Angiographic Assessment of the Performance of Flow Divertors to Treat Cerebral Aneurysms

Imaging of intracranial aneurysms in animals: a systematic review of modalities

Intracranial aneurysm (IA) animal models are paramount to study IA pathophysiology and to test new endovascular treatments. A number of in vivo imaging modalities are available to characterize IAs at different stages of development in these animal models. This review describes existing in vivo imaging techniques used so far to visualize IAs in animal models. We systematically searched for studies containing in vivo imaging of induced IAs in animal models in PubMed and SPIE Digital library databases between 1 January 1945 and 13 July 2022. A total of 170 studies were retrieved and reviewed in detail, and information on the IA animal model, the objective of the study, and the imaging modality used was collected. A variety of methods to surgically construct or endogenously induce IAs in animals were identified, and 88% of the reviewed studies used surgical methods. The large majority of IA imaging in animals was performed for 4 reasons: basic research for IA models, testing of new IA treatment modalities, research on IA in vivo imaging of IAs, and research on IA pathophysiology. Six different imaging techniques were identified: conventional catheter angiography, computed tomography angiography, magnetic resonance angiography, hemodynamic imaging, optical coherence tomography, and fluorescence imaging. This review presents and discusses the advantages and disadvantages of all in vivo IA imaging techniques used in animal models to help future IA studies finding the most appropriate IA imaging modality and animal model to answer their research question.

The development and understanding of intracranial aneurysm based on rabbit model

In modern society, intracranial aneurysms have seriously affected people's life. To better study and treat intracranial aneurysm, animal models are ideal candidates to perform biological research and preclinical endovascular device testing. Rabbit aneurysm model is one of the most commonly used animal models, and the rabbit aneurysms share similarities in histology, morphology, and hemodynamic aspects with human intracranial aneurysms, which is an ideal model for intracranial aneurysm pre-clinical and basic research. In this review, we will summarize the main methods of establishing rabbit aneurysms model and will further discuss the current biological mechanisms of intracranial aneurysms based on rabbit model. Further improvements of rabbit aneurysm model and more deep studies based on this model are needed to provide new insights into studying and clinical treating intracranial aneurysm.

Balloon-Mounted Stents for Treatment of Refractory Flow Diverting Device Wall Malapposition

BACKGROUND

As indications for flow diversion (FD) have expanded, new challenges in deployment of flow diverting devices (FDDs) have been encountered. We present 4 cases with aneurysms in which deployment of FDDs were complicated by device malapposition and compromised opening in regions of parent vessel stenosis. In all 4 cases, a balloon-mounted stent was ultimately deployed within the FDD.

OBJECTIVE

To describe the use of balloon-mounted stents (BMS) within FDDs for correction of flow-limiting stenosis and device malapposition.

METHODS

Patients undergoing FD for treatment of aneurysms complicated by refractory flow-limiting stenosis were identified through multi-center retrospective review. Those cases requiring use of BMS were identified. Further investigation in one of the cases was performed with a simulated pulsatile blood flow model.

RESULTS

After attempts to perform balloon angioplasty proved unsuccessful, BMS deployment successfully opened the stenotic parent artery and improved FDD wall apposition in all 4 cases. Simulated pulsatile blood flow modeling confirmed improvements in the distribution of velocity, wall shear stress, oscillatory shear index, and flow pattern structure after stent deployment. One case was complicated by asymptomatic in-stent thrombosis.

CONCLUSION

In cases of FDD deployment complicated by flow-limiting stenosis refractory to conventional techniques, a BMS deployed within the FD can provide radial support to open both the stenotic device and parent artery. Resulting improvements in device wall apposition may portend greater long-term efficacy of FD. In-stent occlusion can occur and may reflect a thrombogenic interaction between the devices.

In vitro angiographic comparison of the flow-diversion performance of five neurovascular stents

