In Vitro Evaluation of Flow Divertors in an Elastase-Induced Saccular Aneurysm Model in Rabbit

Results of Double Low-Profile Visualized Intraluminal Support Blue Stenting for the Treatment of Fusiform Cerebral Aneurysms

BACKGROUND

The flow diversion technique is increasingly used for reconstructive endovascular treatment of fusiform cerebral aneurysms. Double stenting with the Low-profile Visualized Intraluminal Support (LVIS) Blue stent is one of the flow diversion techniques. The aim of this study was to analyze the clinical and angiographic outcomes of LVIS Blue double stenting for fusiform cerebral aneurysms.

METHODS

Between March 2016 and July 2020, double LVIS Blue stenting was attempted in 25 fusiform cerebral aneurysms. Patient medical records and radiological images were carefully reviewed.

RESULTS

The technical success rate was 100% (25/25). Six aneurysms (24.0%) were located in the anterior circulation and 19 aneurysms (76.0%) were located in the posterior circulation. Intraprocedural thromboembolic complications occurred in 1 patient (4.0%). During the follow-up period (30.8 ± 14.2 months), there were no deaths or delayed complications. The mean angiographic follow-up duration was 28.2 ± 12.8 months. Follow-up angiography revealed complete obliteration (O'Kelly-Marotta D) in 21 (84.0%) patients and near-complete obliteration (O'Kelly-Marotta C + 2 matched with Kamran-Byrne grade 3) in 2 (8.0%) patients. Two patients (8.0%) showed worsening of obliteration grades. One (4.0%) patient required retreatment. There was no significant in-stent stenosis or branch occlusion covered by stents.

CONCLUSIONS

Double stenting using LVIS Blue stents for the treatment of fusiform cerebral aneurysms is effective and safe.

"Trapped labelled spins"-related signal on arterial spin labelling in the assessment of flow-diverted aneurysms: preliminary experience

PURPOSE

To investigate ASL-MRI features of flow-diverted aneurysms, review their haemodynamic surrogates, and discuss their pertinent clinical implications.

METHODS

Retrospective single institutional analysis was performed on the clinical and imaging data of patients who underwent digital subtraction angiography (DSA) and ASL-MRI after endovascular flow diversion for cerebral aneurysms. Pseudo-continuous ASL-MRI was performed with post-label delays of 1525-1800 ms. Intra-aneurysmal "trapped labelled spins" (TLS)-related hypersignal, as seen on cerebral blood flow (CBF)-weighted maps of ASL-MRI, was investigated. Intermodality equivalence with DSA [O'Kelly-Marotta (OKM) grading for occlusion], 3D-TOF-MRA, and 3D spin-echo T1-weighted ("black-blood") images was assessed.

RESULTS

Ten cases were included. "TLS" signal was demonstrable in 7/8 (87.5%) of the DSA-visible flow-diverted aneurysms (OKM grade B3, n = 6; OKM grade A3, n = 2). No TLS was seen in both OKM-D (excluded) aneurysms. TLS was not visualised in an OKM-B3 aneurysm with < 3 mm opacifying remnant. 3D-TOF-MRA and ASL-MRI were discordant at 5 instances (45.4%; TOF-MRA false negative, n = 4; false positive, n = 1). Loss of flow void on black-blood images corresponded to the absence of TLS and vice versa in all cases but one.

CONCLUSION

"Trapped labelled spins"-related signal on ASL-MRI occurs in patent large aneurysms that have undergone successful endovascular flow diversion. This phenomenon likely represents an interplay of a multitude of haemodynamic factors including decelerated intra-aneurysmal inflow and outflow restriction. Serial intra-saccular TLS signal changes may hold diagnostic value, including contexts where 3D-TOF-MRA interpretation becomes dubious. "Trapped labelled spins"-related signal as a non-invasive proxy marker of aneurysm patency can possibly obviate unnecessary DSA.

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.

Mechanism of Action and Biology of Flow Diverters in the Treatment of Intracranial Aneurysms

Flow diverters have drastically changed the landscape of intracranial aneurysm treatment and are now considered first-line therapy for select lesions. Their mechanism of action relies on intrinsic alteration in hemodynamic parameters, both at the parent artery and within the aneurysm sac. Moreover, the device struts act as a nidus for endothelial cell growth across the aneurysm neck ultimately leading to aneurysm exclusion from the circulation. In silico computational analyses and investigations in preclinical animal models have provided valuable insights into the underlying biological basis for flow diverter therapy. Here, we review the present understanding pertaining to flow diverter biology and mechanisms of action, focusing on stent design, induction of intra-aneurysmal thrombosis, endothelialization, and alterations in hemodynamics.

Surpass Streamline Flow-Diverter Embolization Device for Treatment of Iatrogenic and Traumatic Internal Carotid Artery Injuries

Iatrogenic and traumatic cerebral internal carotid artery injuries are uncommon but potentially lethal complications. Direct surgical repair of ICA injuries may be difficult in an acute setting. However, endovascular treatment with a flow-diverter embolization device is a feasible alternative technique that we experienced. In this clinical report, we describe demographic data, radiographic images, lesion characteristics, endovascular procedure notes, postprocedural hospital course, and follow-up digital subtraction angiography of 5 patients. At least 6-month follow-up was available in all patients without occurrence of rebleeding and other complications.

