Stent retriever expansion as a corrective maneuver to optimize inadequately deployed flow diverter stents

Abstract

Background and Purpose

As flow diversion (FD) is becoming increasingly important in the endovascular treatment of intracranial aneurysms, the rate of technical complications is also increasing. Inadequate FD implantation may lead to both ischemic complications and decreased treatment efficacy. The aim of this study was to evaluate the efficacy of off-label stent retriever (SR) use in managing technical complications associated with FD implantation.

Materials and Methods

A retrospective analysis of data from patients who underwent FD treatment at two neuroradiology centers was performed. The objective was to identify cases in which the FD was inadequately deployed and SR expansion was performed as a corrective maneuver. The analysis included anatomic characteristics, technical information, angiographic and clinical outcomes, and complications.

Results

A total of 35 corrective maneuvers with SR were performed in 25 FD treatments. The corrective maneuvers in all treatments were successful, and no additional devices or therapies were required. No procedural complications or technical difficulties were documented.

Conclusion

With the growing role of FDs in neurointerventional treatment, familiarity with corrective maneuvers after technical complications or inadequate implantation is important. The findings in our selected cohort demonstrated that SR expansion is an effective and safe corrective maneuver for incompletely opened FDs.

Introduction

Over the past 15 years, flow diverters (FDs) have revolutionized the treatment of intracranial aneurysms.^1,2 The development of coatings has further increased the safety of FD treatment for both ruptured and unruptured aneurysms.^3,4 Despite increased FD use, growing experience of interventional neuroradiologists, and remarkable advances in these devices, intraprocedural and postprocedural complications persist. ⁵ The most common intraprocedural complications include suboptimal opening and wall apposition of the FD in the parent vessel, which can manifest in a variety of ways, including collapse, torsion, “fish mouth,” segmental stenosis, or suboptimal wall adaptation. ⁶ These technical difficulties can lead to acute complications such as circulatory failure or ischemic stroke, ⁵ as well as long-term complications such as endoleak formation or inadequate aneurysm closure. ⁷ To avoid these potential complications, optimization of inadequately placed flow-directed stents is necessary. ⁸ However, this interventional maneuver requires advanced interventional experience and substantial material knowledge. ⁹

If improved adaptation with the microcatheter (MC), microwire, and delivery system is unsuccessful, alternative solutions can be considered, including removal of the device by “stentectomy,” stent implantation across the FD, or more aggressive expansion of the FD device with a balloon catheter or Comaneci device.^10–12

In this study, we describe the use of self-expanding stent retrievers (SR) as an effective tool for treating patients with twisted or collapsed FD stents after implantation.

Materials and methods

Patient population

In this retrospective study, we report data from two high-volume neurointerventional centers. We analyzed all ruptured and unruptured intracranial aneurysm cases treated with FDs between June 2020 and June 2024. We specifically focused on cases with technical complications associated with FD deployment.

The present study included cases in which an SR was used for stent angioplasty of a suboptimally deployed FD. Treatments in which no SR was used were excluded from the analysis. Demographic data, anatomic characteristics, pre- and postprocedural complications, and clinical and angiographic findings at the last available follow-up were recorded for all patients.

Technical complications of FDS

The expected technical complications of FD treatment were as follows:

• - Twisting

• - Segmental partial opening

• - Incomplete vessel wall apposition

Flow diverter implantation and medication

The following FD models were implanted:

• - p64 MW HPC (phenox)

• - p48MW HPC (phenox)

• - Pipeline embolization device (Medtronic)

• - Derivo 2heal (Accandis)

Flow diversion diameter and length were selected according to two- or three-dimensional measurements of parent artery diameter. Measurements were made during the procedure or a prior digital subtraction angiography examination.

Patients scheduled to receive HPC-coated FDs were administered single antiplatelet therapy with either 1 × 10 mg prasugrel per os (PO) daily for at least 5 days before treatment or a loading dose of 30 mg prasugrel 24 h before treatment. Patients receiving uncoated FDs were administered dual antiplatelet therapy consisting of 1 × 100 mg acetylsalicylic acid (ASA) PO daily, and 2 × 90 mg ticagrelor PO, 1 × 10 mg prasugrel PO, or 1 × 75 mg clopidogrel PO daily for at least 5 days before treatment. Other patients received a loading dose of 500 mg ASA and 600 mg clopidogrel, 180 mg ticagrelor, or 30 mg prasugrel 24 h before the procedure. Postprocedural medication for patients implanted with uncoated FDs included 100 mg ASA PO, to be continued indefinitely, and 1 × 75 mg clopidogrel, 2× 90 mg ticagrelor, or 1× 10 mg prasugrel PO daily for at least one year.