Background and purpose Data differentiating flow diversion properties of commercially available low- and high-porosity stents are limited. This in vitro study applies angiographic analysis of intra-aneurysmal flow to compare the flow-diversion performance of five neurovascular devices in idealized sidewall and bifurcation aneurysm models. Methods Five commercial devices (Enterprise, Neuroform, LVIS, FRED, and Pipeline) were implanted in silicone sidewall and bifurcation aneurysm models under physiological average flow of blood analog fluid. High-speed angiographic images were acquired pre- and post-device implantation and contrast concentration-time curves within the aneurysm were recorded. The curves were quantified with five parameters to assess changes in contrast transport, and thus aneurysm hemodynamics, due to each device. Results Inter-device flow-diversion performance was more easily distinguished in the sidewall model than the bifurcation model. There were no obvious overall statistical trends in the bifurcation parameters but the Pipeline performed marginally better than the other devices. In the sidewall geometry, overall evidence suggests that the LVIS performed better than the Neuroform and Enterprise. The Pipeline and FRED devices were statistically superior to the three stents and Pipeline was superior to FRED in all sidewall parameters evaluated. Conclusions Based on this specific set of experiments, lower-porosity flow diverters perform significantly better in reducing intra-aneurysmal flow activity than higher-porosity stents in sidewall-type geometries. The LVIS device is potentially a better flow diverter than the Neuroform and Enterprise devices, while the Pipeline is potentially better than the FRED.

Early angiographic changes of intra-aneurysmal flow after flow-diverter stent treatment are not predictive of therapeutic success

BACKGROUND AND PURPOSE

Flow-diverter stents (FDS) are new devices for the endovascular treatment of intracranial aneurysms (IAs) promoting progressive aneurysmal thrombosis. To date, the delay of aneurysmal exclusion remains unclear. We evaluated the correlation between angiographic changes in the first 24 hours and 12-month occlusion in aneurysms treated with FDS.

METHODS

We retrospectively analyzed the intra-aneurysmal flow by evaluating the in-flow and out-flow delays on preoperative, immediate postoperative, 24-hour and 12-month follow-up angiography. Dichotomy of in-flow and out-flow within the aneurysm was considered as the time of contrast filling and time of contrast washing relatively to the parent artery. The delay times were compared and correlated with the therapeutic success of FDS at 12 months of follow-up.

RESULTS

Out of 14 treated IAs, in 13 consecutive patients, n = 10 (71%) aneurysms showed complete occlusion at 12 months. Between immediate postoperative and 24-hour control, 10 aneurysms (71%) demonstrated in-flow modification, with eight increasing, two decreasing and four having no change. There were no statistical differences in therapeutic success in relation to the different flow-related profiles of intra-aneurysmal flux.Out-flow modifications were found in 11 aneurysms (79%) between immediate postoperative and 24-hour control, with five increasing, six decreasing and three having no change. Similar to the in-flow changes, there were no statistical differences in therapeutic success relative to the flow-related profiles.

CONCLUSIONS

Early angiographic changes after FDS placement are very frequent, but are not correlated with the 12-month technical success of flow-diversion techniques.

From bench to bedside: utility of the rabbit elastase aneurysm model in preclinical studies of intracranial aneurysm treatment

Preclinical studies are important in helping practitioners and device developers improve techniques and tools for endovascular treatment of intracranial aneurysms. Thus an understanding of the major animal models used in such studies is important. The New Zealand rabbit elastase induced arterial aneurysm of the common carotid artery is one of the most commonly used models in testing the safety and efficacy of new endovascular devices. In this review we discuss: (1) the various techniques used to create the aneurysm, (2) complications of aneurysm creation, (3) natural history of the arterial aneurysm, (4) histopathologic and hemodynamic features of the aneurysm, (5) devices tested using this model, and (6) weaknesses of the model. We demonstrate how preclinical studies using this model are applied in the treatment of intracranial aneurysms in humans. The model has similar hemodynamic, morphological, and histologic characteristics to human aneurysms, and demonstrates similar healing responses to coiling as human aneurysms. Despite these strengths, however, the model does have many weaknesses, including the fact that the model does not emulate the complex inflammatory processes affecting growing and ruptured aneurysms. Furthermore, the extracranial location of the model affects its ability to be used in preclinical safety assessments of new devices. We conclude that the rabbit elastase model has characteristics that make it a simple and effective model for preclinical studies on the endovascular treatment of intracranial aneurysms, but further work is needed to develop aneurysm models that simulate the histopathologic and morphologic characteristics of growing and ruptured aneurysms.

A Fourier-based approach to the angiographic assessment of flow diverter efficacy in the treatment of cerebral aneurysms

Flow diversion is an emerging endovascular treatment option for cerebral aneurysms. Quantitative assessment of hemodynamic changes induced by flow diversion can aid clinical decision making in the treatment of cerebral aneurysms. In this article, besides summarizing past key research efforts, we propose a novel metric for the angiographic assessment of flow diverter deployments in the treatment of cerebral aneurysms. By analyzing the frequency spectra of signals derived from digital subtraction angiography (DSA) series, the metric aims to quantify the prevalence of frequency components that correspond to the patient-specific heart rate. Indicating the decoupling of aneurysms from healthy blood circulation, our proposed metric could advance clinical guidelines for treatment success prediction. The very promising results of a retrospective feasibility study on 26 DSA series warrant future efforts to study the validity of the proposed metric within a clinical setting.

