Overview of Different Flow Diverters and Flow Dynamics

Comparing the safety and effectiveness of overlapping stents with flow diverters for unruptured vertebral artery dissecting aneurysms

BACKGROUND

Endovascular treatment for vertebral artery dissecting aneurysms (VADAs) includes overlapping stents and flow diverters. This study compared the safety and effectiveness of overlapping stents and flow diverters for unruptured VADAs.

METHODS

We retrospectively enrolled patients with unruptured VADAs who underwent overlapping stents or flow diverters at two tertiary hospitals in South Korea. The primary clinical outcome was the occurrence of stroke. The primary angiographic outcomes (>12 months) were categorized as regression, no decrease in size, recanalization, or stent occlusion, of which only regression was defined as a favorable angiographic outcomes.

RESULTS

Of the 146 patients with VADAs, 25 (17.1%) had flow diverters and 121 (82.9%) had overlapping stents. For the primary angiographic outcomes over 12 months, the rate of favorable angiographic outcomes for flow diverters was 81.8% and for overlapping stents (triple stents) was 98.8% (P=0.006). In the multivariale analysis, after adjusting for partially thrombosed aneurysms, aneurysm shape, non-dominant vessel, posterior inferior cerebellar artery involvement, and procedure type, overlapping stents (triple stents) was not associated with favorable angiographic outcomes compared with flow diverters (OR 7.040, 95% CI 0.549 to 90.294; P=0.134), but partially thrombosed aneurysms was inversely associated with favorable angiographic outcomes (OR 0.056, 95% CI 0.005 to 0.589; P=0.016). The primary clinical outcome followed up to the last angiography did not occur in all patients.

CONCLUSION

There was no difference in safety and effectiveness between overlapping stents and flow diverters in unruptured VADAs. Further endovascular treatment studies are needed regarding the association of partially thrombosed aneurysms with unfavorable angiographic outcomes.

Appraisal of the Flow Diversion Effect Provided by Braided Intracranial Stents

Objective: Comparison of the results of stent-assisted coiling (SAC) with braided stents (BS), flow diverters (FD), and laser-cut stents (LCS) to determine the relative flow-diverting capacity of BS (Leo baby and Accero). Methods: Saccular intracranial aneurysms treated by SAC and FD-assisted coiling were retrospectively evaluated. Aneurysm occlusion, as graded per Raymond-Roy score, was categorized as either recanalization/stable residual filling (Group A; lacking a flow diversion effect) or stable/progressive occlusion (Group B with a "flow diversion effect"). Factors predicting the flow diversion effect were evaluated. Results: Of the 194 aneurysms included, LCS, BS, and FD were used in 70 (36.1%), 86 (44.3%), and 38 (19.6%) aneurysms, respectively. Aneurysms treated by FD were larger, had wider necks, and were located on larger parent arteries (p < 0.01, 0.02, and <0.01, respectively). The mean imaging follow-up duration was 24.5 months. There were 29 (14.9%) aneurysms in Group A and 165 (85.1%) in Group B. Among a spectrum of variables, including sex, age, aneurysm size, neck width, parent artery diameter, follow-up duration, and stent type, the positive predictors for stable/progressive aneurysm occlusion were aneurysm size and placement of an FD or BS (p < 0.01 and p < 0.01, respectively, and were positive predictors over LCS: ORs 6.34 (95% CI: 1.62-24.76) and 3.11 (95% CI: 1.20-8.07), respectively) in multivariate analysis. Conclusions: The placement of BS was a predictor of flow diversion over laser-cut stents. However, the flow diversion effect was approximately half that of FDs, suggesting that BS may only be considered to have some (partial) flow diversion effects.

