Aneurysm permeability following coil embolization: packing density and coil distribution

Aneurysm dome and vessel pressure measurements with coiling, stent assisted coiling and flow diversion

BACKGROUND

Variability in long-term endovascular treatment outcomes for intracranial aneurysms has prompted questions regarding the effects of these treatments on aneurysm hemodynamics. Endovascular techniques disrupt aneurysmal blood flow and shear, but their influence on intra-aneurysmal pressure remains unclear. A better understanding of aneurysm pressure effects may aid in predicting outcomes and guiding treatment decisions.

METHODS

Medium and large aneurysm models with intramural pressure taps on the dome and parent artery were designed and 3D-printed with vessel-like physical properties from UV-cured materials. The models were connected to a comprehensive flow system consisting of a pulsatile pump and a viscosity-matched blood analog. The system provided physiological pressure and flow control. Real-time pressures were recorded in the aneurysm dome and parent artery during initial placement of coils, stents, flow diverters, and temporary balloons under simulated surgical conditions. Coiling, stent-assisted coiling, and flow diverter placement were performed in both aneurysm sizes. Temporary balloon placement was performed in a large aneurysm model.

RESULTS

Coiling resulted in 24-30% packing density and diminished intra-aneurysmal flow. Flow diverter placement reduced intra-aneurysmal flow with near complete flow interruption after placement of three consecutive devices across the aneurysm neck. Compared to untreated controls, real-time pressure measurements during coiling and flow diversion showed minimal changes (< 5%) in intra-aneurysmal pressures. Temporary balloon occlusion blocked the parent artery, increasing the pressure proximal to the site of occlusion (by 9%), and reducing the pressure distally (by 14%). This maneuver also dampened intra-aneurysmal pressure to the average distal vessel pressure measurement. Positive control aneurysm models were 3D-printed with a sealed, "healed" neck. These controls verified a sealed neck eliminates intra-aneurysmal pressure.

CONCLUSION

Findings quantified minimal changes in intra-aneurysmal pressure during and immediately post-coiling and flow diversion. Intra-aneurysmal flow disruption alone has negligible impact on intra-aneurysmal pressures.

Endovascular Treatment of Basilar Apex Aneurysms: An Updated Systematic Review and Meta-Analysis in the Era of Flow Diversion

BACKGROUND

Endovascular options for the treatment of basilar apex aneurysms (BAAs) are heterogeneous, and evidence is limited to retrospective cohorts and case series. We seek to evaluate the efficacy and complications associated with various endovascular treatment methods of BAAs.

METHODS

Systematic review of PubMed, Embase, and Web of Science adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Retrospective and prospective studies evaluating endovascular treatment of BAAs between January 2010 and July 2024 were included. Relevant information including occlusion rates, aneurysm recurrence, retreatment rates, and complications were subjected to meta-analysis.

RESULTS

Fifteen studies with 1049 BAAs were included. The median aneurysm diameter was 8.5 mm (range, 4.6-19.75), with a median follow-up of 33.7 months (range, 6.0-117.6). Residual aneurysm filling occurred in 24% after primary coiling (95% CI = 0.16-0.32), 25% after single stent-assisted coiling (s-SAC; 95% CI = 0.04-0.46), 25% after Y-stents (95% CI = 0.12-0.37), and 23% after flow diverter stent (FDS; 95% CI = 0.11-0.35). Recurrence rates were high for primary coiling (27%, 95% CI = 0.18-0.36) and s-SAC (19%, 95% CI = 0.13-0.26), but significantly lower for Y-stents (9%, 95% CI = 0.03-0.15) and FDS (4%, 95% CI = -0.04-0.11). Retreatment rates were 19% for primary coiling (95% CI = 0.12-0.26), 17% for s-SAC (95% CI = 0.07-0.27), 5% for Y-stents (95% CI = -0.03-0.12), and 13% for FDS (95% CI = -0.01-0.27). Meta-regression indicated larger aneurysms had higher complication rates (P = 0.02). Thromboembolic events were most frequent with FDS and Y-stents(12%).

CONCLUSIONS

Occlusion rates were similar across treatments, but recurrence rates were significantly lower after Y-stents and FDS compared to primary coiling, although they carried a higher number of thromboembolic complications.

Long-Term Hemorrhage and Reperfusion Rates of Coiled Aneurysms: A Single-Center Experience

Background: The endovascular approach has emerged as standard therapy for many intracranial aneurysms (IAs) to prevent hemorrhage, yet its long-term durability varies considerably. The aim of this study was to evaluate the safety and effectiveness of an initially deliberate endovascular approach regarding IA hemorrhage rates over a long-term follow-up period. Methods: This retrospective single-center study included all consecutive patients with endovascularly treated IAs who presented between January 2008 and December 2020 with a follow-up of at least 12 months. The primary endpoint was the proportion of patients with long-term IA hemorrhage rates and reperfusion. The secondary endpoint was treatment-related morbidity and mortality. Independent risk factors for IA reperfusion over the long term were analyzed using multivariate logistic regression. Results: Endovascular treatment was the therapy of choice for 333 patients with IAs, among whom 188 (57%) experienced rupture upon presentation. Complete coiling (Raymond I) was noted in 162 (49%) of the patients, with primary supportive devices being used in 51 (15%) patients. After a median (±SD) follow-up time of 34 ± 41 months (range 12-265 months), IA reperfusion was noted in 158 (47%), necessitating retreatment in 105 (32%) of the patients. Over the long term, hemorrhage was noted in four (1%) patients. Multivariate analysis revealed aneurysmal multilobarity (HR 1.8, 95%CI 1.2-2.7; p = 0.004) and a patient age of ≥50 years (HR 1.7, 95% CI 1.1-2.5, p = 0.01) as independent predictors of reperfusion over time. Intervention-related morbidity was noted in 16 (4.8%) patients, namely, thrombosis formation and contrast extravasation in 8 (2.4%) patients each, while no intervention-induced mortality was observed. Conclusion: In the long term, the hemorrhage rate in patients with IA with an initially more conservative endovascular approach is low. Therefore, a deliberate endovascular treatment approach might be justified.

