The solitaire AB stent for endovascular treatment of atherosclerotic stenosis of the basilar artery without snowplow phenomenon

Abstract

Background

Atherosclerotic disease of the basilar artery (BAAD) is a known cause of brainstem infarction. Frequent complications of endovascular treatment led to drug treatment as first choice, although it does not treat the cause. The self-expanding Solitaire AB stent has potentially beneficial properties in the treatment of BA stenoses. We compared balloon-only dilation (B), stent-assisted balloon dilation (StB), and sole Solitaire (SO) implantation without balloon dilation for safety and efficacy in the treatment of BAAD.

Methods

We retrospectively analyzed the outcomes of patients with symptomatic BAAD, who received endovascular treatment in our department. Patients received digital subtraction angiography (DSA) follow-up 3, 6, and 9 months and annually thereafter. All treatment complications, strokes and restenoses were investigated.

Results

Twenty-five patients were treated using SO, including seven in the acute stroke setting. Forty-two patients received treatment with B (n = 9) or StB (n = 33), including 24 in the acute setting. Periinterventional complications appeared in B and StB group only. Median DSA follow-up was 441 days (0-2433 days). In-stent restenosis occurred in 4% in the SO group, 24% in the B/StB group. Patients treated with SO had a longer time to retreatment. The risk of complications was generally lower with SO, and SO showed a remodeling effect in which the vessel diameter slowly increased in the follow-up examinations.

Conclusion

In the treatment of symptomatic BAAD, SO showed equal safety and efficacy compared to B and StB. The lower rate of perforator infarction may be due to SOs’ principle of slow remodeling.

Introduction

Perforator infarction is a well-known and fairly common complication of stent angioplasty of intracranial vessels [1, 2] and, together with hemorrhagic complications, was responsible for the poor performance of the endovascular arm in the SAMMPRIS trial [3, 4], which was even poorer in the VISSIT trial using balloon-mounted stents exclusively [5]. The likely mechanism underlying perforator infarcts, also known as the “snowplow phenomenon,” is based on the occlusion of perforator origins by atherosclerotic plaque material during balloon dilation [1].

Although the WEAVE trial showed that underdilation of the stenosis decreases the risk of the snowplow phenomenon [6, 7], this risk could not be avoided. The rate of 30-day stroke and death, and in combination with other periprocedural complications, was comparatively high, at 4.5% in the WEAVE trial.

Because of the risk of these other types of potential complications (e.g., hemodynamically relevant vasospasm, vessel dissection, and guidewire perforation), stent-assisted balloon dilation (StB) as a treatment for intracranial atherosclerotic disease (ICAD) remains a technically challenging and potentially hazardous procedure. Therefore, guidelines recommend this treatment as a second-line option after failure of antiplatelet therapy [8, 9].

Given that ischemic stroke is the second leading cause of disability and death worldwide [10], and that intracranial atherosclerosis is likely to be a leading cause, accounting for as many as 50% of cases [11–13], safe and effective endovascular treatment of ICAD remains an unmet clinical need.

Recently, however, an increasing number of researchers have called for a re-evaluation of endovascular treatment of ICAD on the basis of studies describing new devices and findings [14–16], advocated by recent advances in this area particularly due to researchers from Asia [17–22].

The Solitaire AB stent was designed as a retrievable and electrolytically detachable device for assisted coiling of wide-necked aneurysms [23]. The Solitaire AB stent has high radial force, does not require balloon support for expansion and straightens the target vessel [24]. Therefore, it is less complex to handle than conventional stents, and, because it is fully retrievable and detachable, it is relatively easy to place within a stenotic vessel segment.

We retrospectively evaluated the outcomes of elective and emergency symptomatic basilar artery (BA) stenoses treated with the detachable Solitaire AB alone at our institution, and compared the results with patients treated with balloon dilation alone (B) or StB. The study is retrospective and exploratory in nature. It serves as a pilot study to evaluate hypotheses in order to design a possible subsequent prospective multicenter study.

Materials and methods

Patient population

We retrospectively evaluated the outcomes of all patients who underwent endovascular treatment for BA stenosis in our department between April 2015 and November 2023. To be eligible for treatment (inclusion criteria), patients were required to.

