Neuroform Atlas stent in treatment of iatrogenic dissections of extracranial internal carotid and vertebral arteries: a single-centre experience

Abstract

Aim of the study

To present our experience in the treatment of iatrogenic dissections of extracranial internal carotid and vertebral arteries with the Neuroform Atlas stent.

Materials and methods

Between January 2017 and February 2018 we treated iatrogenic dissections of three internal carotid arteries and three vertebral arteries. These iatrogenic dissections occurred during the endovascular treatment of ruptured and unruptured intracranial aneurysms. The indication for stenting was haemodynamically significant, flow-limiting dissection with threatening flow arrest. In all six cases, the dissections were treated by placement of Neuroform Atlas stents in the dissected segments of internal carotid or vertebral arteries. Deployment of the stent was followed by the usual dual antiplatelet regimen.

Results

Single or multiple Neuroform Atlas stents were deployed without any technical difficulties, and blood flow was restored immediately after placement of the stents in all six cases. Midterm follow-up (6–8 months) showed complete reconstruction of the shape and lumen of all treated arteries, with negligible intimal hyperplasia.

Conclusion

Our results indicate that a favourable outcome can be achieved by treating iatrogenic dissections of extracranial internal carotid and vertebral arteries with the Neuroform Atlas stent.

Introduction

Arterial dissection is defined as intimal splitting due to numerous aetiological factors and may be spontaneous, traumatic or iatrogenic.¹ Iatrogenic dissections of cervical segments of internal carotid and vertebral arteries are well known complications occurring during diagnostic cerebral angiographies or neurointerventional procedures. The overall incidence of iatrogenic dissections as complications of cerebral angiographies varies between 0.15% and 0.6%.^2,3 A systematic review of the literature showed that 16% of carotid dissections are iatrogenic.⁴ All dissections of cervical arteries, regardless of aetiology, carry the risk of ischaemic lesions of the brain, cerebellum, or brain stem. The extent of these lesions depends on the degree of dissection and the presence of collaterals distal to the dissection. The cerebral damage that ensues is caused either by considerable diminishing of blood flow in the affected cervical artery or by thromboembolic material generated in the dissection itself.⁵ Spontaneous or traumatic dissections cause ischaemic lesions due to thromboembolic materials originating from a dissection, while iatrogenic dissections cause ischaemic lesions by haemodynamically significant diminishing of blood flow distal to the dissection.⁶ Dissections can be treated conservatively, with antiplatelet agents or more aggressively by implantation of stents to reconstruct the lumen of artery and re-establish flow through the dissected segment of the artery. There are relatively few data indicating which of these two treatment strategies is optimal and provides the best outcome.⁵ Stenting of a dissected artery is the treatment of choice regardless of aetiology if symptoms are refractory to medical management or if dissection limits flow, causes haemodynamically significant stenosis, the intimal flap is unstable, or progressive enlargement of pseudoaneurysm is noted (see Hassan et al.).⁷ The first case of dissection of the internal carotid artery successfully treated by stent was reported by Matsuura et al. in 1997.⁸ Since then, numerous studies on the treatment of dissections with stents have been published (see Hassan et al.).⁷ Both laser-cut and braided conventional stents and flow-diverting stents may be used in the treatment of dissected aneurysms.^7,9,10 We report our experience in the treatment of iatrogenic dissections of cervical arteries with the Neuroform Atlas stent (Stryker; 47900 Bayside Parkway Fremont, CA, USA).

Material and methods

A total of 2401 angiographies and 1631 interventions were performed at our institution in the period between 2011 and 2018. Iatrogenic dissections have occurred in 18 cases or 0.78% of the total number of angiographies and interventions. This percentage slightly exceeds the data from the literature.^2,3 The incidence of iatrogenic dissections of cervical carotid and vertebral arteries has increased twice in this period, the first time in 2012 and the second time in 2017. Between January 2017 and February 2018, six patients (two men, mean age 49 years; and four women, mean age 55.2 years) were treated with Neuroform Atlas stents for iatrogenic dissections of the cervical segments of the internal carotid and vertebral arteries. All demographic data as well as all technical details of the interventions and results of follow-up are shown in Table 1.

Table 1.

Demographic data, details of interventions and follow-up results.