Hemodynamic characteristics of vertebrobasilar artery fenestration combined with vertebrobasilar dolichoectasia: a study based on magnetic resonance angiography

PURPOSE

This study delves into the hemodynamic characteristics of Vertebrobasilar Artery Fenestration (VBAF) combined with Vertebrobasilar Dolichoectasia (VBD) using Magnetic Resonance Angiography (MRA). By summarizing the hemodynamic features and identifying high-risk populations, we aim to provide insights for clinical treatment.

METHODS

Utilizing MRA images as a foundation, arterial three-dimensional geometric models were constructed. A total of 22 cases were categorized into control, S, L, U, and Spiral groups, and numerical simulation analysis of the vessels was conducted using computational fluid dynamics methods.

RESULTS

Hemodynamic parameters of the VBAF combined with the VBD model were obtained, including blood flow velocity, oscillatory shear stress (OSI), wall shear stress (WSS), and aneurysm formation indicator (AFI). The V, OSI, and WSS indices of the L, U, and Spiral groups were significantly higher than those of the control group (P < 0.05). High-speed blood flow, elevated WSS, and increased OSI in these groups were concentrated at the fenestration site, with scattered distribution along the tortuous vertebral artery and basilar artery segments, accompanied by significant differences in the parameters of the bilateral vertebral arteries.

CONCLUSION

This preliminary investigation identifies the L, U, and Spiral groups as high-risk populations. Abnormal hemodynamics may lead to a vicious cycle in vascular wall pathology, increasing the likelihood of adverse events such as cerebral infarction. Clinical attention should focus on individuals within these groups and their corresponding vascular regions.

A novel self-expanding shape memory polymer coil for intracranial aneurysm embolization: 1 year follow-up in Chile

BACKGROUND

Aneurysm recurrence remains a challenge when coiling cerebral aneurysms. Development of next generation coils has focused on accelerating thrombus maturation and increasing coil packing density. Ultra low density shape memory polymer is a novel embolic material designed for this purpose. The polymer is crimped over a platinum-tungsten coil for catheter delivery and self-expands to a predefined volume on contact with blood.

METHODS

This prospective study in humans evaluated aneurysms 5-16 mm (inclusive) in diameter that were indicated for endovascular coil embolization. At least 70% coil volume was required to be shape memory polymer coils. Patients were followed-up according to standard of care for 12 months.

RESULTS

Nine patients (89% women, mean age 55.8±11.7 years) were treated with shape memory polymer coils and completed 12 months of follow-up. Aneurysms were all unruptured and were in the ophthalmic segment of the internal carotid artery (n=7), posterior communicating artery, and anterior cerebral artery A1-A2 segment. Aneurysms were a mean of 7.8±2.9 mm in diameter (range 5.2-14.9 mm). The mean packing density based on unexpanded polymer was 17±6%. Packing density based on expanded polymer was 43±13%. At 12 months, no recurrence had occurred, and a Raymond-Roy occlusion classification of 1 (n=5) or 2 (n=4) was observed. No serious adverse events related to the study device occurred over the 12 months after the procedure.

CONCLUSIONS

Shape memory polymer coils were safe and effective in treating intracranial aneurysms over 12 months in this first study in human subjects.

Packing density and the angiographic results of coil embolization of intracranial aneurysms: A systematic review and meta-analysis

BACKGROUND

Endovascular coil embolization (ECE) for intracranial aneurysms has been proven as an effective minimally invasive treatment. However, the aneurysm recanalization after coiling is a serious complication of this technique. Among all the proposed factors associated with recanalization, the impact of packing density (PD) is still controversial.

OBJECTIVE

To clarify the role of PD in the aneurysm recanalization following ECE, via conducting a systematic review and meta-analysis.

METHODS

A systematic literature search was conducted using PubMed, Scopus, Embase, and Web of Science databases, until November 28, 2022, by adhering to the Preferred Reporting Items for Systematic Review and Meta-Analyses statement guidelines. Considering the eligibility criteria, all the studies reporting the outcomes of interest were included. Data elements of interest were extracted and analyzed using R software version 4.2.1.

RESULTS

The pooled analysis of the 17 eligible papers revealed a 29% higher PD of the nonrecanalized aneurysms (ROM = 1.29, 95% confidence interval [CI] = 1.18-1.40, p < 0.001), even after removing outlier studies to reduce heterogeneity. However, the pooled estimates from multivariable regression models within nine included studies showed no significant effect of PD on recanalization odds when incorporated into a multivariable model with other predictors (odds ratio [OR] = 0.93, 95% CI = 0.84-1.02, p = 0.126), even after removing outlier studies.

CONCLUSION

The current literature does not support PD as a significant predictor of aneurysm treatment outcomes, especially with adjusting for other variables. This finding necessitates further prospective multicenter studies with a larger sample size to overcome the current methodological shortcomings.

