Correlation between angiographic and particle image velocimetry quantifications of flow diverters in an in vitro model of elastase-induced rabbit aneurysms

Safety and anatomical outcome analysis after flow diverter coverage of the anterior cerebral artery

OBJECTIVES

Few studies on ischemic complications and flow changes after a flow diverter covering the anterior cerebral artery. The purpose of the study was to explore the ischemic complications and anatomical alterations associated with the flow diverter after it covers the anterior cerebral artery.

MATERIALS AND METHODS

In this single-center study, patients treated with FD covering the anterior cerebral artery at the First Affiliated Hospital of Zhengzhou University were retrospectively collected. The primary endpoint was ischemic complications related to the anterior cerebral artery. Secondary endpoints were anatomical changes in the anterior cerebral artery postoperatively and at follow-up.

RESULTS

A total of 59 patients were included in this study. Four (6.8%) patients presented with ischemic stroke symptoms. Immediately after the procedure, complete occlusion of A1 and decreased blood flow was observed in 13 (22.0%) and 21 patients (35.6%), respectively. At follow-up, A1 artery was occluded in 34 patients (57.6%) and decreased blood flow was observed in 10 patients (16.9%). Symptoms of neurological deficits related to the anterior cerebral artery were not observed in all patients at follow-up.

CONCLUSION

Coverage of A1 is safe, with a low incidence of ischemic stroke, when using an FD to treat aneurysms. Risk of reduced perfusion of the anterior cerebral artery postoperatively even if the anterior communicating artery is open. In cases with A1 occlusion, the blood flow in the distal the anterior cerebral artery can be adequately compensated by opening the anterior communicating artery and good vascular anastomoses.

Risk factor analysis of changes in blood flow in the A1 segment of the anterior cerebral artery after flow-diverter coverage of it

Few studies have explored the effect of a flow-diverter device (FD) on blood flow in the A1 segment of the anterior cerebral artery (ACA), after treatment of intracranial aneurysms in the bifurcation region of the internal carotid artery (ICA). The main objective of this article is to investigate the factors that affect A1 blood flow after FD covers the A1 artery. This is a single-center, retrospective study. Data were collected retrospectively from our center, and patients whose FDs were placed for treatment from the terminal of the ICA to the M1 segment were analyzed. A total of 42 patients were included in the study. Immediate post-procedural angiography following device placement revealed decreased blood flow in the A1 of 15 (35.7%) patients and complete occlusion of the A1 segment in 11 (26.2%) patients. During an average follow-up period of 9.8 months, the A1 segment was ultimately occluded in 25 patients (59.5%) and decreased blood flow in 4 patients (9.5%). When using FD to cover the A1 artery for the treatment of intracranial aneurysms, patients with preoperative opening of the anterior communicating artery (AcomA) are more prone to occlusion or decreased blood flow of the A1 artery, compared to patients without opening.

Trends in Ruptured and Unruptured Aneurysmal Treatment from 2010 to 2020: A Focus on Flow Diversion

OBJECTIVE

Flow diverters are a promising new tool in the neurosurgeon's arsenal for aneurysm management. We sought to quantify the trends of flow diversion in comparison to traditional endovascular coiling and surgical clip ligation techniques in the United States from 2010 to 2020 with an emphasis on aneurysm location and preferences in usage for ruptured versus unruptured aneurysms.

METHODS

In this large cross-sectional study, patients aged 18 and older within the MARINER database were analyzed. Descriptive characteristics were calculated for all included patients. χ2 tests were used to compare categorical variables. P values < 0.05 were statistically significant.

RESULTS

A total of 45,542 procedures were conducted in the United States from 2010 to 2020 (clipping: 14,491; coiling: 28,840; flow diversion: 2211). The Southern United States had the largest operative volume across all 3 intervention types, closely followed by the Midwest. Aneurysms of the middle cerebral artery were mostly clipped, whereas coiling and flow diversion techniques were most utilized for anterior communicating and posterior communicating artery aneurysms. Flow diversion is growing most rapidly in the treatment of unruptured aneurysms, though there were also significant increases in usage for ruptured aneurysm treatment from 2019 to 2020.

CONCLUSIONS

Flow diverters have gained significant traction in the treatment for both unruptured and ruptured aneurysms. In the coming years, the indications and use of flow diversion will undoubtedly grow further, but excitement over their application should be tempered by the safety and efficacy data that continues to emerge.

