. The primary focus of these devices is simply to keep the coils in the aneurysm and out of the parent vessel. Strategies to accomplish this goal fall into 2 general



PETERSON ET AL

FIGURE 3. Flowchart of unruptured aneurysms treated with an adjunctive device.

categories: temporarily inflating a balloon across the neck of the aneurysm, and the permanent placement of a stent across the neck of the aneurysm. These devices have allowed for substantial expansion of the number aneurysms that are amenable to coil embolization, but the exact choice of device to use is controversial for 2 reasons. First, both techniques are associated with increased morbidity in comparison with stand-alone coiling, with stents generally conferring more risk than balloons, which in turn confer more risk than simple coiling.2,6 However, more recent series have shown that balloon assistance is of similar risk to stand-alone coiling.4 Second, the devices are costly, particularly stents. Morphology of Balloon-Remodeled vs Stent-Coiled Aneurysms In ruptured aneurysms, the balloon-remodeling technique is preferred over stent-assisted coiling because of the requirement for antiplatelet agents if a stent is used. Because of this reason, lesions that are unfavorable for coiling even with balloon remodeling are often referred to surgery, although some centers are pushing the envelope with stenting even in ruptured cases.7-9 In the unruptured population, however, there is concern about dualantiplatelet therapy. We chose to compare the morphological parameters of aneurysms treated with balloon remodeling with those treated with stent assistance in unruptured aneurysms rather than in ruptured aneurysms, because, in theory, the operator will choose balloon remodeling when the morphology is unfavorable for stand-alone coiling, but not so unfavorable that a permanent intraluminal device is needed. In ruptured


aneurysms, by contrast, operators may push the envelope with balloon assistance since stenting ruptured aneurysms is so problematic. Our results suggest that, far from being different ways of treating the same types of aneurysms, the techniques of balloon-assisted coiling and stent-assisted coiling are not interchangeable. There exists a population of unruptured aneurysms that is not amenable to balloon remodeling and instead requires a stent. Specifically, we found that aneurysms selected for stent-assisted coiling had wider necks and smaller aspect ratios than those selected for balloon remodeling. This is significant because it speaks to the critical role

TABLE 1. Aneurysms Stratified by Locationa Aneurysm Location Acomm Basilar tip Pcomm PICA MCA Ophthalmic ICA terminus Cavernous VB junction

Stent-Assisted, n (%) Balloon-Assisted, n (%) 5 8 9 1 5 14 3 7 5

(7.9) (12.7) (14.3) (1.6) (7.9) (22.2) (4.8) (11.1) (7.9)

11 3 3 1 2 9 4 2 0

(32.4) (8.8) (8.8) (2.9) (5.9) (26.5) (11.8) (5.9) (0)

a

Acomm, anterior communicating artery; Pcomm, posterior communicating artery; PICA, posterior inferior cerebellar artery; MCA, middle cerebral artery; ICA, internal carotid artery; VB, vertebrobasilar.




TABLE 2. Comparison of Aneurysms Treated With Balloon Assistance vs Stent Assistancea

Number Aspect ratio Dome-to-neck Re-treatment rate Major complications Minor complications a b

Stent, %

Balloon, %

P Value

63 1.16 (IQR 0.7-1.6) 1.18 (IQR 1.01-1.59) 8/63 (12.7) 5/71 (7.1) 6/71 (8.5)

34 1.44 (IQR 1.05-1.78) 1.5 (IQR 1.16-1.66) 2/35 (5.7) 0/0 (0) 3/35 (8.6)

NA .009b .01b .233 .001b .342

NA, not available; IQR, interquartile range. Statistically significant.

