Computational Study of Hemodynamic Changes Induced by Overlapping and Compacting of Stents and Flow Diverter in Cerebral Aneurysms

Stand-alone small low-profile braided stents for challenging unruptured posterior inferior cerebellar artery aneurysms compared to conventional endovascular methods: A cohort study

ObjectivePosterior inferior cerebellar artery (PICA) aneurysms are uncommon and may be challenging to treat, especially if they are very small saccular or dissecting pseudoaneurysms at proximal and mid-PICA locations. They are usually technically difficult to treat with conventional reconstructive endovascular methods. We present our experience with PICA aneurysms treated by a stand-alone small, low-profile stent with a moderate flow-diverting effect (low-profile visualized intraluminal support junior (LVIS Jr)) compared to conventional endovascular methods.MethodsSingle institution cases of treated unruptured PICA aneurysms from 2015 to May 2022 were retrospectively reviewed. Patient characteristics, pre-and postoperative images, and last clinical and radiological outcomes were analyzed. Comparative statistical analysis was used.ResultsNine cases of unruptured PICA aneurysms treated with stand-alone LVIS Jr (group 1) and seven cases treated with other conventional methods (group 2) were identified. The mean age was 56 versus 61.43 years, sex was female in 7 versus 6 cases, and the left side was involved in 7 versus 4 cases in group 1 and group 2, respectively. All aneurysms were in the proximal PICA segment except for one case in the mid-PICA segment aneurysm in each group. There was a difference in aneurysm type in both groups (p = 0.008). All aneurysms were of saccular type except for five dissecting types in group 1 and 2 in group 2. The mean aneurysm size was 1.91 ± 0.62 in group 1 and 9.04 ± 5.82 mm in group 2 (p < 0.0002). In group 2, treatment was with PICA sacrifice (one case), primary aneurysm coiling (three cases), stent-assisted coiling (one case), and flow diverter (two cases). Complications were only puncture site-related that occurred once in each group. There were no differences in mean clinical or radiological follow-up. Aneurysm recurrence with retreatment occurred in two cases in each group. All patients had an mRS 0-2 at the last follow-up.ConclusionIn selected cases, unruptured small or dissecting PICA aneurysms may be treated safely and effectively using single stand-alone LVIS Jr. Prospective studies are needed to validate safety and efficacy.

Comparing the safety and effectiveness of overlapping stents with flow diverters for unruptured vertebral artery dissecting aneurysms

BACKGROUND

Endovascular treatment for vertebral artery dissecting aneurysms (VADAs) includes overlapping stents and flow diverters. This study compared the safety and effectiveness of overlapping stents and flow diverters for unruptured VADAs.

METHODS

We retrospectively enrolled patients with unruptured VADAs who underwent overlapping stents or flow diverters at two tertiary hospitals in South Korea. The primary clinical outcome was the occurrence of stroke. The primary angiographic outcomes (>12 months) were categorized as regression, no decrease in size, recanalization, or stent occlusion, of which only regression was defined as a favorable angiographic outcomes.

RESULTS

Of the 146 patients with VADAs, 25 (17.1%) had flow diverters and 121 (82.9%) had overlapping stents. For the primary angiographic outcomes over 12 months, the rate of favorable angiographic outcomes for flow diverters was 81.8% and for overlapping stents (triple stents) was 98.8% (P=0.006). In the multivariale analysis, after adjusting for partially thrombosed aneurysms, aneurysm shape, non-dominant vessel, posterior inferior cerebellar artery involvement, and procedure type, overlapping stents (triple stents) was not associated with favorable angiographic outcomes compared with flow diverters (OR 7.040, 95% CI 0.549 to 90.294; P=0.134), but partially thrombosed aneurysms was inversely associated with favorable angiographic outcomes (OR 0.056, 95% CI 0.005 to 0.589; P=0.016). The primary clinical outcome followed up to the last angiography did not occur in all patients.

CONCLUSION

There was no difference in safety and effectiveness between overlapping stents and flow diverters in unruptured VADAs. Further endovascular treatment studies are needed regarding the association of partially thrombosed aneurysms with unfavorable angiographic outcomes.

Endovascular Treatment of Large Proximal Basilar Artery Fenestrated Aneurysms: Overlapping Stent with Coil Embolization-A Case Report

This detailed case report presents and discusses the endovascular treatment of a large proximal basilar artery fenestrated aneurysm (PBAFA). Aneurysms occur rarely at the vertebrobasilar junction, with a moderate proportion of cases presenting fenestrations. Considering the high risk associated with posterior circulation aneurysms, including estimated rupture risk, periprocedural complications, or treatment difficulties in surgical procedures, endovascular treatment options are becoming increasingly favored, particularly considering the advancements in stent and flow diverter techniques. Our report focuses on a case of a 58-year-old male with a large unruptured PBAFA, treated using overlapping stent with coil embolization (OSCE) and triple catheter technique. This method was selected considering the size of the aneurysm, its complex vascular structure, and the risk of recurrence and complications. Our findings emphasize that a comprehensive understanding of vascular anatomy, hemodynamics, and the characteristics of endovascular treatment devices is essential for the treatment success. In addition, they demonstrate that the OSCE using low-profile visible intraluminal support devices combined with the triple catheter technique are an effective treatment option for large PBAFAs.

