“Y” and “X” Stent-Assisted Coiling of Complex and Wide-Neck Intracranial Bifurcation Aneurysms

Discussion

Complex and wide-neck bifurcation aneurysms that incorporate ≥2 parent vessels are rarely treated with a single stent, due to the risk of coil prolapse and parent vessel occlusion. Different techniques have been proposed to obviate this problem. Balloon remodeling and double-balloon remodeling were the first endovascular techniques used to treat wide-neck aneurysms.^11,12 Safety and efficacy are similar to those in standard coiling,²⁶ and the immediate occlusion rate in ruptured aneurysms is higher than that in standard coiling.²⁷ These techniques are effective for the treatment of aneurysms in the setting of SAH, to minimize the risk of early rebleeding even if total aneurysm occlusion is not obtained. Unfortunately, this technique does not provide an arterial reconstruction, and long-term follow-up showed a recurrence rate similar to that in standard coiling, in particular for wide-neck and large aneurysms.²

Crossover stent placement for basilar tip and AcomA aneurysms has been illustrated in few publications. Kelly et al²⁸ described this technique in bifurcation aneurysms with unfavorable distal limb configuration. For the authors, this technique, compared with Y stent placement, offered a better coverage of the aneurysmal neck and limited the use of multiple stents, decreasing the risk of thrombogenicity. Nevertheless, this technique cannot be used with MCA aneurysms and in AcomA and basilar tip aneurysms when the circle of Willis is incomplete.

The waffle-cone technique has been described in small series^15,29 as a valid alternative to Y and X stent placement when the latter cannot be performed due to an unfavorable distal limb configuration. In this case, the distal part of the stent is placed inside the aneurysmal sac and the blood flow is direct into the aneurysmal sac. This technique is technically easier than Y stent placement but probably presents a higher risk of coil protrusion due to the incomplete neck coverage. The major drawback is the risk of recurrence due to the redirection of the flow inside the aneurysm.

In our single-center retrospective series, all cases of unruptured aneurysms were previously discussed during our interventional meetings. We treated most small aneurysms (85.7%) that we considered suitable for Y or X stent-assisted coiling. We could have treated some with single stent-assisted coiling for wide-neck aneurysms or with a flow diverter for complex aneurysms, but during the discussion, we finally decided to perform Y or X stent-assisted coiling. Concerning the indication to treat this subgroup of aneurysms, 17/90 (18.9%) were recurrences and 33/90 (36.7%) were in patients with multiple intracranial aneurysms with or without a previous history of SAH.

In our series, stent placement was performed before coiling in most cases, to scaffold the aneurysmal neck and reduce the risk of coil protrusion. We used different stent combinations, always overlapping. In most of our cases, an open-cell stent was deployed as a first stent in the smaller and more acute vascular branch. This stent, compared with closed-cell-design stents, presented 2 advantages, a better vessel conformability in acute curvature and an outward prolapse of the struts at the convexity.³⁰ A better conformability reduces the risk of thromboembolic events³¹; the outward prolapse improves neck coverage and should reduce friction during the deployment of the second stent. The second stent, open- or closed-cell, was delivered in the larger and less angulated vascular branch. We used flat panel CT to evaluate stent apposition. Recently, Cho et al,³² described a nonoverlapping Y stent placement technique in wide-neck basilar tip aneurysms with the Enterprise stent, advising that this technique presents the advantages of both open and closed stents together. Cekirge et al²¹ described an overlapping Y stent placement technique by using 2 closed-cell-design stents without endosaccular coiling; they preferred this combination of stents because it is easier to deliver and deploy but also seems more likely to provide superior modification on aneurysm hemodynamic parameters. However, 2 closed stents in overlapping configuration, in particular in an acute curvature, may lead to inappropriate vessel wall apposition and to higher thrombogenicity. Furthermore, there is a high risk of kinking of the second stent and, therefore, minor scaffolding at the neck.

Technical problems were previously encountered, but in our series the friction between the stents was not a major matter. Our major problem was the navigation of the microcatheter in the most angulated branch. To obviate this matter, we always used a triaxial access to improve proximal support, and in few cases, we turned the microguidewire inside the aneurysmal sac with a higher risk of perforation. Another difficulty was to achieve a correct proximal position of the first stent to avoid its displacement during the navigation of the microcatheter in the second branch. A proper length selection of the first stent of at least 20 mm is necessary to cover the neck completely and to stabilize the stent, in particular in MCA and AcomA aneurysms. However in these locations, the proximal part of the first stent must not land in the terminal carotid artery; otherwise catheterization of the second branch becomes more difficult to achieve.

In our series, including successful and attempted stent placements, we observed a relatively high rate of complications, with a mortality rate of 1.0% and permanent neurologic morbidity of 10.0%. The comparison of complications across reported series is difficult due to the limited number of procedures performed with Y and X stent placement in other series. Recently, a larger retrospective multicenter series,²³ with ruptured and unruptured aneurysms, reported a good outcome (mRS 0–2) in 93% of the patients. In this series, most were basilar tip aneurysms (87%), a location where the navigation and the deployment of stents are easier due to favorable distal limb configuration. In a large retrospective series²⁴ consisting of 193 bifurcation aneurysms, by using mostly closed-cell stents, the authors reported a low rate of permanent morbidity (1.1%) and mortality (0.5%). Although we also applied a strict antiaggregation protocol and checked 1 week before the procedure, our hemorrhagic and ischemic complications led to a higher rate of permanent morbidity.

Our immediate angiographic complete occlusion rate was quite low, as previously reported^2,3,6,33 in stent-assisted coiling. The procedure was performed with the patient under heparin, clopidogrel, and aspirin; therefore, thrombus formation was slow and achieving attenuated packing, in particular at the neck, was quite difficult due to the immobility of the microcatheter. Nevertheless, Chalouhi et al³⁴ suggested that a moderate packing attenuation seems to be effective in stent-assisted coiling to achieve complete occlusion. At angiographic follow-up, we observed an improvement in 42.4% (36/85) of the aneurysms. This progressive thrombosis was reported in many stent-assisted coiling series,^2,6,33 probably due to antiplatelet discontinuity and “intimal overgrowth” at the neck. Cekirge et al²¹ also described a “flow remodeling effect” in aneurysms treated by Y closed-cell stent placement, which showed promising results in their retrospective series consisting of 193 bifurcation aneurysms, with a recanalization rate of 2.2%.²⁴