Flow diverter expansion using SR

Correction maneuvers after FD implantation were performed only when mechanical adaptation “massaging” with the MC or device delivery system failed. For the correction maneuvers, the MC used to implant the FD was inserted through the delivery system to the distal end of the FD. The delivery system was then removed, and the SR was delivered through the MC at the level of the segment with mechanical complications or suboptimal deployment. Stent angioplasty was then performed with the SR. This maneuver could be repeated from distal to proximal locations as needed, particularly in FD telescoping treatments. For stent expansion, most SRs were oversized, to achieve the best vessel wall adaptation. The diameter of the SR can be selected based on the details of the case. In many cases, the diameter of the SR does not need to exceed that of the FD. To illustrate, if an FD with a diameter of 5 mm is only 2 mm open, an SR with a diameter of 4 mm may be an adequate means of opening the collapsed FD. Conversely, if the FD is already largely open and wall apposition is to be improved, an SR with a diameter larger than that of the FD is recommended. After the correction maneuver was completed and the operator was satisfied with the FOUND's position, the SR was collected with the MC without traction on the device. This technique was used in all patients. The SR expansion maneuver is demonstrated in Figures 1 and 2.

Figure 1.

Restoration of segmental stenosis of an implanted p64MW HPC flow diverter (FD) during endovascular treatment of a patient with a fusiform internal carotid artery (ICA) aneurysm with a telescoping FD. Digital subtraction angiography (DSA) with contrast injection into the right ICA confirmed the fusiform ICA aneurysm in the supraclinoid segment (A). After implantation of a second FD, the device showed a segmental stenosis that remained unresolved despite mechanical massage with the delivery system (B). The microcatheter (MC) was introduced distal to the narrow segment (arrow) over the moveable wire of the FD (C, D). A pRESET-6–30 stent retriever (SR) was delivered through the 0.021-inch ID MC (E). The SR was deployed, thus resulting in device expansion and improved vessel wall adaptation of the FDs (F, G). The final DSA images showed complete coverage of the aneurysm with the FDs and full opening of the FD (H).

Figure 2.

Restoration of twisting of an implanted flow diverter (FD) during endovascular treatment in a patient with an internal carotid artery (ICA) aneurysm. Digital subtraction angiography (DSA) with contrast injection into the left ICA confirmed the presence of the paraophthalmic ICA aneurysm (A). Subsequently, the FD showed twisting (arrow, B). Despite mechanical massage with the delivery system, the twisting remained unresolved. The microcatheter (MC) was then advanced over the wire of the FD distal to the twisted segment (arrow, C). A pRESET-6–30 stent retriever (SR) was delivered and deployed through the 0.021 inch ID MC, thus resulting in improved vessel wall adaptation of the FD (D, E). A follow-up DSA at 6 months demonstrated complete aneurysm occlusion with patency of the ophthalmic artery (F).

The radiopacity of the FD used is sufficiently high. Therefore, in the majority of cases, regular fluoroscopy is sufficient to detect whether the FD is fully deployed. Only in a few cases is it necessary to use cone beam CT.

Results

Between June 2020 and June 2024, a total of 1029 FD implantations were performed in both participating centers (Stuttgart: 823; Marburg, 206), The 35 FD expansion maneuvers with SR were performed in FD treatments to improve the vessel wall apposition of the implanted devices.

A summary of the enrolled patients’ demographic data, aneurysm dimensions, and vessel anatomy, as well as the device characteristics, is presented in Table 1.

Table 1.

Demographic data, aneurysms, and FD characteristics.

