Effects of stent porosity on hemodynamics in a sidewall aneurysm model

Predictors of In-Stent Stenosis Following the Implantation of Pipeline Embolization Devices for the Treatment of Aneurysms Located at or beyond the Circle of Willis in the Anterior Circulation

BACKGROUND AND PURPOSE

In-stent stenosis is commonly observed after stent implantation. There is no consensus on the contributing factors for in-stent stenosis, especially for aneurysms located at or beyond the circle of Willis in the anterior circulation. This study aimed to investigate the morbidity and determinants of in-stent stenosis in distal anterior circulation aneurysms following the implantation of Pipeline Embolization Devices.

MATERIALS AND METHODS

Patients who underwent Pipeline Embolization Device treatment at our center between January 1, 2018, and June 15, 2023, were enrolled. Distal anterior circulation aneurysms were defined as those occurring at or beyond the circle of Willis, including anterior communicating artery aneurysms, anterior cerebral artery aneurysms, and MCA aneurysms. Baseline information, aneurysm characteristics, and follow-up data of patients were analyzed. Patients were divided into 2 groups: the in-stent stenosis group (patients with a loss of >25% of the lumen diameter of the parent artery) and the non-in-stent stenosis group. Binary logistic regression and restricted cubic spline curves were used to explore risk factors.

RESULTS

We included 85 cases of 1213 patients treated with flow-diverter devices at our hospital. During an average follow-up period of 9.07 months, the complete occlusion rate was 77.64%. The overall incidence of in-stent stenosis was 36.47% (31/85), of which moderate stenosis accounted for 9.41% (8/85), and severe stenosis, 5.88% (5/85) (triglyceride-glucose index ≥ 8.95; OR = 6.883, P = .006). The difference in diameters between the stent and parent artery of ≥0.09 mm (OR = 6.534, P = .015) and 55 years of age or older (OR = 3.507, P = .036) were risk factors for in-stent stenosis. The restricted cubic spline curves indicated that the risk of in-stent stenosis increased as the difference in diameter between stent and parent artery and the triglyceride-glucose index increased.

CONCLUSIONS

Compared with the on-label use of Pipeline Embolization Devices, the rate of in-stent stenosis did not obviously increase when treating distal anterior circulation aneurysms with these devices. The incidence of in-stent stenosis was 36.47% when defined as a lumen diameter loss of >25%, and 15.2% when defined as a lumen diameter loss of >50%. Stent-size selection and biochemical indicators can potentially impact the incidence of in-stent stenosis.

Effect of the pipeline embolization device placement on branching vessels in anterior circulation: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Pipeline embolization device (PED) is widely used in intracranial aneurysms, and the scope of applications for the PED, which is frequently used to treat cerebral aneurysms, is also growing. It has some effect on branching vessels as a result of its inherent properties. The effects of PED on the complications rate and branching vessels blockage have not yet been thoroughly investigated.

OBJECTIVE

We conducted a systematic review searching reports from multiple databases on PED use for intracranial aneurysms, and analyzed the influence of PED on the occlusion rate of different branching vessels, and the influence of the amount of PED on the occlusion rate of branching vessels by meta-analysis.

METHODS

We searched the literature using PUBMED, Web of Science, and OVID databases until August 2023. Inclusion criteria were that the study used only PED, included at least 10 patients, and recorded branching vessels occlusion rates, mortality, and neurological complications.

RESULTS

Nine studies were analyzed consisting of 706 patients with 986 side branches. The results of the meta-analysis showed that application of more than one PED did not significantly elevate the rate of branching vessels occlusion compared to application of one PED (OR = 0.70; 95% CI: 0.34 to 1.43; P = 0.33). In the comparison of branching vessels occlusion rates in the anterior circulation, the anterior cerebral artery (ACA) had a significantly higher occlusion rate compared to the ophthalmic artery (OphA) (OR = 6.54; 95% CI: 3.05 to 14.01; P < 0.01), ACA also had a higher occlusion rate compared to the anterior choroidal artery (AchA) (OR = 15.44; 95% CI: 4.11 to 57.94 P < 0.01), ACA versus posterior communicating artery (PcomA) occlusion rate difference was not statistically significant (OR = 2.58; 95% CI: 0.63 to 12.82; P = 0.17), OphA versus AchA occlusion rate difference was not statistically significant (OR = 2.56; 95% CI: 0.89 to 7.38; P = 0.08), and the occlusion rate was significantly higher for PcomA compared to AchA (OR = 7.22; 95% CI: 2.49 to 20.95; P < 0.01) and lower for OphA compared to PcomA (OR = 0.33; 95% CI: 0.19 to 0.55; P < 0.01).