The Effect of Stents in Cerebral Aneurysms: A Review

The etiology of up to 95% of cerebral aneurysms may be accounted for by hemodynamically-induced factors that create vascular injury. The purpose of this review is to describe key physical properties that stents have and how they affect cerebral aneurysms. We performed a two-step screening process. First, a structured search was performed using the PubMed database. The following search terms and keywords were used: “Hemodynamics,” “wall shear stress (WSS),” “velocity,” “viscosity,” “cerebral aneurysm,” “intracranial aneurysm,” “stent,” “flow diverter,” “stent porosity,” “stent geometry,” “stent configuration,” and “stent design.” Reports were considered if they included original data, discussed hemodynamic changes after stent-based treatment of cerebral aneurysms, examined the hemodynamic effects of stent deployment, and/or described the geometric characteristics of both stents and the aneurysms they were used to treat. The search strategy yielded a total of 122 articles, 61 were excluded after screening the titles and abstracts. Additional articles were then identified by cross-checking reference lists. The final collection of 97 articles demonstrates that the geometric characteristics and configurations of deployed stents influenced hemodynamic parameters such as aneurysmal WSS, inflow, and pressure. The geometric characteristics of the aneurysm and its position also had significant influences on intra-aneurysmal hemodynamics after treatment. In conclusion, changes in specific aneurysmal hemodynamic parameters that result from stenting relate to a number of factors including the geometric properties and configurations of deployed stents, the geometric properties of the aneurysm, and the pretreatment hemodynamics.

Long-Term Outcomes of Patients with Stent Tips Embedded into Internal Carotid Artery Branches during Aneurysm Coiling

BACKGROUND AND PURPOSE

During stent-assisted coiling of ICA aneurysms, stent tips are sometimes unintentionally embedded into ICA branches. Stent tips can be visualized because they have radiopaque markers. Concerns regarding stent tip misplacement include risks of artery perforation and occlusion. The aim of this study was to evaluate the long-term outcomes of ICA branches with embedded stent tips.

MATERIALS AND METHODS

ICA branches with embedded stent tips were identified among 35 patients with unruptured ICA aneurysms treated with stent-assisted coiling between November 2003 and November 2014. Patient clinical and angiographic outcomes associated with the embedded stent tip were analyzed.

RESULTS

Most of the 35 studied aneurysms were paraclinoid ICA aneurysms (n = 30). The most commonly involved ICA branch was the posterior communicating artery (26 patients, 74.3%), followed by the anterior choroidal artery (8 patients, 22.9%) and ophthalmic artery (1 patient, 2.9%). During the follow-up period (38.6 ± 17.9 months), no new neurologic deficits developed. Neither hemorrhagic nor thromboembolic events occurred. Angiography was performed during the final follow-up evaluation at a mean of 32.7 ± 18.0 months, and all ICA branches with embedded stent tips showed patent blood flow without severe luminal narrowing.

CONCLUSIONS

In our experience, placement of a stent tip into ICA branches during stent-assisted coiling was not associated with any major adverse events.

Phase-contrast MRI versus numerical simulation to quantify hemodynamical changes in cerebral aneurysms after flow diverter treatment

Cerebral aneurysms are a major risk factor for intracranial bleeding with devastating consequences for the patient. One recently established treatment is the implantation of flow-diverters (FD). Methods to predict their treatment success before or directly after implantation are not well investigated yet. The aim of this work was to quantitatively study hemodynamic parameters in patient-specific models of treated cerebral aneurysms and its correlation with the clinical outcome. Hemodynamics were evaluated using both computational fluid dynamics (CFD) and phase contrast (PC) MRI. CFD simulations and in vitro MRI measurements were done under similar flow conditions and results of both methods were comparatively analyzed. For preoperative and postoperative distribution of hemodynamic parameters, CFD simulations and PC-MRI velocity measurements showed similar results. In both cases where no occlusion of the aneurysm was observed after six months, a flow reduction of about 30-50% was found, while in the clinically successful case with complete occlusion of the aneurysm after 6 months, the flow reduction was about 80%. No vortex was observed in any of the three models after treatment. The results are in agreement with recent studies suggesting that CFD simulations can predict post-treatment aneurysm flow alteration already before implantation of a FD and PC-MRI could validate the predicted hemodynamic changes right after implantation of a FD.

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.

Large Basilar Apex Aneurysms Treated with Flow-Diverter Stents

BACKGROUND AND PURPOSE

The treatment of wide-neck, large basilar apex aneurysms is challenging with either an endovascular or a surgical approach. The aim of the present study was to report our experience treating basilar apex aneurysms with flow-diverter stents and to evaluate their efficacy and safety profile in this specific anatomic condition.

MATERIALS AND METHODS

We retrospectively analyzed data from all consecutive patients treated with flow-diverter stents at our institution between January 2011 and January 2015. Patients with large basilar apex aneurysms treated with a flow-diverter stent were included in the study. Clinical presentations, technical details, intra- and perioperative complications, and clinical and angiographic outcomes were recorded, with a midterm follow-up.

RESULTS

Of the 175 aneurysms treated with flow-diverter stents at our institution, 5 patients (2 women and 3 men; age range, 44-58 years) received flow-diverter stent for basilar apex aneurysms. The mean follow-up after stent deployment was 21 months (range, 15-24 months). One patient died on day 31 from an early postprocedural midbrain hemorrhage. One patient had a right cerebellar hemispheric ischemic lesion with a transient cerebellar syndrome resolved within 24 hours without neurologic sequelae at the latest follow-up. The mRS was 0 in 4 patients and 6 in 1 patient at last follow-up.

CONCLUSIONS

Flow diversion is a feasible technique with an efficacy demonstrated at a midterm follow-up, especially in the case of basilar apex aneurysm recurrences after previous endovascular treatments. Concern about its safety profile still exists.