Modeling Flow in Cerebral Aneurysm After Coils Embolization Treatment: A Realistic Patient-Specific Porous Model Approach

PURPOSE

Computational fluid dynamics (CFD) has been used to evaluate the efficiency of endovascular treatment in coiled cerebral aneurysms. The explicit geometry of the coil mass cannot typically be incorporated into CFD simulations since the coil mass cannot be reconstructed from clinical images due to its small size and beam hardening artifacts. The existing methods use imprecise porous medium representations. We propose a new porous model taking into account the porosity heterogeneity of the coils deployed in the aneurysm.

METHODS

The porosity heterogeneity of the coil mass deployed inside two patients' cerebral aneurysm phantoms is first quantified based on 3D X-ray synchrotron images. These images are also used to compute the permeability and the inertial factor arising in porous models. A new homogeneous porous model (porous crowns model), considering the coil's heterogeneity, is proposed to recreate the flow within the coiled aneurysm. Finally, the validity of the model is assessed through comparisons with coil-resolved simulations.

RESULTS

The strong porosity gradient of the coil measured close to the aneurysmal wall is well captured by the porous crowns model. The permeability and the inertial factor values involved in this model are closed to the ideal homogeneous porous model leading to a mean velocity in the aneurysmal sac similar as in the coil-resolved model.

CONCLUSION

The porous crowns model allows for an accurate description of the mean flow within the coiled cerebral aneurysm.

Physiologic Flow Diversion Coiling Technique for Wide-Necked Aneurysms with an Asymmetric Bidirectional Flow at the Aneurysm Neck

PURPOSE

Wide-necked aneurysms in the circle of Willis (CoW) are prone to recur due to reciprocal bidirectional flow. We present a novel concept of coil embolization to prevent recurrence that uses physiologic flow diversion at the CoW.

MATERIALS AND METHODS

We enrolled 14 patients (15 aneurysms) who underwent aneurysm coiling for wide-necked aneurysms with asymmetric bidirectional inflow into the aneurysm. Four patients had recurrent aneurysms after coiling. The concept of physiologic flow diversion included obliterating antegrade flow into the aneurysm sac as well as opposite CoW flow by performing compact coil packing with intentional protrusion out of the aneurysm neck to the communicating part.

RESULTS

Fifteen aneurysms, including 4 recurrent aneurysms, in an anterior communicating artery (n=7), posterior communicating artery (n=5), and tip of the basilar artery (n=3) were treated with coil embolization (n=10) and stent-assisted coiling (n=5). All aneurysms had a wide neck, and the mean largest diameter was 9.0 mm. The mean packing density was 45.1%. Twelve aneurysms were completely occluded, and 3 aneurysms had tiny residual neck remnants. There was neither a neurological event nor recurrence during the mean 12.5 months of follow-up.

CONCLUSION

Wide-necked aneurysms at the CoW tend to recur. As a strategy to prevent a recurrence, physiologic flow diversion can be an option in treating wide-necked aneurysms in the CoW.

Investigating atherosclerotic plaque phantoms for ultrasound therapy

PURPOSE

The aim of the proposed study was to conduct a feasibility study using a flat rectangular (2 × 10 mm2) transducer operating at 4.0 MHz for creating thermal lesions in an arterial atherosclerotic plaque phantom. The proposed method can be used in the future for treating atherosclerotic plaques in human arteries.

MATERIALS AND METHODS

The flat rectangular transducer was firstly assessed in agar/silica evaporated milk phantom, polyacrylamide phantom and freshly excised turkeytissue phantom. Then, the same transducer was assessed in an arterial atherosclerotic plaque phantom which was created in the laboratory with a very low cost. The recipe of the atherosclerotic plaque phantom was 4% w/v agar, 1% w/v gypsum, 2% w/v butter and 93% water. The amount of plaque removal was evaluated visually and using an X-Ray system.

RESULTS

It was shown that the flat rectangular transducer can create thermal lesions on the agar/silica evaporated milk phantom, polyacrylamide phantom and in excised tissue. The size of the lesions matches the geometry of the transducer. Moreover, this transducer destroyed 27.1% of the atherosclerotic plaque phantom with 8 W acoustical power and 30 s duration.

CONCLUSIONS

This feasibility study demonstrated that atherosclerotic plaque can be destroyed using a very small flat rectangular (2 × 10 mm2) transducer in a very small time interval of 30 s. In future clinical trials the transducer will be incorporated in a catheter which will be inserted intravascular (1-3 mm) wide and can be used to treat atherosclerotic plaques in the coronary arteries.

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

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

Risk factors for recanalization of dense coil packing for unruptured cerebral aneurysms in endovascular coil embolization: Analysis of a single center's experience

In coil embolization of cerebral aneurysms, inadequate packing is known to increase the probability of recanalization. Even tightly embolized aneurysms may be recanalized, but predictive factors for recanalization have not been fully investigated. This retrospective study aimed to identify risk factors for recanalization of treated aneurysms with a volume embolization ratio (VER) ≥ 25%. A total of 301 unruptured aneurysms in 248 patients who underwent coil embolization between March 2012 and January 2021 were analyzed. Cases involving dissecting aneurysm, intraluminal thrombosis, parent artery occlusion, intraoperative rupture, re-treatment, rupture the day after surgery, postoperative coil migration, and postoperative parent artery occlusion were excluded due to the inaccuracy of VER. A total of 105 aneurysms (34.9%) treated with VER ≥ 25% were extracted. Clinical features (age, sex, medical history, family history), anatomical features (shape, location, aneurysm size, inflow angle, and volume), procedural features (stent-assisted, Raymond-Roy occlusion classification [RROC] immediately after treatment, re-treatment rate), and follow-up period were compared between Recanalization and Non-recanalization groups. Predictors of recanalization were determined using logistic regression and receiver operating characteristic (ROC) curve analyses. Eleven aneurysms were recanalized. In multivariate analysis, RROC class 3 (odds ratio [OR] 11.0; 95% confidence interval [CI] 2.03-59.4) and aneurysm volume (OR 1.005; 95%CI 1.001-1.008) were independent predictors of recanalization. ROC curve analysis showed optimal cutoff values for aneurysm volume of 69.5 mm³ (sensitivity, 81.8%; specificity, 72.3%). In coil embolization of unruptured aneurysms that VER ≥ 25%, cases with RROC class 3 or high aneurysm volume may be associated with a higher risk of recanalization, and should be carefully followed-up.

