X-Configured Stent-Assisted Coiling in the Endovascular Treatment of Complex Anterior Communicating Artery Aneurysms: A Novel Reconstructive Technique

Discussion

Application of endovascular coil embolization for the treatment of wide-neck cerebral aneurysms has been rapidly evolving subsequent to the introduction of compliant microballoons into clinical use,⁶ thereafter followed by the introduction of neurodedicated self-expanding stents in recent years. Stents are used not only to treat wide-neck aneurysms by the scaffold they provide but also to achieve better initial occlusion rates while sparing the parent artery lumen and to decrease the likelihood of recanalization by the alteration they create in the intra-aneurysmal hemodynamics.^7,8

The multicenter registry, including preliminary results with the Enterprise stent without follow-up data, revealed a relatively high success rate of stent deployment (failure in 3%) and a ≥90% rate of occlusion in 76% of cases associated with the rates of 2% mortality and 2.8% morbidity.⁴ Previously reported smaller series by Weber et al⁹ and Lubicz et al¹⁰ indicated the ease of navigation with the use of the Prowler Plus catheter, excluding the exchange procedure. Precise placement with anchoring flared ends 0.5 mm larger than the diameter of the stent and the possibility of repositioning are major advantages of the Enterprise stent. Overall, in all 3 series, the Enterprise stent was found to be a safe and an effective tool for the treatment of complex intracranial aneurysms, with high initial occlusion rates.

Although the stents for intracranial use were originally designed for mechanical scaffolding purposes, recently appearing laboratory and clinical reports on their hemodynamic effects by alteration of intra-aneurysmal flow velocity are attracting increasing interest.⁸ Laboratory investigation on a patient-specific silicone aneurysm model based on clinical images, according to Tateshima et al,⁸ showed significant alteration of flow direction, velocity, and pattern before and after stent placement. In another in vitro study, the magnitude and pulsatility of the wall shear rate were found to be reduced by stent placement in the lateral aneurysm models.¹¹ There have been clinical reports to support these in vitro findings^10,12,13; Lubicz et al¹⁴ reported a 53% rate of further thrombosis in their series of aneurysms treated with stent-assisted coiling and suggested the adjunctive effect of the stent in stabilizing or significantly improving long-term anatomic results.

During the early experience with the self-expanding intracranial stents, double-stent treatment with a Y-configuration had been introduced to improve the application of coiling to wide-neck basilar bifurcation aneurysms.¹⁵ Successful initial occlusion rates and follow-up results have been achieved with Y-configured dual-stent-assisted coiling.¹⁶ With our evolving experience and more meticulous preoperative antiaggregation preparation and assessment, Y-configured dual-stent placement has been part of our routine practice in complex bifurcation aneurysms. Our experience with long-term follow-up of >70 patients (unpublished data, S.C., December, 2009) suggested very durable results. We, herein, describe a new dual-stent placement technique of X-configured stent placement for the treatment of AcomA aneurysms with wide-neck complex anatomy located on the AcomA and involving both A1-A2 junctions.

Far beyond the neck size and dome-to-neck ratio, AcomA aneurysms pose different morphologic features for success of initial treatment and long-term durability, such as dome direction, neck location, and the presence of associated anomalies.⁵ Aneurysms with large neck sizes located at the AcomA or with domes directed posteriorly have shown a tendency for greater recanalization rates, independent of the initial occlusion rates.⁵ Birknes et al¹⁷ analyzed the results of endovascular treatment in their exclusive group of 123 ruptured AcomA aneurysms with respect to aneurysm morphology and reported, overall, a 9.7% failure of endovascular treatment and a 69.9% rate of so-called successful embolization (≥90% occlusion of the aneurysm sac) in the entire group, 52% in the group of aneurysms with wider necks (≥4 mm). The recanalization in the follow-up was 33.3% and 66.7%, respectively, in these patients. To achieve endovascular reconstruction of the complex AcomA aneurysms, adjunctive stent placement has been used to facilitate coil embolization, though it is more limited than that in other aneurysm locations.¹⁸

AcomA aneurysms are not only challenging for the endovascular techniques but also for microsurgical clipping¹⁹ and demonstrate the highest incidence of postoperative morbidity among anterior circulation aneurysms. Both A2s emanating from the aneurysm, in addition to the wide base of the aneurysm where the AcomA is partly incorporated within the sac, may pose technical challenges during the microsurgery. In our series, all 5 aneurysms had very wide necks located on the AcomA involving both A1-A2 junctions, and this was the reason that the dual-stent placement was entertained in this group of patients.

Technically, placement of stents from the ipsilateral A2 to the A1 segment might be considered an option; however, we believe that sharp angles between the A1-A2 segments due to very wide-neck and complex anatomy may make application of X-stent placement more feasible in these selected cases. Besides, alteration of flow direction at the neck of the aneurysm, which, hypothetically, has an impact on long-term durability, is thought to be more efficient with the X-configuration rather than ipsilateral placement of stents with “opposite L” configurations. Moreover, the patency of the reconstructed AcomA is preserved, whereas it may become occluded with the latter stent configuration. However, of course, X-stent placement is to be reserved for patients having good-sized A1s, bilaterally. Otherwise, Y-stent placement through the large-sized A1 is the option for patients with hypoplasia/aplasia of A1 on 1 side.

Despite low initial occlusion rates (class C) encountered in our patients, follow-up data revealed further thrombosis of all aneurysms into Raymond-Roy class A occlusion. The follow-up results in this small group may indicate not only the favorable mechanical and hemodynamic impact of X-stent placement for AcomA aneurysms but also the roll of the stent-cell type in the long-term results. Although, in the series of Thorell et al, ¹⁶ the aneurysms were located at the terminal bifurcations, which were known to be more prone to recanalization, 2 of their 7 aneurysms treated with Y-stent-placement-assisted coiling were recanalized despite initial complete or near-complete occlusion. The open-cell design of the Neuroform stent used in that series may have had an effect on the hemodynamics. We can speculate that the closed-cell design of the stents may result in flow diversion at the intersection point, possibly due to the slight narrowing of the second stent while crossing. On the other hand, we did not encounter any disadvantage of the closed-cell design of the stents used herein,²⁰ either during the procedure or in the follow-up results as one may have anticipated, such as constriction of the second stent within the first stent at the intersection point with resultant compromise of the flow or possible narrowing of the lumen at this site in the follow-up. In the literature, in-stent stenosis has been reported in the patients whose aneurysms were treated with stent-assisted coiling.¹⁴ However, there has been no in-stent stenosis or artery occlusion in this small group of patients, despite dual-stent placement in relatively small vessels.