Hemodynamics of Flow Diverters

Cerebral aneurysms are pathological focal evaginations of the arterial wall at and around the junctions of the circle of Willis. Their tenuous walls predispose aneurysms to leak or rupture leading to hemorrhagic strokes with high morbidity and mortality rates. The endovascular treatment of cerebral aneurysms currently includes the implantation of fine-mesh stents, called flow diverters, within the parent artery bearing the aneurysm. By mitigating flow velocities within the aneurysmal sac, the devices preferentially induce thrombus formation in the aneurysm within hours to days. In response to the foreign implant, an endothelialized arterial layer covers the luminal surface of the device over a period of days to months. Organization of the intraneurysmal thrombus leads to resorption and shrinkage of the aneurysm wall and contents, eventually leading to beneficial remodeling of the pathological site to a near-physiological state. The devices' primary function of reducing flow activity within aneurysms is corollary to their mesh structure. Complete specification of the device mesh structure, or alternately device permeability, necessarily involves the quantification of two variables commonly used to characterize porous media—mesh porosity and mesh pore density. We evaluated the flow alteration induced by five commercial neurovascular devices of varying porosity and pore density (stents: Neuroform, Enterprise, and LVIS; flow diverters: Pipeline and FRED) in an idealized sidewall aneurysm model. As can be expected in such a model, all devices substantially reduced intraneurysmal kinetic energy as compared to the nonstented case with the coarse-mesh stents inducing a 65–80% reduction whereas the fine-mesh flow diverters induced a near-complete flow stagnation (∼98% reduction). We also note a trend toward greater device efficacy (lower intraneurysmal flow) with decreasing device porosity and increasing device pore density. Several such flow studies have been and are being conducted in idealized as well as patient-derived geometries with the overarching goals of improving device design, facilitating treatment planning (what is the optimal device for a specific aneurysm), and predicting treatment outcome (will a specific aneurysm treated with a specific device successfully occlude over the long term). While the results are generally encouraging, there is poor standardization of study variables between different research groups, and any consensus will only be reached after standardized studies are conducted on collectively large datasets. Biochemical variables may have to be incorporated into these studies to maximize predictive values.

Evaluation of Pipeline Flex delivery system for the treatment of unruptured aneurysms

INTRODUCTION

Refinements in endovascular technology have revolutionized the treatment of intracranial aneurysms (IAs) with the development of flow-diversion technology. The first generation of the Pipelin Embolization Device (PED) has demonstrated its safety and efficacy. However, the deployment technique was a difficult task that often led to complex maneuvers. The Pipeline Flex Embolization Device (PED Flex) is the second generation and its introduction has arrived with high expectations due to a completely redesigned delivery system that intends to overcome deployment difficulties seen in the previous generation. Areas covered: Preclinical studies, mechanism of action of flow-diverters, technical aspects and deployment system of the PED Flex, and clinical outcomes with both PED generations. Expert commentary: Flow diversion has allowed us to treat lesions that would be otherwise challenging for surgical clipping or unsuitable for other endosaccular strategies. Although the experience with PED Flex is limited, initial results suggest its safety and short-term efficacy.

In Vitro Investigation of a New Thin Film Nitinol-Based Neurovascular Flow Diverter

Fusiform and wide-neck cerebral aneurysms (CAs) can be challenging to treat with conventional endovascular or surgical approaches. Recently, flow diverters have been developed to treat these cases by diverting flow away from the aneurysm rather than occluding it. The pipeline embolization device (PED), which embodies a single-layer braided design, is best known among available flow diverters. While the device has demonstrated success in recent trials, late aneurysmal rupture after PED treatment has been a concern. More recently, a new generation of dual-layer devices has emerged that includes a novel hyperelastic thin film nitinol (HE-TFN)-covered design. In this study, we compare fluid dynamic performance between the PED and HE-TFN devices using particle image velocimetry (PIV). The PED has a pore density of 12.5–20 pores/mm2 and a porosity of 65–70%. The two HE-TFN flow diverters have pore densities of 14.75 pores/mm2 and 40 pores/mm2, and porosities of 82% and 77%, respectively. Conventional wisdom suggests that the lower porosity PED would decrease intra-aneurysmal flow to the greatest degree. However, under physiologically realistic pulsatile flow conditions, average drops in root-mean-square (RMS) velocity (VRMS) within the aneurysm of an idealized physical flow model were 42.8–73.7% for the PED and 68.9–82.7% for the HE-TFN device with the highest pore density. Interestingly, examination of collateral vessel flows in the same model also showed that the HE-TFN design allowed for greater collateral perfusion than the PED. Similar trends were observed under steady flow conditions in the idealized model. In a more clinically realistic scenario wherein an anatomical aneurysm model was investigated, the PED affected intra-aneurysmal VRMS reductions of 64.3% and 56.3% under steady and pulsatile flow conditions, respectively. In comparison, the high pore density HE-TFN device reduced intra-aneurysmal VRMS by 88% and 71.3% under steady and pulsatile flow conditions, respectively. We attribute the superior performance of the HE-TFN device to higher pore density, which may play a more important role in modifying aneurysmal fluid dynamics than the conventional flow diverter design parameter of greatest general interest, absolute porosity. Finally, the PED led to more elevated intra-aneurysmal pressures after deployment, which provides insight into a potential mechanism for late rupture following treatment with the device.