CONCLUSION

The meta-analysis shows that use of multiple PEDs did not significantly increase the occlusion rate of branching vessels, and the larger the diameter of branching vessels covered by PED, the higher the occlusion rate of branching vessels. However, the incidence of complications is low after branching vessels occlusion in anterior circulation, which is related to the collateral circulation compensation of the branching vessels.

Application of Dynamic Mode Decomposition to Study Temporal Flow Behavior in a Saccular Aneurysm

Aneurysms are abnormal expansion of weakened blood vessels which can cause mortality or long-term disability upon rupture. Several studies have shown that inflow conditions spatially and temporally influence aneurysm flow behavior. The objective of this investigation is to identify impact of inflow conditions on spatio-temporal flow behavior in an aneurysm using dynamic mode decomposition (DMD). For this purpose, low-frame rate velocity field measurements are performed in an idealized aneurysm model using particle image velocimetry (PIV). The inflow conditions are precisely controlled using a ViVitro SuperPump system where nondimensional fluid parameters such as peak Reynolds number (Rep) and Womersely number (α) are varied from 50-270 and 2-5, respectively. The results show the ability of DMD to identify the spatial flow structures and their frequency content. Furthermore, DMD captured the impact of inflow conditions, and change in mode shapes, amplitudes, frequency, and growth rate information is observed. The DMD low-order flow reconstruction also showed the complex interplay of flow features for each inflow scenario. Furthermore, the low-order reconstruction results provided a mathematical description of the flow behavior in the aneurysm which captured the vortex formation, evolution, and convection in detail. These results indicated that the vortical structure behavior varied with the change in α while its strength and presence of secondary structures are influenced by the change in Rep.

Application of Proper Orthogonal Decomposition to Study Coherent Flow Structures in a Saccular Aneurysm

Aneurysms are localized expansions of weakened blood vessels that can be debilitating or fatal upon rupture. Previous studies have shown that flow in an aneurysm exhibits complex flow structures that are correlated with its inflow conditions. Therefore, the objective of this study was to demonstrate the application of proper orthogonal decomposition (POD) to study the impact of different inflow conditions on energetic flow structures and their temporal behavior in an aneurysm. To achieve this objective, experiments were performed on an idealized rigid sidewall aneurysm model. A piston pump system was used for precise inflow control, i.e., peak Reynolds number (Rep) and Womersley number (α) were varied from 50 to 270 and 2 to 5, respectively. The velocity flow field measurements at the midplane location of the idealized aneurysm model were performed using particle image velocimetry (PIV). The results demonstrate the efficacy of POD in decomposing complex data, and POD was able to capture the energetic flow structures unique to each studied inflow condition. Furthermore, the time-varying coefficient results highlighted the interplay between the coefficients and their corresponding POD modes, which in turn helped explain how POD modes impact certain flow features. The low-order reconstruction results were able to capture the flow evolution and provide information on complex flow in an aneurysm. The POD and low-order reconstruction results also indicated that vortex formation, evolution, and convection varied with an increase in α, while vortex strength and formation of secondary structures were correlated with an increase in Rep.

Endovascular Treatment of Anterior Circulation Aneurysms With the p64 Flow Modulation Device: Mid- and Long-Term Results in 617 Aneurysms From a Single Center

BACKGROUND

Flow diverters have become an important tool in the treatment of intracranial aneurysms, especially when dealing with difficult-to-treat or complex aneurysms. The p64 is the only fully resheathable and mechanically detachable flow diverter available for clinical use.