The evolution of intracranial aneurysm treatment techniques and future directions

Treatment techniques and management guidelines for intracranial aneurysms (IAs) have been continually developing and this rapid development has altered treatment decision-making for clinicians. IAs are treated in one of two ways: surgical treatments such as microsurgical clipping with or without bypass techniques, and endovascular methods such as coiling, balloon- or stent-assisted coiling, or intravascular flow diversion and intrasaccular flow disruption. In certain cases, a single approach may be inadequate in completely resolving the IA and successful treatment requires a combination of microsurgical and endovascular techniques, such as in complex aneurysms. The treatment option should be considered based on factors such as age; past medical history; comorbidities; patient preference; aneurysm characteristics such as location, morphology, and size; and finally the operator’s experience. The purpose of this review is to provide practicing neurosurgeons with a summary of the techniques available, and to aid decision-making by highlighting ideal or less ideal cases for a given technique. Next, we illustrate the evolution of techniques to overcome the shortfalls of preceding techniques. At the outset, we emphasize that this decision-making process is dynamic and will be directed by current best scientific evidence, and future technological advances.

Branch vessel occlusion in aneurysm treatment with flow diverter stent

Flow diverter placement for treatment of intracranial aneurysms gained growing consensus in the past years. A major concern among professionals is the side branch coverage which leads in some cases to vessel occlusion. However, the lost vessel patency only infrequently is accompanied by a new onset of neurological deficits secondary to ischaemic lesions. A retrospective analysis of all patients treated with flow diversion at our hospital was aimed to better understand this phenomenon in order to formulate a hypothesis about the causes. We concluded that vessel occlusion occurs due to a reduced blood pressure gradient in those vessels with a strong collateral or anastomotic vascularization that refurnishes the same distal vascular territories. Indeed, we detected no new brain infarction since blood flow was always guaranteed.

Hemodynamics of Cerebral Aneurysms: Connecting Medical Imaging and Biomechanical Analysis

In the last two decades, numerous studies have conducted patient-specific computations of blood flow dynamics in cerebral aneurysms and reported correlations between various hemodynamic metrics and aneurysmal disease progression or treatment outcomes. Nevertheless, intra-aneurysmal flow analysis has not been adopted in current clinical practice, and hemodynamic factors usually are not considered in clinical decision making. This review presents the state of the art in cerebral aneurysm imaging and image-based modeling, discussing the advantages and limitations of each approach and focusing on the translational value of hemodynamic analysis. Combining imaging and modeling data obtained from different flow modalities can improve the accuracy and fidelity of resulting velocity fields and flow-derived factors that are thought to affect aneurysmal disease progression. It is expected that predictive models utilizing hemodynamic factors in combination with patient medical history and morphological data will outperform current risk scores and treatment guidelines. Possible future directions include novel approaches enabling data assimilation and multimodality analysis of cerebral aneurysm hemodynamics.

Cognitive Imaging

This article, an extended version of ICCI*CC-2017 paper, co-authored by biomedical engineers specializing in brain blood circulation modeling and by experts in meaning-based NLP. This article suggests a cognitive computing technology for medical imaging analysis that removes image artifacts resulting in visual deviations from reality, such as discontinuous blood vessels or two vessels shown merged when they are not. It is implemented by supplying the pertinent knowledge that humans have to the computer and letting it initiate the corrective post-processing. The existing OST resource is centered on the ontology that is made to accommodate the domain with a minor adjustment effort; however, any ontology can be used, as demonstrated in this article. The examples from the ontology demonstrate the disparities between what the image shows and what the human knows. The computer detects them autonomously and can initiate the appropriate post-processing. If and when this cognitive imaging prevails, the post-processed images may replace the current ones as legitimate artifact-free MRIs.

Flow-diverter stenting of post-traumatic bilateral anterior cerebral artery pseudoaneurysm: A case report

The use of flow-diverter (FD) stents in recent years has positively changed the therapeutic approach to some vascular diseases, especially of certain types of aneurysms. This paper describes the case of a young patient after a major head trauma causing multiple skull fractures. The trauma occasioned two pseudoaneurysms from the A1 segment of the right anterior cerebral artery and from the A2 segment of the left anterior cerebral artery. Both lesions were treated with two Pipeline devices (ev3, Irvine, CA, USA) in two different sessions. The CT study and angiographic investigations performed in the following month showed a complete resolution of the post-traumatic pseudoaneurysmal lesions. Although the use of FD stents is described in the literature, particularly in the treatment of selected aneurysms, this paper shows good technical results in the use of these stents in cases of intracranial post-traumatic pseudoaneurysms with clinical improvement.

