Hemodynamic Effect of Flow Diverter and Coils in Treatment of Large and Giant Intracranial Aneurysms

Influence of framing coil orientation and its shape on the hemodynamics of a basilar aneurysm model

Aneurysms are bulges of an artery, which require clinical management solutions. Due to the inherent advantages, endovascular coil filling is emerging as the treatment of choice for intracranial aneurysms (IAs). However, after successful treatment of coil embolization, there is a serious risk of recurrence. It is well known that optimal packing density will enhance treatment outcomes. The main objective of endovascular coil embolization is to achieve flow stasis by enabling significant reduction in intra-aneurysmal flow and facilitate thrombus formation. The present study numerically investigates the effect of framing coil orientation on intra-aneurysmal hemodynamics. For the purpose of analysis, actual shape of the embolic coil is used, instead of simplified ideal coil shape. Typically used details of the framing coil are resolved for the analysis. However, region above the framing coil is assumed to be filled with a porous medium. Present simulations have shown that orientation of the framing coil loop (FCL) greatly influences the intra-aneurysmal hemodynamics. The FCLs which were placed parallel to the outlets of basilar tip aneurysm (Coil A) were found to reduce intra-aneurysmal flow velocity that facilitates thrombus formation. Involving the coil for the region is modeled using a porous medium model with a packing density of 20 % . The simulations indicate that the framing coil loop (FCL) has a significant influence on the overall outcome.

Treatment Outcome of Flow Diverter Device for Medium-Sized Cerebral Aneurysms: A Single-Center Report

Objective

Flow diverters (FDs), first introduced in Japan in 2015, were initially limited to wide-necked large cerebral aneurysms, which pose a high treatment risk. However, based on the results of the PREMIER study, the indications have expanded since 2020, and the number of treatment cases is increasing in Japan. At our hospital, FD placement with adjunctive coil embolization has been actively performed for medium-sized cerebral aneurysms, as indicated in the PREMIER study; herein, we report the outcomes of this treatment.

Methods

Of the 25 patients with 28 aneurysms who underwent FD placement at our institution between April 2022 and June 2023, 15 with 17 wide-necked unruptured cerebral aneurysms with a maximum diameter of <12 mm in the internal carotid artery (ICA) or vertebral artery (VA) were included. Postoperative complications were investigated in each case, and the aneurysm occlusion status was assessed using ultrashort echo time (UTE)-MRA at 3 months postoperatively and angiography at 6 months postoperatively. Fifteen patients who underwent coiling or stent-assisted coiling (SAC) for the same criteria during the same period were compared. Baseline characteristics and treatment results were compared between FD and coiling/SAC cases.

Results

Four males and 11 females with a mean age of 61.7 ± 12.8 years were included, and the median follow-up period was 9 months (6-18 months). There were 14 aneurysms of the ICA and 3 of the VA, and the mean maximum aneurysm diameter was 7.9 ± 1.7 mm. All patients were treated using the Pipeline Flex with Shield Technology (Medtronic, Minneapolis, MN, USA), and 14 aneurysms (82.4%) were treated with adjunctive coil embolization. There were no symptomatic strokes in the perioperative period; only one patient receiving corticosteroid therapy for thyroid eye disease had asymptomatic ICA occlusion at 3 months. Fifteen aneurysms (88.2%) were not visible on UTE-MRA at 3 months postoperatively, and angiography at 6 months showed complete occlusion in 16 (94.1%) aneurysms. The coiling/SAC group had a smaller neck size and higher volume embolization ratio than the FD group; however, complete occlusion was higher in the FD group.

Conclusion

FD placement with adjunctive coil embolization for medium-sized cerebral aneurysms is expected to result in good occlusion rates in the early postoperative period.

A model with multiple intracranial aneurysms: possible hemodynamic mechanisms of aneurysmal initiation, rupture and recurrence

BACKGROUND

Hemodynamic factors play an important role in aneurysm initiation, growth, rupture, and recurrence, while the mechanism of the hemodynamic characteristics is still controversial. A unique model of multiple aneurysms (initiation, growth, rupture, and recurrence) is helpful to avoids the confounders and further explore the possible hemodynamic mechanisms of aneurysm in different states.

METHODS

We present a model with multiple aneurysms, and including the states of initiation, growth, rupture, and recurrence, discuss the proposed mechanisms, and describe computational fluid dynamic model that was used to evaluate the likely hemodynamic effect of different states of the aneurysms.

RESULTS

The hemodynamic analysis suggests that high flow impingement and high WSS distribution at normal parent artery was found before aneurysmal initiation. The WSS distribution and flow velocity were decreased in the new sac after aneurysmal growth. Low WSS was the risk hemodynamic factor for aneurysmal rupture. High flow concentration region on the neck plane after coil embolization still marked in recanalized aneurysm.

CONCLUSIONS

Associations have been identified between high flow impingement and aneurysm recanalization, while low WSS is linked to the rupture of aneurysms. High flow concentration and high WSS distribution at normal artery associated with aneurysm initiation and growth, while after growth, the high-risk hemodynamics of aneurysm rupture was occurred, which is low WSS at aneurysm dome.

Treatment of aneurysmal artery with PED: A case report

RATIONALE

Pipeline embolization devices are a new treatment for intracranial aneurysms, especially irregular, giant aneurysms.

PATIENT CONCERNS

A 48-year-old female patient presented with a headache in the frontal part for 3 weeks.

DIAGNOSES

Cerebral computed tomographic angiography and magnetic resonance angiography showed a saccular aneurysm in the right internal carotid artery that wrapped the parent artery. Digital subtraction angiography provided images with 1 large saccular internal carotid aneurysm.

INTERVENTIONS

The patient was treated by flow diverter stent and coil embolization and dual antiplatelet therapy with aspirin and ticagrelor in the ICU and was discharged after 10 days without complications.

OUTCOMES

One year after interventional therapy, repeated digital subtraction angiography showed no recurrence of aneurysm and embolization well, and the patient reported improvement in neurological symptoms.

LESSONS

Aneurysmal parent artery is a rare phenomenon. The combination of flow diverter stents and coil embolization to treat cases with large saccular aneurysms has important clinical significance and this may provide a reference for clinical treatment of aneurysmal parent artery.

