Stent-Assisted Coiling Versus Balloon Remodeling of Wide-Neck Aneurysms: Comparison of Angiographic Outcomes

Discussion

The most important findings of the present study are the following: 1) SAC of wide-neck aneurysms provides higher rates of complete obliteration (Raymond 1) at follow-up than does BAC. The rates of adequate aneurysm occlusion (Raymond 1–2), however, did not significantly differ between the 2 techniques. 2) Lower retreatment rates were observed with SAC versus BAC in wide-neck aneurysms. 3) SAC causes delayed occlusion of incompletely coiled wide-neck aneurysms at a significantly higher rate than does BAC. 4) Both treatment strategies are associated with low rates of morbidity and excellent clinical outcomes.

The high rate of aneurysm recanalization is considered the major drawback of endovascular therapy. Raymond et al⁹ found some degree of recurrence in as many as 33.6% of coiled aneurysms and identified aneurysm size ≥10 mm, treatment during the acute phase of subarachnoid hemorrhage, incomplete initial occlusion, and duration of follow-up as significant predictors of recurrence. In the International Subarachnoid Aneurysm Trial retreatment was done 4.6 times more commonly after endovascular therapy (17.4%) than after microsurgical clipping (3.8%).^10,11 The risk of late rebleeding was also higher after endovascular repair (2.9%) than after open surgery (0.9%). In a systematic review of the literature that included 8161 coiled aneurysms, Ferns et al¹² reported aneurysm reopening in 20.8% of cases and retreatment in 10.3% and identified location in the posterior circulation and size >10 mm as risk factors for aneurysm reopening. The adjunctive use of endovascular devices such as nondetachable balloons or self-expanding stents has notably improved the long-term durability of endovascular treatment. As such, in a large study, Piotin et al² found remarkably lower angiographic recurrence rates with stent-assisted coiling compared with conventional coiling (14.9% versus 33.5%, respectively). In a recent large multicenter French study (CLARITY), Pierot et al¹ identified 3 factors associated with the quality of midterm aneurysm occlusion after endovascular therapy, namely, neck size, the use of the balloon remodeling technique, and the quality of postoperative occlusion. The authors concluded that future treatment strategies should be focused on reinforcement and neoendothelialization at the level of the neck, especially for wide-necked aneurysms.

Initial patient comparability is a significant limitation of studies comparing SAC or BAC with conventional coiling, because aneurysms treated with SAC or BAC tend to be wide-neck, larger, and typically more complex than those treated with conventional coiling. In contrast to previous studies, the present study has the advantage of comparing 2 homogeneous groups of patients harboring wide-neck aneurysms treated by BAC or SAC. Our results are in line with the findings of recent reports showing that stented aneurysms have better angiographic outcomes than nonstented aneurysms coiled with or without balloon assistance. Lawson et al¹³ compared the follow-up angiographic outcomes of 37 stented versus 72 nonstented (with or without balloon assistance) incompletely coiled aneurysms and found that the odds of progression of occlusion of stent-coiled aneurysms were 18.5 times that of nonstented aneurysms. The authors attributed their results, at least in part, to the “flow remodeling” effects of self-expanding stents. In fact, stents may elicit a neointimal response that leads to endovascular vessel reconstruction and ultimately excludes the aneurysm from the circulation. Lopes and Sani¹⁴ described complete endothelialization of a Neuroform stent 4 months after its placement in an explanted human aneurysm specimen, with significant de novo fibroelastic tissue formation along the neck of the aneurysm. Such in-growth of endothelial tissue over the stented segment may potentially alter intra-aneurysmal flow dynamics causing stasis and thrombosis inside the aneurysm. This could explain why SAC yields higher rates of aneurysm occlusion and progressive thrombosis than conventional coiling or even BAC. Because of this potential flow-remodeling effect of self-expanding stents, we generally avoid overpacking stented aneurysms and may settle for more modest packing densities. At most neurovascular centers, however, the same range of packing density is achieved in aneurysms coiled with or without stent assistance. In vitro studies have also shown that higher packing densities are associated with significant flow reduction at the neck of the aneurysm.¹⁵ In addition, obtaining high packing densities remains a priority in ruptured aneurysms treated with SAC to minimize the risk of rebleeding. As such, packing density was 23.4% on average in ruptured aneurysms versus 16.7% in unruptured aneurysms.

The main limitation of BAC remains the inability to pack the neck of the aneurysm, because 65% of aneurysms initially and 35% at follow-up showed a neck remnant in the present series. This translated into significantly lower rates of complete aneurysm occlusion (Raymond 1) and higher rates of retreatment with BAC versus SAC. The difference between the 2 groups, however, was less prominent when comparing the rates of adequate aneurysm occlusion (Raymond 1–2 versus 3), with only a trend favoring SAC in multivariate analysis. Both techniques appear to have high efficacy with respect to adequate aneurysm occlusion at follow-up (94.2% with SAC and 84.4% with BAC).