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.

4D Flow MRI in Neuroradiology: Techniques and Applications

Assessment of the intracranial flow is important for the understanding and management of cerebral vascular diseases. From brain aneurysms and arteriovenous malformations lesions to intracranial and cervical stenosis, the appraisal of the blood flow can be crucial and influence positively on patients' management. The determination of the intracranial hemodynamics and the collateral pattern seems to play to a major role in the management of these lesions. 4D flow magnetic resonance imaging is a noninvasive phase contrast derived method that has been developed and applied in neurovascular diseases. It has a great potential if followed by further technical improvements and comprehensive and systematic clinical studies.

Flow Diversion for Ophthalmic Artery Aneurysms

Endovascular treatments of ophthalmic segment aneurysms are commonly used but visual outcomes remain a concern. We performed a retrospective review of patients with carotid-ophthalmic aneurysms treated with flow diversion from June 2009 to June 2015. The following outcomes were studied through chart review: visual outcomes, complications, postoperative stroke and intraparenchymal hemorrhage, and clinical outcomes. Angiographic outcomes were studied with angiography and MRA at 6 months, 1 year, and 3 years. We evaluated 50 carotid-ophthalmic aneurysms in 48 patients, among whom 44 patients with 46 aneurysms underwent treatment. The mean clinical follow-up was 29 ± 22 months (range, 0-65 months). There were no permanent adverse visual outcomes. There was 1 death because of late intraparenchymal hemorrhage (2.2%). Six-month angiography showed complete occlusion in 24 of 37 patients (64.9%), and 3-year angiography results showed occlusion in 24 of 25 patients (96%). In conclusion, flow diversion is a safe and effective treatment for carotid-ophthalmic aneurysms in carefully selected patients. The risk of adverse visual outcomes is low, and most aneurysms progress to complete occlusion.

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.

The Silk flow-diverter stent for endovascular treatment of intracranial aneurysms

Flow diverter (FD) stents represent a new endovascular technique developed for the treatment of complex intracranial aneurysms (wide neck, fusiform, large, and giant aneurysms) that are challenging for classic endovascular techniques such as coiling, balloon-assisted coiling and stent-assisted coiling. Low porosity, high metal coverage, and high pore density are the main properties of FD stents. These properties induce hemodynamic changes redirecting the blood flow away from the aneurysm and into the parent artery leading to gradual thrombosis of the aneurysm. FD stents also provide scaffolding for subsequent neoendothelial proliferation, and vessel wall remodeling. This is considered as a paradigm shift compared to prior endovascular methods, which predominantly aimed at providing treatment inside the aneurysmal sac. This paper describes in detail the first released FD stent, the Silk flow-diverter stent (Balt Extrusion, Montmorency, France), its mechanism of action and deployment technique. It reviews the pertinent literature regarding safety, efficacy and potential risks and complications associated with the use of this stent.

Patency of the anterior choroidal artery after flow-diversion treatment of internal carotid artery aneurysms

BACKGROUND AND PURPOSE

Treatment of cerebral aneurysms with flow diverters often mandates placement of the device across the ostia of major branches of the internal carotid artery. We determined the patency rates of the anterior choroidal artery after placement of flow-diversion devices across its ostium.

MATERIALS AND METHODS

We analyzed a consecutive series of patients in whom a Pipeline Embolization Device was placed across the ostium of an angiographically visible anterior choroidal artery while treating the target aneurysm. Patency of the anterior choroidal artery after Pipeline Embolization Device placement was determined at immediate postoperative and follow-up angiography. Data on pretreatment aneurysm rupture status, concomitant coiling, number of Pipeline Embolization Devices used, neurologic status at follow-up, and follow-up MR imaging/CT findings were collected.

RESULTS

Fifteen patients with 15 treated aneurysms were included in this study. In the immediate postprocedural setting, the anterior choroidal artery was patent on posttreatment angiography for all 15 patients. Of the 14 patients with follow-up angiography at least 6 months after Pipeline Embolization Device placement, 1 (7%) had occlusion of the anterior choroidal artery and 14 had a patent anterior choroidal artery (93%). No patients had new neurologic symptoms or stroke related to anterior choroidal artery occlusion at follow-up. Of the 9 patients with follow-up CT or MR imaging, none had infarction in the vascular territory of the anterior choroidal artery.