Global tendencies and frontier topics in hemodynamics research of intracranial aneurysms: a bibliometric analysis from 1999 to 2022

Background: Hemodynamics plays a crucial role in the initiation, enlargement, and rupture of intracranial aneurysms (IAs). This bibliometric analysis aimed to map the knowledge network of IA hemodynamic research. Methods: Studies on hemodynamics in IAs published from 1999 to 2022 were retrieved from the Web of Science Core Collection (WoSCC). The contributions of countries, institutions, authors, and journals were identified using VOSviewer, Scimago Graphica, and Microsoft Excel. Tendencies, frontier topics, and knowledge networks were analyzed and visualized using VOSviewer and CiteSpace. Results: We identified 2,319 publications on hemodynamics in IAs. The annual number of publications exhibited an overall increasing trend. Among these, the United States, Japan, and China were the three major contributing countries. Capital Medical University, State University of New York (SUNY) Buffalo University, and George Mason University were the three most productive institutions. Meng H ranked first among authors regarding the number of articles and citations, while Cebral JR was first among co-cited authors. The American Journal of Neuroradiology was the top journal in terms of the number of publications, citations, and co-citations. In addition, the research topics can be divided into three clusters: hemodynamics itself, the relationship of hemodynamics with IA rupture, and the relationship of hemodynamics with IA treatment. The frontier directions included flow diverters, complications, morphology, prediction, recanalization, and four-dimensional flow magnetic resonance imaging (4D flow MRI). Conclusion: This study drew a knowledge map of the top countries, institutions, authors, publications, and journals on IA hemodynamics over the past 2 decades. The current and future hotspots of IA hemodynamics mainly include hemodynamics itself (4D flow MRI), its relationship with IA rupture (morphology and prediction), and its relationship with IA treatment (flow diverters, complications, and recanalization).

Coiling embolization strategy for medium-to-giant-sized intracranial aneurysms treated with pipeline embolization device: a propensity score-weighted study

OBJECTIVES

We aim to investigate associations between different coil strategies and outcomes in the aneurysms treated by a pipeline embolization device (PED).

METHODS

Patients with medium-to-giant-sized aneurysms treated by PED were included. The total cohort was divided into PED-alone and PED-coiling groups, and the PED-coiling group was further divided into loose and dense packing subgroups. Multivariate logistic analyses and stabilized inverse probability of treatment weighting (sIPTW) were performed to investigate the relationships between coiling strategies and outcomes. Restricted cubic spline (RCS) curves were used to describe the coiling degree and angiographic outcome relationship.

RESULTS

A total of 398 patients with 410 aneurysms were included. Aneurysms treated with PED coiling had a lower incomplete occlusion rate (15.3% vs. 30.3%, p = 0.002), higher total perioperative complication rate (14.2% vs. 3.5%, p = 0.001), longer production time (142.14 min vs. 101.26 min, p < 0.001), and higher total cost ($45,158.63 vs. $34,680.91, p < 0.001) than those treated with PED alone. There were no differences in outcomes between the loose and dense packing subgroups. However, the total cost was higher in the dense packing group ($43,787.46 vs. $47,288.32, p = 0.001) than in the loose packing group. The result was still robust in the multivariate and sIPTW analyses. The RCS curves showed "L-shape" relationships between the coil degree and angiographic outcomes.

CONCLUSION

Compared with PED alone, PED coiling could improve aneurysm occlusion. However, it could also increase the total complication risk, prolong procedure time, and increase the total cost. Compared with loose packing, dense packing did not enhance the treatment effectiveness but increased the treatment cost.

CLINICAL RELEVANCE STATEMENT

The additional treatment effect from coiling embolization declines sharply after a certain point. Specifically, the aneurysm occlusion rate is roughly stable when the coil number is greater than 3 or the total coil length is longer than 150 cm.

KEY POINTS

• Compared with pipeline embolization device (PED) alone, PED combined with coiling can improve aneurysm occlusion. • Compared with PED alone, PED combined with coiling increases the total complication risk, cost, and prolongs procedure time. • Compared with loose packing, dense packing did not increase the treatment effectiveness but increased the cost.

A novel flow diverter device (Tubridge) for the treatment of intracranial aneurysms: a systematic review and meta-analysis

The flow diverter (FD) device has become a feasible and effective option for treating intracranial aneurysms. This study aimed to evaluate the efficacy and safety of Tubridge FD (TFD) in treating intracranial aneurysms and provide evidence for further research and clinical application. Electronic databases, including PubMed, Web of Science, Embase, and the Cochrane Library from inception to July 31, 2022, were searched. The eligible studies should include TFD investigations in treating intracranial aneurysms. Pooled technical success rate, complete occlusion rate, improvement rate, stable rate, symptom elimination rate, and adverse events rate were calculated with either the fixed-effects model or the random-effects model, depending on the results of tests for heterogeneity. Egger's tests were performed to assess the potential publication bias. A total of 7 studies (145 patients) were included in this study. The pooled technical success rate was 0.98, the complete occlusion rate was 0.79, the improvement rate was 0.21, and the stable rate was 0.05. One included study reported that the surgery-related mortality rate in the Tubridge group was higher than that in the control group (3.66% vs. 1.61%), while the surgery-related morbidity rate in the Tubridge group was 2.4% and that in the control group was 0. Findings of this meta-analysis indicate that TFD manifests promising and effective performance with acceptable adverse events in the treatment of intracranial aneurysms.

Coiling followed by staged flow diversion for large and giant intracranial aneurysms

Objective

Delayed aneurysm rupture is a fatal complication after flow diversion treatment for large and giant intracranial aneurysms. This study aimed to investigate the feasibility and safety of coiling first and followed by planned flow diversion to prevent delayed aneurysm rupture.

Methods

From January 2017 to December 2021 in two institutions, patients with unruptured intracranial aneurysms treated by coiling first and planned flow diversion were retrospectively collected. Data on demographic and aneurysmal characteristics, procedural details, and clinical and angiographic outcomes were reviewed.