• have an intracranial stenosis with at least 70% lumen loss; or to.

• suffer from neurological symptoms most likely cause by BA ICAD with < 70% stenosis, but refractory to BMT; or to.

• present symptoms of ischemic stroke with BA stenosis as a likely cause.

Patients receiving BMT were required to have had a previous stroke or transient ischemic attack caused by a BA stenosis and to have had recurrence of symptoms despite subsequent BMT. BMT consisted of antiplatelet therapy monitored through point-of-care response tests (Multiplate, Roche Diagnostics; VerifyNow, Accriva), lipid-lowering therapy with statins, and antihypertensive medication.

Drug regimen

All procedures were performed under confirmed dual antiplatelet therapy, which was achieved in elective interventions (eSO; eB/StB) by loading with two antiplatelet agents. The drug regimen consisted of acetylsalicylic acid (ASA) at 100 mg/d and ticagrelor at 180 mg/d, or prasugrel at 10 mg/d, or clopidogrel at 75 mg/d, started at least 5 days before the procedure. Sufficiency of platelet inhibition was assessed in advance with a Multiplate Analyzer (MP; Roche Diagnostics, Mannheim, Germany) and VerifyNow (VN; Accriva, San Diego, CA, USA) on the day of the treatment. In the event of inadequate platelet inhibition, the relevant medication dosage was adjusted accordingly, and the treatment was postponed. In the event of inadequate response or intolerance to any of the agents, the drug was changed to another agent described above. Dual antiplatelet therapy (DAPT) was continued for at least 3 months, and then switched to lifelong ASA at 100 mg/d.

In acute stenting (aSO; aB/StB), patients received a single intravenous dose of 500 mg ASA, a single bolus of eptifibatide in a body weight-adapted dose, and oral antiplatelet therapy with 180 mg ticagrelor or 300 mg clopidogrel or 30–60 mg (</> 60 kg body weight) prasugrel administered via a gastric tube.

On the day after endovascular treatment, follow-up CT or MRI, and the aforementioned MP and VN tests were performed. DAPT was adjusted according to the test results.

Endovascular treatment

We focused on procedures in which only a Solitaire AB stent covered the stenosis. No balloon dilation was performed before or after SO, and the BA was not allowed to be occluded at the time of stent deployment. Patients with acute BA thrombosis who were found to have stenosis after successful thrombectomy were included.

All procedures were performed in patients under general anesthesia. Access was obtained via the iliac or radial artery. In elective cases, the patient received an intravenous bolus injection of 3000 IU non-fractionated heparin sodium.

A guide catheter (5 F for stenting only, 7 F for thrombectomy and stenting) was inserted into the larger diameter, less elongated VA. Under roadmap guidance, a 0.021 inch inner diameter microcatheter (e.g., Phenom21, Medtronic; Rebar-18, Medtronic; or Trevo pro 18, Stryker) was inserted with the tip of the microcatheter 1–2 cm beyond the BA stenosis.

In patients with acute BA occlusion due to underlying atherosclerotic stenosis, thrombectomy (either mechanical or aspiration, e.g., SOLUMBRA [25]) was performed first. After the BA perfusion was restored to the extent that the stenosis became visible, a Solitaire AB stent was inserted, deployed, and finally electrolytically detached to cover the stenosis. Except for the thrombectomy required in patients with acute stroke, the same procedure was followed in acute and elective cases.

At each follow-up visit (described above) and during hospitalization, MP and VN tests were used to monitor treatment efficacy and adjust the antiplatelet medication if necessary.

The inclusion criteria were the same for acute and elective cases. The technical procedures within the three treatment groups (B, StB and SO) were identical – with the exception of intervention. The treatment technique was chosen according to the personal preferences of the operators between 2015 and 2021. After 2021, SO was preferred over the other two options.

The outcome criteria were identical in the three groups. Recurrent stroke due to brainstem, cerebellum, or occipital lobe ischemia, and peri- or post-procedural intracranial hemorrhage were the primary endpoints. Delayed in-stent stenosis, stent occlusion, and ischemic stroke associated with stent location (BA) were the secondary endpoints.