that intracranial stents play in the treatment of unruptured aneurysms, a role that cannot be played by simple balloon remodeling. Although there has been extensive investigation into the morphology of intracranial aneurysms, the vast majority of studies focus on morphological analysis to predict either future rupture risk of unruptured aneurysms or the risk of aneurysm recurrence after endovascular treatment. The use of aneurysm morphology to determine the use of adjunctive devices is less well studied. Debrun et al10 published a series on morphology of aneurysms that could be coiled with stand-alone coiling techniques, prior to the introduction of balloon remodeling or stents. They found dometo-neck ratio of less than 2 or a neck greater than 5 mm to be unfavorable for coiling, with a 50% incidence of incomplete coiling in this subgroup. Brinjikki et al11 evaluated the morphology of 170 aneurysms to determine what was the best predictor of the need for an adjunctive device vs stand-alone coiling. They found that the combination of dome-to-neck ratio ,1.2 and aspect ratio of ,1.2 predicted the need for an adjunctive device in almost all cases. In contrast, 75% of cases with ratios .1.6 were successfully treated with stand-alone coiling. They found the aspect ratio to be the most powerful predictor of the need for an adjunctive device. Several groups have also evaluated the relationship between the center of the parent artery and the aneurysm ostia and found the angle to be predictive of the need for a stent.12,13 However, no study has directly compared the morphology of balloon-remodeled aneurysms with stent-assisted aneurysms. It also seems clear that certain locations are predisposed for more challenging morphology when it comes to dome-to-neck and aspect ratios. The vertebrobasilar junction in particular is well known for its difficulty in treating with stand-alone coiling, and in our series no patient could be treated with balloon assistance, with all cases requiring a permanent stent to preserve the parent vessel. The anterior communicating artery, on the other hand, frequently was able to be treated with balloon assistance. Use of an adjunctive device is not a panacea, as evidenced by the 16% rate of persistent aneurysmal filling at 1 year in the stented group. Some very challenging morphologies are resistant to endovascular obliteration even with an endoluminal stent in place to allow for tighter

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packing. It is this group in which flow diverters represent a particularly important advance, because even advanced (but not flow-diverting) endovascular techniques are insufficient to obliterate the aneurysm. Recurrence Rates A second important finding of our study is that, despite the more challenging morphology in the stent group, the occlusion rates and re-treatment rates were similar between the balloon-remodeling group and the stent-assisted group. This suggests that stents allow the successful and durable treatment of a more difficult subset of wide-necked aneurysms that were not amenable to balloon-assisted coiling, refuting the notion that stents are simply another device that can be used for wide-necked aneurysms, interchangeable with balloons. These recurrence rates are in line with that of several large series of assisted coil techniques. Cekirge et al4 reported their results of 800 balloon-remodeled aneurysms and found a 9% retreatment rate, although the majority of their aneurysms presented with subarachnoid hemorrhage. A recent review of balloon remodeling reported an overall rate of persistent Raymond class 3 filling (persistent filling of aneurysm dome) of 10% at 6 months.14 A large series of aneurysms treated with stent-assisted coiling reported a recurrence rate of 15%; re-treatment rates were not reported. Two recently published series containing long-term follow-up of stent-assisted coiling found a re-treatment rate of 14% and 15%.3,15 This is despite near-universal mention in the articles cited that these aneurysms were deemed morphologically unsafe for temporary balloon remodeling. A more recent series of stent-assisted coiling documented a similar 12% recanalization rate but a lower re-treatment rate of 6.4%.16 Complication Rates Discussions regarding complication rates for adjunctive devices require some nuance, as the devices carry different risk profiles, and there seems to be a higher complication rate (both thromboembolic and intraprocedural rupture) in the treatment of ruptured aneurysms in comparison with unruptured aneurysms. For balloon remodeling, the majority of the literature supports a low rate of thromboembolic complications, in the



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range of 5% for unruptured lesions17 and 10% for ruptured lesions.18,19 The largest series of balloon remodeling (the majority of which presented with subarachnoid hemorrhage) to date reports the lowest rate of symptomatic thromboembolic (TE) complications in the literature at 1.3%.4 A recent literature review evaluating rates of TE complications for balloon remodeling found rates similar to that reported for stand-alone coiling at 8%.14 A subgroup analysis of the ATENA series of unruptured aneurysms likewise found no differences in TE complications in those treated with balloon remodeling vs those treated with stand-alone coiling.20 Stent-assisted coiling is consistently associated with higher rates of complications, despite the fact that the vast majority is performed in the unruptured population, with its more favorable TE environment. The largest single series of 216 aneurysms treated with stent-assisted coiling reported a 7.4% incidence of permanent device-related morbidity, including a 5% rate of TE complications. Several smaller series report similar rates of morbidity and TE complications,15,21 including a recent series from Santillan et al3 that reported a remarkable 0% incidence of TE complications in over 70 stent-assisted aneurysms; major device-related morbidity was 5.1%. Our overall rate of major complications was 4.7%, all of which occurred in the stented group. While in line with national data on this issue, a nearly 5% rate of permanent morbidity along with a 10% re-treatment rate highlights the fact that treatment of these lesions is challenging, no matter what tool is used. Importantly, it contributes to the knowledge base about the rates of complication with assistance devices. As flow diverters enter the postmarket stage, new complications are becoming clear that were not reported in earlier studies.22,23 Because flow diverters will likely supplant a significant subset of aneurysms previously treated with balloon and stent assistance, it is important to remember the benchmark complication rate against which flow diverters are to be measured. Limitations Our study has several limitations, including its relatively small size and retrospective nature. Another limitation is the subjective nature in which the operators decided which adjunctive device to use. However, a major objective of the study was to attempt to quantify this subjective process into a real morphological difference. We feel we made some progress toward this objective. In addition, there were some aneurysms that were morphologically worse on follow-up angiography, but were not re-treated. The nuances behind the decision to treat these small recurrences were not addressed in our analysis, and could have affected our retreatment rates when viewed by another center. In addition, the small size of the balloon-assist cohort may represent a statistical bias in the study.