Results

Thirty patients were included (7 Males and 23 Females; Median age 57 years). Aneurysmal size ranged from 11.8 to 26.8 mm, with a median value of 18.5 mm. All aneurysms were located within the intradural segment of internal carotid arteries. Coiling and planned flow diversion were successfully performed in all patients. The time interval between coiling and flow diversion was 3.9–6.7 weeks, with a median value of 5.2 weeks. No hemorrhagic or ischemic complications occurred during the procedures and follow-up. Complete or subtotal occlusion was achieved in 86.7% (26/30) at the last angiographic follow-up (median 6.7 months).

Conclusion

The preliminary data suggested that coiling unruptured intracranial aneurysms followed by planned flow diversion is both safe and effective. Further studies with larger cohorts are needed to verify the effect of this new strategy in preventing delayed rupture after flow diversion.

Case Report: Tubridge flow diverter for a ruptured fusiform aneurysm of the M1 segments of the middle cerebral artery

We report a case of the middle cerebral artery (MCA) M1 segment ruptured fusiform aneurysm that was successfully treated using a domestic Tubridge flow diverter (TFD). A 40-year-old man was admitted to the hospital because of a headache and was diagnosed with subarachnoid hemorrhage. Cerebral angiography revealed a ruptured fusiform aneurysm in the M1 segment of the right MCA. TFD, combined with coil embolization, was used for perioperative treatment. No obvious complications were observed. Follow-up digital subtraction angiography 2 and 12 months after the surgery showed that the aneurysm was occluded, and the patient recovered well. This is the first known case of this treatment with this type of stent in such an aneurysm and demonstrates that TFD can be used to treat ruptured fusiform aneurysms in the M1 segment of the MCA.

Flow diversion effect of the leo braided stent for aneurysms in the posterior and distal anterior circulations: A multicenter cohort study

Background and purpose

The treatment of aneurysms located in the posterior and distal anterior circulations remains a challenge. Leo stents with a flow diversion (FD) effect may be a potential option, which needs to be clearly studied.

Methods

From January 2016 to October 2021, 133 patients with 145 aneurysms in the posterior and distal anterior circulations, treated with Leo stents, were retrospectively analyzed in three neurosurgical centers. Data on demographic information, aneurysm characteristics, procedural outcomes, postoperative course, and aneurysm occlusion were retrospectively analyzed.

Results

After immediate surgery, 90 aneurysms (60.1%) were in complete occlusion [Raymond-Ray Occlusion Class (RROC) 1 and O'Kelly Marotta (OKM) grade D], 29 aneurysms (20%) in good occlusion (RROC 2 and OKM grade C), 17.9% in incomplete occlusion (RROC 3a or OKM grade B), and no aneurysms in invalid occlusion (RROC 3b and OKM grade A). A total of 112 patients with 117 aneurysms received angiographic follow-up (mean 11.4 months), and the degree of occlusion showed a significant improvement (Z = 3.900, p < 0.001). The complete occlusion rate increased to 84.6% (99/117), while good and incomplete occlusion decreased to 6.8% (8/117) and 8.6% (10/117), respectively. A total of 14 cases (10.5%) presented narrowing of the parent artery, and nine cases (6.8%) had injured side branches. Cerebral hemorrhage occurred in four patients (3.0%), and symptomatic ischemic infarction occurred in six patients (4.5%). The final permanent morbidity (mCS ≥3) and mortality were 2.8% (3/133) and 0.8% (1/133), respectively. For 82 aneurysms treated by stent-assisted with coiling (SAC), large-sized, ruptured aneurysms (χ² = 7.767, p = 0.005) occurred. For 63 aneurysms treated by LEO stent monotherapy (LSM), multiple aneurysms, fusiform aneurysms (χ² = 18.958, p < 0.01), and/or small-sized aneurysms (Z = −2.692, p = 0.007) occurred.

Conclusions

Leo stents are safe and effective for aneurysms located in the posterior and distal anterior circulations. The overall degree of occlusion improved during a follow-up because of the FD effect of Leo stents. Aneurysms in these areas should be treated with personalized measures.

Comparison of the Pipeline embolisation device alone or combined with coiling for treatment of different sizes of intracranial aneurysms

Objectives

The aim of this study was to compare complications and outcomes between intracranial aneurysms treated with the Pipeline embolisation device (PED) alone or with PED combined with coiling for different-sized aneurysms.

Method

Patients with aneurysms treated by PED were collected from the PED in China postmarket multicentre registry study. We performed a propensity match analysis to compare the efficacy and safety between PED alone and PED combined with coiling treatment, and then aneurysms were organised into three groups based on their size: small (≤7 mm), medium (≤15 mm to >7 mm) and large/giant (>15 mm). Complications and aneurysm occlusion rates in the aneurysm size groups were compared between PED alone and PED combined with coiling patients.

Result

A total of 1171 patients with 1322 aneurysms were included. All patients received clinical follow-up, while angiographic follow-up was available in 967 aneurysms. For small aneurysms, there was no difference in the aneurysm occlusion rate between two groups (79.1% vs 88.4%, respectively), while there was a significant increase in the ischaemic complication rate (8.3% vs 19.3%, respectively, p=0.0001). For medium and large/giant saccular aneurysms, PED combined with coiling significantly improved the occlusion rate (medium aneurysms: 74.7% vs 88.8%, respectively, p<0.0001; large/giant saccular aneurysms: 72.9% vs 86.9%, respectively, p=0.018), while there were no differences in the total complication rate. For large/giant non-saccular aneurysms, two groups showed no differences.

Conclusion

Use of the PED with adjunctive coils can significantly improve the occlusion rate of medium aneurysms, without increasing the total complication rate.

Hemodynamic mechanism of pulsatile tinnitus caused by venous diverticulum treated with coil embolization

BACKGROUND AND OBJECTIVE

Coil embolization has become a new treatment method for pulsatile tinnitus (PT) caused by sigmoid sinus diverticulum (SSD). Although this therapy has achieved good results in clinical reports, the hemodynamic mechanism of coils in the treatment of PT in SSD remained unclear.