CONCLUSIONS

In this small study, placement of a Pipeline Embolization Device across the anterior choroidal artery ostium resulted in occlusion of the artery in only 1 patient. It was not associated with ischemic changes in the distribution of the anterior choroidal artery in any patient.

Particle imaging velocimetry evaluation of intracranial stents in sidewall aneurysm: hemodynamic transition related to the stent design

We investigated the flow modifications induced by a large panel of commercial-off-the-shelf (COTS) intracranial stents in an idealized sidewall intracranial aneurysm (IA). Flow velocities in IA silicone model were assessed with and without stent implantation using particle imaging velocimetry (PIV). The use of the recently developed multi-time-lag method has allowed for uniform and precise measurements of both high and low velocities at IA neck and dome, respectively. Flow modification analysis of both regular (RSs) and flow diverter stents (FDSs) was subsequently correlated with relevant geometrical stent parameters. Flow reduction was found to be highly sensitive to stent porosity variations for regular stents RSs and moderately sensitive for FDSs. Consequently, two distinct IA flow change trends, with velocity reductions up to 50% and 90%, were identified for high-porosity RS and low-porosity FDS, respectively. The intermediate porosity (88%) regular braided stent provided the limit at which the transition in flow change trend occurred with a flow reduction of 84%. This transition occurred with decreasing stent porosity, as the driving force in IA neck changed from shear stress to differential pressure. Therefore, these results suggest that stents with intermediate porosities could possibly provide similar flow change patterns to FDS, favourable to curative thrombogenesis in IAs.

Implantation of pipeline flow-diverting stents reduces aneurysm inflow without relevantly affecting static intra-aneurysmal pressure

BACKGROUND

Flow-diverting stent (FDS) implantation is an endovascular treatment option for intracranial aneurysms. However, little is known about the hemodynamic effects.

OBJECTIVE

To assess the effect of stent compression on FDS porosity, to evaluate the influence of single and overlapping implantation of FDS on intra-aneurysmal flow profiles, and to correlate stent porosity with changes in static mean intra-aneurysmal pressure.

METHODS

Intra-aneurysmal time-density curves were recorded in a pulsatile in vitro flow model before and after implantation of FDSs (Pipeline Embolization Device; ev3) in 7 different types of aneurysm models. Reductions in the maximum contrast inflow and time to maximum intra-aneurysmal contrast were calculated. Micro--computed tomography was performed, and compression-related FDS porosity was measured. The influence of FDS placement on mean static intra-aneurysmal pressure was measured.

RESULTS

FDS compression resulted in an almost linear reduction in stent porosity. Stent porosity (struts per 1 mm) correlated significantly with the reduction of aneurysm contrast inflow (R = 0.81, P < .001) and delay until maximum contrast (R = 0.34, P = .001). Circulating intra-aneurysmal high-velocity flow was terminated in all sidewall models after implantation of a single stent. Superimposition of 2 stents reduced maximum intra-aneurysmal contrast by 69.1 ± 3.1% (mean ± SD) in narrow-necked sidewall aneurysm models, whereas no substantial reduction in maximum intra-aneurysmal contrast was observed in wide-necked sidewall aneurysm models. Intra-aneurysmal mean static pressure did not correlate with FDS porosity or number of implanted stents.

CONCLUSION

Implantation of FDS effectively reduces aneurysm inflow in a porosity-dependent way without relevantly affecting static mean intra-aneurysmal pressure.

ABBREVIATIONS

FDS, flow-diverting stentMAP, mean arterial pressurePED, Pipeline Embolization Device.

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.