Pipeline embolization device for giant internal carotid artery aneurysms: 9-month follow-up results of two cases

The pipeline™ embolization device (PED) is a braided, tubular, bimetallic endoluminal implant used for occlusion of intracranial aneurysms through flow disruption along the aneurysm neck. The authors report on two cases of giant internal carotid artery aneurysm treated with the PED. In the first case, an aneurysm measuring 26.4 mm was observed at the C3-C4 portion of the left internal carotid artery in a 64-year-old woman who underwent magnetic resonance imaging (MRI) for dizziness and diplopia. In the second case, MRI showed an aneurysm measuring 25 mm at the C4-C5 portion of the right internal carotid artery in a 39-year-old woman with right ptosis and diplopia. Each giant aneurysm was treated with deployment of a PED (3.75 mm diameter/20 mm length and 4.5 mm diameter/25 mm length, respectively). Nine months later, both cases showed complete radiological occlusion of the giant intracranial aneurysm and sac shrinkage. We suggest that use of the PED can be a therapeutic option for giant intracranial aneurysms.

Cellular mechanisms of aneurysm occlusion after treatment with a flow diverter

PURPOSE

To characterize the progression of healing across aneurysm necks following treatment with a flow diverter in a rabbit aneurysm model.

MATERIALS AND METHODS

With institutional animal care and use committee approval, saccular aneurysms were created in 20 rabbits and treated with flow diverters. On days 1, 3, and 7 and weeks 4 and 8 after implantation, the aneurysm and the device-implanted vessel were harvested. En face staining of the gross specimen was performed for endothelial cells, endothelial progenitor cells, smooth muscle cells, and inflammatory cells.

RESULTS

The parent artery segments covered by the flow diverters were completely devoid of endothelial cells at 1 and 3 days but had completely reendothelialized by 7 days. At all time points, the struts along the patent portions of the aneurysm necks harbored scattered tissue islands composed exclusively of inflammatory cells. At 4 and 8 weeks, all samples contiguous with the tissue along the parent arteries had translucent tissue present along the occluded segments of the aneurysm neck. The vast majority of endothelial cells were contiguous with the parent artery and had smooth muscle cells underlying them. Endothelial progenitor cells were not observed along the neck of any aneurysm. Aneurysm closure was noted only when complete or nearly complete endothelialization over the device struts was present.

CONCLUSION

The initial event following flow diversion treatment is adherence of clusters of inflammatory cells across the aneurysm neck. Endothelialization is relatively delayed and derived exclusively from cells in the adjacent parent artery.

New Generation of Flow Diverter (Surpass) for Unruptured Intracranial Aneurysms

Background and Purpose—

In patients harboring intracranial aneurysms, the major goal in treatment is to prevent bleeding. A new generation of an endoluminal device (Surpass Flow Diverter [Surpass]) was developed to reconstruct parent artery and occlude the aneurysm. We present our clinical and angiographic single-center experience.

Methods—

Patients with a wide range of complex unruptured aneurysms were treated with the Surpass placed in the parent artery and bridging the aneurysm. Clinical and angiographic follow-up were performed at 6 months. Data were prospectively collected.

Results—

Thirty seven patients (mean age, 56 years; range, 32–79), harboring 49 unruptured aneurysms were treated at our center. All except 1 patient were treated with a single device. Successful delivery of the device was achieved in all patients. All 35 nonbifurcation aneurysm necks were covered completely, whereas 14 bifurcation aneurysms were only partially covered. There was no major periprocedural morbidity or mortality. During follow-up, 4 patients (10.4%) experienced transient neurological deficit. One patient (3%) developed a minor stroke at 4-month follow-up with persistent neurological deficit. Twelve patients had neurological symptoms related to their aneurysm and 7 showed improvement of these symptoms during follow-up. At 6-month follow-up, 29 of 31 aneurysms studied that had complete neck coverage showed a complete occlusion (94%) including 1 case with a 95% to 100% occlusion, whereas 5 of the 10 bifurcation aneurysms were occluded.

Conclusions—

Our study shows high safety and efficacy profile of a new generation endoluminal device in treatment of complex intracranial aneurysms. Long-term studies of treated bifurcation aneurysms are needed.