Two-stage reconstructive overlapping stent LEO+ and SILK for treatment of intracranial circumferential fusiform aneurysms in the posterior circulation

Intracranial circumferential fusiform aneurysms of the posterior circulation involving arterial branches or perforating vessels are difficult to treat. This article shows an endovascular reconstruction technique not yet described, using a telescoping self-expandable stent (LEO+) and flow-diverter device (SILK) at different surgical times. Two patients with circumferential fusiform aneurysm, one being an aneurysm of the segments P2 and P3 of the posterior cerebral artery, diagnosed after a headache, and the other a partially thrombosed aneurysm of the lower basilar artery, diagnosed following ischemia of the brain stem. Endovascular treatment was performed by means of a vascular reconstruction technique that used at different surgical times: overlapping; a telescoped self-expandable stent, LEO+; and a flow-diverter device, SILK. Angiographic control was carried out at 6 and 12 months, to evaluate arterial patency, flow maintenance in the arterial branches and perforating vessels, and thrombosis of the aneurysm. The combined use at different surgical times of the self-expandable stent and flow-diverter device was technically successful in both patients. There were no complications during the procedure, nor in the long-term follow-up with full arterial vascular reconstruction, maintenance of cerebral perfusion and complete aneurysm occlusion at the 6- and 12-month angiographic follow-up. There was no aneurysm recanalization nor intra-stent stenosis. Circumferential fusiform aneurysm of the posterior circulation involving arterial branches or perforating vessels to the brain stem may be treated with this arterial reconstruction technique at different surgical times, using the self-expandable stent called LEO+ and the flow-diverter device SILK, minimizing the risk of complications and failure of the endovascular technique, with the potential for arterial reconstruction with thrombosis of the aneurysmatic sac, as well as flow maintenance in the eloquent arteries, in this type of cerebral aneurysm.

In Vitro Evaluation of Intra-Aneurysmal, Flow-Diverter-Induced Thrombus Formation: A Feasibility Study

BACKGROUND AND PURPOSE

Intracranial aneurysm treatment by flow diverters aims at triggering intra-aneurysmal thrombosis. By combining in vitro blood experiments with particle imaging velocimetry measurements, we investigated the time-resolved thrombus formation triggered by flow diverters.

MATERIALS AND METHODS

Two test setups were built, 1 for particle imaging velocimetry and 1 for blood experiments, both generating the same pulsatile flow and including a silicone aneurysm model. Tests without flow diverters and with 2 different flow-diverter sizes (diameter: 4.5 and 4.0 mm) were performed. In the blood experiments, the intra-aneurysmal flow was monitored by using Doppler sonography. The experiments were stopped at 3 different changes of the spatial extent of the signal.

RESULTS

No thrombus was detected in the aneurysm model without the flow diverter. Otherwise, thrombi were observed in all aneurysm models with flow diverters. The thrombi grew from the proximal side of the aneurysm neck with fibrin threads connected to the flow diverter and extending across the aneurysm. The thrombus resulting from the 4.0-mm flow diverter grew along the aneurysm wall as a solid and organized thrombus, which correlates with the slower velocities near the wall detected by particle imaging velocimetry. The thrombus that evolved by using the 4.5-mm flow diverter showed no identifiable growing direction. The entire thrombus presumably resulted from stagnation of blood and correlates with the central vortex detected by particle imaging velocimetry.

CONCLUSIONS

We showed the feasibility of in vitro investigation of time-resolved thrombus formation in the presence of flow diverters.

Incidence and clinical implications of carotid branch occlusion following treatment of internal carotid artery aneurysms with the pipeline embolization device

BACKGROUND

The use of flow diverters such as the pipeline embolization device (PED) for treatment of intracranial aneurysms carries the risk of side branch occlusion.

OBJECTIVE

To determine the incidence and clinical outcomes associated with supraclinoid internal carotid artery (ICA) branch occlusion after deployment of PEDs for ICA aneurysms.

METHODS

We reviewed patients who underwent endovascular treatment with PEDs for ICA aneurysms between June 2011 and March 2013. Forty-nine patients (43 women, mean age 56.3±1.8 years, 68 aneurysms) in whom PEDs traversed the origin of supraclinoid ICA branches (ophthalmic [OA], posterior communicating [PcommA], and anterior choroidal artery [AChA]) were selected for this study. Follow-up angiograms (mean follow-up, 12.8±0.8 months) were studied to determine the location of PEDs and the patency of ICA branches.

RESULTS

PEDs were placed across the ostia of 49 OAs, 14 PcommAs, and 11 AChAs. Multiple PEDs were deployed in 16 patients. Rate of branch occlusion was 4% (2/49) for the OA, 7.1% (1/14) for the PcommA, and 0% for the AChA. Patients with branch occlusion did not endure new neurological deficits. ICA branch occlusion was not associated with the number of PEDs covering the ostia (P=.76) or the origin of ICA branches from the aneurysm (P=.24).

CONCLUSION

The incidence of major supraclinoid ICA branch occlusion after treatment with PEDs was low. These events were not associated with new neurological deficits nor were they related to the number of PEDs deployed or the origin of ICA branches from the aneurysm.

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.

Anterior choroidal artery patency and clinical follow-up after coverage with the pipeline embolization device

BACKGROUND AND PURPOSE

Endoluminal reconstruction with the Pipeline Embolization Device is an effective treatment option for select intracranial aneurysms. However, concerns for the patency of eloquent branch arteries covered by the Pipeline Embolization Device have been raised. We aimed to examine the patency of the anterior choroidal artery and clinical sequelae after ICA aneurysm treatment.

MATERIALS AND METHODS

We prospectively analyzed all patients among our first 157 patients with ICA aneurysms treated by the Pipeline Embolization Device who required placement of at least 1 device across the ostium of the anterior choroidal artery. The primary outcome measure was angiographic patency of the anterior choroidal artery at last follow-up. Age, sex, type of aneurysm, neurologic examination data, number of Pipeline Embolization Devices used, relationship of the anterior choroidal artery to the aneurysm, and completeness of aneurysm occlusion on follow-up angiograms were also analyzed.

RESULTS

Twenty-nine aneurysms requiring placement of at least 1 Pipeline Embolization Device (median = 1, range = 1-3) across the anterior choroidal artery ostium were identified. At angiographic follow-up (mean = 15.1 months; range = 12-39 months), the anterior choroidal artery remained patent, with antegrade flow in 28/29 aneurysms (96.5%), while 24/29 (82.7%) of the target aneurysms were angiographically occluded by 1-year follow-up angiography. Anterior choroidal artery occlusion, with retrograde reconstitution of the vessel, was noted in a single case. A significant correlation between the origin of the anterior choroidal artery from the aneurysm dome and failure of the aneurysms to occlude following treatment was found.

