Endovascular treatment of intracranial aneurysms by endovascular coiling has become an alternative treatment to surgical clipping, with lower morbidity and mortality rates in selected cases.17) However, the possibility of coil migration and long-term angiographic recurrence pose limitations in the treatment of complex or wide-necked aneurysms.17)23) Self-expanding stents allow denser aneurysm packing with increased neck coverage, and may also improve treatment durability through a combination of flow-diversion, parent vessel straightening, and fibroelastic tissue formation along the neck of the aneurysm.14)23) Currently, two stents have been approved for stent-assisted coiling in the USA: the Enterprise vascular reconstruction device (Enterprise; Codman Neurovascular/Johnson & Johnson, Raynham, MA, USA) and the Neuroform stent (Neuroform; Boston Scientific/Stryker, Kalamazoo, MI, USA). The Enterprise is a self-expandable nitinol stent with a highly flexible closed-cell design. The stent can be delivered through a standard microcatheter, technically easier than the exchange procedure.20)23)

There are many reports of the feasibility and safety of stent-assisted coiling. However, little information is available regarding the follow-up results of the technique. Thus, in this study, we report our initial and follow-up clinical experience with Enterprise stent placement in 39 consecutive patients with 40 wide-neck intracranial aneurysms.

We reviewed the clinical and radiological records in a single-center registry of all patients who were treated with Enterprise stent-assisted coil embolization during the 30-month period from June 2009 to December 2011. Thirty-nine patients with 40 wide-necked aneurysms were enrolled, including nine men and 30 women with mean age 61.3 years (range 44-85 years). Thirty patients were asymptomatic, four had cerebrovascular accident sequelae, and five had suffered acute subarachnoid hemorrhage. A "wide-necked" aneurysm was defined as having a neck of > 4 mm diameter or an aspect ratio of > 2.0. Twenty-eight aneurysms were located in the anterior and 12 in the posterior circulation (Table 1). Thirty-four aneurysms were found incidentally. Seven were dissecting aneurysms. One aneurysm had reopened after prior coil embolization, while 39 had not been treated. All aneurysms were judged impossible to treat using other techniques.

All patients underwent endovascular treatment under general anesthesia. Clopidogrel 300 mg per day was given in the morning of the procedure in patients with unruptured aneurysms. Because of the risk of rebleeding, no premedication with platelet inhibitors was administered to patients with acutely ruptured aneurysms unless thromboembolic events occurred. Heparin was administered for anticoagulation in a bolus infusion of 4000 IU, followed by 1000 IU/h.

Three neurointerventionalists reviewed the angiographic records. Angiographic results were classified as: complete occlusion (no contrast filling the sac), remnant neck (residual filling of the neck), and remnant sac (residual filling of the sac).22)

During follow-up, the aneurysm could change from one class to another or remain unchanged. The clinical and angiographic findings are summarized in Table 1. Follow-up angiography was carried out after more than six months. If conventional angiography was not feasible, 3.0-Tesla magnetic resonance angiography (MRA) was performed.

Wide-necked aneurysms are difficult to treat, either surgically or endovascularly, because of their unfavorable geometry, which reduces the possibility of achieving dense packing and elimination of the aneurysm from the circulation. The development of intracranial stents allows treatment of intracerebral aneurysms with unfavorable anatomy. The stent serves as a scaffold in the parent artery to prevent coil migration.17) Furthermore, stent placement across the aneurysm neck enables additional obliteration by denser and safer packing of the aneurysm lumen and may improve aneurysm occlusion by redirection of flow.11)12)17)

The Enterprise stent is the first closed-cell stent designed to treat wide-necked intracranial aneurysms. Advantages of the design include the ability of the stent to be partially deployed, recaptured, and redeployed, and it may improve the stability of coils within the aneurysm.12) Furthermore, the Enterprise stent's delivery system facilitates its navigation and placement. Reported rates for the inability to navigate or deploy the Neuroform stent are as high as 19.8%, compared with only 0-5% for the Enterprise. Despite recent improvements in the delivery system, the failure rate of the Neuroform has remained high.1)2)6)12)19) However, concerns have been raised in experimental and clinical reports regarding the conformability and apposition of the Enterprise stent's closed-cell design within curved vessels.4)9) Furthermore, Heller et al. found that incomplete stent apposition, as assessed by 3-Tesla MRA, was more common in Enterprise (55%) versus Neuroform stents (0%).10) For this reason, problems such as stent migration, in-stent restenosis, and periprocedural thromboembolism can occur frequently. For example, Kadkhodayan et al.12) reported that the periprocedural rates of transient ischemic attack and periprocedural stroke were higher for the Enterprise (6.1% and 2.6%, respectively) than for the Neuroform (1.4% and 0%, respectively). Cases of stent migration have been reported.13)15) However, despite the structural weaknesses, numerous other studies reported that periprocedural stroke, in-stent thrombosis, stent migration and clinical outcome did not differ between the Enterprise and the Neuroform.3)5)7)11)24)

With intracranial atherosclerotic disease, thromboembolic events such as periprocedural stroke and in-stent thrombosis occur frequently.18) However, stent-assisted coiling is associated with a low rate of thromboembolic events. Exceptionally, in the case of subarachnoid hemorrhage, the risk of hemorrhage or a thromboembolic event is increased.3)

Chalouhi et al. analyzed 508 patients with 552 aneurysms who were treated with stent-assisted coiling. The risks for procedural complications were subarachnoid hemorrhage and aneurysm location (carotid terminus, middle cerebral artery). The risks for recanalization were age, retreatment, large size, incomplete occlusion, Neuroform stent, and aneurysm location, and for a worse clinical outcome were subarachnoid hemorrhage, age, and procedural complication.3)

Ease of use may influence periprocedural risk. If a device is difficult to use, the operator may need to make several attempts. As a result, the procedure time will increase and the doctor's concentration may be affected, raising the risk of complications. Thus, ease of use can have a strong effect on the angiographic and clinical outcome.

In our study, the immediate angiographic results were disappointing, showing only 20% cases with complete occlusion, 15% with a remnant neck, and 65% with a remnant sac. However, angiographic follow-up showed an improvement, with 72% complete occlusion, 22% remnant neck, and only 6% recanalizations (Fig. 1, 2). Thromboembolic complications affecting the clinical outcome occurred in only one case (2.5%). These results are consistent with the pattern reported in a recent large study,8) and agree with other recent reports that stent-assisted coiling has a favorable long-term outcome.11)12)14)17) However, Enterprise can cause thromboembolic complications.12) In the patients who had angiographic follow-up, evidence of stent migration or in-stent thrombosis was not observed. Furthermore, in the cases that had only MRA follow-up, there was no evidence of recurrence.

This study showed that stent-assisted coiling is an effective treatment that stabilizes or improves the long-term anatomical results in most cases. However, there is a possibility of thromboembolic events due to the use of the stent.

Although this study is limited by its retrospective nature, these results indicate that Enterprise stent-assisted coil embolization is an effective technique in the treatment of wide-necked cerebral aneurysms. Further studies are needed to evaluate the long-term durability of stent-assisted aneurysm occlusion and the rate of thromboembolic events due to stent use.