METHODS

Finite element method (FEM) and computational fluid dynamics (CFD) were combined to explore the hemodynamic mechanism of coil embolization in SSD treatment. Three personalized geometric models of sigmoid sinus were established according to the CTA data of patients. Coil model were established by FEM, and the hemodynamic differences of SSD before and after coiling were compared by transient CFD method.

RESULTS

Velocity streamlines disappeared in the SSD after coiling. At the peak time (t1 = 0.22 s), the SSD-average velocity decreased in every patient. The average value of the decreased in three patients was 0.154 ± 0.028 m/s (mean ± SD). Wall average pressure (P_avg) also showed a decline in every patient. Average of decrements of three patients was 17.69 ± 4.91 Pa (mean ± SD). Average WSS (WSS_avg) was also reduced in every patient. The average value of WSS drop was 9.74 ± 3.02 Pa (mean ± SD). After coiling, the proportion of low-velocity region in the sigmoid sinus cortical plate dehiscence (SSCPD) area increased. Average of increments was 22.1 ± 5.36% (mean ± SD).

CONCLUSIONS

A reduction in SSD-average velocity, wall pressure, and WSS were the short-term hemodynamic mechanism of coil embolization for PT. Coil embolization increased the proportion of low-velocity region in the SSCPD area, thereby creating a hemodynamic environment that easily produced thrombus and protects blood vessels from the impact of blood flow. This phenomenon was the long-term effect of coil embolization.

Safety and Efficacy of Coils in Conjunction With the Pipeline Flex Embolization Device for the Treatment of Cerebral Aneurysms

Background: Flow diverters (FD) have shown promising results in the treatment of intracranial aneurysms (IAs). However, there is still controversy whether pipeline flex embolization device (PED flex)-assisted coils can facilitate the curing of aneurysms. Our aim was to assess the safety and effectiveness of PED flex adjunctive with coils (PED flex + coil) in the treatment of IAs. Method: Patients who underwent PED flex treatment in combination with coiling between January 2018 and June 2020 were included in this study. The clinical and radiographic characteristics before and after treatments were retrospectively evaluated. The study cohort comprised of 125 patients with 140 IAs, which was subdivided into two subgroups: one group included patients treated only through PED alone, and the other group included patients treated through PED flex adjunctive with coil. Patient baseline characteristics, aneurysm characteristics, treatment-related factors, and outcomes were analyzed to determine the effectiveness of both techniques. Results: Aneurysms in the PED flex + coil group were larger (10.0 ± 5.8 mm, P < 0.001) and wider (7.2 ± 4.6 mm, P = 0.002) compared with those in the PED flex group. There was no statistical difference in the perioperative complication rate between the two groups. The overall complete occlusion rate was 75.7% at 6.2 months, with 71.7% at 6.2 ± 1.7 months in the PED flex group and 85.4% at 6.2 ± 1.8 months in the PED flex + coil group, respectively. A higher percentage of satisfactory angiography results was found in the PED flex + coil group during follow-up (92.7 vs. 78.8%, P = 0.047). Conclusion: PED flex placement with adjunctive coil embolization represents a safe alternative option for the treatment of IAs. In these cases, coil embolization increases the occlusion rate in PED flex-treated patients without increasing the periprocedural complications.

Hemodynamic Investigation of the Effectiveness of a Two Overlapping Flow Diverter Configuration for Cerebral Aneurysm Treatment

Flow diverters (FDs) are widely employed as endovascular treatment devices for large or wide-neck cerebral aneurysms. Occasionally, overlapped FDs are deployed to enhance the flow diversion effect. In this study, we investigated the hemodynamics of overlapping FDs via computational fluid dynamics (CFD) simulations. We reproduced the arterial geometry of a patient who had experienced the deployment of two overlapping FDs. We utilized two stent patterns, namely the patterns for one FD and two overlapping FDs. We calculated the velocity, mass flow rate, wall shear stress, and pressure loss coefficient as well as their change rates for each pattern relative to the no-FD pattern results. The CFD simulation results indicated that the characteristics of the blood flow inside the aneurysm were minimally affected by the deployment of a single FD; in contrast, the overlapping FD pattern results revealed significant changes in the flow. Further, the velocity at an inspection plane within the aneurysm sac decreased by up to 92.2% and 31.0% in the cases of the overlapping and single FD patterns, respectively, relative to the no-FD pattern. The simulations successfully reproduced the hemodynamics, and the qualitative and quantitative investigations are meaningful with regard to the clinical outcomes of overlapped FD deployment.

Effect of foam insertion in aneurysm sac on flow structures in parent lumen: relating vortex structures with disturbed shear

Numerous studies suggest that disturbed shear, causing endothelium dysfunction, can be related to neighboring vortex structures. With this motivation, this study presents a methodology to characterize the vortex structures. Precisely, we use mapping and characterization of vortex structures' changes to relate it with the hemodynamic indicators of disturbed shear. Topological features of vortex core lines (VCLs) are used to quantify the changes in vortex structures. We use the Sujudi-Haimes algorithm to extract the VCLs from the flow simulation results. The idea of relating vortex structures with disturbed shear is demonstrated for cerebral arteries with aneurysms virtually treated by inserting foam in the sac. To get physiologically realistic flow fields, we simulate blood flow in two patient-specific geometries before and after foam insertion, with realistic velocity waveform imposed at the inlet, using the Carreau-Yasuda model to mimic the shear-thinning behavior. With homogenous porous medium assumption, flow through the foam is modeled using the Forchheimer-Brinkman extended Darcy model. Results show that foam insertion increases the number of VCLs in the parent lumen. The average length of VCL increases by 168.9% and 55.6% in both geometries. For both geometries under consideration, results demonstrate that the region with increased disturbed shear lies in the same arterial segment exhibiting an increase in the number of oblique VCLs. Based on the findings, we conjecture that an increase in oblique VCLs is related to increased disturbed shear at the neighboring portion of the arterial wall.

Significant flow velocity reduction at the intracranial aneurysm neck after endovascular treatment leads to favourable angiographic outcome: a prospective study

BACKGROUND

With widely usage of flow diverter in intracranial aneurysm treatment, some previously used predictors may not be effective in evaluating the recurrence risk. We aimed to comprehensively re-evaluate the predictors of intracranial aneurysm outcome with various endovascular treatment methods and devices.