OBJECTIVE

To evaluate the safety and effectiveness of p64 for the treatment of intracranial saccular unruptured aneurysms arising from the anterior circulation over a long-term follow-up period.

METHODS

We retrospectively reviewed our prospectively maintained database to identify all patients who underwent treatment for an intracranial saccular (unruptured or beyond the acute hemorrhage phase) aneurysm arising from the anterior circulation with ≥1 p64 between December 2011 and December 2019. Fusiform aneurysms and dissections were excluded. Aneurysms with prior or concomitant saccular treatment (eg, coiling and clipping) were included. Aneurysms with parent vessel implants other than p64 were excluded. Anatomic features, intraprocedural complications, clinical outcome, as well as clinical and angiographic follow-ups were all recorded.

RESULTS

In total, 530 patients (388 females; median age 55.9 yr) with 617 intracranial aneurysms met the inclusion criteria. The average number of devices used per aneurysm was 1.1 (range 1-3). Mean aneurysm dome size was 4.8 mm (range 1-27 mm). Treatment-related morbimortality was 2.4%. Early, mid-term, and long-term angiographic follow-up showed complete or near-complete aneurysm occlusion in 76.8%, 89.7%, and 94.5%, respectively.

CONCLUSION

Treatment of intracranial saccular unruptured aneurysms of the anterior circulation using p64 is a safe and effective treatment option with high rate of occlusion at long-term follow-up and low morbimortality.

Particle Image Velocimetry Measurements of the Flow-Diverting Effects of a New Generation of the eCLIPs Implant for the Treatment of Intracranial Bifurcation Aneurysms

Flow diverters (FDs) for the endovascular treatment of intracranial aneurysms are effective for sidewall aneurysms, but their use at a bifurcation is problematic because FDs only partially cover the aneurysm neck and impede flow into a daughter branch; they are thus not employed routinely in this anatomy. eCLIPs was developed as a non-tubular implant to completely cover the neck of an aneurysm and serve as a coil retention device necessary for the adequate treatment of wide-neck bifurcation aneurysms. eCLIPs has shown some flow diversion effects in bifurcation anatomy but not equal to those exhibited by clinically accepted flow diverters in sidewall anatomy. A new generation of eCLIPs implant, the eCLIPs bifurcation flow diverter (eBFD), with higher metal coverage, was developed to achieve a similar flow diversion as a Pipeline Embolization Device (PED), a prototypical FD. Particle image velocimetry was used to capture the fluid dynamics and velocity reduction within silicone aneurysm replicas. A circulatory mimicking loop was developed to circulate the flow through the silicone models. All generations of eCLIPs implants had some flow-diverting effect, with increasing metal coverage density of the implant proportionately increasing the flow diversion effect. The eBFD, with a metal density of 35%, showed greater flow diversion than PED, with 30% metal density, for bifurcation anatomy. The eBFD showed similar reduction of flow in a bifurcation anatomy to PED in a sidewall, both sufficient to permit early thrombosis of the aneurysm. Thus, the eBFD can potentially provide sufficient flow diversion for the treatment of bifurcation aneurysms to avoid adjunctive coiling.

Optimization of porous stents for endovascular repair of abdominal aortic aneurysms

This study presents a simulation-based methodology to design porous stents to induce suitable hemodynamic environments inside abdominal aortic aneurysm (AAA) sacs. In the proposed methodology, an optimization algorithm iteratively modifies the porosity distribution of the stent and executes a computational fluid dynamics (CFD) simulation to determine the effect of these changes on the hemodynamic conditions inside the aneurysm sac. The optimization iterations proceed until relevant hemodynamic parameters are within ranges prescribed a priori by the user as desirable to control the progression of the AAA. The resulting porosity distribution uniquely describes the porous stent design that can control the hemodynamic environment (eg, shear stress at the aneurysm wall, pressure distribution, residence time), reducing AAA rupture risks and improving treatment efficacy. To demonstrate its potential, the proposed methodology is applied to idealized AAA geometry under steady-state flow conditions, though it may be easily applied to more complex AAA geometries under transient, pulsatile flow conditions. The proposed methodology has the potential to enable the design of a new generation of porous stents tailored to patient-specific geometries and flow conditions, to improve patient outcomes.