Endovascular Treatment of Intracranial Aneurysm: The Importance of the Rheological Model in Blood Flow Simulations

Hemodynamics in intracranial aneurysm strongly depends on the non-Newtonian blood behavior due to the large number of suspended cells and the ability of red blood cells to deform and aggregate. However, most numerical investigations on intracranial hemodynamics adopt the Newtonian hypothesis to model blood flow and predict aneurysm occlusion. The aim of this study was to analyze the effect of the blood rheological model on the hemodynamics of intracranial aneurysms in the presence or absence of endovascular treatment. A numerical investigation was performed under pulsatile flow conditions in a patient-specific aneurysm with and without the insertion of an appropriately reconstructed flow diverter stent (FDS). The numerical simulations were performed using Newtonian and non-Newtonian assumptions for blood rheology. In all cases, FDS placement reduced the intra-aneurysmal velocity and increased the relative residence time (RRT) on the aneurysmal wall, indicating progressive thrombus formation and aneurysm occlusion. However, the Newtonian model largely overestimated RRT values and consequent aneurysm healing with respect to the non-Newtonian models. Due to the non-Newtonian blood properties and the large discrepancy between Newtonian and non-Newtonian simulations, the Newtonian hypothesis should not be used in the study of the hemodynamics of intracranial aneurysm, especially in the presence of endovascular treatment.

Aneurysm Treatment With the Pipeline Vantage Embolization Device in Retrospective Evaluation: Periprocedural Results from the Pipe-VADER Study

OBJECTIVE

The Pipeline Vantage Embolization Device is a fourth-generation flow diverter with an antithrombotic coating and a reduced profile compared to previous Pipeline versions. The objective of this study was to evaluate the procedural feasibility, safety, and efficacy of this device.

METHODS

The Pipe-VADER study was designed as a retrospective, observational study of consecutive patients treated with the Vantage at 3 neurovascular centers. Patient and aneurysm characteristics, procedural parameters, early complications, and extent of postinterventional contrast retention were analyzed on an intention-to-treat basis.

RESULTS

Twenty-eight patients with 31 aneurysms (median size: 5.0 mm, posterior circulation: 4 [12.9%], ruptured: 5 [16.1%]) were included. The technical success rate was 100%, with multiple stents used in 4/30 (13.3%) procedures. Of the 30 procedures, adjunctive coiling was performed in 3 (10.0%) and balloon angioplasty in 2 (6.7%). Median procedure time was 62 minutes. Procedural ischemic stroke occured in 4 (13.3%) cases, whereof 2 were major strokes (6.6%). There were no hemorrhagic complications. Initial contrast retention was observed in 29/31 (93.5%) aneurysms. All 27 overstented side vessels were patent at the end of the procedure. Short-term follow-up (median: 5 months) showed complete and favorable occlusion rates of 70% (14/20) and 80% (16/20), respectively.

CONCLUSIONS

The new Pipeline Vantage appears to be safe and feasible for the treatment of intracranial aneurysms and warrants further evaluation.

Ongoing Geometric Remodeling of the Parent Artery After Flow-Diverter Stent Reconstruction in Cerebral Aneurysms: The Device Design Matters

OBJECTIVE

Configuration changes of the parent artery (PA) after flow-diverter (FD) stent reconstruction, caused by the bending force of the device, may have an additional role in aneurysm occlusion as a result of the secondary alteration of intra-aneurysmal hemodynamics related to the geometry alteration of the vessel. To determine the degree of PA deformation and aneurysm occlusion rates after deployment of 2 different types of FD.

METHODS

Patients treated with 2 different designs of cobalt-chromium braid (48 and 64 wire braid) structure FD were subject to analysis. Vascular angle changes at the level of the reconstructed segment immediately after FD deployment and at 1 year follow-up were measured and the potential relationship with aneurysmal occlusion rate was analyzed.

RESULTS

Forty-two patients harboring 48 aneurysms were included in the present study. The aneurysms were divided into side wall (85.4%) and bifurcation types (14.6%). Twenty-six aneurysms were treated using the Pipeline FD (48 wire braid; 54.2%) and 22 using the Evolve FD (64 wire braid; 45.8%). Of the 48 aneurysms, 42 (87.5%) met the primary end point of complete occlusion at 12 months. The median postdeployment angle change was 7.04°± 4.59° for the Pipeline and 5.05°± 2.49° for the Evolve, whereas the median 12 months follow-up angle change was 15.49°± 10.99° and 10.01°± 8.83°, respectively. PA angle changes were significantly higher in the bifurcation group compared with the side wall group both during procedure and at 12 months follow-up. Angle change had a statistically nonsignificant association with complete aneurysm occlusion.