Patients
Number of cases	29
Female/Male	22/7
Age	Mean 60 years (range 14–82 years)
Aneurysm location
Ruptured/Unruptured	4/25
ICA, cavernosal segment	5/29
ICA, ophthalmic segment	2/29
ICA, supraclinoidal segment	10/29
ICA, posterior communicating segment	1/29
AcomA	2/29
MCA (M1)	2/29
VA (V4)	2/29
PICA	1/29
BA	4/29
Aneurysm type
Megadolichoectasia	3/29
Blister	1/29
Dissecting	4/29
Saccular	13/29
Fusiform	8/29
Aneurysm size
maximum diameter (mean)	Mean 13,7 mm (range 1–37 mm)
Neck (mean)	Mean 11,1 mm (range 1–37 mm)
FD
FD diameter	Mean 4,5 mm (range 3–6 mm)
FD length	Mean 24,3 mm (range 12–40 mm)
Number of FDs per session	Mean 1,7 mm (range 1–6)
EVT
Simultaneous treatment (coiling)	13,7% (n = 4/29)
Pretreated (FD)	37.9% (n = 11/29)

FD: flow diversion; ICA: internal carotid artery; AcomA: anterior communicating artery; MCA: middle cerebral artery; VA: vertebral artery; PICA: posterior inferior cerebellar artery; EVT: endovascular therapy.

Among all aneurysms treated with FD implantation, four were ruptured, and 25 were unruptured. In all cases, FD implantation was initially planned, and 12 of the procedures were FD telescoping treatments.

Treatments were performed with a p64 MW HPC (WallabyPhenox) (n = 25), p48 MW HPC (WallabyPhenox) (n = 1), Pipeline Vantage (Medtronic) (n = 2), or Derivo 2heal (Accandis) (n = 1).

The SRs used for the correction maneuvers were pRESET (WallabyPhenox), Solitaire-AB (Medtronic), or Solitaire-X (Medtronic). The mean diameter and length of the SRs used were 5.3 and 29.3 mm, respectively. The indications for SR angioplasty were as follows: FD twisting (n = 6/35), segmental stenosis (n = 15/35), or suboptimal wall apposition (n = 14/35). In six cases, the SR maneuver was used in multiple attempts, because of the implantation of multiple FDs and the need for multiple adaptations. All technical complications were successfully addressed through SR expansion, and no procedures required the use of an additional device (e.g., balloon catheter).

No periprocedural complications regarding the target vessel or device were documented. Technical characteristics and complications of the treatments are presented in Table 2.

Table 2.

Technical characteristics and complications.

FD Typ	Number/cases
p64 MW HPC	47/25
P48 MW HPC	1/1
Derivo 2 heal	1/1
Pipeline Vantage	2/2
Mechanical complication
Partial segmental opening	15/35
Incomplete wall apposition	14/35
Twisting	6/35
SR Typ
pRESET	24/29
Solitaire-X	2/29
Solitaire-AB	3/29
SR size
SR diameter	Mean 5,3 mm (range 3–6 mm)
SR length	Mean 29,3 mm (range 20–40 mm)
SR-angioplasty
number of Maneuvers	35 Mean 1,2 (range 1–2 mm)
retreatment using other devices	_
Complications
iatrogenic vessel complication	_
clinical complication	_
mRS detoriation pre- and posttreatment	_
iatrogenic mechanical complication	_

FD: flow diverter; MW: movable wire; HPC: hydrophilic polymer coating; SR: stent retriever.

Discussion

Since the introduction of FDs in Europe in 2008 for the treatment of intracranial aneurysms, the number of treatments has gradually but steadily increased. ¹ The rapid evolution of FDs has enabled the introduction of devices into more distal vessels and challenging anatomies by using MCs with thinner profiles. These developments have enabled the treatment of many intracranial aneurysms that were previously impossible or very difficult to treat, including blister aneurysms, dissection aneurysms, and giant aneurysms. Several recently reported studies on the safety and efficacy of FD treatment of ruptured and distal aneurysms have shown promising results.^4,13 As the number and complexity of aneurysms treated with FDs has grown, the frequency and severity of complications potentially occurring during or after treatment have also increased.

The primary intraprocedural complications associated with FD stent implantation include technical difficulties. These devices have lower radial force than other stents, thus increasing the likelihood of technical complications, including deployment difficulties; structural deformations such as stent twisting, stretching, or luminal narrowing; and inadequate wall apposition. ¹⁴

The main factors increasing the risk of such technical difficulties in FD implantation include challenging vascular anatomy, such as highly curved vessels, and the complex morphology of aneurysms, including fusiform aneurysms, dissecting aneurysms, long-distance aneurysm expansion, and the presence of vascular stenosis immediately distal or proximal to the aneurysm. ¹⁵ In addition, the mass of the FD relative to the target vessel is a significant factor associated with the occurrence of technical difficulties: excessive oversizing can lead to twisting or collapse, whereas undersizing can lead to displacement of the implanted device, because of a lack of adhesion to the vessel wall. ¹⁶ Clearly, operator experience is a critical factor in both the selection of the device to be implanted and the success of the subsequent implantation maneuver.