Treatment of High Surgical Risk Thoracoabdominal Aortic Aneurysms with Stent Graft and Multilayer Bare Stents Joint Technique: Mid-Long-Term Clinical Results

BACKGROUND

This study aims to present the performance data on stent-graft and multilayer bare stents (MBS) joint technique in the treatment of high-risk thoracoabdominal aortic aneurysm (TAAA).

METHODS

From May 2012 to December 2015, 8 selective TAAA cases (ages 46-75 years) ineligible for surgical repair underwent the stent-graft and MBS joint procedure, and were closely followed up for a median of 32 months (range 14-58). Using computed tomography images, the aneurysm size, luminal blood flow diameter, and the covered visceral branches were analyzed.

RESULTS

Technical success was achieved in all patients (100%, 8/8). Twenty-four visceral branches were covered by MBS in total. There was no complication or death during hospital stay. During follow-up period, no death or complication occurred. Aneurysm shrinkage (maximum diameter decrease ≥5 mm) was observed in 7 patients. No aneurysm expansion was observed. Total aneurysm sac thrombosis was observed in all patients. The majority of covered side branches (23/24) were successfully preserved. No visceral ischemia or bleeding complications was observed during follow-up.

CONCLUSIONS

Total endovascular repair of TAAA using stent-graft and MBS joint technique may be a safe and effective alternative in high surgical risk patients. More approving clinical evidences about the safety and efficacy of this procedure are anticipated.

A Rare Case of Jejunal Pseudoaneurysm Presenting as Acute Small Bowel Obstruction After Blunt Trauma: Discussion, Management Dilemmas, and a Review of Relevant Literature

 Visceral artery aneurysms (VAAs) and visceral artery pseudoaneurysms (VAPAs) are often found incidentally through imaging of a patient presenting with vague symptoms of abdominal pain, hematochezia, hematemesis, and melena. Due to the asymptomatic nature, the etiology is often unknown. However, suspicion for VAA and VAPA should remain high for those presenting with symptoms listed above after trauma or pancreatitis. Here we discuss a case of traumatic ileocolic pseudoaneurysm that has only been discussed a handful of times in the literature.

Hemodynamic Performance of Multilayer Stents in the Treatment of Aneurysms with a Branch Attached

Although multilayer stents (MSs) can be used to treat aneurysm effectively, for some aneurysms with branches attached, the hemodynamic mechanisms are still unclear. In this work, we modeled five cases that involve 1-4-layer stents implanted in aneurysms with side branches, and the numerical approach was used. Case 1 corresponds to an aneurysm without a stent, and cases 2-5 represent 1-4-layer stents being employed within aneurysms, respectively. The results showed that the velocity within the sac declined dramatically and the eddies' intensity weakened with increased number of stent layers, time-averaged wall shear stress (TAWSS), and nitric oxide production rate (TARNO) dropped linearly with increase in stent porosity, and oscillatory shear index (OSI) and relative residence time (RRT) increased evidently with MS intervention. Moreover, the MSs had a slight effect on the patency of the side branch; its flow rate was still above the normal case than without aneurysm. It can be concluded that MSs are helpful in promoting the growth of thrombus within the aneurysm through an isolated hemodynamic environment and keeping the branch unobstructed, but more clinical evidences are required.

A Study on the Pressure-Lowering Effect of the Multilayer Stent

BACKGROUND

The objective of the study was to investigate the hemodynamic changes of the blood flow in the aneurysm model after the multilayer stent placement using the fluid dynamic method, to analyze the effectiveness and properties of the multilayer stent in the treatment of aortic aneurysms.

METHODS

A water tank was filled with 5 L of experimental liquid after the circular flow pressure test platform with a glass aneurysm model, and a multilayer stent was built. Pressure at the middle part and the distal aneurysm neck part of the model was then measured. At each site, the pressure was measured 20 times at 1-min intervals, and the testing results were averaged for accuracy.