CONCLUSIONS

After placement of 36 Pipeline Embolization Devices across 29 anterior choroidal arteries (median = 1 device, range = 1-3 devices), 1 of 29 anterior choroidal arteries was found occluded on angiographic follow-up. The vessel occlusion did not result in persistent clinical sequelae. Coverage of the anterior choroidal artery origin with the Pipeline Embolization Device, hence, may be considered reasonably safe when deemed necessary for aneurysm treatment.

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.

Evaluation of a newly designed flow diverter for the treatment of intracranial aneurysms in an elastase-induced aneurysm model, in New Zealand white rabbits

INTRODUCTION

In this study, we analyzed angiographic and histologic aneurysm occlusion of a newly designed flow diverting device. Visibility and flexibility, as well as occlusions of side branches and neointimal proliferation were also evaluated.

METHODS

Aneurysms were induced in 18 New Zealand white rabbits and treated with a braided, “closed-loop-designed” device of nitinol. Additional devices were implanted in the abdominal aorta to cover the origin of branch arteries.Angiographic follow-ups were performed immediately after placement of the device, after 3 months (n=9) and 6 months(n =9). The status of aneurysm occlusion (using a five-point scale) and the patency of branch arteries were assessed.

RESULTS

Aneurysm occlusion rates were noted as grade 0 in 2 (11 %), grade I in 1 (6 %), grade II in 1 (6 %), grade III in 9(50 %), and grade IV in 5 (28 %) of 18 aneurysms, respectively, indicating a complete or near-complete occlusion of 78 % under double antiplatelet therapy. Aneurysm occlusion was significantly higher at 6 months follow-up (P =0.025). Radiopaque markers provided excellent visibility. Limited device flexibility led to incomplete aneurysm neck coverage and grade 0 occlusion rates in two cases. Distal device occlusions were found in three cases, most likely due to an extremely undersized vessel diameter in the subclavian artery.No case of branch artery occlusion was seen. Intimal proliferation and diameter stenosis were moderate.

CONCLUSION

The tested flow diverter achieved near-complete and complete aneurysm occlusion under double antiplatelet therapy of elastase-induced aneurysms in 78 %, while preserving branch arteries.

Hemodynamic analysis of fast and slow aneurysm occlusions by flow diversion in rabbits

PURPOSE

To assess hemodynamic differences between aneurysms that occlude rapidly and those occluding in delayed fashion after flow diversion in rabbits.

METHODS

Thirty-six elastase-induced aneurysms in rabbits were treated with flow diverting devices. Aneurysm occlusion was assessed angiographically immediately before they were sacrificed at 1 (n=6), 2 (n=4), 4 (n=8) or 8 weeks (n=18) after treatment. The aneurysms were classified into a fast occlusion group if they were completely or near completely occluded at 4 weeks or earlier and a slow occlusion group if they remained incompletely occluded at 8 weeks. The immediate post-treatment flow conditions in aneurysms of each group were quantified using subject-specific computational fluid dynamics and statistically compared.

RESULTS

Nine aneurysms were classified into the fast occlusion group and six into the slow occlusion group. Aneurysms in the fast occlusion group were on average significantly smaller (fast=0.9 cm, slow=1.393 cm, p=0.024) and had smaller ostia (fast=0.144 cm2, slow=0.365 cm2, p=0.015) than aneurysms in the slow occlusion group. They also had a lower mean post-treatment inflow rate (fast=0.047 mL/s, slow=0.155 mL/s, p=0.0239), kinetic energy (fast=0.519 erg, slow=1.283 erg, p=0.0468), and velocity (fast=0.221 cm/s, slow=0.506 cm/s, p=0.0582). However, the differences in the latter two variables were only marginally significant.

CONCLUSIONS

Hemodynamic conditions after flow diversion treatment of cerebral aneurysms in rabbits are associated with the subsequent aneurysm occlusion time. Specifically, smaller inflow rate, kinetic energy, and velocity seem to promote faster occlusions, especially in smaller and small-necked aneurysms. These results are consistent with previous studies based on clinical series.

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.

Strategy for analysis of flow diverting devices based on multi-modality image-based modeling

Quantification and characterization of the hemodynamic environment created after flow diversion treatment of cerebral aneurysms is important to understand the effects of flow diverters and their interactions with the biology of the aneurysm wall and the thrombosis process that takes place subsequently. This paper describes the construction of multi-modality image-based subject-specific CFD models of experimentally created aneurysms in rabbits and subsequently treated with flow diverters. Briefly, anatomical models were constructed from 3D rotational angiography images, flow conditions were derived from Doppler ultrasound measurements, stent models were created and virtually deployed, and the results were compared with in vivo digital subtraction angiography and Doppler ultrasound images. The models were capable of reproducing in vivo observations, including velocity waveforms measured in the parent artery, peak velocity values measured in the aneurysm, and flow structures observed with digital subtraction angiography before and after deployment of flow diverters. The results indicate that regions of aneurysm occlusion after flow diversion coincide with slow and smooth flow patterns, whereas regions still permeable at the time of animal sacrifice were observed in parts of the aneurysm exposed to larger flow activity, that is, higher velocities, more swirling, and more complex flow structures.

Surpass flow diverter in the treatment of intracranial aneurysms: a prospective multicenter study

BACKGROUND AND PURPOSE

Incomplete occlusion and recanalization of large and wide-neck brain aneurysms treated by endovascular therapy remains a challenge. We present preliminary clinical and angiographic results of an experimentally optimized Surpass flow diverter for treatment of intracranial aneurysms in a prospective, multicenter, nonrandomized, single-arm study.

