The Use of Balloon-Expandable Stents in the Management of Intracranial Arterial Diseases: A 5-Year Single-Center Experience

Patients and Methods

From 1998 to 2003, 75 patients presented to our department with intracranial saccular, dissecting, or fusiform aneurysms and atheromatous stenotic lesions. They were divided into 2 groups: group 1, which consisted of 59 patients (76.6%) with wide-necked, large, or giant intracranial aneurysms, and group 2, which consisted of 16 patients (20.8%) with atheromatous intracranial stenoses. They underwent intracranial BES placements alone or as a first step of the procedure. A senior neuroradiologist (C.M., M.P., L.S., and J.M.) reviewed their medical records. Clinical data were collected and recorded in a specifically designed case, which included the collection of modified Rankin scale (MR spectroscopy) (13), cranial nerve deficits, adverse events, and each change from baseline neurologic status. Whether morbidity or mortality was related to the device, the procedure, or the disease or was unrelated to the procedure was also recorded.

The clinical and radiologic outcomes were determined mainly by review of medical records and by neurologic evaluation during control angiography.

Results

Discussion

With rapidly advancing technology, stent-assisted intracranial procedures are becoming routine clinical practice. Nevertheless, there have been relatively few large studies published in the literature regarding the application of the BES technology in the treatment of intracranial arterial diseases (20).

Possible indications for the deployment of microstents in intracranial vessels are the balloon dilation of atherosclerotic stenoses, endovascular occlusion of arteriovenous fistulas, and stent-assisted coil occlusion of wide-necked aneurysms. Rare conditions treatable by stent deployment are vessel dissections and herniations of coil loops into the parent vessel during coil occlusion of intracranial aneurysms (21).

The stent itself reduces aneurysm inflow and might thereby induce stasis and thrombosis with occlusion of the aneurysm. In combination with embolization by using detachable coils, the stent serves as a scaffold that prevents coil herniation. A stent may also provide an endoluminal matrix for endothelial growth (22). Furthermore, BES provides endovascular reconstruction at the aneurysmal site to allow for more attenuated packing of coils and possibly to reduce the occurrence of coil compaction through the hemodynamic flow (23).

Several authors have achieved good results with BES-assisted coil occlusion of intracranial aneurysms, whereas others have encountered significant complications related to these devices, mostly dissection or rupture of the parent vessel (24).

The disadvantage of these BESs is their relatively poor flexibility and pushability, which often makes it impossible to navigate the systems to a suitable position. Stent placement always poses a risk of acute in-stent thrombosis, necessitating sufficient premedication with antiplatelet drugs. Therefore, in the treatment of acutely ruptured broad-necked aneurysms, stent placement should be avoided, unless there is no other solution.

The use of self-expandable stents can be an alternative, because it is less traumatic to the patient and should carry a lower risk of dissection or vessel rupture. Unless an additional remodeling balloon is used, the risk of coil loop protrusion through the self-expandable stent struts exists (25).

The BRT, first introduced in 1997 by Moret et al, revolutionized the treatment of wide-necked intracranial aneurysms. BRT (ie, temporary occlusion of the parent vessel and the aneurysm neck with a nondetachable balloon during aneurysm coiling through a second microcatheter) has the obvious advantage of avoiding a permanent intravascular implant and the associated antiplatelet medication. The low-pressure (4–6-atmosphere) inflation of a soft balloon during the remodeling procedure may cause less injury to the vessel wall than balloon deployment of a stent. When compared with stent coil–assisted technique (19.5%), BRT has had significantly lower morbimortality rates in our department (1%). That is why, instead of being riskier, we indicated the former, only in cases where the conventional techniques or BRT were not feasible.

Technical complications observed in our series have also been described in the literature. Some authors have achieved good results with BES-assisted coil occlusion of intracranial aneurysms, whereas others have encountered significant complications related to these devices, mostly due to dissection or rupture of the parent vessel (26).

Nevertheless, we underscore that this treatment option was reserved, first, for patients with no other therapeutic option and, second, for patients who have been discussed in another center before coming to our institution and finally sent to our department.

We should also consider that the hemodynamic effect of a porous stent bridging the neck of an aneurysm is insufficient to induce thrombosis of the aneurysmal sac alone, often requiring an association of an embolic agent. This is partly due to the high porosity of available stents and required use of anticoagulation, as well as antiplatelet medication.

The choice of standard coils as embolic agent has been made on the basis of good results already obtained (46 cases), but Onyx (8 cases) or coil and Onyx combined (5 cases) were also used to treat giant aneurysms, with satisfying immediate total occlusion rates of 74.6%, 71% in 3–6 months, and 78% in 12 months, respectively.

The finding of highest morbimortality in the patients embolized at the same time as stent placement (P < .001) should be considered. In all likelihood, the most recent flexible stents, with better trackability, or the self-expandable stents are promising devices to improve the performance of the procedure, saving time and minimizing risk.