RESULTS

Without the stent, mean pressure at the middle part and at the distal aneurysm neck part of the model was 11.19 ± 0.23 Kpa and 13.31 ± 0.28 Kpa, respectively. With the stent, the mean pressure decreased to 10.60 ± 0.27 Kpa and 12.60 ± 0.29 Kpa, and the average difference was 0.59 ± 0.15 Kpa and 0.71 ± 0.15 Kpa, respectively.

CONCLUSIONS

After the placement of the multilayer stent, pressure inside the model at the middle part and distal neck part could both be diminished, yet the mean dropped pressure may be too small to be sufficient to cause significant impact on preventing the expansion of abdominal aortic aneurysm; therefore, the pressure-lowering effect of the multilayer stent for abdominal aortic aneurysm may not be ideal compared with the traditional covered stents.

Endovascular Metal Devices for the Treatment of Cerebrovascular Diseases

Cerebrovascular disease involves various medical disorders that obstruct brain blood vessels or deteriorate cerebral circulation, resulting in ischemic or hemorrhagic stroke. Nowadays, platinum coils with or without biological modification have become routine embolization devices to reduce the risk of cerebral aneurysm bleeding. Additionally, many intracranial stents, flow diverters, and stent retrievers have been invented with uniquely designed structures. To accelerate the translation of these devices into clinical usage, an in-depth understanding of the mechanical and material performance of these metal-based devices is critical. However, considering the more distal location and tortuous anatomic characteristics of cerebral arteries, present devices still risk failing to arrive at target lesions. Consequently, more flexible endovascular devices and novel designs are under urgent demand to overcome the deficiencies of existing devices. Herein, the pros and cons of the current structural designs are discussed when these devices are applied to the treatment of diseases ranging broadly from hemorrhages to ischemic strokes, in order to encourage further development of such kind of devices and investigation of their use in the clinic. Moreover, novel biodegradable materials and drug elution techniques, and the design, safety, and efficacy of personalized devices for further clinical applications in cerebral vasculature are discussed.

Bailout Strategies and Complications Associated with the Use of Flow-Diverting Stents for Treating Intracranial Aneurysms

Background

Flow-diverting stents (FDS) have revolutionized the endovascular management of unruptured, complex, wide-necked, and giant aneurysms. There is no consensus on management of complications associated with the placement of these devices. This review focuses on the management of complications of FDS for the treatment of intracranial aneurysms.

Summary

We performed a systematic, qualitative review using electronic databases MEDLINE and Google Scholar. Complications of FDS placement generally occur during the perioperative period.

Key Message

Complications associated with FDS may be divided into periprocedural complications, immediate postprocedural complications, and delayed complications. We sought to review these complications and novel management strategies that have been reported in the literature.

The Effect of Stents in Cerebral Aneurysms: A Review

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

Hemodynamic Changes Caused by Multiple Stenting in Vertebral Artery Fusiform Aneurysms: A Patient-Specific Computational Fluid Dynamics Study

BACKGROUND AND PURPOSE

The multiple stent placement technique has largely improved the long-term outcomes of intracranial fusiform aneurysms, but the hemodynamic mechanisms remain unclear. In this study, we analyzed the hemodynamic changes caused by different stent-placement strategies in patient-specific models using the computational fluid dynamics technique, aiming to provide evidence for clinical decision-making.

MATERIALS AND METHODS

Ten vertebral artery fusiform aneurysms were included, and their patient-specific computational fluid dynamics models were reconstructed. A fast virtual stent placement technique was used to simulate sequential multiple stent placements (from a single stent to triple stents) in the vertebral artery fusiform aneurysm models. Hemodynamic parameters, including wall shear stress, pressure, oscillatory shear index, relative residence time, and flow pattern, were calculated and compared among groups with different numbers of stents.