Technical success, periinterventional complications, recurrent stroke and restenosis

Treatments were considered technically successful when.

• the Solitaire AB, stent and/or balloon reached the stenosis, and.

• the stenosis was appropriately dilated;

• blood flow through the stenosis was not slowed after the procedure; and.

• stenosis did not increase after the procedure.

The comparatively low requirements for technical success took into account possible different dilation strategies used in acute and elective procedures, with acute procedures being more likely to involve aggressive dilation. In addition, the assessment had to be set low due to the remodeling effect of the Solitaire AB stent, which can lead to only a slight difference in vessel diameter if measured directly after implantation – since no balloon dilatation is required.

The degree of stenosis was determined with the NASCET method [26] as the WASID-method [27] may not applicable in cases of stenosis at the basis of the basilar artery. We defined stenosis greater than 70% as high grade.

Periinterventional complications were defined as.

• Events resulting in an unintended acute occlusion of an intracranial or cervical artery vessel, requiring in angioplasty or thrombectomy; or.

• Visible intracranial hemorrhage on angiogram; or.

• an ischemic or hemorrhagic event most likely caused by the intervention and occurring until discharge, resulting in a permanent rise of at least one point on the mRS scale.

All ischemic and hemorrhagic events occurring in the follow-up, resulting in temporal or permanent neurologic deterioration were considered as recurrent strokes.

Follow-up

Before discharge from the hospital, all patients underwent a neurological history and clinical examination and were given a magnetic resonance imaging scan of the skull, including FLAIR and DWI sequences. Regardless of the size, all diffusion restrictions red as new in the MRI following intervention and most likely caused by the angioplasty were recorded.Subsequently, DSA of the treated vessel was performed at 3, 6, 9, and 12 months after treatment, and at annual intervals thereafter. DSA examinations were accompanied by a clinical examination and update of the medical history of the respective patient. The degree of stenosis was measured according to the NASCET method, in at least two planes.

Statistical analysis

Continuous data are described as the mean, median, minimum, and maximum. Numbers and percentages were used to describe categorical data. Logistic regression with 95% confidence intervals was fit on the data to measure the probability of complications to occur and need for retreatment and its significance, depending on the percentage of stenosis reduction. IC 16.1 for Unix was used for the statistical analysis.

Ethical standards

This single-center retrospective analysis was conducted in accordance with the Declaration of Helsinki and approved by the local ethics committee (Landesärztekammer Baden-Württemberg, Stuttgart, Germany; IRB number F-2012–077).

Patients were required to be at least 18 years of age. In elective cases, all patients or their legal representatives provided written informed consent at least 1 day before the procedure, after being informed of the planned treatment strategy and possible complications, and consented to data collection, analysis, and anonymous publication.

For the treatment of acute stroke, only patients who provided informed consent before treatment or for whom consent was assumed because of a lack of capacity were included. For the latter patients, data were used in this study only if consent for scientific evaluation had been provided in a later stage after stroke treatment.

Results

Of 305 identified revascularization procedures of the BA in the indicated period, 25 patients could be included in the SO group, eight of whom were women (32%). Forty-two patients were identified for inclusion in the B or StB group, of which 14 were women (33%). Eighteen Solitaire AB cases (72%) were in theeSO group and 18 cases (43%) in the B/StB (eB/StB). Thus, in the acute setting, seven cases (28%) were included the aSO group and 24 cases (57%) in the aB/StB group (Fig. 1).

Fig. 1.

Flowchart of patients included, 2015–2023

In group B/StB (N = 42), n = 9 patients received treatment with balloon catheters only (B), and n = 33 patients were treated with balloon angioplasty and additional stent implantation (StB).

Table 1 provides an overview of the materials used in the B/StB group.

Table 1.