Simulation analysis of aneurysm embolization surgery: Hemorheology of aneurysms with different embolization rates (CTA)

BACKGROUND

Embolization degree acts as an important factor affecting recurrence of aneurysm.

OBJECTIVE

To analyze the role of hemodynamics parameters of different degrees of embolization in the occurrence, development and post-treatment of aneurysms, and to determine the specific factors causing the occurrence and recurrence of aneurysms after hemodynamics treatment. Our study provides a theoretical basis for the prevention and treatment of aneurysms.

METHODS

Computed tomography angiography data of a patient with cerebral aneurysm was used to model 0%, 24%, 52%, 84% and 100% of endovascular embolization, respectively. The time average wall shear stress, time average wall shear stress, oscillatory shear index, hemodynamics formation index and relative retentive time were used to analyze the changes of hemodynamics indexes in different embolic models.

RESULTS

With the increase of embolic rate, the values of time average wall shear stress, time average wall shear stress grade and aneurysm index formation gradually increased, and the values of relative retention time gradually decreased. Oscillatory shear index was higher in patients with incomplete embolization and decreased in patients with complete embolization.

CONCLUSIONS

As the degree of embolization increased, the blood flow tended to stabilize, reducing the risk of cerebral aneurysm rupture, and finding that the wall of the vessel junction was susceptible to injury.

Optimal Woven EndoBridge (WEB) Device Size Selection Using Automated Volumetric Software

INTRODUCTION

Selecting the appropriate Woven EndoBridge (WEB) device sizing for the treatment of wide-neck bifurcation aneurysms (WNBAs) remains challenging. The aim of this study was to evaluate different volumetric-based imaging methodologies to predict an accurate WEB device size selection to result in a successful implantation.

METHODS

All consecutive patients treated with WEB devices for intracranial aneurysms from January 2019 to June 2020 were included. Aneurysm dimensions to calculate aneurysm volumes were measured using three different modalities: automated three-dimensional (3D) digital subtraction angiography (DSA), manual 3D DSA, and two-dimensional (2D) DSA. The device-aneurysm volume (DAV) ratio was defined as device volume divided by the aneurysm volume. WEB volumes and the DAV ratios were used for assessing the device implantation success and follow-up angiographic outcomes at six months. Pearson correlation, Wilcoxon Rank Sum test, and density approximations were used for estimating the WEB volumes and the imaging modality volumes for successful implantation.

RESULTS

A total of 41 patients with 43 aneurysms were included in the study. WEB device and aneurysm volume correlation coefficient was highest for 3D automatic (r = 0.943), followed by 3D manual (r = 0.919), and 2D DSA (r = 0.882) measurements. Measured median volumes were significantly different for 3D automatic and 2D DSA (p = 0.017). The highest rate of successful implantation (87.5%) was between 0.6 and 0.8 DAV ratio.

CONCLUSION

Pre-procedural assessment of DAV ratios may increase WEB device implantation success. Our results suggest that volumetric measurements, especially using automated 3D volumes of the aneurysms, can assist in accurate WEB device size selection.

Lagrangian Trajectory Simulation of Platelets and Synchrotron Microtomography Augment Hemodynamic Analysis of Intracranial Aneurysms Treated With Embolic Coils

As frequency of endovascular treatments for intracranial aneurysms increases, there is a growing need to understand the mechanisms for coil embolization failure. Computational fluid dynamics (CFD) modeling often simplifies modeling the endovascular coils as a homogeneous porous medium (PM), and focuses on the vascular wall endothelium, not considering the biomechanical environment of platelets. These assumptions limit the accuracy of computations for treatment predictions. We present a rigorous analysis using X-ray microtomographic imaging of the coils and a combination of Lagrangian (platelet) and Eulerian (endothelium) metrics. Four patient-specific, anatomically accurate in vitro flow phantoms of aneurysms are treated with the same patient-specific endovascular coils. Synchrotron tomography scans of the coil mass morphology are obtained. Aneurysmal hemodynamics are computationally simulated before and after coiling, using patient-specific velocity/pressure measurements. For each patient, we analyze the trajectories of thousands of platelets during several cardiac cycles, and calculate residence times (RTs) and shear exposure, relevant to thrombus formation. We quantify the inconsistencies of the PM approach, comparing them with coil-resolved (CR) simulations, showing the under- or overestimation of key hemodynamic metrics used to predict treatment outcomes. We fully characterize aneurysmal hemodynamics with converged statistics of platelet RT and shear stress history (SH), to augment the traditional wall shear stress (WSS) on the vascular endothelium. Incorporating microtomographic scans of coil morphology into hemodynamic analysis of coiled intracranial aneurysms, and augmenting traditional analysis with Lagrangian platelet metrics improves CFD predictions, and raises the potential for understanding and clinical translation of computational hemodynamics for intracranial aneurysm treatment outcomes.