MATERIALS AND METHODS

At 24 centers, 165 patients with 190 intracranial aneurysms of the anterior and posterior circulations were enrolled. The primary efficacy end point was the percentage of intracranial aneurysms with 100% occlusion on 6-month DSA. The primary safety end point was neurologic death and any stroke through a minimum follow-up of 6 months.

RESULTS

Successful flow-diverter delivery was achieved in 161 patients with 186 aneurysms (98%); the mean number of devices used per aneurysm was 1.05. Clinical follow-up (median, 6 months) of 150 patients (93.2%), showed that the primary safety end point occurred in 18 subjects. Permanent neurologic morbidity and mortality were 6% and 2.7%, respectively. Morbidity occurred in 4% and 7.4% of patients treated for aneurysms of the anterior and posterior circulation, respectively. Neurologic death during follow-up was observed in 1.6% and 7.4% of patients with treated intracranial aneurysms of the anterior and posterior circulation, respectively. Ischemic stroke at ≤30 days, SAH at ≤7 days, and intraparenchymal hemorrhage at ≤7 days were encountered in 3.7%, 2.5%, and 2.5% of subjects, respectively. No disabling ischemic strokes at >30 days or SAH at >7 days occurred. New or worsening cranial nerve deficit was observed in 2.7%. Follow-up angiography available in 158 (86.8%) intracranial aneurysms showed 100% occlusion in 75%.

CONCLUSIONS

Clinical outcomes of the Surpass flow diverter in the treatment of intracranial aneurysms show a safety profile that is comparable with that of stent-assisted coil embolization. Angiographic results showed a high rate of intracranial aneurysm occlusion.

Analysis of hemodynamics and aneurysm occlusion after flow-diverting treatment in rabbit models

BACKGROUND AND PURPOSE

Predicting the outcome of flow diversion treatment of cerebral aneurysms remains challenging. Our aim was to investigate the relationship between hemodynamic conditions created immediately after flow diversion and subsequent occlusion of experimental aneurysms in rabbits.

MATERIALS AND METHODS

The hemodynamic environment before and after flow-diversion treatment of elastase-induced aneurysms in 20 rabbits was modeled by using image-based computational fluid dynamics. Local aneurysm occlusion was quantified by using a voxelization technique on 3D images acquired 8 weeks after treatment. Global and local voxel-by-voxel hemodynamic variables were used to statistically compare aneurysm regions that later thrombosed to regions that remained patent.

RESULTS

Six aneurysms remained patent at 8 weeks, while 14 were completely or nearly completely occluded. Patent aneurysms had statistically larger neck sizes (P = .0015) and smaller mean transit times (P = .02). The velocity, vorticity, and shear rate were approximately 2.8 times (P < .0001) larger in patent regions-that is, they had larger "flow activity" than regions that progressed to occlusion. Statistical models based on local hemodynamic variables were capable of predicting local occlusion with good precision (84% accuracy), especially away from the neck (92%-94%). Predictions near the neck were poorer (73% accuracy).

CONCLUSIONS

These results suggests that the dominant healing mechanism of occlusion within the aneurysm dome is related to slow-flow-induced thrombosis, while near the neck, other processes could be at play simultaneously.

Flow diverter stents for unruptured saccular anterior circulation perforating artery aneurysms: safety, efficacy, and short-term follow-up

BACKGROUND

Anterior circulation perforating artery aneurysms including anterior choroidal artery and lenticulostriate artery aneurysms are rare. Injury to these vessels can lead to severe debilitating symptoms.

OBJECTIVE

To present a new approach to treatment using flow diversion technology.

METHODS

Patients treated with a Pipeline embolization device (PED) for perforator artery aneurysms at our institution between June 2012 and May 2013 were identified and included in our retrospective analysis. We evaluated patient vascular risk factors; family history of aneurysms; aneurysm characteristics; National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS) on admission; and angiography follow-up and patient clinical outcome at discharge, 6 months, and 1 year.

RESULTS

We included four patients with a mean age of 59.8 years. Two patients had a positive family history of aneurysms. Patient vascular risk factors included smoking, dyslipidemia, and hypertension. All patients presented with a NIHSS and mRS of 0 on admission. Aneurysms were located at the anterior choroidal (n=2) or lenticulostriate artery (n=2) and were treated with a single PED. No periprocedural or postprocedural complications occurred. The patients were discharged with no change in NHISS or mRS score. Six-month and 1-year follow-up angiography showed complete aneurysm occlusion. Mild intimal hyperplasia was seen in 2 cases at 6 months, but was resolved at the 1-year follow-up. No re-treatment was necessary. NIHSS and mRS remained 0 at follow-up time points.

CONCLUSIONS

Our preliminary results show that flow diversion technology is an effective and safe therapy for complex, hard-to-treat aneurysms in perforating arteries. Larger studies with long-term follow-up are needed to validate our promising results.

Hemodynamics in two tandem aneurysms treated with flow diverters

The purpose of this study was to investigate whether the occlusion time of cerebral aneurysms treated with flow diverters depends on the hemodynamic conditions created immediately after treatment. A case study of a pair of tandem intracranial aneurysms that were treated with flow-diverting devices and occluded at different times was carried out. A patient-specific computational fluid dynamics model was constructed from 3D rotational angiography images. Blood flow simulations were carried out under pulsatile physiologic conditions, and hemodynamic variables before and after deployment of the flow-diverting devices were quantified and compared. The flow-diverting devices reduced aneurysm inflow rates, intra-aneurysmal flow velocities, shear rates, and wall shear stresses. The flow patterns after flow modulation by the flow diverters were smoother and with less swirling. The reductions in hemodynamic quantities depended on the aneurysm and parent artery and were larger in the aneurysm that occluded faster. The results of this case study suggest that the larger the reduction in the hemodynamic variables considered, the shorter the time it takes for the aneurysm to thrombose. This result can help us better define the goal of these interventions.