Age/sex	Artery	Diameter proximally and distally to dissection (mm)	Caused by	Extent of dissection (segment)	Length of dissections (mm)	Stent/s	Residual dissection at the end of intervention	Residual dissection at the end of FU period	Flow-limiting intimal hyperplasia at the end of FU period
63/F	Internal carotid artery	4.1 and 4.2	Guide catheter	C1	22.9	4.5 × 21; 4.5 × 30	Yes	No	No
45/M	Vertebral artery	3.4 and 3.4	Guide wire	V2, V3	63.1	4.5 × 21; 4.5 × 30a	Yes	No	No
39/F	Vertebral artery	2.7 and 3.3	Guide catheter	V2	12.1	4 × 24	Yes	No	No
52/F	Internal carotid artery	4.1 and 4.4	Guide catheter	C1	17.6	4.5 × 21; 4.5 × 30	Yes	No	No
67F	Vertebral artery	3.8 and 3.7	Guide catheter	V2, V3	50.6	4.5 × 21; 4.5 × 30; 4.5 × 30	Yes	No	No
53/M	Internal carotid artery	3.8 and 3.8	Guide catheter	C1	16.3	4.5 × 30; 4.5 × 30	Yes	No	No

^aThe third stent was a braided stent.

FU: follow-up.

The dissections occurred during endovascular treatment of unruptured or ruptured aneurysms as a result of damage to the arterial wall caused by the guiding catheter in five cases and the guide-wire in one case. The technical details of endovascular treatment of aneurysms are described elsewhere.¹¹ The indication for treatment with stents was haemodynamically significant dissections with rapidly diminishing flow through the dissected segment. In all cases, the Headway 17 microcatheter (MicroVention, Inc., Worldwide Innovation Center, 35 Enterprise, Aliso Viejo, CA, USA) was used as the stent delivery catheter. All patients received 0.124 mg/kg abciximab IV immediately before deployment of the stent(s). This single dose of abciximab was followed by oral aspirin 75 mg daily for one year and ticagrelor (90 mg, twice a day) for at least 3 months. The dissections were treated with one stent in one case, two stents in four cases and three stents in one case. Multiple stents were deployed in telescopic fashion. The proximal lending zone of the stent(s) was always proximal to the in-flow zone of the dissection.

Follow-up angiographies were performed 6–8 months after the intervention according to the hospital protocol. The follow-up period terminated in September 2018.

Results

In all cases, the lumen of the dissected arteries was repaired, and flow through dissected segments re-established immediately after deployment of the stent(s) (Figures 1 and 2). Residual dissections not affecting blood flow were noted in all cases (Figures 1 and 2, Table 1). No complications were registered, and all interventions were technically successful. The gross morphology of the arteries was preserved in all cases after the stenting, regardless of the number of stents and morphology of the artery (Figure 1).

Figure 1.

Patient 1 (a) Subtracted angiography, right carotid artery, lateral projection shows tip of the guiding catheter proximal to the tonsillar loop of the internal carotid artery (arrow) and middle cerebral artery aneurysm (arrowhead). (b) Subtracted angiography, right carotid artery, antero-posterior projection shows occluded aneurysm (arrow). (c) Subtracted angiography, cervical right carotid artery, antero-posterior projection shows dissection involving tonsillar loop of the artery. (d) Non-subtracted angiography, cervical right carotid artery, antero-posterior projection: two Atlas stents (4.5 × 21 and 4.5 × 30) are deployed in telescopic fashion covering an entire tonsillar loop. Arrowhead indicates distal markers and double arrowheads indicate proximal markers. (e) Subtracted angiography, cervical right carotid artery, antero-posterior projection shows reconstructed lumen of the artery and minimal residual dissection (arrow). (f) Follow-up at 6 months. Subtracted angiography, cervical right carotid artery, antero-posterior projection shows reconstructed lumen of the artery, unchanged gross morphology of the tonsillar loop and minimal, haemodynamically insignificant intimal hyperplasia.

Figure 2.