Atherosclerotic Diseases

Intracranial atherosclerotic disease is a high-risk cause of stroke that is potentially treatable. The Northern Manhattan Stroke Study (27) found a 5.9% adjusted risk of recurrent stroke at 30 days in 57 patients relative to a nonatherosclerotic stroke group. Stroke rates in patients with symptomatic intracranial stenoses who are receiving medical therapy may be as high as 10%–24% per year (28). The risk of stroke and death appears to increase early and dramatically for patients whose medical therapy is not successful. Although the first treatment choice for patients with intracranial atherosclerotic stenoses is medical therapy, adjunctive stroke-prevention therapies should be given. Because the angioplastic microballoon catheter, which can be used in intracranial vessels, emerged in the field of neuroendovascular treatment, reports of PTA for intracranial atherosclerotic stenoses have shown an increasing trend. Several investigators reported the efficacy of PTA for intracranial atherosclerotic stenoses. There has, however, been a reluctance to apply it more widely because of complication rates as high as 9.1%–38%. The shortcomings of PTA alone are elastic recoil, severe dissection, vessel rupture, distal embolization, and high rate of late restenosis leading to stroke (29).

The use of stent-assisted angioplasty is an alternative treatment for intracranial atherosclerotic stenoses in symptomatic patients resistant to medical therapy and at high risk for stroke. Several reports have been published concerning the successful deployment of stents with a relatively low rate of mortality and morbidity. The advent of more flexible coronary BESs has allowed safe and relatively reliable endovascular access to intracranial arteries. These stents are of an appropriate length to follow arterial tortuosity and can be made to conform to vascular morphology (30).

Moreover, stent-assisted angioplasty, which can achieve satisfactory angiographic results, minimizes the risk of elastic recoil and intimal dissection. Kiyosue et al (31) reported 2 cases of endovascular stent placement for restenosis of the intracranial vertebrobasilar artery after balloon angioplasty and reviewed 33 cases from the literature. They found an estimated risk of periprocedural complications and restenosis after PTA alone of approximately 20% and 27%, respectively. Otherwise, the overall complication rates related to stent placement and restenosis were 5.6% and 7.8%, respectively. Procedural complications of stent placement—such as vessel rupture—are strongly related to the diameter of the balloon and the stent.

Because the intracranial vessel is a thin-walled artery, careful sizing of the balloon is needed. Oversizing the stent may result in intimal dissection at the stent margins by dumbbell-shaped balloon expansion. Therefore, to avoid these complications sizing the stent 0.5 mm smaller than the assumed diameter has been used. De Rochemont et al (32) evaluated prospectively the safety and efficacy of undersized stents used in 18 patients with high-grade intracranial stenoses and recurrent ischemic symptoms. The technical success rate was 90% and the degree of stenosis was reduced from a median of 82% to a median of 16%. No immediate complication—including thromboembolism, dissection compromising the blood flow, or vessel ruptures—occurred.

Despite being less common—but harboring potentially more serious complications—cerebral hyperperfusion syndrome after percutaneous intracranial stent placement has been described in the literature (0.3%–1.2%) (33). Meyers et al (34) performed a retrospective review of 140 patients who underwent PTA/stent placement of the craniocervical arteries. They found 5% of cerebral hyperperfusion syndrome with prevalence greater in patients who belonged to a high-risk cohort according to the NASCET Trial as well as in cases of carotid stenoses rated as >80%.

The complication rate of 25% (4 of 16) described in our report is relatively high compared with other series of intracranial stenoses and stent placement. All 4 patients who experienced complications belonged to a high-risk cohort according to the NASCET trial, and the diameter of the stent deployed was in the 1 : 1 ratio to the parent artery. Three of the 4 patients presented with SAHs. Among these 3 patients, 2 developed clinical and radiologic manifestations recognized as cerebral hyperpefusion syndrome and presented with high-grade stenoses (>90%).

Our findings suggest that, in high-risk cohorts and in cases of high-grade stenoses, a possible technical strategy would be the use of undersized stents, as well as the adoption of prophylactic measures, including prevention of cerebral hyperfusion syndrome.

Conclusion

Development of stents for the management of intracranial atherosclerotic stenoses and aneurysms has been a challenge. The combination of endovascular reconstruction of the parent vessel by using this kind of neurovascular stent followed by a device of embolization offers a promising therapeutic alternative in the treatment of wide-necked aneurysms not amenable to coil embolization alone or BRTs, or when the occlusion of the main artery is not allowed.

Although recent experience suggests that there have been significant improvements in techniques and materials, several factors must be addressed to reduce complications.

Because coil-assisted stenting has been found to be riskier than BRTs in our practice, it is essential that the treating physicians have expertise in managing the potential complications. Probably, recent development of self-expandable stents, with better trackability and flexibility, might reduce these risks in general.

On the other hand, the use of more flexible BESs may prove useful and effective in treating intracranial atherosclerotic lesions, because the advantages and limitations of this endovascular device, lesion-specific characteristics, and proper selection of patient must be considered.

Prospective and controlled clinical studies are necessary to support the routine use of stents in intracranial vessels.