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.

Evaluation of a newly designed flow diverter for the treatment of intracranial aneurysms in an elastase-induced aneurysm model, in New Zealand white rabbits

INTRODUCTION

In this study, we analyzed angiographic and histologic aneurysm occlusion of a newly designed flow-diverting device. Visibility and flexibility, as well as occlusions of side branches and neointimal proliferation were also evaluated.

METHODS

Aneurysms were induced in 18 New Zealand white rabbits and treated with a braided, "closed-loop-designed" device of nitinol. Additional devices were implanted in the abdominal aorta to cover the origin of branch arteries. Angiographic follow-ups were performed immediately after placement of the device, after 3 months (n = 9) and 6 months (n = 9). The status of aneurysm occlusion (using a five-point scale) and the patency of branch arteries were assessed.

RESULTS

Aneurysm occlusion rates were noted as grade 0 in 2 (11 %), grade I in 1 (6 %), grade II in 1 (6 %), grade III in 9 (50 %), and grade IV in 5 (28 %) of 18 aneurysms, respectively, indicating a complete or near-complete occlusion of 78 % under double antiplatelet therapy. Aneurysm occlusion was significantly higher at 6 months follow-up (P = 0.025). Radiopaque markers provided excellent visibility. Limited device flexibility led to incomplete aneurysm neck coverage and grade 0 occlusion rates in two cases. Distal device occlusions were found in three cases, most likely due to an extremely undersized vessel diameter in the subclavian artery. No case of branch artery occlusion was seen. Intimal proliferation and diameter stenosis were moderate.

CONCLUSION

The tested flow diverter achieved near-complete and complete aneurysm occlusion under double antiplatelet therapy of elastase-induced aneurysms in 78 %, while preserving branch arteries.

Hemodynamic Changes by Flow Diverters in Rabbit Aneurysm Models

Background and Purpose—

The effect of flow diverter (FD) on hemodynamic changes observed in aneurysms is inevitably affected by the actual structural configuration of deployed FD. We studied the resultant hemodynamic changes after implantation of FDs using computational fluid dynamic simulations based on micro–computed tomography reconstructions in rabbit aneurysm model.

Methods—

The FDs by micro–computed tomography images and vascular model based on rabbit-specific angiograms in 14 rabbits were reconstructed for computational fluid dynamic studies, and rabbit-specific inlet flow waveforms were used as boundary conditions. The occluded group (n=10) and unoccluded group (n=4) were divided according to the follow-up angiography. Hemodynamic parameters were separately evaluated for significance with respect to FD implantation and healing.

Results—

The normalized mean wall shear stress of the aneurysm sac and inflow volume were significantly reduced after FD deployment, and the relative residence time was significantly increased after treatment, without significant differences in mean pressure of aneurysm sac. When compared with the unoccluded group, the average relative residence time increment and percentage of inflow volume reduction in occluded group were higher. Additionally, the inlet of stream after FD deployment in the occluded group was more prevalent near the central region of the neck, whereas in the unoccluded group, it was more likely to occur near the proximal part of the neck.

Conclusions—

This study provided the real structural configurations of fully deployed FDs in vivo. We demonstrated the decrease of wall shear stress, inflow volume, increase of relative residence time, and change of inflow stream induced by FD implantation. The higher relative residence time increment, percentage of inflow volume reduction, and location of stream inlet near the central part of the neck may be closely related to healing.

Hemodynamic Changes Caused by Flow Diverters in Rabbit Aneurysm Models: Comparison of Virtual and Realistic FD Deployments Based on Micro-CT Reconstruction

Adjusting hemodynamics via flow diverter (FD) implantation is emerging as a novel method of treating cerebral aneurysms. However, most previous FD-related hemodynamic studies were based on virtual FD deployment, which may produce different hemodynamic outcomes than realistic (in vivo) FD deployment. We compared hemodynamics between virtual FD and realistic FD deployments in rabbit aneurysm models using computational fluid dynamics (CFD) simulations. FDs were implanted for aneurysms in 14 rabbits. Vascular models based on rabbit-specific angiograms were reconstructed for CFD studies. Real FD configurations were reconstructed based on micro-CT scans after sacrifice, while virtual FD configurations were constructed with SolidWorks software. Hemodynamic parameters before and after FD deployment were analyzed. According to the metal coverage (MC) of implanted FDs calculated based on micro-CT reconstruction, 14 rabbits were divided into two groups (A, MC >35%; B, MC <35%). Normalized mean wall shear stress (WSS), relative residence time (RRT), inflow velocity, and inflow volume in Group A were significantly different (P<0.05) from virtual FD deployment, but pressure was not (P>0.05). The normalized mean WSS in Group A after realistic FD implantation was significantly lower than that of Group B. All parameters in Group B exhibited no significant difference between realistic and virtual FDs. This study confirmed MC-correlated differences in hemodynamic parameters between realistic and virtual FD deployment.

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.

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).

Stents and flow diverters in the treatment of aneurysms: device deformation in vivo may alter porosity and impact efficacy

INTRODUCTION

High-porosity (HP) and flow-diverting (FD) stents are increasingly used to treat intracranial aneurysms. In vivo device deformations and their impact on the porosity of the segment of device lying over the aneurysm neck remain inadequately characterized.

METHODS

Porosities of different braided FDs were studied in straight and 90° curved glass tubes. In vivo, 11 experimental lateral wall aneurysms were treated with FD (n = 7) or HP (n = 4) stents. At 3 months, the segment of FDs and HP stents over the aneurysm neck was analyzed, paying attention to changes in device diameter, metallic porosity, and neointimal closure of pores over the aneurysm or branch ostia. Device deformations were reproduced with benchtop experiments.