METHODS

This is a prospective registered study. We analysed 6-month and 18-month follow-up angiographic data from the prospective study. Data on patient demographics, aneurysm morphology and type of treatment were recorded. Patient-specific haemodynamic simulations were performed. An unfavourable angiographic outcome was defined as recurrence of aneurysm in cases with coiling or stent-assisted coiling, patency of aneurysm in cases with flow diverters or retreatment during follow-up.

RESULTS

In total, 165 patients (177 intracranial aneurysms) with at least one angiographic follow-up data were analysed. For the short-term (6-month) results, after univariate analysis, the demographic, morphological and treatment-related factors did not achieve significantly statistical differences. The reduction ratio (RR) of velocity at aneurysm neck after embolisation was significantly lower in the unfavourable angiographic group than the favourable angiographic outcome group (p=0.002). After the Cox regression analysis, the RR of velocity at aneurysm neck was the only independent factor associated with favourable angiographic outcome (OR 0.028; p=0.001) and had an acceptable area under the curve (0.714) with a clear cut-off value (46.14%). Similarly, for the analysis of midterm (18-month) results, the RR of velocity at the aneurysm neck was the only independent significant factor for the unfavourable angiographic outcome (OR 0.050; p=0.017). The area under the curve was 0.754 and the cut-off value was 48.20%.

CONCLUSIONS

The haemodynamics showed an independent effect on angiographic follow-up results and may provide helpful suggestions for clinical practice in the future.

Evaluating the Tubridge™ flow diverter for large cavernous carotid artery aneurysms

Background

The Tubridge™ flow diverter (TFD) was recently developed in China; however, its safety and efficacy in treating large cavernous carotid artery aneurysms (LCCAs) are unclear. Our objective was to evaluate the safety and efficacy of the TFD in patients receiving TFDs to treat LCCAs (10–25 mm).

Methods

Between June 2013 and May 2014, seven patients with LCCAs were enrolled in our study, and all seven patients underwent TFD implantation combined with coils.

Results

Angiographic follow-up images were available for all seven patients at a median of 57.5 ± 16.7 (range, 6–69) months. Seven patients obtained favorable angiographic results defined as O’Kelly–Marotta Scale C and D. Clinical follow-up data were available for all seven patients at a median of 73.32 ± 3.6 (range, 66–78) months. No patients developed new neurological deficits. Six patients achieved a modified Rankin scale score of 0, and diplopia improved in the remaining patient.

Conclusions

The results were excellent for the aneurysms treated with TFDs in our patients with LCCAs. TFDs are feasible for the treatment of LCCAs, but a multicenter, controlled clinical trial is needed to evaluate the long-term safety and efficacy of the TFD to treat LCCAs.

Giant aneurysm of the bilateral vertebrobasilar junction treated by pipeline and coils: A case report and literature review

Giant aneurysm of the posterior circulation is associated with a higher risk of rupture compared with that of the anterior circulation. Furthermore, surgical clipping and interventional embolization for giant aneurysm of the posterior circulation are more difficult and complex to perform. The present study reported on the case of a 26-year-old female who exhibited a giant spherical aneurysm of the vertebrobasilar junction (VBJ) with a maximum diameter of ~35 mm that caused cervical discomfort. In addition, the patient experienced symptoms including left-sided walking and hoarseness caused by the compression of the brainstem and the posterior cranial nerves. The risks associated with performing surgery in this area are high and the prognosis is mainly poor. The patient of the present study was treated using the Pipeline Flex device with coil embolization. As a giant aneurysm of the VBJ simultaneously affects the bilateral vertebral arteries (VAs) and basilar artery, it is a unique condition and the treatment strategy must be personalized. Based on an analysis of the hemodynamic influence on the aneurysm in the present case, the Pipeline was placed through the left VA, the coils were packed through the right VA, and finally, the right VA was proximally occluded. At 7 months after embolization, the patient's modified Rankin scale score was 1 point. Upon analysis of the hemodynamic influence on the aneurysm of the VBJ, the VA with the larger shear force on the wall of the aneurysm was selected for occlusion to simplify the treatment of the aneurysm and to maximize the probability to achieve recovery.

Computational Fluid Dynamics Using a Porous Media Setting Predicts Outcome after Flow-Diverter Treatment

BACKGROUND AND PURPOSE

Knowledge about predictors of the outcome of flow-diverter treatment is limited. The aim of this study was to predict the angiographic occlusion status after flow-diverter treatment with computational fluid dynamics using porous media modeling for decision-making in the treatment of large wide-neck aneurysms.

MATERIALS AND METHODS

A total of 27 patients treated with flow-diverter stents were retrospectively analyzed through computational fluid dynamics using pretreatment patient-specific 3D rotational angiography. These patients were classified into no-filling and contrast-filling groups based on the O'Kelly-Marotta scale. The patient characteristics, morphologic variables, and hemodynamic parameters were evaluated for understanding the outcomes of the flow-diverter treatment.

RESULTS

The patient characteristics and morphologic variables were similar between the 2 groups. Flow velocity, wall shear stress, shear rate, modified aneurysmal inflow rate coefficient, and residual flow volume were significantly lower in the no-filling group. A novel parameter, called the normalized residual flow volume, was developed and defined as the residual flow volume normalized by the dome volume. The receiver operating characteristic curve analyses demonstrated that the normalized residual flow volume with an average flow velocity of ≥8.0 cm/s in the aneurysmal dome was the most effective in predicting the flow-diverter treatment outcomes.

CONCLUSIONS

It was established in this study that the hemodynamic parameters could predict the angiographic occlusion status after flow-diverter treatment.

Variation of Mass Effect After Using a Flow Diverter With Adjunctive Coil Embolization for Symptomatic Unruptured Large and Giant Intracranial Aneurysms

Background: Mass effect associated with large or giant aneurysms is an intractable problem for traditional endovascular treatments. Preventing recurrence of aneurysms requires dense coiling, which may aggravate the mass effect. However, the flow diverter (FD) is a new device that avoids the need for dense coiling. This study was performed to investigate whether use of FDs with adjunctive coil embolization can relieve the aneurysmal mass effect and to explore the factors that affect the variation of compressional symptoms.