CONCLUSIONS

PA deformation starts immediately after deployment and remodeling continues for 1 year after. Aneurysms located in the vessel bifurcation were more prone to PA straightening after FD deployment than were side wall aneurysms. Furthermore, Pipeline seemed to be more prone to inducing vascular deformation, compared with Evolve.

Flow Diversion for the Treatment of Intracranial Aneurysms in a Peruvian Cohort: Experiences from a Limited-Resource Setting and Barriers to Implementation

BACKGROUND

Stenting with flow diverter devices (FDDs) has increasingly emerged as a treatment for intracranial aneurysms. The use of FDDs in the developing world has not been described.

METHODS

A retrospective review was performed of a cohort of patients who underwent flow diversion at 4 tertiary-care centers in Lima, Peru between January 2017 and June 2021. Demographics, clinical features, and aneurysm morphology were evaluated. Clinical outcomes were observed 3 months after discharge and occlusion rates were assessed 12 months after treatment.

RESULTS

Sixty-nine patients (mean age, 46 ±14.5 years; 17% female) were treated with FDDs; 4% (n = 3) of the treated aneurysms were ruptured. Most aneurysms were saccular (n = 65; 94%), <10 mm in maximum size (n = 60; 87%), and located in the anterior circulation (n = 67; 97%). Minor complications, such as groin hematoma, occurred in 7 cases. No serious complications or deaths occurred. Patients' functional status was excellent (modified Rankin Scale score 0-1) in 99% (n = 66) at discharge and 100% (n = 67) at 3 months. Although some patients were lost to follow-up, complete occlusion was seen in 76% (n = 31) of 41 treated patients at 12 months.

CONCLUSIONS

We report the largest multicenter experience of FDDs for cerebral aneurysm treatment in Peru, with reasonable outcomes that are comparable to other settings despite various challenges, suboptimal circumstances, and lack of resources.

Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide-Neck Aneurysms - SCENT: 3-year outcomes

BACKGROUND

To report the 3-year safety and effectiveness of the Surpass Streamline flow diverter in the SCENT trial (Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide-Neck Aneurysms).

METHODS

The Surpass Streamline flow diverter device was evaluated in a multicenter, prospective, single-arm, non-randomized interventional trial including patients with uncoilable or previously treated but failed aneurysms of the intracranial internal carotid artery. 3-year outcomes were tabulated with descriptive statistics and compared with 1-year outcomes.

RESULTS

Of 180 patients in the modified intent-to-treat (mITT) cohort, 36-month clinical and angiographic follow-up was available in 134 and 117 cases, respectively. Effectiveness endpoint of complete aneurysm occlusion without clinically significant stenosis or retreatment was met in 71.8% (79/110, 95% CI 62.4% to 80.0%) of cases. Safety composite endpoint was 12.2% (22/180) over the 3-year period, with two major safety events (ipsilateral ischemic strokes) occurring between 12-36 months. Complete aneurysm occlusion was noted in 77.8% (91/117), and 99.1% (116/117) of the patients demonstrated adequate aneurysm occlusion (complete occlusion or neck residual). There were four cases (2.2%) of aneurysm rupture, all occurring within the first month of the index procedure. Target aneurysm retreatment rate was 2.8% (5/180).

CONCLUSION

The present findings support the long-term safety and effectiveness of the Surpass Streamline flow diverter device.

TRIAL REGISTRATION

NCT01716117.