The 'Sphere': A Dedicated Bifurcation Aneurysm Flow-Diverter Device

We present flow-based results from the early stage design cycle, based on computational modeling, of a prototype flow-diverter device, known as the 'Sphere', intended to treat bifurcation aneurysms of the cerebral vasculature. The device is available in a range of diameters and geometries and is constructed from a single loop of NITINOL^® wire. The 'Sphere' reduces aneurysm inflow by means of a high-density, patterned, elliptical surface that partially occludes the aneurysm neck. The device is secured in the healthy parent vessel by two armatures in the shape of open loops, resulting in negligible disruption of parent or daughter vessel flow. The device is virtually deployed in six anatomically accurate bifurcation aneurysms: three located at the Basilar tip and three located at the terminus bifurcation of the Internal Carotid artery (at the meeting of the middle cerebral and anterior cerebral arteries). Both steady state and transient flow simulations reveal that the device presents with a range of aneurysm inflow reductions, with mean flow reductions falling in the range of 30.6-71.8% across the different geometries. A significant difference is noted between steady state and transient simulations in one geometry, where a zone of flow recirculation is not captured in the steady state simulation. Across all six aneurysms, the device reduces the WSS magnitude within the aneurysm sac, resulting in a hemodynamic environment closer to that of a healthy vessel. We conclude from extensive CFD analysis that the 'Sphere' device offers very significant levels of flow reduction in a number of anatomically accurate aneurysm sizes and locations, with many advantages compared to current clinical cylindrical flow-diverter designs. Analysis of the device's mechanical properties and deployability will follow in future publications.

Parent artery reconstruction for large or giant cerebral aneurysms using a Tubridge flow diverter (PARAT): study protocol for a multicenter, randomized, controlled clinical trial

BACKGROUND

The treatment of large (10-25 mm) or giant (≥25 mm) cerebral aneurysms remains technically challenging, with a much higher complication and recanalization rate than that is observed for smaller aneurysms. The use of a flow diverter seems to facilitate the treatment of this special entity. In a previous single-center prospective study approved by the Ethics Committee and China Food and Drug Administration (CFDA), we obtained promising results, showing remarkable safety and effectiveness for the Tubridge flow diverter. Nevertheless, the previous study may have been limited by biases due to its single-center design and limited number of subjects. Furthermore, although various articles have reported durable results from treating aneurysms using flow diverters, increasing questions have arisen about this form of treatment. Thus, prospective, multiple-center, randomized trials containing more subjects are needed.

METHODS/DESIGN

This study is a multicenter, randomized, controlled clinical trial comparing clinical outcomes for patients with unruptured large/giant intracranial aneurysms treated with either conventional stent-assisted coiling or flow diverter implantation. A total of 124 patients who fulfill the inclusion and exclusion criteria will be randomized into either a treatment group or a control group in the ratio of 1:1. The treatment group will receive Tubridge implantation alone or combined with bared coils, and the control group will be treated with stent-assisted coiling (bare coils). The primary endpoint will be the complete occlusion rate at 6-month follow-up. Secondary endpoints include the immediate technique success rate, overall mortality, adverse events (ischemic stroke or intracranial bleeding) within 30 days, 90 days and 1 year post-operation, and the rate of intra-stent stenosis and thrombosis 6 months post-operation.

DISCUSSION

This prospective trial may provide more information on the safety and efficacy of the Tubridge flow diverter and may potentially change the strategy for treatment of large or giant aneurysms.

TRIAL REGISTRATION

The trial is registered on the Chinese Clinical Trial Registry: ChiCTR-TRC-13003127.

Patency of the posterior communicating artery after flow diversion treatment of internal carotid artery aneurysms

BACKGROUND AND PURPOSE

Cerebral aneurysm treatment with the Pipeline Embolization Device (PED) often mandates device placement across the ostia of arteries of the Circle of Willis. We determined the patency rates of the posterior communicating artery (Pcomm) after placement across its ostium a PED and studied neurologic outcomes in these patients.

METHODS

We analyzed, retrospectively, a consecutive series of patients in whom a PED was placed across the ostium of Pcomm while treating the target aneurysm. Pcomm arterial flow after PED placement was graded on a 3-point scale at post-operative angiography and follow-up angiography. Data on pretreatment aneurysm rupture status, concomitant coiling, number of PEDs used, and neurologic status at follow-up were collected.

RESULTS

Eleven patients with 13 aneurysms were included in this study. All patients had an ipsilateral posterior cerebral artery arising from the basilar artery (P1). In the immediate post-procedural setting, four patients (36%) had diminished Pcomm flow rates. After a mean follow-up of 12.6±6.7 months, three Pcomm arteries (27%) were occluded and two Pcomm arteries (18%) had diminished flow. Of patients with diminished flow/occluded Pcomm at follow-up, 80% (4/5) had diminished flow at initial post-procedure angiography compared to none of the six patients without diminished/occluded flow immediately post treatment. No patients suffered new neurologic symptoms at follow-up.

CONCLUSIONS

Approximately one half of Pcomm arteries demonstrated occlusion or decreased flow at follow-up if the ostia are covered with a flow diversion device. Covering the Pcomm ostium in patients with a P1 did not result in any neurologic deficits.