Patient 5 (a) Non-subtracted angiography, vertebrobasilar system, antero-posterior projection, status after coiling of a basilar tip aneurysms and stenting of basilar artery and both P1 segments with two Atlas stents deployed in ‘Y’ fashion; two flow-diverting stents deployed in left internal carotid artery in previous treatment. (b) Subtracted angiography, vertebral artery, antero-posterior projection: dissection of V2 segment of right vertebral artery with significant stenosis of the lumen and unstable intimal flap (arrow). (c) Non-subtracted angiography, vertebral artery, antero-posterior projection: status after deployment of a 4 × 20 Atlas stent; arrowhead indicates distal markers and double arrowheads indicate proximal markers. (d) Subtracted angiography, vertebral artery, antero-posterior projection: residual dissection, but significantly widened true lumen of the artery. (e) Follow-up at 6 months: Subtracted angiography, vertebral artery, antero-posterior projection: completely reconstructed lumen without dissection remnants.

Midterm follow-up showed a reconstructed lumen in all treated segments, with minimal, haemodynamically insignificant intimal hyperplasia along the stent(s) (Figures 1 and 2, Table 1).

Discussion

According to Groves et al.,⁵ conservative treatment of iatrogenic dissections is safe and reliable, and neurological complications that could be attributed to artery dissections occur in less than 3% of all cases of iatrogenic dissections. However, the treatment of dissections with stents, regardless of aetiology, is always advocated if dissection causes life-threatening flow limitation, a pseudoaneurysm increases in size, or if dissection is refractory to conservative treatment.^7,12,13

The dissections have been treated with all types of stents. Ansari et al. reported successful treatment of nine patients with different types of arterial dissections with the laser-cut open-cell Neuroform stent.¹⁴ Three of these patients had iatrogenic dissections. Adel et al. treated 10 patients for dissections of the internal carotid artery.¹⁵ Three of these dissections were iatrogenic. In all cases, the authors used high radial force self-expandable stainless-steel stents, Nitinol shape-memory alloy self-expandable stents or pre-mounted balloon-expandable stainless-steel stents. To et al. reported treatment of a short dissection of the internal carotid artery with the low radial force laser-cut closed-cell Solitary stent.⁹ Rahal et al. described treatment of six patients with dissection of the tonsillar loop of internal carotid artery with the laser-cut closed-cell Enterprise stent. One of these dissections was iatrogenic.¹⁶ Cohen et al. showed that even flow-diverting stents may be used in the treatment of dissection of the cervical arteries.¹⁷

Carotid, high radial force self-expandable or balloon-mounted stents are stents which provide effective and durable reconstruction of the arterial lumen. Despite high radial force, these stents must be used in combination with balloon dilation if the flow-limiting stenosis of the artery is caused by arteriosclerotic thickening of the arterial wall. Unlike arteriosclerotic narrowing of the internal carotid artery, intimal flap detached from the media, which is the pathological substrate of iatrogenic dissection, does not require high radial force for attachment of the intima to the media. High radial force is, however, an important disadvantage if the stent is used to reconstruct tortuous segments of the internal artery or distal internal carotid artery. Bench tests of commercially available carotid stents have shown bending stiffness that progressively increases in maximally bent segments of an artery.¹⁸ Therefore, traditional carotid stents are not appropriate for treatment of stenotic lesions in tortuous or distal segments of the internal carotid artery. On the other hand, the majority of intracranial stents designed for treatment of aneurysms are much more flexible, but do not possess enough radial force for reconstruction of the lumen of a large cervical artery with dissected wall.¹⁹

Coronary stents and intracranial stents with higher radial force are recommended as reliable stents for the treatment of dissections of the vertebral arteries.^20,21 Use of these stents in our cases would have implied more or less complicated exchange manoeuvres. However, we chose to use a 1.7F (inner diameter 0.017″) microcatheter that was already placed in the artery as a stent delivery catheter, thereby avoiding the exchange manoeuvre.

In our series, the dissections occurred as a result of a conflict between the relatively stiff tip of a guiding catheter or guide-wire and the wall of an artery in the distal, bent segments of the internal carotid artery or a tortuous vertebral artery. Anatomical variants of the internal carotid artery, like tonsillar loops, coils, or kinks, have been shown to be significantly associated with different types of dissections.^22–24

Flow reduction caused solely by a detached instable intimal flap predominantly located in distal bent segments of the internal carotid artery renders iatrogenic dissection an ideal target for treatment with highly flexible stents that possess moderate radial force.