Early clinical experience with the new generation Pipeline Vantage flow diverter in the treatment of unruptured saccular aneurysms using short-term dual antiplatelet therapy

PURPOSE

The Pipeline Vantage flow diverter with Shield technology (PV) used in this study is a 4th-generation flow diverter (FD) designed to reduce thrombogenicity, promote endothelialization of the implant and increase efficiency in achieving aneurysm closure. In this study, we report the aneurysm occlusion rate, complication rate and clinical outcome with short-term dual antiplatelet therapy (DAPT) in the treatment of unruptured intracranial saccular aneurysms using the PV.

METHODS

We retrospectively identified patients treated between September 2021 and January 2023 with the PV and subsequently underwent short-term DAPT for 3 months. Patient and aneurysm characteristics, peri- and post-procedural complications, clinical outcomes and the grade of aneurysm occlusion were documented.

RESULTS

Thirty patients with 32 aneurysms were treated. Successful FD implantation was achieved in all cases (100%). No periprocedural complications were documented. The overall symptomatic complication rate was 10% and the neurologic, treatment-related symptomatic complication rate was 6.6%. Only one symptomatic complication (3.3%) was device-related. Permanent clinical deterioration occurred in 2/30 patients (6.6%), leading to deterioration of the mRS within the first 3 months after treatment. No mortality was documented. The rate of complete aneurysm occlusion after 3 months and after a mean imaging follow-up of 9.9 months was 65.6% and 75%, respectively.

CONCLUSION

Implantation of the PV for the treatment of saccular intracranial aneurysms achieves a good aneurysm occlusion rate with a low rate of complications. In addition, the use of short-term DAPT after PV implantation appears to be safe.

Circulation remodeling after flow diversion of an anterior communicating artery aneurysm: A case report

Anterior communicating artery aneurysms are the most common intracranial aneurysm and have a high risk of rupture which can lead to morbidity and mortality. Traditionally, intracranial aneurysms were treated by clipping with neurosurgical access. However, certain patients may prefer less invasive approaches or not represent open surgical candidates. Flow diverters, including flow-redirection endoluminal devices (FRED), are new-generation stents that are placed endovascularly by transfemoral or transradial access. Recent studies have demonstrated that FRED is both safe and effective, with complete occlusion of aneurysms in over 90% of patients. This case highlights an interesting phenomenon of post-flow diversion circulatory remodeling, where flow diverter treatment can alter the circle of Willis anatomy and physiology.

Reinforcement learning for patient-specific optimal stenting of intracranial aneurysms

Developing new capabilities to predict the risk of intracranial aneurysm rupture and to improve treatment outcomes in the follow-up of endovascular repair is of tremendous medical and societal interest, both to support decision-making and assessment of treatment options by medical doctors, and to improve the life quality and expectancy of patients. This study aims at identifying and characterizing novel flow-deviator stent devices through a high-fidelity computational framework that combines state-of-the-art numerical methods to accurately describe the mechanical exchanges between the blood flow, the aneurysm, and the flow-deviator and deep reinforcement learning algorithms to identify a new stent concepts enabling patient-specific treatment via accurate adjustment of the functional parameters in the implanted state.

PREDICT: Precise deployment of Silk Vista Baby in confined territory: A technical note

Flow diverters (FD) have become increasingly useful in treating complex intracranial aneurysms, particularly wide-necked and recurrent aneurysms. Their use has progressively expanded to smaller vessels beyond the circle of Willis (CoW), and Silk Vista Baby (SVB) is one such low-profile FD which stands out because of deliverability through a 0.017″ microcatheter and smoother navigability. Precise deployment of SVB, specifically, the proximal end, can be challenging in certain anatomical locations when the proximal landing zone is very short, limited by vessel bifurcation or important branches arising from the artery or its geometry. We present our series to describe our technique and rule to 'PREDICT' the final deployment of SVB in real time, and discuss the nuances, exceptions and bail-out strategies. Using this technique, we were able to precisely deploy SVB in distal intracranial vessels with a mean proximal landing zone as short as 2.6 mm in 80% instances, requiring bail-out strategies in only 20% cases. This rule can be reliably followed in treating complex intracranial aneurysms with SVB FD within a confined territory, until validated software-based real-time planning tools are developed.