RESULTS

In 90° curved tubes, FD porosity was higher (P = 0.025) and pore density was lower (P = 0.01) on convex compared to concave surfaces, but variations remained within 5-10 %. After in vivo deployment, a spindle-shaped deformation of FDs occurred, with focal expansion at the level of the aneurysm neck (P = 0.004). This deformation translated into an accordion-like distribution of stent struts across the aneurysm neck, where porosity was not uniform. The midsection of the aneurysm ostium had more metal coverage than adjacent ostial areas (P = 0.002). Mean porosity over the aneurysm neck was 78 ± 9.4 and 32.6 ± 12.1 % for HP and FD stents, respectively (P = 0.008), decreasing to 13.0 ± 10.1 and 1.4 ± 0.6 % (P = 0.022) following neointimal coverage, respectively. Spindle-shaped deformations and accordion effects were reproduced with benchtop manipulations; fluctuations in porosity and diameter changes correlated closely (R = 0.81; P = 0.005).

CONCLUSION

Alterations in porosity may occur following in vivo implantation.

In vitro and in silico study of intracranial stent treatments for cerebral aneurysms: effects on perforating vessel flows

BACKGROUND

Many cerebral aneurysms can be treated effectively with intracranial stents. Unfortunately, stents can occlude perforating vessels near the treatment site which can decrease cerebral perfusion and increase the risk of stroke.

METHODS

Particle image velocimetry was used to investigate the effects of intracranial stents on flows in perforators near a treated aneurysm. In Phase 1 of the study, different stent configurations were deployed into an idealized physical model of a sidewall aneurysm with perforating vessels. The configurations investigated were the Pipeline embolization device (PED) and one, two and three telescoping Neuroform stents. In Phase 2 of the study a single Neuroform stent was deployed so that the stent struts directly occluded the perforating vessel.

RESULTS

In Phase 1 of the study it was found that even three telescoping stents affected perforating vessel flow less than a single PED under pulsatile conditions (average reduction 32.7% vs 46.5%). Results from Phase 2 indicated that the location of the occluding strut across the perforating vessel orifice had a greater impact on perforating vessel flow than the percentage occlusion.

CONCLUSION

The findings of this study show that the use, configuration and positioning of intracranial stents can all have considerable influence on flow in affected perforating vessels near treated cerebral aneurysms.

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.

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.

Perianeurysmal brain inflammation after flow-diversion treatment

BACKGROUND AND PURPOSE

Flow-diverter stents are an alternative treatment for challenging and recurrent aneurysms. Thrombosis of the sac is thought to induce perianeurysmal brain inflammation, but such phenomena have never been studied in flow-diverter devices. We developed imaging data to explain the clinical exacerbation of symptoms after flow-diversion treatment.

MATERIALS AND METHODS

Seventeen patients with unruptured aneurysms were treated by using a flow-diverter device. Clinical symptoms and angiographic and MR imaging features were recorded before and after treatment, during both the acute and chronic phases, to look for inflammatory reaction.

RESULTS

Seven of the 17 patients (41%) showed a delayed clinical aggravation of symptoms posttreatment consisting of a headache (n = 7) with aggravation of pre-existing compressive symptoms (n = 4) and the appearance of compressive symptoms (n = 1). This clinical deterioration was transient; it was observed between 3 and 15 days posttreatment and resolved by day 30. MR imaging revealed signs highly suggestive of perianeurysmal inflammation with vasogenic edema and blood-brain barrier breakdown. The association between MR imaging inflammatory features and clinical aggravation was statistically significant. Large aneurysmal size and its proximity to surrounding brain tissue were predictive of this inflammatory reaction after flow diversion.

CONCLUSIONS

The main finding of the series is that MR imaging-defined perianeurysmal inflammation is observed with a high frequency after treatment of unruptured aneurysms with flow diverters and is, in most cases, associated with a transient clinical deterioration.

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.

Sensitivity of CFD based hemodynamic results in rabbit aneurysm models to idealizations in surrounding vasculature

Computational fluid dynamics (CFD) studies provide a valuable tool for evaluating the role of hemodynamics in vascular diseases such as cerebral aneurysms and atherosclerosis. However, such models necessarily only include isolated segments of the vasculature. In this work, we evaluate the influence of geometric approximations in vascular anatomy on hemodynamics in elastase induced saccular aneurysms in rabbits. One representative high aspect ratio (AR-height/neck width) aneurysm and one low AR aneurysm were created at the origin of the right common carotid artery in two New Zealand white rabbits. Three-dimensional (3D) reconstructions of the aneurysm and surrounding arteries were created using 3D rotational angiographic data. Five models with varying extents of neighboring vasculature were created for both the high and low AR cases. A reference model included the aneurysm sac, left common carotid artery (LCCA), aortic arch, and downstream trifurcation/quadrification. Three-dimensional, pulsatile CFD studies were performed and streamlines, wall shear stress (WSS), oscillatory shear index, and cross sectional velocity were compared between the models. The influence of the vascular domain on intra-aneurysmal hemodynamics varied between the low and high AR cases. For the high AR case, even a simple model including only the aneurysm, a small section of neighboring vasculature, and simple extensions captured the main features of the steamline and WSS distribution predicted by the reference model. However, the WSS distribution in the low AR case was more strongly influenced by the extent of vasculature. In particular, it was necessary to include the downstream quadrification and upstream LCCA to obtain good predictions of WSS. The findings in this work demonstrate the accuracy of CFD results can be compromised if insufficient neighboring vessels are included in studies of hemodynamics in elastase induced rabbit aneurysms. Consideration of aspect ratio, hemodynamic parameters of interest, and acceptable magnitude of error when selecting the vascular domain will increase reliability of the results while decreasing computational time.

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.