The Neuroform Atlas stent is a new generation stent with some characteristics that differ from other low-profile stents (Figure 3). All the other low-profile adjunctive stents, regardless of type (woven and laser-cut, open-cell, closed-cell) are single-structured and symmetric. The structure of these stents along the working segment of the stent is uniform, and the proximal/distal ends of this segment are symmetrically constructed (Figure 3). The Neuroform Atlas stent is dual-structured and asymmetric along the length of the stent. This stent consists of two types of ‘crowns’ alternately arranged along the working length of the stent (Figure 3). According to the manufacturer, the eight-cell ‘crown’ is designed to provide coil support and anchoring, while the 12-cell ‘crown’ is designed to provide flexibility, improve scaffolding, and prevent ‘gapping’ on a bend. ‘Crowns’ on the flared ends of the stent are different: the distal is designed as ‘open-cell’ type, while the proximal is designed as ‘closed-cell’ type (Figure 3). The third feature of this stent is higher radial force in comparison to other low-profile adjunctive stents. The unconstrained diameter of the largest Neuroform Atlas stent is 5 mm, which corresponds approximately to the mean diameter of the extracranial internal carotid artery and exceeded the diameter of the vertebral and internal carotid arteries in our series (Table 1). The radial force of the Neuroform Atlas stent decreases progressively with opening of the stent, which indicates that the Neuroform Atlas stent should be oversized whenever it is possible in order to achieve enough high radial force for reconstruction of the arterial lumen (Figure 4). The diameter of the internal carotid arteries in our series never exceeded 4.4 mm, and the lumen of these arteries was successfully reconstructed with the Neuroform Atlas stent in all cases. However, since the radial force of the fully open Neuroform Atlas stent is very low, one should be very cautious about using this stent in arteries whose diameter is close to 5 mm.

Figure 3.

Low-profile braided (a, b), laser-cut, closed-cell (c, d) and laser-cut, open-cell (e) intracranial, single-structured stents. Note the same structure of the mesh along the working segment of all stents (between vertical black lines) and symmetrical design of ends of working segments. (f) Atlas stent. Dual structured. Working length corresponds to the total length. The ends of the stent are asymmetrically designed. The mesh is composed of alternately arranged eight-cell and 12-cell structural elements.

Figure 4.

The results of the measurement of radial force of different types of stents show that the radial force of the Neuroform Atlas stent is higher than the radial force of several other low-profile intracranial stents. Note negative correlation between radial force and the degree of constraint of all stents.

All these features, flexibility, adaptability, relatively high radial force and diameter, allow the use of this stent in the treatment of dissections of even larger arteries, such as extracranial internal carotid and vertebral arteries.

One of the factors which prevented us from treating dissections with traditional carotid stents was the diameter of guiding catheters we used for the treatment of the primary pathology. The inner diameter of those 6F guide catheters does not fit the outer diameter of the delivery catheters of traditional carotid stents, which must be at least 7F. On the other hand, the Neuroform Atlas stent, regardless of the size of the stent, can be delivered by 1.6F (inner diameter 0.0165″) microcatheters. Thus, even 5F guide catheters can be used if urgent deployment of the stent is necessary. All the dissections we treated with the Neuroform Atlas stent occurred suddenly and demanded immediate reconstruction of the arterial lumen. In this situation, any exchange manoeuvre involving guiding catheters was considered to be too risky.

Despite good results, our study has some limitations. The small number of patients and the review of retrospectively collected data are the main limitations.

Conclusion

The main advantages of the Neuroform Atlas stent in comparison with other low-profile intracranial stents in the treatment of iatrogenic dissections of extracranial arteries are higher radial force and superior adaptability to the shape of arteries. The radial force of the Neuroform Atlas stent is significantly lower than the radial force of traditional carotid stents. But, unlike traditional carotid stents, the Neuroform Atlas stent can be deployed in very tortuous segments of cervical arteries thanks to the unique construction and technical properties of this stent.

In our experience, the Neuroform Atlas stent is user-friendly and seems to be a safe and reliable device for the treatment of iatrogenic dissections of large cervical arteries. To our knowledge, no prior reports exist on the treatment of iatrogenic dissections of extracranial internal carotid and vertebral arteries with this type of stent.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.