The Pipeline Embolization Device: a decade of lessons learned in the treatment of posterior circulation aneurysms in a multicenter cohort

OBJECTIVE

The Pipeline Embolization Device (PED) has prompted a paradigm shift in the approach to posterior circulation aneurysms. The year 2021 marks a decade since FDA approval of this flow diverter, and during this time operators have adapted to its off-label uses. The authors examined whether case selection, practice trends, and patient outcomes have changed over this 10-year period.

METHODS

This study is a retrospective review of consecutive posterior circulation aneurysms managed with the PED at four academic institutions in the US between January 1, 2011, and January 1, 2021. Factors related to case selection, rates of aneurysm occlusion, or complications were identified and evaluated. Angiographic outcomes as well as thromboembolic and hemorrhagic complications were investigated.

RESULTS

This study included 117 patients (median age 60 years). At a median follow-up of 12 months, adequate occlusion (> 90%) was attained in 73.2% of aneurysms. Aneurysm occlusion rates were similar over the study interval. Thromboembolic and hemorrhagic complications were reported in 12.0% and 6.0% of the procedures, respectively. There was a nonsignificant trend toward a decline in the rate of thromboembolic (14.1% in 2011-2015 vs 9.4% in 2016-2021, p = 0.443) and hemorrhagic (9.4% in 2011-2015 vs 1.9% in 2016-2021, p = 0.089) complications.

CONCLUSIONS

The authors observed a trend toward a decline in the rate of thromboembolic and hemorrhagic complications with improved operator experience in using the PED for posterior circulation aneurysms. The use of single-device PED flow diversion significantly increased, as did the tendency to treat smaller aneurysms and observe large unruptured fusiform/dolichoectatic lesions. These findings reflect changes attributable to evolving judgment with maturing experience in PED use.

Shape Memory Polymer-Based Endovascular Devices: Design Criteria and Future Perspective

Devices for the endovascular embolization of intracranial aneurysms (ICAs) face limitations related to suboptimal rates of lasting complete occlusion. Incomplete occlusion frequently leads to residual flow within the aneurysm sac, which subsequently causes aneurysm recurrence needing surgical re-operation. An emerging method for improving the rates of complete occlusion both immediately after implant and in the longer run can be the fabrication of patient-specific materials for ICA embolization. Shape memory polymers (SMPs) are materials with great potential for this application, owing to their versatile and tunable shape memory properties that can be tailored to a patient’s aneurysm geometry and flow condition. In this review, we first present the state-of-the-art endovascular devices and their limitations in providing long-term complete occlusion. Then, we present methods for the fabrication of SMPs, the most prominent actuation methods for their shape recovery, and the potential of SMPs as endovascular devices for ICA embolization. Although SMPs are a promising alternative for the patient-specific treatment of ICAs, there are still limitations that need to be addressed for their application as an effective coil-free endovascular therapy.

Treatment of large and giant posterior communicating artery aneurysms with the Surpass streamline flow diverter: results from the SCENT trial

BACKGROUND

The Surpass flow diverter was developed to treat intracranial aneurysms not amenable to standard treatment. Indications for use allow placement in the internal carotid artery to the terminus, including the communicating artery segment.

METHODS

The Surpass Intracranial Aneurysm Embolization System Pivotal Trial to Treat Large or Giant Wide Neck Aneurysms (SCENT) trial is an international, multicenter, prospective, non-randomized trial comparing the outcomes of Surpass flow diverter treatment with historic control designed to evaluate the effectiveness and safety of Surpass for the treatment of wide neck (≥4 mm) large or giant intracranial aneurysms ≥10 mm. The primary effectiveness endpoint is the percentage of subjects with 100% aneurysm occlusion without significant stenosis of the parent artery and without retreatment of the target aneurysm at 12 months. The primary safety endpoint is the percentage of subjects experiencing neurologic death or major ipsilateral stroke at 12 months. We report the effectiveness and safety of flow diversion in the subgroup of posterior communicating artery (PComA) aneurysms.