Devices used in the B/StB group; * used in combination with pITA

Balloon catheters in the B group	Balloon catheters and stents in the StB group
	Balloon catheters	Stents
pITA (WallabyPhenox) n = 9	pITA (WallabyPhenox) n = 33	Enterprise (Johnson & Johnson) n = 21
Ryujin and Ryujin plus (Terumo) n = 2*	Ryurei (Terumo) n = 2	Solitaire (Medtronic) n = 6
		pEGASUS (WallabyPhenox) n = 5
		Neuroform Atlas (Stryker) n = 1

The mean degree of stenosis was 68% (57–76%) in group B, 75% (54–92%) in the StB group, and 74% (55–93%) in the SO group.

At the end of the intervention, the mean stenosis grade was 42% (29–51%) in the B group, 41% (9–63%) in the StB group, and 63% (45–79%) in the SO group.

Table 2 displays the mean stenosis grades before and after treatment, split up in the acute and elective setting (Table 2).

Table 2.

Mean stenosis grades and clinical details of patients split up into elective and acute treatment

Age	Mean total	aB/StB	aSO	eB/StB	eSO
	74 (49–89)	76 (57–89)	73 (55–89)	72 (52–85)	75 (49–86)
Sex f/m	22/45	9/15	3/4	5/13	5/13
DAPT received before incidence	85%	25%	57%	100%	100%
Mean degree of stenosis before treatment	73.5% (54–93%)	72% (54–92%; IQR 15)	71% (55–93%; IQR 5)	76% (57–92%; 13)	75% (60–90%; IQR 14)
Mean degree of stenosis after treatment	49.2% (9–79%)	38% (9–51%; IQR 16)	56% (45–68%, IQR4)	44% (16–63%; IQR 14)	65% (52–79%; IQR 10)

In terms of the extent or aggressiveness of stenosis reduction, the mean post-intervention stenosis grade was 35% below baseline (9–46%) in the B group, 33% (10–60%) in the StB group, and 11% (2–24%) in the SO group. The mean stenosis grade reduction was 34% vs. 31% in aB/StB vs. eB/StB, and 15% vs. 10% in aSO vs. eSO. However, these values are purely descriptive, taking into account possible different strategies of dilation in the acute vs. elective setting as well as the remodeling principle as mentioned in the methods section.

Periprocedural complications included major ischemic stroke in two patients in the B/StB group. Another patient in the B/StB group experienced dissection or plaque rupture with extensive intracranial hemorrhage immediately after balloon angioplasty. In all three patients, the discharge mRS was two points lower than the admission mRS, in the patient with intracranial hemorrhage death occurred.

No periprocedural complications were observed in the SO group.

The degree of stenosis reduction in the two patients with major stroke was 46% (B) and 13% (StB); in the patient suffering the intracranial hemorrhage, due to the complication, the degree of stenosis reduction could not be assessed. The first two cases occurred in the elective setting, and the intracranial hemorrhage with consecutive death occurred in the acute setting.

In the SO group, n = 11 (61%) patients (all eSO) had clinically inapparent small DWI lesions on discharge MRI (mean 2.3; n = 1–9), as compared with 100% in the B/StB group (mean 7; n = 1–26).

During follow-up, one patient with restenosis required retreatment in the SO group (aSO, 4%) at 119 days, and ten patients with restenoses required retreatment (24%) in the B/StB group at a mean of 239.5 days (41–908days, B vs. StB = 2 vs. 8; IQR 224).

In 6 patients (60% of restenosis) in the B/StB group, restenosis occurred in the acute treatment group, as well as in n = 1 (100% of restenosis) in the SO-group. 80% (n = 8) of patients with restenosis were initially treated with StB. In the SO group and in nine patients in the B/StB group, follow-up treatment was performed with ballon-angioplasty only. One patient in the B/StB group initially treated with balloon-angioplasty only (B) received a coronary balloon-expandable stent to treat the recurrent stenosis.

In the B/StB group, the vessel diameter in patients without restenosis did not change or did not change significantly over time. In the SO group, a remodeling effect occurred during follow-up, thus further decreasing the degree of stenosis (Fig. 2).

Fig. 2.