In recent years, several tools and software programs have been developed to facilitate device sizing, particularly in the field of FDs, with the aim of avoiding intraprocedural technical difficulties.^17,18 Despite the development of new tools and software, complications remain inevitable. In a study by Kuhn et al., balloon angioplasty was required in 12.5% (27/215) of cases, laser-cut stenting was required in 4.1% (9/215) of cases, and a second FD was required in 0.9% (2/215) of cases after pipeline FD implantation. ¹⁹ In the PRIMER trial reported by Hanel et al., balloon angioplasty was required in 22% (31/144) of cases after treatment with pipeline devices. ²⁰ Moreover, in studies by Jee et al. ²¹ and Orru et al. ²² involving intracranial aneurysm treatment with Surpass Evolve implantation, device adjustment was required in 25.7% (8/31) and 36% (9/25) of cases, respectively.

Beyond the intraprocedural complications that may occur because of suboptimal FD positioning, long-term consequences may also affect treatment safety and efficacy. These consequences are due primarily to device shortening and migration, thus potentially leading to the FD's migration into the aneurysm or repositioning within the vessel, and resulting in flow disruption and inadequate delivery to the aneurysms.^23,24

The introduction of the SR device in 2008 marked a major advance in ischemic stroke treatment. ²⁵ More recently, the use of SRs in other neurointerventional treatments, such as stent angioplasty for cerebral vasospasm, has been described. ²⁶ The off-label technique presented herein provides a valuable addition to the available treatment modalities for optimizing inadequately adapted FDs after implantation. SR angioplasty is similar in concept to balloon angioplasty. However, as with the Comaneci device, navigation with an MC through the entire stent is required, particularly distal to the malapposed segment of the FD.

Overall, SRs offer several notable advantages over other treatment methods, as follows:

• No blood flow interruption.

• Potential for guiding the SR into the distal vascular system.

• Potential operator familiarity with the use of SR from mechanical thrombectomy procedures, including those in the distal vasculature.

• Likely lower risk of vascular injury and dissection due to operator-independent stent expansion than observed with balloon angioplasty.

• Relatively short procedure times.

• Automatic adaptation of the SR to the maximum possible diameter of the implanted FD.

Herein, the results of corrective maneuvers with the SR in the included cases showed high efficacy: all maneuvers were successful, and no cases required the use of another device. All 35 maneuvers were performed in a safe manner, with no evidence of iatrogenic vascular complications or defect formation at the FD. Similarly, we observed no neurological deterioration or treatment-related clinical complications in any patients.

In this cohort, we observed no significant differences in outcomes among SR devices. Angiographic follow-up at 3–6 months showed no recurrence or new mechanical complications in the FDs.

Unlike balloon angioplasty, SR angioplasty does not require reprobing, because the MC used to implant the FD can be brought distally over the wire of the device. The SR can then be deployed, thereby eliminating the need for an exchange maneuver through the inadequately opened FD. Although the development of balloon technology has improved treatment options, catheters have a stable tip that hinders microprobing. Balloon angioplasty requires active dilation of the vessel by the treating physician, which may cause vascular injury, particularly if the physician lacks extensive experience and applies excessive radial force. ²⁷ In addition, balloon angioplasty often requires multiple cycles of inflation and deflation, which increase the risk of thrombus formation.

Compared with the Comaneci device, which has a diameter limit of 4.5 mm, SRs have diameters of 3–6 mm. Larger diameter SRs can be inserted through a 0.021-inch MC, including the pRESET-6–50 (WallabyPhenox) and Solitaire X 5–40 (Medtronic). For small profile FDs that can be inserted through a 0.017-inch MC, such as the Silk Vista Baby (Balt), smaller SRs, such as the pRESET-LT, can be used, thus eliminating the need for further probing or changing the MC. Similarly, the SRs are substantially wider than the Comaneci device, thus enabling interventionalists to become more proficient and experienced with SR insertion, regardless of the manufacturer.