RESULTS

Of the 180 patients treated, 38 harbored a PComA aneurysm. Mean aneurysm size was 12.2 mm and mean neck width was 4.8 mm. The mean number of Surpass devices used was 1.1 per procedure, with 94.7% of aneurysms treated with one flow diverter. The 12 month primary effectiveness rate was 73.7% (28/38). At 36 months, 68.4% (26/38) of aneurysms remained completely occluded. The 12 month major ipsilateral stroke or neurological death rate was 10.5%. No patients with PComA occlusion after flow diverter placement (54.5%) had clinical sequelae.

CONCLUSIONS

SCENT demonstrated acceptable 12 month effectiveness of flow diversion in PComA aneurysms. Despite associated PComA occlusions in many cases, arterial occlusions were clinically silent.

TRIAL REGISTRATION NUMBER

URL: https://www.

CLINICALTRIALS

gov. Unique identifier: NCT01716117.

Magnetic particle imaging for artifact-free imaging of intracranial flow diverter stents: A phantom study

PURPOSE

Magnetic Particle Imaging (MPI) is a new, background- and radiation-free tomographic imaging method that enables near real-time imaging of superparamagnetic iron-oxide nanoparticles (SPIONs) with high temporal and spatial resolution. This phantom study aims to investigate the potential of MPI for visualization of the stent lumen in intracranial flow diverters (FD).

METHODS

Nitinol FD of different dimensions (outer diameter: 3.5 mm, 4.0 mm, 5.5 mm; total length: 22-40 mm) were scanned in vascular phantoms in a custom-built MPI scanner (in-plane resolution: ~ 2 mm, field of view: 65 mm length, 29 mm diameter). Phantoms were filled with diluted (1:50) SPION tracer agent Ferucarbotran (10 µmol (Fe)/ml; NaCL). Each phantom was measured in 32 different projections (overall acquisition time per image: 3200 ms, 5averages). After image reconstruction from raw data, two radiologists assessed image quality using a 5-point Likert scale. The signal intensity profile was measured using a semi-automatic evaluation tool.

RESULTS

MPI visualized the lumen of all FD without relevant differences between the stented vessel phantom and the reference phantom. At 3.5 mm image quality was slightly inferior to the larger diameters. The FD themselves neither generated an MPI signal nor did they lead to relevant imaging artifacts. Ratings of both radiologists showed no significant difference, interrater reliability was good (ICC 0.84). A quantitative evaluation of the signal intensity profile did not reveal any significant differences (p > 0.05) either.

CONCLUSION

MPI visualizes the lumen of nitinol FD stents in vessel phantoms without relevant stent-induced artifacts.

First multicenter experience using the Silk Vista flow diverter in 60 consecutive intracranial aneurysms: technical aspects

Background

The aim of this study was to assess the technical success and procedural safety of the new Silk Vista device (SV) by evaluating the intraprocedural and periprocedural complication rate after its use in several institutions worldwide.

Methods

The study involved a retrospective review of multicenter data regarding a consecutive series of patients with intracranial aneurysms, treated with the SV between September 2020 and January 2021. Clinical, intra/periprocedural and angiographic data, including approach, materials used, aneurysm size and location, device/s, technical details and initial angiographic aneurysm occlusion, were analyzed.

Results

60 aneurysms were treated with SV in 57 procedures. 66 devices were used, 3 removed and 63 implanted. The devices opened instantaneously in 60 out of 66 (91%) cases and complete wall apposition was achieved in 58 out of 63 (92%) devices implanted. In 4 out of 66 (6%) devices a partial opening of the distal end occurred, and in 5 (8%) devices incomplete apposition was reported. There were 3 (5%) intraprocedural thromboembolic events managed successfully with no permanent neurological morbidity, and 4 (7%) postprocedural events. There was no mortality in this study. The initial occlusion rates in the 60 aneurysms were as follows: O’Kelly–Marotta (OKM) A in 34 (57%) cases, OKM B in 15 (25%) cases, OKM C in 6 (10%) cases, and OKM D in 5 (8%) cases.