Multiple telescopic stenting versus single flow diverter for the treatment of vertebral artery dissecting aneurysm

OBJECTIVE

Reconstruction methods, including stent-assisted coiling, multiple telescopic stents, and flow diverters, are preferred modalities for the treatment of unruptured vertebral artery dissecting aneurysms (VADAs). We aimed to compare the clinical outcomes between two reconstructive flow diversion techniques: single flow diverter (FD) device and multiple telescopic stenting (TS).

METHODS

We retrospectively reviewed the clinical data of 39 patients with unruptured VADAs. Of these, 17 patients were treated with multiple TS and 22 with a single FD device. Aneurysm characteristics and clinical outcomes were compared between the two groups.

RESULTS

All aneurysms included in this study successfully achieved flow diversion, regardless of the treatment modality and duration. However, the mean procedure duration to complete the diversion was shorter in the FD group. Subgroup analysis in TS group showed that there were no significant clinical differences between the low-profile visualized intraluminal support and Enterprise stents, except for the mean procedure duration.

CONCLUSIONS

Both the single FD and multiple TS methods showed excellent angiographic and clinical outcomes in the treatment of unruptured VADAs. However, single FD required a shorter procedure duration and was associated with faster achievement of complete flow diversion.

Clinical and Angiographic Outcomes of Endovascular Treatment for Acute Intracranial Vertebral Artery Dissecting Aneurysms Using Double-Overlapping Stents : Low-Profile Visualized Intraluminal Support within Enterprise Stents

OBJECTIVE

The use of reconstructive treatment with a double-overlapping stents has proven to be effective and safe in the current treatment of intracranial vertebral artery dissecting aneurysms (VADAs). We employed a combination of overlapping stents, using low-profile visualized intraluminal support (LVIS) within the Enterprise stent. This combination was chosen to minimize the outward bulging of the inner LVIS by overlapping it with the Enterprise stent while maintaining flow diversion and stability. This study aimed to evaluate the clinical and angiographic outcomes following the use of double-overlapping stents with LVIS within the Enterprise stent for the treatment of VADAs.

METHODS

From March 2016 to January 2022, total 28 patients with unruptured VADAs were treated with the double-overlapping stent technique using LVIS within an Enterprise stent in our institute. The Enterprise stent was deployed first, followed by the LVIS stent. Patient clinical and angiographic characteristics, procedural complications, and follow-up outcomes were retrospectively reviewed.

RESULTS

All 28 patients (18 males and 10 females) were successfully treated with double-overlapping stent deployment. There were no procedural complications or new neurological deficits in any patient. Of the 28 patients, four VADAs had posterior inferior cerebellar artery involvement. Procedure-related parent artery occlusion did not occur during the angiographic follow-up conducted 6 to 12 months after the procedure. Out of 28 patients, 24 showed complete healing, three had focal residual stenosis or dilatation with residual sac and only one had a residual dissecting flap with aneurysm. All patients, including the four patients, did not require any additional procedures. The postoperative modified Rankin scale scores were 0-1 for all patients.

CONCLUSION

A double-overlapping stent, with a flow-diversion effect, is a safe and effective treatment for patients with VADAs. In particular, when using the LVIS stent within an Enterprise stent, it minimizes the bulging of the inner LVIS stent while maintaining flow diversion and stability. Therefore, both can be effectively utilized as overlapping stents.

Quantitative analysis of hemodynamic changes induced by the discrepancy between the sizes of the flow diverter and parent artery

The efficacy of flow diverters is influenced by the strut configuration changes resulting from size discrepancies between the stent and the parent artery. This study aimed to quantitatively analyze the impact of size discrepancies between flow diverters and parent arteries on the flow diversion effects, using computational fluid dynamics. Four silicone models with varying parent artery sizes were developed. Real flow diverters were deployed in these models to assess stent configurations at the aneurysm neck. Virtual stents were generated based on these configurations for computational fluid dynamics analysis. The changes in the reduction rate of the hemodynamic parameters were quantified to evaluate the flow diversion effect. Implanting 4.0 mm flow diverters in aneurysm models with parent artery diameters of 3.0-4.5 mm, in 0.5 mm increments, revealed that a shift from oversized to undersized flow diverters led to an increase in the reduction rates of hemodynamic parameter, accompanied by enhanced metal coverage rate and pore density. However, the flow diversion effect observed transitioning from oversizing to matching was less pronounced when moving from matching to undersizing. This emphasizes the importance of proper sizing of flow diverters, considering the benefits of undersizing and not to exceed the threshold of advantages.