An SR can generate sufficient force to cause a significant increase in vessel radius without causing vessel injury, even in spastic vessels. ²⁶ SRs exert progressive angioplasty in collapsed FDs without active device dilatation. Simultaneously, SRs exhibit a Romdell effect, thereby following the shape of the target vessel without straightening or altering the anatomy. This treatment technique can also be performed in an overlapping manner from distal to proximal, particularly in conditions following telescoping treatments.

Presumably, the more radial force the SR has, the better the expansion of the FD. We assume, without having tested it, that an eccentric stent structure (e.g., Solitaire, Medtronic; pRESET, Wallaby Phenox) is more favorable for the expansion of a FD than a concentric structure (e.g., Aperio, Acandis). A distal wire tip (e.g., Embotrap, Cerenovus) may become entangled in the cells of the FD if the wire diameter is sufficiently small or the cells of the FD are sufficiently large. Expansion of an incompletely deployed FD with a thrombectomy stent should generally be possible with any self-expanding implant. In general, it can be assumed that more rigid implants may require an SR with more radial force (e.g., NeVa, Vesalio) for better wall apposition.

In the present clinical practice, if a flow diverter is not fully deployed, the initial approach is to expand it with an SR. If this is unsuccessful, a compliant balloon catheter can be used and escalated to a noncompliant balloon catheter. This treatment strategy is applicable to newly implanted FDs in the same treatment session. In the case of previously implanted devices, the collapse or stenosis of the FD may be fixed by endothelialization. However, the use of SR or balloons as a corrective maneuver to optimize the inadequate position of the FD is usually unsuccessful. This fixation can then be released by a very defensive implantation of an undersized coronary stent, thereby allowing for the gain of additional lumen. Figure 3 illustrates a case in which a stenosed endothelialized FD was treated.

Figure 3.

Restoration of segmental in-stent stenosis of a previously implanted p64MW HPC flow diverter (FD) fixed by endothelialization was conducted 16 months after the treatment of a patient with SAH and dissection of the vertebral artery (VA) in the V4 segments with a telescoping FD on both sides. Digital subtraction angiography (DSA) with contrast injection into the left VA confirmed the dissection V4 aneurysm (A). Complete coverage of the dissection with the three FDs (telescoping) and full opening of the devices (B, C). In the DSA follow-up after 15 months, a device showed a segmental stenosis (arrow) (D–F). Following dilatation with a noncompliant Ryujin balloon 3/10 mm, the segmental stenosis remained unchanged (arrow) (G, H). A coronary Coroflex ISAR NEO stent 3/9 mm (arrowhead) was introduced and implanted at the level of the segmental stenosis, thereby widening the FD lumen (I–K). A follow-up examination conducted by DSA after 6 weeks revealed a persistent improvement in the FD lumen and a reduction in the size of the residual aneurysm (L).

Although technical complications during FD implantation are relatively infrequent, the lack of guidelines for various situations can complicate the treatment course. The literature has reported undesirable consequences of corrective maneuvers such as the balloon angioplasty maneuver, which can lead to vessel rupture or device migration, owing to the high and active radial force generated on the defective area of the stent. Therefore, developing new corrective maneuvers to provide options for different situations remains a topic of continued interest.

One potential complication of concern with the SR corrective maneuver was the migration of the FD device during the collection of the SR; however, we did not encounter this complication in any cases. However, it is important to note that the retrieval is performed with the MC without relevant traction on the SR. Overall, no clinically relevant complications were associated with the SR correction maneuver.

Limitation

A major limitation of this study is its retrospective, single-arm design. The lack of a control group undergoing alternative corrective procedures, such as balloon angioplasty or Comaneci device angioplasty, and the relatively small number of patients enrolled limit the generalizability of the results. Consequently, the safety, benefits, and harms of this treatment cannot be accurately assessed on the basis of the present findings.

Conclusion

Technical difficulties with FD stent implantation can result in both serious complications and poor patency rates. Therefore, operator experience with various successful corrective maneuvers is required. The use of SR in an incompletely opened FD as a corrective maneuver was both safe and successful in our case series. Despite the small number of cases in our study, we encountered no periprocedural complications. Thus, the SR expansion maneuver might be considered a viable and potentially effective treatment option, particularly in the context of greater familiarity with mechanical thrombectomy in the stroke setting.