Conclusions

Our study demonstrated that the use of the new flow diverter Silk Vista for the treatment of intracranial aneurysms is feasible and technically safe.

Torsional Characterization of Braided Flow Diverter Stents : A New Method to Evaluate Twisting Phenomenon

PURPOSE

In the interventional treatment of cerebral aneurysms, flow diverter (FD) stents have played a significant role for more than a decade. Many studies have shown good aneurysm occlusion rates and low complication profiles. However, feared complications include acute thrombotic vessel occlusion due to stenotic deformation of the FD during release, the so-called twisting. This work investigates the behavior of different stent types to causative torsion forces in a mechanical model.

MATERIALS AND METHODS

Torsion characterization equipment was custom built, and two different FD stents (Derivo, Acandis and P64, Phenox) with n = 3 were tested. One end of the FD was fixed while the other end was twisted while measuring the torsion force.

RESULTS

In torsional force vs. the twisting angle graph, a very sharp decrease and increase in force was recorded when the stent collapsed or reopened, respectively, making it possible to characterize for twisting. All six devices showed partial/complete collapse on torsion and showed significant delayed reopening on untwisting. Interestingly on repeated testing, the stent collapsed at earlier angles, probably due to microscopic material defects. Slight variations between stents of the same type suggest that more extensive data sets are needed.

CONCLUSIONS

We report a new method to characterize torsion for braided FD stents, which is reliable and reproducible. Additionally, the delayed reopening and the tendency to collapse at earlier angles on consequent testing maneuvers can be significant for clinical usage.

WEB Device Shape Changes in Elastase-Induced Aneurysms in Rabbits

BACKGROUND AND PURPOSE

While WEB devices have been shown to be safe and effective for aneurysm treatment, WEB-shape modification compression has been associated with incomplete aneurysm occlusion. We explored the relationship between occlusion rates and WEB-shape modification in different WEB device types in an experimental aneurysm model.

MATERIALS AND METHODS

Elastase-induced aneurysms were created in rabbits and treated with dual-layer (n = 12), single-layer (n = 12), or single-layer sphere (n = 12) WEB devices. Aneurysms were followed up either at 3 or 12 months. Angiographic occlusion was graded using the WEB Occlusion Scale: grade I, complete; grade II, complete but recess filling; grade III, residual neck; or grade IV, residual aneurysm. WEB-shape modification and histologic features were also analyzed.

RESULTS

Grade I or II occlusion was seen in 16 (44%) aneurysms, and grade I, II, or III ("adequate") occlusion was observed in 22 (61.1%) aneurysms at follow-up. WEB-shape modification was observed in 22 (61.1%) aneurysms. WEB-shape modification was higher in single-layer (9/12) and dual-layer (10/12) devices compared with single-layer sphere devices (3/12). Aneurysms with WEB-shape modification had a higher level of thrombus organization in the dome compared with those without WEB-shape modification (68% [15/22] versus 50% [7/14]). WEB-shape modification was not correlated with angiographic or histologic outcomes but was significantly correlated with levels of fibrosis and smooth muscle cells in the aneurysm.

CONCLUSIONS

WEB-shape modification is not associated with incomplete aneurysm occlusion of WEB devices in the rabbit model but may be related to connective tissue formation and the healing response to WEB device implantation.

Postinterventional Assessment after Stent and Flow-Diverter Implantation Using CT: Influence of Spectral Image Reconstructions and Different Device Types

BACKGROUND AND PURPOSE

CTA provides a noninvasive alternative technique to DSA in the follow-up after endovascular aneurysm treatment to evaluate aneurysm occlusion and exclude intraluminal narrowing after stent or flow-diverter implantation; however, assessability may be impeded by stent material artifacts. The objective of this in vitro study was to compare the visual assessability of different conventional stents and flow diverters as well as different reconstructions of dual-layer CT images.