After the initial partial dilation of the stenosis, the remodeling effect increases alignment of the formerly stenosed vessel segment with the non-stenosed lumina. The stenosis and the subsequently treated vessel segment are indicated by white arrows in a patient in the eSO group. Quantitative degrees of stenosis is 72% initially, 67% following Solitaire AB implantation, 48% on 3 month follow-up (3 Mo), 28% on 6 Mo and 33% on 15 Mo and 46 Mo follow-up

After a mean stenosis grade of 63% (45–79%; IQR 11) in the SO group immediately post-intervention, the mean stenosis grade was 54% (35–78%; IQR17 at n = 21) at 3 months, 53% (10–69%; IQR 17 at n = 12) at 6 months, 53% (42–69%; IQR 9 at n = 8) at 9 months, and 45% (30–60%; IQR 11 at n = 9) at 12 months (Fig. 3).

Fig. 3.

Follow-up DSA of the BA in a patient receiving SO, showing the remodeling effect over time. The “9 mo” and “24 mo” follow-ups are in a slightly tilted projection from the initial plane. White arrows indicate the location of the stenosis and the remodeled vessel. Quantitative degrees of stenosis are 64% proximal and 68% distal initially, 60% proximal and 62% distal after implantation, and 42% thereafter

Mean follow-up time was 396 d for SO (12–2433d) and 485 d for B/StB (0–1983d). Five patients in the SO group underwent long-term follow-up of at least 24 months (829–2433d) and showed a mean residual stenosis grade of 45% (33–60%) (Fig. 4).

Fig. 4.

Evolution of the degree of stenosis of the BA after SO. Time point “0” is the degree of stenosis before treatment. The last time point corresponds to at least 24 months. All data on stenosis degree are mean values

Logistic regression was used fit the data to measure the probability of restenosis, by comparing the SO and B/StB groups, showing a lower probability of restenosis in the SO group (6.45% vs. 25% in B/StB). However, due to the clear imbalance in the number of restenoses between the SO and B/StB groups, the significance of this statistical test has to be set aside and the difference in restenosis has to be seen als descriptive. This also applies to the difference in complications, for which no tangible level of significance can be achieved due to the small number of cases.

The admission and 3-month post-treatment mRS scores averaged 3.2 vs. 2.6 (range mRS 0–6 BStB; mRS 0–5 SO), respectively, in the B/StB group and 2.3 vs. 1.2, respectively, in the SO group. The outcome mRS score refers to n = 23 patients (92%) in the SO group, in which one patient died within 3 months for reasons unrelated to treatment and one patient was lost to follow-up. In the B/StB group, the data refer to 83% of the initially enrolled patients, because seven patients died within 3 months due to non-treatment-related causes. Patients who died from a cause unrelated to the procedure were not counted as mRS 6 outcomes in this study; instead, their last representation of the treatment effect was recorded as their mRS score (Fig. 5).

Fig. 5.

Mean mRS scores over time comparing acute and elective procedures in the Solitaire implantation (SO) and conventional (B/StB) groups Due to the low case number, however, the comparison has to be seen as descriptive

Discussion

To our knowledge, this study is the first to compare the results of SO, B, and StB in acute and elective settings.

Striking differences in DWI lesions and infarct size were observed between the SO group and the B/StB group. We attributed their absence or significantly lower incidence in the SO group to the different principles of stenosis expansion. Conventional, balloon-assisted, and balloon-stent-assisted angioplasty are known to display the so-called “plaque shifting” or “snowplow” phenomenon, which refer to the displacement of stenotic material by balloon dilation into the ostia of perforator vessels, that are then occluded, thus ultimately leading to perforator infarcts—a possible complication known in cardiology and neuroradiology [28, 29]. In fact, perforator infarction was a common complication [13] in the interventional arm of the SAMMPRIS trial, which used only stent-assisted balloon angioplasty [3, 30] The Solitaire AB stent has a high radial force [31] and may therefore provide a slow, steady widening of the stenosis over time, possibly reducing or even avoiding the snowplow effect. Since radial force appears to be crucial for the remodeling effect, one might want to look for the device with the highest radial force that is currently available on the market and that is intended for intracranial use: in a 2011 comparison by Krischek et al., the Enterprise Stent showed to have a much higher potential in terms of radial force [24]. As a closed-cell stent, the Enterprise stent family also does not have the disadvantages of Wingspan and Neuroform stents, which are open-cell designs. The Wingspan and Neuroform stents, on the other hand, may be advantageous in tortuous vessel anatomy, but their radial force is likely to be lower than that of the Solitaire AB stent, and as open-cell stents, they are significantly more complex in cases where repeat angioplasty is required.