Influence of neurovascular embolic coil primary wind diameter on aneurysm packing density and case costs

AIMS

Endovascular coiling is a common modality for treating intracranial aneurysms; however, recanalization occurs in approximately 1 in 5 cases, with downstream consequences of regrowth and rupture. Aneurysm packing density >24% reduces recanalization risk; packing density can be increased by inserting additional coils or by using coils with larger volumetric filling. Coil volume depends on length and primary wind diameter (PWD). This study evaluated the influence of PWD on packing density and total case costs.

MATERIALS AND METHODS

Two hypothetical scenarios and one case study were analyzed. In scenario one, the number of coils required to achieve packing density >24% in a hypothetical aneurysm was determined for 0.012″ vs. 0.010″ PWD coils. In scenario two, the total length of 0.010″ vs. 0.012″ PWD coils required to achieve a packing density >24% was analyzed relative to aneurysm volume. In the case study, packing densities with one 0.012″ PWD coil (actual scenario) and one 0.010″ PWD coil (theoretical scenario) were compared.

RESULTS

In scenario one, cost savings would be realized by using four 0.012″ PWD coils vs. seven 0.010″ PWD coils to achieve packing density >24%. In scenario two, greater volumetric filling of 0.012″ vs. 0.010″ PWD coils was correlated with lower total length of coil required. In the case study, a 0.012″ PWD coil achieved packing density >24%, whereas an equivalent length 0.010″ PWD coil would not.

LIMITATIONS

Theoretical modeling was used to explore the impact of coil PWD on aneurysm packing density. In clinical practice, packing density depends not only on PWD but on its length, shape, distribution within an aneurysm, and other recanalization risk factors.

CONCLUSIONS

Coil PWD influences packing density, the number of coils required to achieve a specific packing density, and total case costs. Using 0.012″ PWD coils may provide cost and procedural efficiencies.

Early major recurrence of cerebral aneurysms after satisfactory initial coiling

BACKGROUND AND PURPOSE

Early major recurrence (EMR) of cerebral aneurysms treated by coiling has not been investigated. The purpose of this study is to characterize the frequency and risk factors of this phenomenon.

MATERIALS AND METHODS

A retrospective review was performed of consecutive patients who presented with ruptured and unruptured cerebral aneurysms and underwent coiling from July 2009 to June 2019 at a university hospital. We defined EMR as recurrence of the aneurysm greater than its initial size within the first 6 months of an initial satisfactory coil embolization. Patient demographics, clinical information, aneurysm characteristics, angiographic and technical details were reviewed.

RESULTS

From July 2009 to June 2019, 338 aneurysms (190 unruptured aneurysms and 148 ruptured cerebral aneurysms) underwent coiling and satisfied our study criteria. Among these patients, 23 patients (19 ruptured and 4 unruptured aneurysms) were found to have recurrent aneurysm. Of those, 4 were found to have early major aneurysm regrowth occurring within 6 months after coiling (1.2%). The detection of the EMR was as early as 4 weeks and as late as 20 weeks after the initial coil embolization. The average detection time was 10 ± 7.2 weeks (mean ± SD, range:4-20 weeks). In each case, the recurrent aneurysm cavity was more than twice the initial size of presentation. All aneurysms with major recurrence were ruptured with low aspect ratios (dome height to neck ratio) and involved a communicating segment. All patients underwent successful retreatment of the recurrent aneurysm with good outcome.

CONCLUSIONS

Early major recurrence of treated aneurysms is a rare but important complication that harbors an impending risk of re-rupture. Early control angiography after endovascular coiling may be warranted for small ruptured aneurysms, even in cases in which the initial result seems technically satisfactory.

Persistent Blood Flow inside the Woven EndoBridge Device More Than 6 Months after Intracranial Aneurysm Treatment: Frequency, Mechanisms, and Management-A Retrospective Single-Center Study

BACKGROUND AND PURPOSE

Due to its high safety and great efficacy, flow disruption with the Woven EndoBridge (WEB) device is increasingly used to treat intracranial aneurysms. We recently identified patients with intracranial aneurysm treated with the WEB who presented with residual blood flow inside the device ("contrast-in-WEB" phenomenon) more than 6 months posttreatment. This series reports the frequency and underlying mechanisms and discusses management of this phenomenon.

MATERIALS AND METHODS

All patients presenting with the contrast-in-WEB phenomenon in the prospectively collected data base of patients with aneurysm treated with the WEB were retrospectively collected and analyzed.

RESULTS

From June 2011 to February 2019, one hundred twenty-seven patients with 133 aneurysms were treated with the WEB and had DSA follow-up at 6 months or later. Eight patients (6.3%) presented with the phenomenon. All aneurysms were wide-neck bifurcation aneurysms, including 7 unruptured and 1 ruptured aneurysm located at the MCA (5 aneurysms), anterior communicating artery (2 aneurysms), and basilar artery (1 aneurysm). All except 1 patient received dual-antiplatelet therapy preprocedure. All except 1 patient received dual-antiplatelet therapy postoperatively for at least 1 month. The most likely mechanism of the phenomenon is the absence of intradevice thrombosis related to perioperative dual-antiplatelet medication. The phenomenon is also likely associated with a low risk of bleeding except when there is residual blood flow against the aneurysm wall or in the dome.

CONCLUSIONS

Contrast-in-WEB is a relatively rare phenomenon possibly induced by dual-antiplatelet therapy continued post-WEB procedure. In most cases, no additional treatment is required.