MATERIALS AND METHODS

Four conventional intracranial stents and 4 flow diverters were implanted in identical aneurysm phantoms. Conventional and monoenergetic images (40, 50, 60, 90, 120, 180 keV) were acquired to evaluate attenuation alteration, visible lumen diameter, and SNR. Image quality was rated subjectively by 2 independent radiologists using a 4-point Likert scale.

RESULTS

Low kiloelectron volt (40-60 keV) monoenergetic reconstructions showed an improved SNR and an improved lumen density ratio compared with high kiloelectron volt reconstructions (90-180 keV) and conventional reconstructions, however without reaching significance compared with the latter. Assessment of the adjacent aneurysm and subjective evaluation was not affected by the imaging technique and stent type. Artifact susceptibility varied with the device used and increased among flow diverters.

CONCLUSIONS

Low kiloelectron volt reconstructions improved the assessment of the stent lumen in comparison with high kiloelectron volt reconstructions. No significant improvement in image quality could be shown compared with conventional images. For some devices, iodine-specific reconstructions led to severe artifacts and are therefore not recommended. There was no relevant improvement in the assessability of the adjacent aneurysm.

Cavernous carotid artery large aneurysm treated with a new flow diverter – Xcalibur aneurysm occlusion device (AOD)

We report a case of an unruptured, symptomatic, large right cavernous internal carotid artery aneurysm successfully treated with a new balloon-expandable flow diverter – Xcalibur Aneurysm Occlusion Device (AOD). Follow up imaging performed at six months demonstrated complete exclusion of the aneurysm and regression in dimensions, resulting in resolution of mass effect and clinical improvement.

Preclinical safety and efficacy evaluation of the Pipeline Vantage Embolization Device with Shield Technology

BACKGROUND

The Pipeline Vantage Embolization Device with Shield Technology is a next generation flow diverter developed to improve aneurysm occlusion and implant endothelialization in addition to lowering thrombogenicity. We report here the in vivo biocompatibility and in vitro hemocompatibility performance of the Pipeline Vantage Embolization Device with Shield Technology (Vantage) compared with the Pipeline Flex Embolization Device (Flex).

METHODS

Biocompatibility (via histology), aneurysm occlusion and vessel patency (via angiography), and endothelial coverage (via scanning electron microscopy (SEM)) for the Vantage and Flex devices were assessed in the rabbit elastase aneurysm model at 90 days (n=29) and 180 days (n=27). In vitro thrombogenicity for Flex and Vantage (n=16) was assessed using a human blood flow loop model at low heparin concentration (0.6 U/mL) with thrombin generation, platelet activation and thrombus visualization as outputs.

RESULTS

Raymond Roy Occlusion Classification grade 1 was higher for Vantage (61%) compared with Flex (46%), but was not statistically significant (p>0.05). All branch vessels were patent. Histological measures for both devices were similar (p>0.05). Endothelial coverage of the implant was significantly better for Vantage compared with Flex (p<0.05). In vitro measurements of thrombin generation (thrombin-antithrombin complex (µg/mL): Vantage 0.49±0.45; Flex 10.57±9.84) and platelet activation (β-thromboglobulin (IU/µl): Vantage 0.41±0.19; Flex 4.14±2.38) were both statistically lower (p<0.05) for Vantage compared with Flex. High resolution microscopy showed less accumulation of thrombus on Vantage as compared with Flex.

CONCLUSION

Vantage improved aneurysm occlusion and implant endothelialization and had significantly lower thrombogenicity as compared with Flex, while preserving the biocompatibility safety profile of Flex.

Promoting endothelialization of flow-diverting stents: a review

Intracranial flow-diverting (FD) stents have revolutionized the treatment of intracranial aneurysms in recent years, but complications resulting from failed endothelialization can still occur. Approaches to promote endothelialization are understudied, but hold promise in mitigating both short- and long-term complications associated with FD stent insertion. The aim of this review is to highlight the various features of and modifications that have been made to FD stents in order to expedite endothelialization. More specifically, we focus on how endothelialization can be influenced by the stent design, wall apposition, surface modifications, and the inclusion of biological agents.