Comparison of the in vitro hemodynamic performance of new flow diverters for bypass of brain aneurysms

One possible treatment for cerebral aneurysms is a porous tubular structure, similar to a stent, called a flow diverter. A flow diverter can be placed across the neck of a cerebral aneurysm to induce the cessation of flow and initiate the formation of an intra-aneurysmal thrombus. This excludes the aneurysm from the parent artery and returns the flow of blood to normal. Previous flow diverting devices have been analyzed to determine optimal characteristics, such as braiding angle and wire diameter. From this information, a new optimized device was designed to achieve equivalent hemodynamic performance to the previous best device, but with better longitudinal flexibility to preserve physiological arterial configuration. The new device was tested in vitro in an elastomeric replica of the rabbit elastase induced aneurysm model and is now in the process of being tested in vivo. Particle image velocimetry was utilized to determine the velocity field in the plane of symmetry of the model under pulsatile flow conditions. Device hemodynamic performance indices such as the hydrodynamic circulation were evaluated from the velocity fields. Comparison of these indices with the previous best device and a control shows that the significant design changes of the device did not change its hemodynamic attributes (p > 0.05).

Midterm and long-term follow-up of cerebral aneurysms treated with flow diverter devices: a single-center experience

OBJECT

The introduction of flow diverter devices is revolutionizing the endovascular approach to cerebral aneurysms. Midterm and long-term results of angiographic, cross-sectional imaging and clinical follow-up are still lacking. The authors report their experience with endovascular treatment of intracranial aneurysms using both the Pipeline embolization device and Silk stents.

METHODS

From October 2008 to July 2011 a consecutive series of 104 intracranial aneurysms in 101 patients (79 female, 22 male; average age 53 years) were treated. Three of the 104 aneurysms were ruptured and 101 were unruptured. Silk stents were implanted in 47 of the aneurysms and Pipeline stents in the remaining 57. In 14 cases a combination of flow diverter devices and coils were used to treat larger aneurysms (maximum diameter > 15 mm). Patients underwent angiographic follow-up examination at 6 months after treatment, with or without CT or MRI, and at 1 year using CT or MRI, with or without conventional angiography.

RESULTS

In all cases placement of flow diverter stents was technically successful. The mortality and morbidity rates were both 3%. Adverse events without lasting clinical sequelae occurred in 20% of cases. Angiography performed at 6 months after treatment showed complete aneurysm occlusion in 78 of 91 cases (86% of evaluated aneurysms) and subocclusion in 11 (12%); only in 2 cases were the aneurysms unchanged. Fifty-three aneurysms were evaluated at 1 year after treatment. None of these aneurysms showed recanalization, and 1 aneurysm, which was incompletely occluded at the 6-month follow-up examination, was finally occluded. Aneurysmal sac shrinkage was observed in 61% of assessable aneurysms.

CONCLUSIONS

Parent artery reconstruction using flow diverter devices is a feasible, safe, and successful technique for the treatment of endovascular treatment of cerebral aneurysms.

Treatment of intracranial aneurysms using the pipeline flow-diverter embolization device: a single-center experience with long-term follow-up results

BACKGROUND AND PURPOSE

Flow-diverting devices now offer a new treatment alternative for cerebral aneurysms. We present the results of a large single-center series of patients treated with the PED, including long-term follow-up.

MATERIALS AND METHODS

Between November 2008 and September 2011, sidewall aneurysms with a wide neck (≥4 mm) or unfavorable dome-neck ratio (≤1.5); large/giant, fusiform, dissecting, blister-like, and recurrent sidewall aneurysms; aneurysms at difficult angles; and aneurysms in which a branch was originating directly from the sac were treated with the PED. Patients were premedicated with dual antiplatelet medications. Data, including demographics, aneurysm features, clinical presentation, complications, results, and follow-up information, for up to 2 years are presented.

RESULTS

Two hundred fifty-one aneurysms in 191 patients were treated. Of these, 96 (38.3%) were large or giant (≥10 mm). In 34/251 (13.5%), PEDs were used for retreatment. Adjunctive coiling was performed in 11 aneurysms (2.1%). The mean number of devices per aneurysm was 1.3. One aneurysm ruptured in the fourth month posttreatment (0.5%), and symptomatic in-construct stenosis was detected in 1 patient (0.5%) treated with percutaneous transarterial angioplasty. Any event rate was 27/191 (14.1%), with a permanent morbidity of 1% and mortality of 0.5%. Control angiography was available in 182 (95.3%) patients with 239 (95.2%) aneurysms. In 121 aneurysms (48.2%), 1- to 2-year control angiography was available. The aneurysm occlusion rate was 91.2% in 6 months, increasing to 94.6%.