Improving accuracy for finite element modeling of endovascular coiling of intracranial aneurysm

BACKGROUND

Computer modeling of endovascular coiling intervention for intracranial aneurysm could enable a priori patient-specific treatment evaluation. To that end, we previously developed a finite element method (FEM) coiling technique, which incorporated simplified assumptions. To improve accuracy in capturing real-life coiling, we aimed to enhance the modeling strategies and experimentally test whether improvements lead to more accurate coiling simulations.

METHODS

We previously modeled coils using a pre-shape based on mathematical curves and mechanical properties based on those of platinum wires. In the improved version, to better represent the physical properties of coils, we model coil pre-shapes based on how they are manufactured, and their mechanical properties based on their spring-like geometric structures. To enhance the deployment mechanics, we include coil advancement to the aneurysm in FEM simulations. To test if these new strategies produce more accurate coil deployments, we fabricated silicone phantoms of 2 patient-specific aneurysms in duplicate, deployed coils in each, and quantified coil distributions from intra-aneurysmal cross-sections using coil density (CD) and lacunarity (L). These deployments were simulated 9 times each using the original and improved techniques, and CD and L were calculated for cross-sections matching those in the experiments. To compare the 2 simulation techniques, Euclidean distances (dMin, dMax, and dAvg) between experimental and simulation points in standardized CD-L space were evaluated. Univariate tests were performed to determine if these distances were significantly different between the 2 simulations.

RESULTS

Coil deployments using the improved technique agreed better with experiments than the original technique. All dMin, dMax, and dAvg values were smaller for the improved technique, and the average values across all simulations for the improved technique were significantly smaller than those from the original technique (dMin: p = 0.014, dMax: p = 0.013, dAvg: p = 0.045).

CONCLUSION

Incorporating coil-specific physical properties and mechanics improves accuracy of FEM simulations of endovascular intracranial aneurysm coiling.

Advances in Biomaterials and Technologies for Vascular Embolization

Minimally invasive transcatheter embolization is a common nonsurgical procedure in interventional radiology used for the deliberate occlusion of blood vessels for the treatment of diseased or injured vasculature. A wide variety of embolic agents including metallic coils, calibrated microspheres, and liquids are available for clinical practice. Additionally, advances in biomaterials, such as shape-memory foams, biodegradable polymers, and in situ gelling solutions have led to the development of novel preclinical embolic agents. The aim here is to provide a comprehensive overview of current and emerging technologies in endovascular embolization with respect to devices, materials, mechanisms, and design guidelines. Limitations and challenges in embolic materials are also discussed to promote advancement in the field.

Mapping the Transport Kinetics of Molecules and Particles in Idealized Intracranial Side Aneurysms

Intracranial side aneurysms (IA) are pathological blood-filled bulges in cerebral blood vessels. Unlike healthy blood vessels where mass transport is dominated by convection, both diffusion and convection can play an active role in aneurysm sites. Here, we study via dye washout experiments and numerical simulations, the transport characteristics of particles (1 micron) and small molecules (300 Da) into simplified side aneurysms models following bolus injection. Time-lapse fluorescent microscopy imaging performed in our idealized aneurysm models showed that the parent artery geometry (located on the inner vs. outer curvature) as well as the aneurysm aspect ratio (AR) affect the washout kinetics while the pulsatile nature of the flow, maintained within the physiological range, carries only a minor effect. Importantly, in the absence of effective diffusion, particles that are located on slow streamlines linger within the aneurysm cavity, a phenomenon that could be of importance in deposition of cells and nano/micro-particles within aneurysms. Altogether, mass transport studies may provide valuable insights for better understanding of aneurysm pathophysiology as well as for the design of new diagnostic and theranostic nano-medicines.

Effect of Local Coil Density on Blood Flow Stagnation in Densely Coiled Cerebral Aneurysms: A Computational Study Using a Cartesian Grid Method

Aneurysm recurrence is the most critical concern following coil embolization of a cerebral aneurysm. Adequate packing density (PD) and coil uniformity are believed necessary to achieve sufficient flow stagnation, which decreases the risk of aneurysm recurrence. The effect of coil distribution on the extent of flow stagnation, however, especially in cases of dense packing (high PD), has received less attention. Thus, the cause of aneurysm recurrence despite dense packing is still an open question. The primary aim of this study is to evaluate the effect of local coil density on the extent of blood flow stagnation in densely coiled aneurysms. For this purpose, we developed a robust computational framework to determine blood flow using a Cartesian grid method, by which the complex fluid pathways in coiled aneurysms could be flexibly treated using an implicit function. This tool allowed us to conduct blood flow analyses in two patient-specific geometries with 50 coil distribution patterns in each aneurysm at clinically adequate PD. The results demonstrated that dense packing in the aneurysm may not necessarily block completely the inflow into the aneurysm and local flow that formed in the neck region, whose strength was inversely related to this local PD. This finding suggests that local coil density in the neck region still plays an important role in disturbing the remaining local flow, which possibly prevents thrombus formation in a whole aneurysm sac, increasing the risk of aneurysm regrowth and subsequent recurrence.

In vitro measurement of the permeability of endovascular coils deployed in cerebral aneurysms

BACKGROUND AND PURPOSE

Aneurysm recurrence is the primary limitation of endovascular coiling treatment for cerebral aneurysms. Coiling is currently quantified by a volumetric porosity measure called packing density (pd). Blood flow through a coil mass depends on the permeability of the coil mass, and not just its pd. The permeability of coil masses has not yet been quantified. Here we measure coil permeability with a traditional falling-head permeameter modified to incorporate idealized aneurysms.