Pipeline for uncoilable or failed aneurysms: results from a multicenter clinical trial

PURPOSE

To evaluate the safety and effectiveness of the Pipeline Embolization Device (PED; ev3/Covidien, Irvine, Calif) in the treatment of complex intracranial aneurysms.

MATERIALS AND METHODS

The Pipeline for Uncoilable or Failed Aneurysms is a multicenter, prospective, interventional, single-arm trial of PED for the treatment of uncoilable or failed aneurysms of the internal carotid artery. Institutional review board approval of the HIPAA-compliant study protocol was obtained from each center. After providing informed consent, 108 patients with recently unruptured large and giant wide-necked aneurysms were enrolled in the study. The primary effectiveness endpoint was angiographic evaluation that demonstrated complete aneurysm occlusion and absence of major stenosis at 180 days. The primary safety endpoint was occurrence of major ipsilateral stroke or neurologic death at 180 days.

RESULTS

PED placement was technically successful in 107 of 108 patients (99.1%). Mean aneurysm size was 18.2 mm; 22 aneurysms (20.4%) were giant (>25 mm). Of the 106 aneurysms, 78 met the study's primary effectiveness endpoint (73.6%; 95% posterior probability interval: 64.4%-81.0%). Six of the 107 patients in the safety cohort experienced a major ipsilateral stroke or neurologic death (5.6%; 95% posterior probability interval: 2.6%-11.7%).

CONCLUSION

PED offers a reasonably safe and effective treatment of large or giant intracranial internal carotid artery aneurysms, demonstrated by high rates of complete aneurysm occlusion and low rates of adverse neurologic events; even in aneurysms failing previous alternative treatments.

Results of Stent-Assisted vs Non-Stent-Assisted Endovascular Therapies in 489 Cerebral Aneurysms

BACKGROUND:

Whether the addition of stenting to intracranial aneurysm coil embolization results in benefit in terms of occlusion rates or additional risk in terms of periprocedural adverse events is not clear.

OBJECTIVE:

To report retrospectively analyzed results of endovascular aneurysm treatment comparing stent-assisted coiling with coiling without stents at our hospital from 2005 to 2009.

METHODS:

In this retrospectively reviewed case series, aneurysms were grouped as intent-to-treat or initially treated with stent-assisted coiling (A) vs coiling alone (B) or as-treated—those that ultimately received a stent (C) or not (D). Complication and occlusion rates were compared between groups. Some patients crossed from group B to C after receiving stent placement at a later treatment following the initial therapeutic modality (without a stent).

RESULTS:

In 459 patients, 489 aneurysms were treated by group as follows: A = 181, B = 308, C = 225, and D = 264. In stent groups (A and C), there were significantly lower frequencies of ruptured aneurysms (A vs B = 11% vs 62%, P < .001; C vs D = 20.4% vs 62.5%, P < .001) and more giant aneurysms (A vs B = 7.3% vs 1.0%, P = .001; C vs D = 5.9% vs 1.1%, P < .001). There was no statistically significant difference in permanent event-related morbidity (A vs B = 4.4% vs 4.2%, P = 1.0; C vs D = 4.4% vs 4.2%, P = 1.0). Average angiographic follow-up after last treatment was 18.2 ± 15 months (median = 14). Higher rates of complete occlusion at last angiographic follow-up were observed in stented aneurysms (A vs B = 64.6% vs 49.7%, P = .001; C vs D = 62.7% vs 48.9%, P = .003).

CONCLUSION:

Stent-assisted aneurysm treatment resulted in higher total occlusion rates than non-stent-assisted treatment, with acceptable, comparable periprocedural event rates.

Analysis of intra-aneurysmal flow for cerebral aneurysms with cerebral angiography

BACKGROUND AND PURPOSE

Hemodynamics is an important factor in the development and rupture of cerebral aneurysms. Current techniques for measuring blood flow in cerebral aneurysms suffer from various limitations and have not been able to address our clinical needs. A new technique has been developed for effective evaluation of intra-aneurysmal flow based on high-frame-rate cerebral angiography, especially for flow-diverters.

MATERIALS AND METHODS

Six patients with 7 unruptured ICA aneurysms were imaged with a specially designed DSA protocol (a 3D DSA and a 2D DSA acquired at 30 frames/s, with a 2-mL/s contrast injection rate). Images of these cases were analyzed to determine the intra-aneurysmal flow based on the newly developed technique. Patient-specific aneurysm models were used for CFD calculation, and intra-aneurysmal flow rates were computed numerically. The intra-aneurysmal flow rates from the 2 methods were then compared.