Methods: We retrospectively evaluated patients with compressional symptoms caused by unruptured aneurysms who underwent endovascular treatment with an FD with adjunctive coil embolization at our center from January 2015 to December 2017. Imaging follow-up included digital subtraction angiography (DSA) ranging from 11 to 14 months and magnetic resonance imaging (MRI) ranging from 24 to 30 months; the former was used to evaluate the intracavitary volume, and the latter was used to measure the variation of the mass effect. Follow-up physical examinations were performed to observe variations of symptoms.

Results: In total, 22 patients with 22 aneurysms were treated by an FD combined with coil embolization. All 22 patients underwent the last clinical follow-up. Regarding compressional symptoms, 12 (54.54%) patients showed improvement, 6 (27.27%) were fully recovered, and 6 (27.27%) showed improvement but with incomplete cranial palsy. However, five (22.72%) patients showed no change, four (18.18%) showed worsening symptoms compared with their preoperative state, and one (4.55%) died of delayed rupture. Seventeen of the 22 patients underwent MRI. Of these 17 patients, the aneurysm shrank in 13 (76.47%) and no significant change occurred in 4 (23.53%). In the multivariate analysis, a short duration from symptom occurrence to treatment (p = 0.03) and younger patient age (p = 0.038) were statistically significant factors benefiting symptom improvement, and shrinkage of the aneurysm was associated with favorable clinical outcomes (p = 0.006).

Conclusions: Use of the FD with adjunctive loose coil embolization might help to alleviate the compressional symptoms caused by intracranial aneurysms. Shrinkage of the aneurysm, a short duration of symptoms, and younger patient age might contribute to favorable outcomes of mass effect-related symptoms.

Natural history and clinical outcomes in patients with complex intracranial aneurysms: a review of 115 bypass cases and 22 nonsurgical cases

The purpose of this study was to evaluate the natural history of patients with these heterogeneous aneurysms to provide guidance for their treatment. This retrospective analysis was performed at a single institution and included 137 patients with complex intracranial aneurysms who underwent a natural history evaluation. Among the 115 patients who underwent bypass surgery, stroke (n = 39, 33.9%) was the most common clinical symptom followed by progressively severe headaches (n = 25, 21.7%). Of the 104 patients with follow-up information, 87 (83.7%) returned to a normal life within a mean follow-up of 4.17 ± 2.09 years. Ten deaths (9.6%) occurred after a mean of 1.3 ± 0.9 years. Among the 22 patients who selected nonsurgical treatment, mass effect (n = 9, 40.9%) was the most common clinical presentation, and 14 deaths (63.6%) occurred after a mean of 3.3 ± 2.5 years. The modified Rankin scale (mRS) scores of 5 survivors (5/22, 22.7%) progressed from 0-2 at initial presentation to 3-4. Bypass surgical treatment for these aneurysms appears to be effective and can achieve good clinical outcomes without additional limitations related to individual aneurysms despite the impact of recent endovascular techniques on vascular surgery.

Is Contrast Stasis After Pipeline Embolization Device Deployment Associated with Higher Aneurysm Occlusion Rates?

OBJECTIVE

To assess the association of degree of contrast stasis in intracranial aneurysms (IAs) immediately after Pipeline embolization device (PED; Medtronic, Dublin, Ireland) deployment with 6- and 12-month angiographic occlusion rates.

METHODS

This retrospective cohort study included consecutive patients undergoing PED deployment for saccular IA treatment at a large-volume cerebrovascular center over a 4-year 9-month period. Angiographic images obtained immediately after PED deployment were graded according to amount of intra-aneurysmal contrast flow during the late venous phase: 0 = no stasis; 1 = <50% contrast stasis; 2 = 50%-75% stasis; and 3 = >75%-99% stasis. Follow-up occlusion rates were determined by digital subtraction angiography, computed tomographic angiography, or magnetic resonance angiography.

RESULTS

The study included 119 patients in whom 182 PEDs were deployed to treat 141 aneurysms. A single PED was deployed in 105 (74.5%) aneurysms. The internal carotid artery was the commonest aneurysm site (119 [85%]). Fifty-two (36.9%) aneurysms were grade 0; 33 (23.4%) were grade 1; 46 (32.6%) were grade 2; and 10 (7.1%) were grade 3 immediately post-treatment. A 6-month follow-up angiogram available for 101 aneurysms showed complete occlusion (no flow into the aneurysm) in 74 (73.3%) aneurysms. A 12-month follow-up study available for 132 aneurysms showed complete occlusion in 79.5%. At last follow-up, occlusion rates were not significantly different for different contrast stasis grades (P = 0.60). Mean angiographic follow up for all IAs was 23v±v17.7 months. IA size, sex, age, and smoking were not significant predictors of occlusion.

CONCLUSIONS

The degree of aneurysm contrast stasis immediately after PED deployment is not statistically associated with 6- and 12-month angiographic occlusion rates.

Relationship between haemodynamic changes and outcomes of intracranial aneurysms after implantation of the pipeline embolisation device: a single centre study

BACKGROUND

Intracranial aneurysms are increasingly being treated by the placement of flow diverters; however, the factors affecting the outcome of aneurysms treated using flow diverters remain unclarified.

METHODS

The present study investigated 94 aneurysms treated with pipeline embolisation device placement, and used a computational fluid dynamics method to explore the factors influencing the outcome of aneurysms.

RESULTS

Seventy-six completely occluded aneurysms and 18 incompletely occluded aneurysms were analysed. Before treatment, inflow jets were found in 13 (72.2%) aneurysms in the incompletely occluded group and 34 (44.7%) in the completely occluded group (P = 0.292). After deployment of the pipeline embolisation device, inflow jets remained in nine (50%) aneurysms in the incompletely occluded group and nine (11.8%) in the completely occluded group (P = 0.001). In the incompletely occluded group, regions with inflow jets after treatment corresponded with the patent areas shown on follow-up digital subtraction angiography. The mean reduction ratios of velocity in the whole aneurysm and on the neck plane were lower in the incompletely occluded than in the completely occluded group (P = 0.003; P = 0.017). Multivariate analysis revealed that the only independent risk factors for incomplete aneurysm occlusion were the reduction ratios of velocity (in the whole aneurysm, threshold 0.362, P = 0.005; on the neck plane, threshold 0.273, P = 0.015).