METHODS

Silicone replicas of idealized aneurysms were manufactured with three different aneurysm diameters (4, 5, and 8 mm). Four different coil types (Codman Trufill Orbit, Covidien Axium, Microvention Microplex 10, and Penumbra 400) were deployed into the aneurysms with a target pd of 35%. Coiled replicas were installed on a falling-head permeameter setup and the time taken for a column of fluid above the aneurysm to drop a certain height was recorded. Permeability of the samples was calculated based on a simple modification of the traditional permeameter equation to incorporate a spherical aneurysm.

RESULTS

The targeted 35% pd was achieved for all samples (35%±1%, P=0.91). Coil permeabilities were significantly different from each other (P<0.001) at constant pd. Microplex 10 coils had the lowest permeability of all coil types. Data suggest a trend of increasing permeability with thicker coil wire diameter (not statistically significant).

CONCLUSIONS

A simple in vitro setup was developed to measure the permeabilities of coil masses based on traditional permeametry. Coil permeability should be considered when evaluating the hemodynamic efficacy of coiling instead of just packing density. Coils made of thicker wires may be more permeable, and thus less effective, than coils made from thinner wires. Whether aneurysm recurrence is affected by coil wire diameter or permeability needs to be confirmed with clinical trials.

Angiographic and clinical outcomes of balloon remodeling versus unassisted coil embolization in the ruptured aneurysm cohort of the GEL THE NEC study

BACKGROUND AND PURPOSE

GEL THE NEC (GTN) was a multicenter prospective registry developed to assess the safety and efficacy of HydroSoft coils in treating intracranial aneurysms. We compared the angiographic and clinical outcomes of aneurysms treated with balloon assisted coil embolization (BACE) versus unassisted coil embolization (CE) in the ruptured aneurysm cohort.

MATERIALS AND METHODS

GTN was performed at 27 centers in five countries. Patients aged 21-90 years with a ruptured aneurysm 3-15 mm in size were eligible for enrollment. We analyzed demographics/comorbidities, aneurysm location, and geometry, including maximum diameter, neck size, and dome to neck ratio, immediate and long term angiographic outcomes (graded by an independent core laboratory using the modified Raymond Scale), and procedure related adverse events. Angiographic and clinical outcomes were studied using χ²and t tests.

RESULTS

Of the 599 patients in the GTN, 194 met the inclusion criteria. 84 were treated with BACE and 110 with CE. There were more prior smokers in the BACE group (p=0.01). The BACE group also had more vertebrobasilar aneurysms (p=0.006) and a larger mean neck size (p=0.02). More aneurysms were immediately completely occluded in the BACE group (p=0.02) Procedure- related major morbidity and mortality were no different between the techniques (p=0.4 and p=1, respectively).

CONCLUSIONS

In this prospective ruptured aneurysm cohort from the GTN, BACE resulted in greater occlusion rates compared with unassisted CE with similar morbi-mortality.

Packing Density Necessary to Reach a High Complete Occlusion Rate in Circumferential Unruptured Intracranial Aneurysms Treated with Stent-Assisted Coil Embolization

BACKGROUND AND PURPOSE

This study is a homogeneous series of circumferential unruptured intracranial aneurysms with large necks treated with stent-assisted coil embolization. Our purpose was to demonstrate which value of packing density is required to produce a durable occlusion.

MATERIALS AND METHODS

We retrospectively evaluated all patients with unruptured intracranial aneurysms who were treated with stent-assisted coil embolization having late angiographic control between 2004 and 2014, in a single large cerebrovascular referral center. To calculate the packing density, aneurysm volume, and coil volume, we used an on-line system.

RESULTS

In 49 circumferential unruptured intracranial aneurysms treated with stent-assisted coil embolization, 38.7% (n = 19) had complete occlusion in the immediate control. Of those with incomplete occlusion, 80% (n = 24) progressed to complete occlusion in the late angiographic follow-up. At late angiographic control, 87.7% (n = 43) of aneurysms were completely occluded. All aneurysms with a packing density of ≥19% were completely occluded. Packing density was the only statistically significant predictor of complete occlusion. None of the aneurysms with complete occlusion at immediate control or at late angiographic control had recurrence.

CONCLUSIONS

In circumferential aneurysms treated with stent-assisted coil embolization, packing density is the main predictor of complete occlusion. In this type of aneurysm, a packing density of ≥19% was enough to reach complete occlusion; knowing this is important to avoid higher packing densities that have more risk.

Safety, immediate and mid-term results of the newer generation of hydrogel coils in the treatment of ruptured aneurysms: a multicenter study

OBJECTIVE

To assess the 'real-world' performance of the newer generation of hydrogel coils in ruptured aneurysms.

METHODS

A multicenter retrospective study was carried out of angiographic and clinical outcome data on consecutive patients with ruptured aneurysms treated with at least 70% of the newer generation of hydrogel coils. Demographics and data on clinical grade, smoking, use of statins, aneurysm size, location, technique used, packing density, immediate angiographic result, angiographic follow-up, rebleeding and clinical outcome were obtained and analyzed.