CONCLUSIONS

Use of the PED is safe, efficacious, and durable in cerebral aneurysm treatment, with low morbidity-mortality and high occlusion rates as confirmed with mid- to long-term control angiography.

Patency of the ophthalmic artery after flow diversion treatment of paraclinoid aneurysms

OBJECT

In this study the authors determined the patency rate of the ophthalmic artery (OphA) after placement of 1 or more flow diversion devices across the arterial inlet for treatment of proximal internal carotid artery (ICA) aneurysms, and correlated possible risk factors for OphA occlusion.

METHODS

Nineteen consecutive patients were identified (mean age 53.9 years, range 23-74 years, all female) who were treated for 20 ICA aneurysms. In all patients a Pipeline Embolization Device (PED) was placed across the ostium of the OphA while treating the target aneurysm. Flow through the OphA after PED placement was determined by immediate angiography as well as follow-up angiograms (mean 8.7 months), compared with the baseline study. Potential risk factors for OphA occlusion, including age, immediate angiographic flow through the ophthalmic branch, status of flow within the aneurysm after placement of PEDs, whether the ophthalmic branch originated from the aneurysm dome, and number of PEDs placed across the ophthalmic branch inlet were correlated with patency rate.

RESULTS

Patients were treated with 1-3 PEDs (3 aneurysms treated with placement of 1 PED, 12 with 2 PEDs, and 5 with 3 PEDs). In 17 (85%) of 20 treated aneurysms, no changes in the OphA flow were noted immediately after placement of the device. Two (10%) of 20 patients had delayed antegrade filling immediately following PED placement and 1 patient (5%) had retrograde flow from collaterals to the OphA immediately after placement of the device. One patient (5%) experienced delayed asymptomatic ICA occlusion; this patient was excluded from analysis at follow-up. At follow-up the OphA remained patent with normal antegrade flow in 13 (68%) of 19 patients, patent but with slow antegrade flow in 2 patients (11%), and was occluded in 4 patients (21%). No visual changes or clinical symptoms developed in patients with OphA flow compromise. The mean number of PEDs in the patients with occluded OphAs or change in flow at angiographic follow-up was 2.4 (SEM 0.2) compared with 1.9 (SEM 0.18) in the patients with no change in OphA flow (p = 0.09). There was no significant difference between the patients with occluded OphAs compared with nonoccluded branches based on patient age, immediate angiographic flow through the ophthalmic branch, status of flow through the aneurysm after placement of PEDs, whether the ophthalmic branch originated from the aneurysm dome, or number of PEDs placed across the ophthalmic branch inlet.

CONCLUSIONS

Approximately one-quarter of OphAs will undergo proximal thrombosis when covered with flow diversion devices. Even though these events were well-tolerated clinically, our findings suggest that coverage of branch arteries that have adequate collateral circulation may lead to spontaneous occlusion of those branches.

Simple measurement of aneurysm residual after treatment: the SMART scale for evaluation of intracranial aneurysms treated with flow diverters

BACKGROUND

Primary endovascular reconstruction with flow diversion represents a fundamental paradigm shift in the technique of endovascular aneurysm treatment. Unlike coil embolization, often there remains residual post-procedural filling within the aneurysm with flow diverters, the curative reconstruction presumably occurring over a period of weeks. Thus, conventional grading scales for post-procedural aneurysm occlusion and recanalization are inadequate. The aim of this paper is to propose a new angiographic grading scale that addresses this fundamentally new treatment option.

METHOD

A five-point grading scale describes the location of residual flow within the aneurysm in the venous phase [grade 1: patent aneurysm with diffuse inflow; grade 2: residual filling of the aneurysm dome (saccular) or wall (fusiform); grade 3: only residual neck (saccular) or only intra-aneurysmal filling with former boundaries covered (fusiform); grade 4: complete occlusion].

FINDINGS

Grade 0 represents any aneurysm, regardless of occlusion rate with early phase, coherent inflow jet. Intra-aneurysmal flow stagnation is categorized into: (a) none, (b) capillary phase, and (c) venous phase. Prevailing parent vessel hemodynamics with in-stent stenosis (ISS) are divided into none (ISS0), mild (ISS1), moderate (ISS2), severe (ISS3), and total (ISS4) occlusion. The proposed grading scales allow assessment of the hemodynamic consequences of stent placement on endosaccular in-flow, stasis, and location of stasis as well as parent vessel hemodynamics.