CONCLUSIONS

After pipeline embolisation device placement, reduction ratios of velocity in the whole aneurysm of less than 0.362 and on the neck plane of less than 0.273 are significantly associated with a greater risk of aneurysm incomplete occlusion. In addition, the persistence of inflow jets in aneurysms is associated with incomplete occlusion in the inflow jet area.

Hodge decomposition of wall shear stress vector fields characterizing biological flows

A discrete boundary-sensitive Hodge decomposition is proposed as a central tool for the analysis of wall shear stress (WSS) vector fields in aortic blood flows. The method is based on novel results for the smooth and discrete Hodge-Morrey-Friedrichs decomposition on manifolds with boundary and subdivides the WSS vector field into five components: gradient (curl-free), co-gradient (divergence-free) and three harmonic fields induced from the boundary, which are called the centre, Neumann and Dirichlet fields. First, an analysis of WSS in several simulated simplified phantom geometries (duct and idealized aorta) was performed in order to understand the nature of the five components. It was shown that the decomposition is able to distinguish harmonic blood flow arising from the inlet from harmonic circulations induced by the interior topology of the geometry. Finally, a comparative analysis of 11 patients with coarctation of the aorta (CoA) before and after treatment as well as 10 control patients was done. The study shows a significant difference between the CoA patients before and after the treatment, and the healthy controls. This means a global difference between aortic shapes of diseased and healthy subjects, thus leading to a new type of WSS-based analysis and classification of pathological and physiological blood flow.

The role of wall shear stress in the parent artery as an independent variable in the formation status of anterior communicating artery aneurysms

OBJECTIVES

The study aimed to determine which hemodynamic parameters independently characterize anterior communicating artery (AcomA) aneurysm formation and explore the threshold of wall shear stress (WSS) of the parent artery to better illustrate the correlation between the magnitude of WSS and AcomA aneurysm formation.

METHODS

Eighty-one patients with AcomA aneurysms and 118 patients without intracranial aneurysms (control population), as confirmed by digital subtraction angiography (DSA) from January 2014 to May 2017, were included in this cross-sectional study. Three-dimensional-DSA was performed to evaluate the morphologic characteristics of AcomA aneurysms. Local hemodynamic parameters were obtained using transcranial color-coded duplex (TCCD). Multivariate logistic regression and a two-piecewise linear regression model were used to determine which hemodynamic parameters are independent predictors of AcomA aneurysm formation and identify the threshold effect of WSS of the parent artery with respect to AcomA aneurysm formation.

RESULTS

Univariate analyses showed that the WSS (p < 0.0001), angle between the A1 and A2 segments of the anterior cerebral artery (ACA) (p < 0.001), hypertension (grade II) (p = 0.007), fasting blood glucose (FBG; > 6.0 mmol/L) (p = 0.005), and dominant A1 (p < 0.001) were the significant parameters. Multivariate analyses showed a significant association between WSS of the parent artery and AcomA aneurysm formation (p = 0.0001). WSS of the parent artery (7.8-12.3 dyne/cm²) had a significant association between WSS and aneurysm formation (HR 2.0, 95% CI 1.3-2.8, p < 0.001).

CONCLUSIONS

WSS ranging between 7.8 and 12.3 dyne/cm² independently characterizes AcomA aneurysm formation. With each additional unit of WSS, there was a one-fold increase in the risk of AcomA aneurysm formation.

KEY POINTS

• Multivariate analyses and a two-piecewise linear regression model were used to evaluate the risk factors for AcomA aneurysm formation and the threshold effect of WSS on AcomA aneurysm formation. • WSS ranging between 7.8 and 12.3 dyne/cm ² was shown to be a reliable hemodynamic parameter in the formation of AcomA aneurysms. The probability of AcomA aneurysm formation increased one-fold for each additional unit of WSS. • An ultrasound-based TCCD technique is a simple and accessible noninvasive method for detecting WSS in vivo; thus, it can be applied as a screening tool for evaluating the probability of aneurysm formation in primary care facilities and community hospitals because of the relatively low resource intensity.

The Combined Use of Intraluminal and Intrasaccular Flow Diversion for the Treatment of Intracranial Aneurysms: Report of 25 Cases

PURPOSE

The Medina Embolic Device (MED) is a new intrasaccular device with promising early results. Previously we documented our initial experience of this device both alone and in combination with other devices including flow diverter stents (FDS). We sought to determine the effect of the MED + FDS strategy for the treatment of selected aneurysms.

MATERIALS AND METHODS

We performed a retrospective analysis of prospectively collected data to identify all patients with aneurysms treated using both the MED and intraluminal FDS. We present our technical success rate, early and mid-term angiographic follow-up, and clinical outcome data.

RESULTS

We identified 25 non-consecutive patients. The treatment was staged in 9 patients and in a single session 16 patients. The average age was 61±12.8 years (range 40-82). The average fundus height was 11±3.6 mm and average fundus width was 10.1±3.4 mm. In the staged cohort (n=9) at delayed angiography (mean 10 mths) 8 aneurysms (89%) showed complete exclusion (mRRC 1) and in one patient there was a parent vessel occlusion. In the simultaneous cohort delayed angiography (n=10, mean 8.1 months) demonstrated complete occlusion (mRRC 1) in 6 aneurysms (60%), 3 neck remnants (mRRC 2) (30%) and 1 patient (10%) showed persistent aneurysmal filling (mRRC 3a). There were 5 complications with permanent morbidity (mRS >2) in two patients. There were no mortalities.

CONCLUSION

The MED can be successfully used in combination with intraluminal FDS and in selected aneurysms this may represent an alternative to FDS and adjunctive coiling.

Morphological and Hemodynamic Parameters for Middle Cerebral Artery Bifurcation Aneurysm Rupture Risk Assessment

OBJECTIVE

To investigate the morphological and hemodynamic parameters associated with middle cerebral artery (MCA)bifurcation aneurysm rupture.