Assessment of procedural safety and clinical outcomes are essential to determine the best therapeutic approach for wide-neck aneurysms. In our study, both techniques were associated with low morbidity rates (3%) and excellent clinical outcomes (>90%). It is worth noting that the significantly higher proportion of patients treated in the setting of subarachnoid hemorrhage in the BAC group has probably favored the stent group. In fact, the rate of procedural complications with BAC is reportedly 11.7% in unruptured aneurysms versus 17% in ruptured aneurysms.^4,16 Likewise, stent procedures in ruptured aneurysms carry a higher rate of morbidity than in unruptured aneurysms.¹⁷ For many neurointerventionalists, BAC is preferred over SAC for treatment of ruptured wide-necked aneurysms because the patient is spared the initiation of an antiplatelet regimen and its potential hemorrhagic complications.¹⁷ Mocco et al¹⁷ reported a 12% procedural mortality rate with SAC of acutely ruptured aneurysms and concluded that extreme caution should be exercised when considering stent deployment in patients with subarachnoid hemorrhage. Amenta et al¹⁸ treated 65 patients with acutely ruptured aneurysms with a 15.4% major complication rate including bleeding secondary to antiplatelet therapy in 7.7% and intraoperative in-stent thrombosis in 7.7%. In a systematic review of the literature of acutely ruptured intracranial aneurysms (339 patients) treated with stents, Bodily et al¹⁹ found that intracranial hemorrhagic and thromboembolic complications occurred in 8% and 6% of patients, respectively, and concluded that adverse outcomes were more common with SAC compared with conventional coiling. The use of a stent may also have considerable influence on flow in perforating vessels near treated cerebral aneurysms.¹⁵ On the other hand, a balloon may protect a side-branch from coil herniation and, in the event of intraprocedural aneurysm rupture, provide proximal control thus preventing devastating consequences for the patient. In a critical review of the literature, Pierot et al²⁰ noted that all except 1 publication showed a similar safety profile between BAC and conventional coiling, with better initial and follow-up anatomic results in aneurysms treated by BAC. On the basis of these data, they recommended wide use of BAC for treatment of wide-neck aneurysms and cautioned against wide use of stents given the potential associated morbidity.

Some operators advocate staging the stent-coil procedure to allow endothelialization of the stent. This may allow for greater stability and less movement of the stent and may also avoid endothelial damage and platelet activation during coil deployment. Accordingly, Lodi et al²¹ compared single-stage (n = 37) and multistage (n = 50) SAC and found higher complication rates with single-stage SAC. On the other hand, staging the stent-coil procedure may carry a theoretic risk of interval aneurysm rupture and loss to follow-up with an increased procedural cost. Currently, both techniques are widely applied in clinical practice.

Flow diversion and flow disruption are potential alternatives in the treatment of wide-neck intracranial aneurysms. In a large series of 191 patients with 251 aneurysms treated with the Pipeline Embolization Device (PED) (Covidien, Irvine, California), Saatci et al²² reported an event rate of 14.1%, with a permanent morbidity rate of 1% and mortality rate of 0.5%. The rate of aneurysm occlusion was 91.2% at 6 months and further increased to 94.6% with longer follow-up. In a prospective study from Hong Kong that included 143 patients with 178 aneurysms treated with the PED, Yu et al²³ noted periprocedural death or major stroke in 3.5% of cases with complete aneurysm occlusion in 84% at 18 months. The authors concluded that PED therapy was safe and effective and should be considered a first choice for treating unruptured aneurysms and recurrent aneurysms after previous treatments. Flow disruption with the WEB device (Sequent Medical, Palo Alto, California) is a new technique that has shown promising results for treatment of wide-neck aneurysms. Lubicz et al²⁴ have recently treated 19 patients with 20 unruptured wide-neck bifurcation aneurysms by WEB placement and reported symptomatic complications in 2 patients. Although additional stent placement and/or coiling was necessary in 3 cases at the acute phase and in 1 case at follow-up, complete or near-complete aneurysm occlusion was achieved in 89% of cases at 6 months. The results of this series showing feasibility of treatment of wide-neck aneurysms with the WEB require confirmation in larger studies.

The limitations of the present study are related to its retrospective design, the relatively short angiographic follow-up time (10.2 months), and the relatively small sample size, especially in the BAC group. Follow-up time was slightly longer in the SAC group, which may have influenced the anatomic results, especially the rate of progression of occlusion. Ruptured aneurysms were also more common in the BAC group, which may have favored better results in the SAC group, because it is well known that recurrences are more common when treatment is undertaken in the acute setting of subarachnoid hemorrhage. As such, ruptured aneurysms were strongly predictive of aneurysm recurrence in the studies by Piotin et al² and Raymond et al.⁹ Likewise, Cognard et al²⁵ found that unruptured aneurysms of <9 mm have a recanalization rate of 7% as opposed to ruptured aneurysms of the same size, which had a recurrence rate of 17%. Also, stent-assisted coiling of ruptured aneurysms has been shown to be associated with lower angiographic obliteration rates at follow-up compared with unruptured aneurysms.⁷ Nevertheless, a multivariate analysis was conducted to account for such differences in baseline characteristics and identify independent predictors of occlusion. Prospective, randomized trials will be needed to provide definitive information on the best therapeutic approach for wide-neck aneurysms.