CONCLUSIONS

Further studies need to show the applicability and possible predictive value of this new grading scale on the efficacy of the stent in promoting intra-aneurysmal flow stagnation, thus creating the potential to harmonize the results of future papers. This may help to optimize treatment and future device design.

Pipeline embolization device (PED) for neurovascular reconstruction: initial experience in the treatment of 101 intracranial aneurysms and dissections

Introduction

The purpose of this study was to evaluate the safety and efficacy of the recently available flow diverter “pipeline embolization device” (PED) for the treatment of intracranial aneurysms and dissections.

Methods

Eighty-eight consecutive patients underwent an endovascular treatment of 101 intracranial aneurysms or dissections using the PED between September 2009 and January 2011. The targeted vessels include 79 (78%) in the anterior circulation and 22 (22%) in the posterior circulation. We treated 96 aneurysms and 5 vessel dissections. Multiple devices were implanted in 67 lesions (66%).

Results

One technical failure of the procedure was encountered. Immediate exclusion of the target lesion was not observed. Angiographic follow-up examinations were carried out in 80 patients (91%) with 90 lesions and revealed complete cure of the target lesion(s) in 47 (52%), morphological improvement in 32 lesions (36%), and no improvement in 11 lesions (12%). Six major complications were encountered: one fatal aneurysm rupture, one acute and one delayed PED thrombosis, and three hemorrhages in the dependent brain parenchyma.

Conclusion

Our experience reveals that the PED procedure is technically straightforward for the treatment of selected wide-necked saccular aneurysms, fusiform aneurysms, remnants of aneurysms, aneurysms with a high likelihood of failure with conventional endovascular techniques, and dissected vessels. While vessel reconstruction, performed after dissection, is achieved within days, remodeling of aneurysmal dilatations may take several months. Dual platelet inhibition is obligatory. Parenchymal bleeding into brain areas dependent on the target vessel is uncommon.

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.

Endoluminal scaffolds for vascular reconstruction and exclusion of aneurysms from the cerebral circulation

The latest class of neuroendovascular devices being evaluated is intended to treat cerebral aneurysms. In addition to inducing flow stasis-mediated thrombosis of aneurysms and thus at times being referred to as flow diverters, these devices reconstitute pathologic arterial segments to near-physiologic normalcy. The successful implementation of such an endoluminal scaffold for vascular reconstruction in the cerebral circulation requires careful consideration of various factors drawn from engineering, physics, and biological sciences. Here we review some of these factors.

The effect of stents on intra-aneurysmal hemodynamics: in vitro evaluation of a pulsatile sidewall aneurysm using laser Doppler anemometry

INTRODUCTION

Hemodynamic modification by means of flow diversion is increasingly used for treatment of intracranial aneurysms. Despite of promising results, there is still a paucity of methods to reliably predict long-term success of this technique. Laser Doppler anemometry (LDA) can be used to quantify the influence of stents on intra-aneurysmal flow in vitro.

METHODS

All experiments were performed with a pulsatile model of a sidewall aneurysm. A physiologic flow was created with a circulatory experimental setup, and a transparent non-Newtonian glycerol-water solution was used to substitute human blood. Flow velocity was measured with a one-component LDA system, recording flow components parallel and perpendicular to the parent vessel. Three different stents (Solitaire, Silk, Phenox flow diverter) were deployed over the aneurysm neck, respectively.

RESULTS

Flow reduction was 67.59% (inflow zone), 9.65% (dome) and 37.94% (outflow zone) by the Solitaire stent. The Silk stent reduced the flow by 58.15% (inflow zone), 89.06% (dome) and 90.06% (outflow zone). The Phenox flow diverter reduced the flow by 96.76% (inflow zone), 90% (dome) and 90.91% (outflow zone) when positioned with narrow stent struts but increased the velocity of up to seven times compared to the unstented model when placed with loose strut packing in the proximal part of the aneurysm.

CONCLUSION

LDA is a feasible method to quantify intra-aneurysmal flow and flow reduction efficacy of stents in vitro. Flow reduction was negligible with a standard self-expanding stent. For dedicated flow diverters, it depended both on stent design and on appropriate positioning.