METHODS

A retrospective study of 67 consecutive patients was carried out based on 3D digital subtraction angiography data. Morphological and hemodynamic parameters including aneurysm size parameters (dome width, height, and perpendicular height), longest dimension from the aneurysm neck to the dome tip, neck width, aneurysm area, aspect ratio, Longest dimension from the aneurysm neck to the dome tip (Dmax) to dome width, and height-width, Bottleneck factor, as well as wall shear stress (WSS), low WSS area (LSA), percentage of LSA (LSA%) and energy loss (EL) were estimated. Parameters between ruptured and un-ruptured groups were analyzed. Receiver operating characteristics were generated to check prediction performance of all significant variables.

RESULTS

Sixty-seven patients with MCA bifurcation aneurysm were included (31 unruptured, 36 ruptured). Dmax (p=0.008) was greater in ruptured group than that in un-ruptured group. D/W (p<0.001) and the percentage of the low WSS area (0.09±0.13 vs. 0.01±0.03, p<0.001) were also greater in the ruptured group. Moreover, the EL in ruptured group was higher than that in un-ruptured group (6.39±5.04 vs. 1.53±0.86, p<0.001). Multivariate regression analysis suggested D/W and EL were significant predictors of rupture of MCA bifurcation aneurysms. Correlation analyses revealed the D/W value was positively associated with the EL (R=0.442, p<0.01).

CONCLUSION

D/W and EL might be the most two favorable factors to predict rupture risk of MCA bifurcation aneurysms.

Haemodynamic analysis for recanalisation of intracranial aneurysms after endovascular treatment: an observational registry study in China

INTRODUCTION

Recanalisation of intracranial aneurysms following endovascular treatment is a major issue. Many factors, including aneurysm morphology, the method of treatment, and haemodynamics, are considered to be associated with recanalisation. However, the underlying haemodynamic mechanisms are not completely understood.

METHODS AND ANALYSIS

This is a prospective, observational, registry study for patients with intracranial aneurysms who are treated endovascularly. It will enrol 200 eligible patients. Data on morphological, haemodynamic, and treatment factors will be collected prospectively. The advanced virtual stenting technique and porous media method will be used in haemodynamic simulations. The clinical and angiographic outcomes at 6 months will be measured and analysed. This observational study will determine the haemodynamic factors that affect the recanalisation of aneurysms.

ETHICS AND DISSEMINATION

Both the study protocol and written informed consent were reviewed and approved by the Institutional Review Board of Beijing Tiantan Hospital (KY2016-023-01). The results of study will be disseminated in professional printed media.

TRIAL REGISTRATION NUMBER

NCT02812108; Pre-results.

Association between hemodynamic modifications and clinical outcome of intracranial aneurysms treated using flow diverters

Treatment of intracranial aneurysms (IAs) has been revolutionized by the advent of endovascular Flow Diverters (FDs), which disrupt blood flow within the aneurysm to induce pro-thrombotic conditions, and serves as a scaffold for endothelial ingrowth and arterial remodeling. Despite good clinical success of FDs, complications like incomplete occlusion and post-treatment rupture leading to subarachnoid hemorrhage have been reported. In silico computational fluid dynamic analysis of the pre- and post-treated geometries of IA patients can shed light on the contrasting blood hemodynamics associated with different clinical outcomes. In this study, we analyzed hemodynamic modifications in 15 IA patients treated using a single FD; 10 IAs were completely occluded (successful) and 5 were partially occluded (unsuccessful) at 12-month follow-up. An in-house virtual stenting workflow was used to recapitulate the clinical intervention on these cases, followed by CFD to obtain pre- and post-treatment hemodynamics. Bulk hemodynamic parameters showed comparable reductions in both groups with average inflow rate and aneurysmal velocity reduction of 40.3% and 52.4% in successful cases, and 34.4% and 49.2% in unsuccessful cases. There was a substantial reduction in localized parameter like vortex coreline length and Energy Loss for successful cases, 38.2% and 42.9% compared to 10.1% and 10.5% for unsuccessful cases. This suggest that for successfully treated IAs, the localized complex blood flow is disrupted more prominently by the FD as compared to unsuccessful cases. These localized hemodynamic parameters can be potentially used in prediction of treatment outcome, thus aiding the clinicians in a priori assessment of different treatment strategies.

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.

Successful Retreatment of Recurrent Intracranial Vertebral Artery Dissecting Aneurysms After Stent-Assisted Coil Embolization: A Self-Controlled Hemodynamic Analysis

BACKGROUND

Intracranial vertebral artery dissecting aneurysms (VADAs) tend to recur despite successful stent-assisted coil embolization (SACE). Hemodynamics is useful in evaluating aneurysmal formation, growth, and rupture. Our aim was to evaluate the hemodynamic patterns of the recurrence of VADA.

METHODS

Between September 2009 and November 2013, all consecutive patients with recurrent VADAs after SACE in our institutions were enrolled. Recurrence was defined as recanalization and/or regrowth. We assessed the hemodynamic alterations in wall shear stress (WSS) and velocity after the initial SACE and subsequently after retreatment of the aneurysms that recurred.

RESULTS

Five patients were included. After the initial treatment, 3 patients showed recanalization and 2 showed regrowth. In the 2 patients with regrowth, the 2 original aneurysms maintained complete occlusion; however, de novo aneurysm regrowth was confirmed near the previous site. Compared with 3 recanalized aneurysms, the completely occluded aneurysms showed high mean reductions in velocity and WSS after initial treatment (velocity, 77.6% vs. 57.7%; WSS, 74.2% vs. 52.4%); however, WSS remained high at the region near the previous lesion where the new aneurysm originated. After the second retreatment, there was no recurrence in any patient. Compared with the 3 aneurysms that recanalized, the 4 aneurysms that maintained complete occlusion showed higher reductions in velocity (62.9%) and WSS (71.1%).

CONCLUSIONS

Our series indicated that hemodynamics might have an important role in recurrence of VADAs. After endovascular treatment, sufficient hemodynamic reduction in aneurysm dome, orifice, and parent vessel may be one of the key factors for preventing recurrence in VADAs.