However, the main advantage of the Solitaire AB stent lies in its’ retrievability: in case of an intraprocedural BA re-occlusion following stent placement, the Solitaire AB stent not only acts as thrombectomy device, but can also be easily repositioned or exchanged – provided the vessel is observed for a short time after Solitaire AB implantation and before detachment.

Additionally, in the comparison of several stents intended for intracranial use by Krischek et al.[24], the Solitaire AB was found to have the lowest mesh density, resulting in a less dense endothelium coverage in comparison to the two other stents used in this study. This lower mesh density and vessel surface covering might have resulted in less plaque displacement.

This aspect might also explain the lower rate of restenosis observed in the SO groups compared to the groups with conventional devices. All patients received adequate DAPT with comparable drug regimens. However, the low mesh density of the Solitaire AB stent in comparison to the Enterprise and Neuroform stent [24] also left a smaller potential surface area for platelet adhesion, which might have had protective effects against restenosis induced by platelet adhesion.

The covered surface area of the endothelium, in which hyperplasia can be induced by the implant struts, is also less with the Solitaire AB stent accordingly. However, this effect might have been neutralized by the chronic pressure maintained by the radial force of the Solitaire AB stent. However, to our knowledge, whether chronic mechanical pressure promotes endothelial hyperplasia has not been studied.

The comparatively small initial stenosis dilation with the Solitaire AB stent might have had a disadvantage of insufficient hemodynamic effects. Finally, a substantial increase in vessel lumen size did not occur on average until several weeks after treatment. However, no recurrent infarctions were observed in our follow-up. The literature is inconclusive regarding the possible risks of “chronic dilation” of BA stenoses. Ultimately, however, this issue must be studied in greater detail in more cases.

The use of the Solitaire AB system as a permanent stent in perforator-rich vessel segments has been described sporadically in the literature [25, 26, 28, 32–34]. However, only Wang et al. and Cao et al. have focused on protecting the perforator vessels by using the self-expanding force of the Solitaire AB stent. Their approach is consistent with the rationale herein, although in Wang et al., 4% of complications with a fatal outcome occurred as a result of Solitaire AB treatment [34]. Cao et al. have reported a rate of periprocedural and 30-day fatal and non-fatal complications of 9.35% [32]. Both studies have reported complication rates lower than those in the SAMMPRIS and VISSIT studies, and have concluded that the Solitaire AB system is effective and suitable for the treatment of atherosclerotic stenoses of the basilar and middle cerebral arteries under certain conditions. However, the authors did not perform a direct comparison with conventional stents.

In contrast, Luo et al. have described rescue stenting for failed thrombectomy attempts, including the Solitaire AB stent, thus, the findings are comparable to those in the acute treatment groups herein [33]. The outcome in terms of mRS points at 90 days differs between studies, 25% mRS 0–2 in Luo et al. versus 83% in our data. Luo et al. critically evaluated stent angioplasty with the Solitaire AB system versus balloon dilation and implantation of an Apollo stent (MicroPort Medical, Shanghai, China) or a Wingspan stent (Stryker, Kalamazoo, USA) and the results favored the Solitaire AB stent. Their still positive results for partially balloon-dependent devices are not reflected in our data. Yet, the difference in the number of treated patients is large, and patients in our study neither Apollo or Wingspan stents were used. Furthermore, we did not count patients dying from causes unrelated to the treatment as mRS 6 outcomes. Mathematically, the results in each group are therefore in a lower mRS score range than would have been the case if these non-treatment-related deaths had also been included. This would have significantly increased the difference in the outcome mRS score between the two groups in favour of the SO group. However, in the authors’ opinion, a non-therapy-related death cannot be attributed to the therapy method, which is why we decided on the assessment described.