Flow Diverter Performance Comparison of Different Wire Materials for Effective Intracranial Aneurysm Treatment

A flow diverter (FD) is an effective method for treating wide-necked intracranial aneurysms by inducing hemodynamic changes in aneurysms. However, the procedural technique remains challenging, and it is often not performed properly in many cases of deployment or placements. In this study, three types of FDs that changed the material of the wire were prepared within the same structure. Differences in physical properties, such as before and after delivery loading stent size, radial force, and radiopacity, were evaluated. The performances in terms of deployment and trackability force were also evaluated in a simulated model using these FDs. Furthermore, changes of deployment patterns when these FDs were applied to a 3D-printed aneurysm model were determined. The NiTi FD using only nitinol (NiTi) wire showed 100% size recovery and 42% to 45% metal coverage after loading. The low trackability force (10.9 to 22.9 gf) allows smooth movement within the delivery system. However, NiTi FD cannot be used in actual surgeries due to difficulties in X-ray identification. NiTi-Pt/W FD, a combination of NiTi wire and platinum/tungsten (Pt/W) wire, had the highest radiopacity and compression force (6.03 ± 0.29 gf) among the three FDs. However, it suffered from high trackability force (22.4 to 39.9 gf) and the end part braiding mesh tended to loosen easily, so the procedure became more challenging. The NiTi(Pt) FD using a platinum core nitinol (NiTi(Pt)) wire had similar trackability force (11.3 to 22.1 gf) to NiTi FD and uniform deployment, enhancing procedural convenience. However, concerns about low expansion force (1.79 ± 0.30 gf) and the potential for migration remained. This comparative analysis contributes to a comprehensive understanding of how different wire materials influence the performance of FDs. While this study is still in its early stages and requires further research, its development has the potential to guide clinicians and researchers in optimizing the selection and development of FDs for the effective treatment of intracranial aneurysms.

Influence of blood viscosity models and boundary conditions on the computation of hemodynamic parameters in cerebral aneurysms using computational fluid dynamics

BACKGROUND

Computational fluid dynamics (CFD) is widely used to calculate hemodynamic parameters that are known to influence cerebral aneurysms. However, the boundary conditions for CFD are chosen without any specific criteria. Our objective is to establish the recommendations for setting the analysis conditions for CFD analysis of the cerebral aneurysm.

METHOD

The plug and the Womersley flow were the inlet boundary conditions, and zero and pulsatile pressures were the outlet boundary conditions. In addition, the difference in the assumption of viscosity was analyzed with respect to the flow rate. The CFD process used in our research was validated using particle image velocimetry experiment data from Tupin et al.'s work to ensure the accuracy of the simulations.

RESULTS

It was confirmed that if the entrance length was sufficiently secured, the inlet and outlet boundary conditions did not affect the CFD results. In addition, it was observed that the difference in the hemodynamic parameter between Newtonian and non-Newtonian fluid decreased as the flow rate increased. Furthermore, it was confirmed that similar tendencies were evaluated when these recommendations were utilized in the patient-specific cerebral aneurysm models.

CONCLUSIONS

These results may help conduct standardized CFD analyses regardless of the research group.

Endovascular Management of Iatrogenic Vertebral Artery Pseudoaneurysm: A Case Report

Iatrogenic injury of the vertebral artery during cervical spine surgery though uncommon is critical. With advances in interventional endovascular techniques, the therapeutic approach for vertebral artery injuries has changed. Nonetheless, an established strategy for their management is lacking. We report a case of pseudoaneurysm due to vertebral artery injury, during cervical spine surgery for a tumor, that was treated successfully with endovascular coiling in a plug-and-patch fashion after triple stenting failed.

Flow Redirection Endoluminal Device Flow Diverter Placement for Recurrent Dolichoectatic Vertebrobasilar Artery Aneurysm Treated with Multiple Low-Profile Visualized Intraluminal Support Stents: A Case Study

Objective

We report a case of dolichoectatic vertebrobasilar aneurysms treated with multiple low-profile visualized intraluminal support (LVIS) stents followed by flow redirection endoluminal device (FRED) flow diverter to prevent the growth of the thrombosed aneurysm.

Case Presentation

A 71-year-old man developed diplopia due to oculomotor nerve palsy after 11 years of follow-up for an enlarging thrombosed dolichoectatic vertebrobasilar artery aneurysm. He initially had a fusiform thrombosed aneurysm from the right vertebral artery to the basilar artery. This lesion was tortuous and strongly compressed the pons. A total of 11 LVISs were deployed from the right posterior cerebral artery to the right vertebral artery. Six months after surgery, there was no enlargement of the thrombosed aneurysm on MRI and the contrast leakage out of the stent was markedly reduced in DSA compared to immediately after surgery. One year and seven months after surgery, contrast leakage out of the stent was increased in DSA. The FRED was placed within the overlapped LVISs, and contrast leakage was somewhat reduced. After 2 years and 7 months from the initial treatment, the contrast leakage was still observed. However, there was no enlargement of the aneurysm and no complications related to treatments were observed.

Conclusion

Treatment with multiple LVIS stents followed by FRED flow diverter treatment for dolichoectatic vertebrobasilar aneurysms (DVAs) may be one of the treatment options for controlling the growth of thrombotic aneurysms without complications, but the long-term prognosis of this case is unclear, and careful follow-up is mandatory.