RESULTS

There is a linear relationship between intra-aneurysmal flow ratios obtained from high-frame-rate cerebral angiography and CFD calculation (R = 0.99). A high frame rate (30 frames/s) provides a better estimate of intra-aneurysmal flow than low frame rates (7.5 frames/s and 15 frames/s).

CONCLUSIONS

The CFD calculation validates the estimate of intra-aneurysmal hemodynamics from cerebral angiography. The linear relationship obtained by using these 2 techniques can be used for real-time assessment of intra-aneurysmal hemodynamics for cerebral aneurysms.

Effects of metal coverage rate of flow diversion device on neointimal growth at side branch ostium and stented artery: an animal experiment in rabbit abdominal aorta

INTRODUCTION

To access the effect of actual metal coverage rate (MCR) on neointimal growth at covered side branch ostium and stented artery after implantation of a flow diversion device.

METHODS

Flow diverters (FDs) were implanted into abdominal aortas of 20 New Zealand rabbits. Four weeks and three months after FD implantation, the patency of side branches covered by the devices was assessed by angiography. The animals were sacrificed after angiography at 3 months postsurgery. The local actual MCR was measured under microscope and calculated. The extent of neointimal coverage at the ostia of branches and the neointima within the stent were examined by histology and scanning electron microscopy.

RESULTS

No side branch occlusion was noted, either immediately after implantation or at follow-ups. At 3 months after implantation, the intimal coverage of branch ostia caused by a 30-40% MCR was not significantly different from that caused by an MCR ≤ 30% (p = 0.792), but it was significantly lower than that caused by an MCR ≥ 40% (p = 0.021). Neointimal thickness in the stented abdominal aorta was positively correlated to MCR (r = 0.523, p = 0.001). The neointima was composed predominantly of smooth muscle cells and collagen fibers.

CONCLUSION

The actual MCR exhibited remarkable differences once FD was implanted in vivo. Significantly more intimal coverage at the side branch ostia could be induced when MCR was ≥40%. The neointimal thickness within the stent was positively correlated to device MCR.

Flow Diversion for Intracranial Aneurysms

The introduction of flow diverters for treatment of intracranial aneurysms represents a major paradigm shift in the treatment of these lesions. The theoretical hallmark of flow diverters is the treatment of the diseased segment harboring the aneurysm instead of treating the aneurysm itself. Flow diverters are designed to induce disruption of flow near the aneurysm neck while preserving flow into parent vessel and adjacent branches. After flow diversion, intra-aneurysmal thrombosis occurs, followed by shrinkage of the aneurysmal sac as the thrombus organizes and retracts. Preliminary clinical series document effective treatment of wide-neck and/or large and giant aneurysms with acceptable complication rates. However, several questions remain unanswered related to the incidence and mechanisms of aneurysm rupture after treatment with flow diverters, fate of small perforating vessels, and long-term patency rates.

Treatment of rabbit elastase-induced aneurysm models by flow diverters: development of quantifiable indexes of device performance using digital subtraction angiography

It has been known for more than a decade that intracranial aneurysms can be successfully treated by deploying a porous meshed tube in the parent vessel of the aneurysm. Such devices are currently called flow diverters because they promote intraneurysmal flow stasis and thrombosis by diverting blood flow away from the aneurysm sac. The objective of this study was to use angiographic data to quantify and compare the performance of flow diverters of original design in successfully occluding an experimental aneurysm model. Three different configurations of a novel flow diverter with varying porosities and pore densities were implanted in 30 rabbit elastase-induced aneurysms. Temporal variations in angiographic contrast intensity within the aneurysms were fit to a mathematical model. Optimized model parameters were supplemented by the angiographic percentage aneurysm occlusion and an angiographic measure of device flexibility to derive composite scores of performance. Angiographic quantification further suggested a parameter, which could be employed to estimate long-term aneurysm occlusion probabilities immediately after treatment. Performance scores showed that the device with a porosity of 70% and pore density of 18 pores/mm (2) performed better than devices with 65% porosity, 14 pores/mm (2), and 70% porosity, 12 pores/mm (2) with relative efficacies of 100%, 84%, and 76%, respectively. The pore density of flow diverters, rather than porosity, may thus be a critical factor modulating device efficacy. A value of the prognostic parameter of less than 30 predicted greater than 97% angiographic aneurysm occlusion over six months with a sensitivity of 73% and specificity of 82%.