A major weakness of this study is the unbalance between both groups, reducing comparability. There is also a certain heterogeneity between the elective and acute treatment groups, particularly with regard to the materials used. This results in a clear explorative, hypothesis-generating nature of the investigation, to prove the superiority of SO on the basis of this data is neither possible nor intended by the authors.

However, the weakness of material inhomogeneity is partially offset by the fact that the object of this study was ultimately the principle of balloon-free PTA. This circumstance at least gives the comparison of the two main groups SO vs. B/StB a certain selectivity and weight.

Furthermore, the small number of cases in this study is a clear weakness - a fact that it has in common with almost all previous studies on this topic. Of course, this manuscript does not claim to fully clarify the possibilities and role of the Solitaire AB stent in the treatment of ICAD. Rather, it is intended to contribute to a re-evaluation of endovascular ICAD treatment, which has long been relegated to the background due to adverse results from old RCTs, in light of improved and new methods and instruments, as well as the more mature global neuroendovascular community. In addition, to the best of the authors’ knowledge, this is the highest number of cases for elective and acute treatment at a single center.

Another weakness of this study is that not all conventional and currently commercially available conventional materials were used. In particular, the absence of the Wingspan stent, which has been extensively described and studied in the literature, might have further influenced the results [6]. However, we generally attribute the positive results in the SO group in this study to the balloon-free application, which, to our knowledge, is not currently possible with any other stent system for the treatment of BA stenoses.

A weakness on the other hand is the different status of availability and approval of the Solitaire AB stent in different countries, resulting in restricted possibilities of reproduction of the displayed BAAD treatment strategy. However, as the role of endovascular ICAD treatment continues to be investigated, the availability of the stent may increase in the future.

On the other hand, the strengths of this study lie in the homogeneity of the data, due to single center conditions. Furthermore, the follow-up period of an average of more than 14 months in this study is prominent among the studies on SO and better accounts for the pathophysiology of ICAD. Finally, DSA examinations can be regarded as the gold standard for follow-up examinations after SO, which has used been exclusively in this study and is a strength due to the preciseness of the data.

The aforementioned, comparably extensive follow-up protocol corresponds to the routine that has been in place for many years following endovascular ICAD treatment in our department. It bases on informed patient consent, which includes the information about less invasive methods like flat-panel or multi-detector computed tomography. For the basilar artery, radial access was preferred for DSA, which possibly influenced the consent rate in a positive way. However, such extensive follow-up care may be limited to high-load endovascular centers.

Conclusion

Acute and elective treatment of symptomatic BA stenosis with the Solitaire AB stent alone was effective and safe in our patient population and achieved treatment outcomes comparable to those of conventional balloon-dependent devices.

In our study, the small initial reduction in stenosis was compensated for by slow remodeling of the vessel through the Solitaire AB stent over the course of the months – at no recurrent stroke. We attribute the remarkably lower rate of perforator infarction in the Solitaire AB groups to this principle of slow remodeling.

Abbreviations

ASA

acetylsalicylic acid

B

balloon dilation

BA

basilar artery

BAAD

Atherosclerotic disease of the basilar artery

BMT

best medical treatment

DAPT

dual antiplatelet therapy

DSA

digital subtraction angiography

DWI

diffusion-weighted magnetic resonance imaging

FLAIR

Fluid Attenuated Inversion Recovery

ICAD

intracranial atherosclerotic disease

MP

Multiplate

NASCET

North American Symptomatic Carotid Endarterectomy Trial, categorizing ICA stenoses as mild (<30%), moderate (30–69%), or severe (70–99%)

RCT

randomized controlled trial

StB

stent-assisted balloon dilation

SAMMPRIS

Stenting and Aggressive Medical Management for Preventing Recurrent Stroke in Intracranial Stenosis, clinical trial

SO

Solitaire only implantation

VA

vertebral artery

VISSIT

Vitesse Intracranial Stent Study for Ischemic Stroke Therapy, clinical trial

VN

VerifyNow

Author contributions

PvG and AK collected the data and wrote the main manuscript.HH, HB and MF advised on the drafting and structuring of the document and in the writing process, selected the references and proofread the document.HK performed the statistical analysis and prepared the figures.All authors reviewed the manuscript.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.