RESULTS

Virtual stents were deployed in all 10 cases successfully, consistent with the real stent configuration. Wall shear stress decreased progressively by 7.2%, 20.6%, and 25.8% as the number of stents increased. Meanwhile, relative residence time and pressure increased on average by 11.3%, 15.4%, and 45.0% and by 15.7%, 21.5%, and 28.2%. The oscillatory shear index showed no stable variation trend. Flow patterns improved by weakening the intensity of the vortices and displacing the vortex center from the aneurysmal wall.

CONCLUSIONS

Stent placement modifies hemodynamic patterns in vertebral artery fusiform aneurysms, which might favor thrombosis formation in the aneurysmal sac. This effect is amplified with the number of stents deployed. However, a potential risk of rupture or recanalization exists and should be considered when planning to use the multiple stent placement technique in vertebral artery fusiform aneurysms.

Alterations of blood flow pattern after triple stent endovascular treatment of saccular abdominal aortic aneurysm: a porcine model

OBJECTIVE

to determine the blood flow pattern changes after endovascular treatment of saccular abdominal aortic aneurysm with triple stent.

METHODS

we conducted a hemodynamic study of seven Landrace and Large White pigs with saccular aneurysms of the infrarenal abdominal aorta artificially produced according to the technique described. The animals were subjected to triple stenting for endovascular aneurysm. We evaluated the pattern of blood flow by duplex scan before and after stent implantation. We used the non-paired Mann-Whitney test for statistical analysis.

RESULTS

there was a significant decrease in the average systolic velocity, from 127.4cm/s in the pre-stent period to 69.81cm/s in the post-stent phase. There was also change in the flow pattern from turbulent in the aneurysmal sac to laminate intra-stent.

CONCLUSION

there were changes in the blood flow pattern of saccular abdominal aortic aneurysm after endovascular treatment with triple stent.

OBJETIVO

determinar as alterações do padrão do fluxo sanguíneo após tratamento endovascular do aneurisma sacular de aorta abdominal com triplo stent.

MÉTODOS

estudo hemodinâmico de sete suínos das raças Landrace e Large White portadores de aneurismas saculares de aorta abdominal infrarrenal artificialmente produzidos segundo técnica descrita. Os animais foram submetidos a implante de triplo stent para correção endovascular do aneurisma e reavaliados por duplex scan quanto ao padrão do fluxo sanguíneo antes e após o implante dos stents. A análise estatística foi realizada com o teste Mann-Whitney não pareado.

RESULTADOS

verificou-se uma queda significativa da velocidade sistólica média de 127,4cm/s na fase pré-stent para 69,81cm/s na fase pós-stent. Houve ainda mudança no padrão do fluxo de turbilhonar no saco aneurismático para laminar intrastent.

CONCLUSÃO

o estudo demonstrou alterações do padrão do fluxo sanguíneo do aneurisma sacular de aorta abdominal após tratamento endovascular com triplo stent.

PID controller design to generate pulsatile flow rate for in vitro experimental studies of physiological flows

Producing accurate pulsatile flow rates is essential for many in vitro experimental studies in biofluid dynamics research. A controller system was developed to control a flow loop to produce easily adjustable pulsatile flow rates with sufficient accuracy. An Arduino board is used as a micro-controller to control a pump to produce various pulsatile flow rates, and an open-source proportional-integral-derivative (PID) control algorithm is developed for this purpose. Four non-trivial pulsatile waveforms were produced by the PID controller, as well as an iterative controller, and the performance of both controllers was evaluated. Both the PID and iterative controllers were able to successfully produce slowly-varying signals (single and multi-harmonic low frequency sine waves), but for high frequency signals where the flow has strong acceleration/deceleration (e.g. for physiological waveforms) the iterative controller exhibited significant undershoot. The comparison of PID and iterative controllers suggests that if the desired flow rate is a low frequency, simple waveform then the iterative controller is preferred due to simplicity of implementation. However, if the desired signal is rapidly changing and more complicated then the PID controller achieves better results. This system can be implemented in many flow loops due to its simplicity and low cost, and does not require a mathematical model of the system.