CONCLUSION There exists a morphologically distinct population of unruptured aneurysms that cannot be treated with temporary balloon


remodeling and instead requires a permanent endoluminal device to be implanted. Our study quantifies this distinction, finding that unruptured aneurysms that are selected for stent-assisted coiling represent a more challenging cohort of aneurysms, with a significantly higher aspect ratio and dome-to-neck ratio. Although the use of flow diverters is increasing, this also increases the complication rates of treatment. Hence, high-porosity stentassisted coil embolization will continue to have an important niche in the treatment of broad-based aneurysms. Newer stent technologies that hybridize the characteristics of high-porosity and flow-diverting stents are emerging as well. These new devices may redefine indications and complications. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

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14. Shapiro M, Babb J, Becske T, Nelson PK. Safety and efficacy of adjunctive balloon remodeling during endovascular treatment of intracranial aneurysms: a literature review. AJNR Am J Neuroradiol. 2008;29(9):1777-1781. 15. Fiorella D, Albuquerque FC, Deshmukh VR, McDougall CG. Usefulness of the Neuroform stent for the treatment of cerebral aneurysms: results at initial (3-6-mo) follow-up. Neurosurgery. 2005;56(6):1191-1201; discussion 1201-1192. 16. Chalouhi N, Jabbour P, Singhal S, et al. Stent-assisted coiling of intracranial aneurysms: predictors of complications, recanalization, and outcome in 508 cases. Stroke. 2013;44(5):1348-1353. 17. Pierot L, Spelle L, Leclerc X, Cognard C, Bonafé A, Moret J. Endovascular treatment of unruptured intracranial aneurysms: comparison of safety of remodeling technique and standard treatment with coils. Radiology. 2009;251(3):846-855. 18. Pierot L, Cognard C, Anxionnat R, Ricolfi F, Investigators C. Remodeling technique for endovascular treatment of ruptured intracranial aneurysms had a higher rate of adequate postoperative occlusion than did conventional coil embolization with comparable safety. Radiology. 2011;258(2):546-553. 19. Sluzewski M, van Rooij WJ, Beute GN, Nijssen PC. Balloon-assisted coil embolization of intracranial aneurysms: incidence, complications, and angiography results. J Neurosurg. 2006;105(3):396-399. 20. Pierot L, Cognard C, Spelle L, Moret J. Safety and efficacy of balloon remodeling technique during endovascular treatment of intracranial aneurysms: critical review of the literature. AJNR Am J Neuroradiol. 2012;33(1):12-15. 21. Hwang G, Park H, Bang JS, et al. Comparison of 2-year angiographic outcomes of stent- and nonstent-assisted coil embolization in unruptured aneurysms with an unfavorable configuration for coiling. AJNR Am J Neuroradiol. 2011;32(9):1707-1710. 22. Siddiqui AH, Kan P, Abla AA, Hopkins LN, Levy EI. Complications after treatment with pipeline embolization for giant distal intracranial aneurysms with or without coil embolization. Neurosurgery. 2012;71(2):E509-E513; discussion E513. 23. Velat GJ, Fargen KM, Lawson MF, Hoh BL, Fiorella D, Mocco J. Delayed intraparenchymal hemorrhage following pipeline embolization device treatment for a giant recanalized ophthalmic aneurysm. J Neurointerv Surg. 2012;4(5):e24.

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CME QUESTIONS: 1. Intracranial aneurysms with what type of morphological features are preferentially treated with adjunctive devices such as balloon or stentassisted coiling? A. High aspect ratio B. Wide-neck C. Daughter sac D. Calcified wall E. Large size

2. What is the most characteristic feature of aneurysms treated by stentassisted coiling as compared to balloon-assisted coiling? A. Lower aspect ratio B. Ruptured aneurysms C. Smaller diameter D. More calcified E. Anterior communicating artery location

3. When comparing aneurysms treated with stent-assisted coiling and those treated with balloon-assisted coiling, what is the most significant difference in outcomes? A. Higher recurrent rates B. Inferior initial angiographic results C. Higher complication rates D. Lower retreatment rates E. Lower intraoperative rupture rate



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