RESULTS

Eighty patients (54F; 26M) with an average age of 55.1 years were entered in the study. Forty-four presented good clinical grade (Hunt and Hess 1 or 2). Forty-two (52.5%) aneurysms were ≤5 mm. 56.7% of the aneurysms were treated with simple coil embolization and 39.6% with balloon-assisted coil. The packing density ranged from 9.3% to 92.6% (mean 48.5%). Immediate occlusion rates (Raymond-Roy Scale) were: complete occlusion (class I) in 57.5%, residual neck (class II) in 32.5% and residual aneurysm (class III) in 10%. Intraoperative rupture occurred in 3 cases (3.75%). Clinical follow-up, available in 73 patients, showed a good outcome (modified Rankin Scale 0-2) in 76.3%. Preliminary data on imaging follow-up were available in 54 patients (average 6.8 months) with complete occlusion in 77.8%, residual neck in 20.3% and residual aneurysm in 1.9%. There was no re-hemorrhage.

CONCLUSIONS

Our data show that the use of the newer-generation hydrogel coils in the treatment of ruptured aneurysms is feasible, safe and effective with high immediate and mid-term occlusion rates and low morbidity.

Computational fluid dynamics of cerebral aneurysm coiling using high-resolution and high-energy synchrotron X-ray microtomography: comparison with the homogeneous porous medium approach

BACKGROUND

Computational modeling of intracranial aneurysms provides insights into the influence of hemodynamics on aneurysm growth, rupture, and treatment outcome. Standard modeling of coiled aneurysms simplifies the complex geometry of the coil mass into a homogeneous porous medium that fills the aneurysmal sac. We compare hemodynamics of coiled aneurysms modeled from high-resolution imaging with those from the same aneurysms modeled following the standard technique, in an effort to characterize sources of error from the simplified model.

MATERIALS

Physical models of two unruptured aneurysms were created using three-dimensional printing. The models were treated with coil embolization using the same coils as those used in actual patient treatment and then scanned by synchrotron X-ray microtomography to obtain high-resolution imaging of the coil mass. Computational modeling of each aneurysm was performed using patient-specific boundary conditions. The coils were modeled using the simplified porous medium or by incorporating the X-ray imaged coil surface, and the differences in hemodynamic variables were assessed.

RESULTS

X-ray microtomographic imaging of coils and incorporation into computational models were successful for both aneurysms. Porous medium calculations of coiled aneurysm hemodynamics overestimated intra-aneurysmal flow, underestimated oscillatory shear index and viscous dissipation, and over- or underpredicted wall shear stress (WSS) and WSS gradient compared with X-ray-based coiled computational fluid dynamics models.

CONCLUSIONS

Computational modeling of coiled intracranial aneurysms using the porous medium approach may inaccurately estimate key hemodynamic variables compared with models incorporating high-resolution synchrotron X-ray microtomographic imaging of complex aneurysm coil geometry.

Optimum coil insertion speed of various coils in brain aneurysm embolization in vitro

A coil must comprise material with shape memory to perform optimal coil embolization. To achieve this, the alloy characteristics of the coil (hardness, shape, and thickness) must be understood. In this experiment, a catheter was fixed in the bright position and the movement of the coil was observed under a constant rate of insertion; the optimal insertion rate during clinical use was investigated. The first coil insertion speed was evaluated using simulated aneurysms in an in vivo arterial model. The results showed that the insertion force relates to the deployment shape of the coil, that the feedback through the force indicator using sound is very effective, and that the recorder is useful for analysis of coil embolization. The inserted coils during aneurysm embolization were able to wind uniformly within the aneurysm due to a variety of factors (guiding or micro-catheter position and kick-back phenomenon such as delivery wire). Optimal speed is achieved with proper coil design, which allows the coil to be inserted into the aneurysm. The shape and size of the aneurysm can help determine the necessary size and design of the coil that should be used during the optimal speed range. Aneurysm wall and coil characteristics are considered, along with the friction state of the coil (hardness, shape, and thickness), leading to improvements in safety during the insertion procedure at optimum speed.

Volume versus standard coils in the treatment of intracranial aneurysms

BACKGROUND

Volume coils were developed to improve occlusion rates of intracranial aneurysms. Previous studies have shown increased packing density and comparable occlusion rates, but subgroup analyses of aneurysm size have not been carried out.

OBJECTIVE

To evaluate the safety and efficacy of the Penumbra Coil 400 (PC400) system in treating intracranial aneurysms compared with standard diameter coils.

METHODS

A monocentric retrospective case review of 260 aneurysms in 233 patients was carried out. In 37 aneurysms the PC400 system was used, while 223 aneurysms were treated with conventional coils. Previously treated aneurysms and aneurysms treated with flow diverters were excluded. Aneurysm and procedure characteristics, packing density, postprocedural and follow-up occlusion grades as well as coil compaction were evaluated.

RESULTS

Aneurysms treated with PC400 coils had higher volume (218.9 vs 47.1 mm(3), p<0.001), wider necks (3.0 vs 2.5 mm, p=0.005), and greater dome/neck ratio (2.0 vs 1.6, p=0.001) in comparison with aneurysms treated with conventional coils. Compared with controls, in the PC400 group we achieved higher packing densities (43.2% vs 34.4%, p<0.001; in aneurysms ≥7 mm 42.2% vs 27.8%, p<0.001). On follow-up angiography we observed less coil compaction (23.8% vs 64.3%, p=0.003) and less aneurysm recurrence (14.3% vs 40.5%, p=0.046) in aneurysms ≥7 mm when using the PC400 system.

CONCLUSIONS

Use of the PC400 system as opposed to conventional coils suggests that the PC400 system is safe and effective in treating intracranial aneurysms. Despite having been applied in a potentially more difficult-to-treat group, the use of PC400 was associated with less coil compaction and aneurysm recurrence in aneurysms ≥7 mm.