Influence of overlapping pattern of multiple overlapping uncovered stents on the local mechanical environment: A patient-specific parameter study

BACKGROUND

Multiple overlapping uncovered stents (MOUS) system has shown potentials in managing complex aortic aneurysms with side branches involvement. It promotes the development of thrombus by modulating local flow pattern that reduces the wall tension, while maintaining patency of side branches. However the modulation of local hemodynamic parameters depends on various factors that have not been assessed comprehensively.

METHODS

Aneurysm 3D geometry was reconstructed based on CT images. One-way fluid-structure interaction analysis was performed to quantify structural stress concentration in the wall, and changes of blood velocity, wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT) and pressure in the sac due to the stent deployment.

RESULTS

High structural stress concentration due to stent deployment was found in the landing zone and it increased linearly with the number of stents deployed. The wall tension in the sac was unaffected by the stent deployment. Stress within the wall was insensitive to the different overlapping pattern. After one stent was deployed, the mean flow velocity in the sac reduced by 36.4%. The deployment of the 2nd stent further reduced the mean sac velocity by 10%. WSS decreased while both OSI and RRT increased after stent deployment, however pressure in the sac remained nearly unchanged. Except for the cases with complete stents struts alignment, different overlapping pattern had little effect on flow parameters.

CONCLUSIONS

Mechanical parameters modulated by the MOUS are insensitive to different overlapping pattern suggesting that endovascular procedure can be performed with less attention to the overlapping pattern.

Intraoperative Computed Tomography (CT) for Treating Giant Carotid Intracavernous Aneurysms

Background

Giant carotid intracavernous aneurysm refers to those lesions larger than 2.5 cm and derived from a cavernous segment, accounting for about 30% of all intracranial tumors. Dynamic CT perfusion imaging (PCT) is a common method recently employed to evaluate cerebral perfusion. This study investigated the efficacy and clinical application of intraoperative CT in the surgery for giant symptomatic carotid intracavernous aneurysm.

Material/Methods

A retrospective analysis was performed on 23 cases with giant symptomatic carotid intracavernous aneurysm. BTO testing was performed before surgery. Differential treatments were performed based on the condition of aneurysm, and some patients received intraoperative PCT. Postoperative anti-coagulation was given with DSA or CTA follow-up examinations at 3–6 months, 1 year, and 2 years after surgery.

Results

A total of 17 patients received aneurysm isolation coupled with high-flow bypass surgery. Among those, 9 developed early-onset neurological function after surgery, with gradual recover within 6 months. One coma patient died 25 months after discharge. One patient had aneurysm isolation with clapping of anterior communicating artery, and the other 5 cases received artery clapping only. In those patients, 4 had improvement at early phase, while 1 patient had numbness of the oculomotor nerve. Six patients received surgery in the CT room, including 5 cases with single proximal ligation of the internal carotid artery plus 1 aneurysm isolation combined with high-flow bypass surgery.

Conclusions

Intraoperative PCT can provide objective evidence and effective evaluation of cerebral perfusion.

In vitro digital subtraction angiographic evaluation of flow diverters in a patient-specific aneurysm

Background The importance of both porosity and pore density of a flow diverter is well recognized in treatment of intracranial aneurysms; however, understanding of the effect of individual wire (wire number and size) is critical in improving device design and use. Methods A total of 10 multi-layered flow diverters with different wire numbers (32, 48, 56, and 72) and sizes (30, 35, and 40 µm) were implanted into identical patient-specific middle cerebral artery aneurysm models. Digital subtraction angiography was acquired at 30 f/s and X-ray signals at three selected regions of interest were compared to determine the amount of intra-aneurysmal flow. Results Flow reduction ranged from 19% for a high porosity (82%) and low pore density (5 pores/mm²) to nearly 80% for a low porosity (49%) and high pore density (36 pores/mm²). An increase in the wire number from 32 to 72 lowers intra-aneurysmal flow and redirects the flow jet; however, the effect of wire size is not observed. Conclusions In our in vitro angiographic study, flow jet is influenced by the wire number in a device qualitatively; quantitatively, intra-aneurysmal flow is affected by both the porosity and pore density. A 2.5 mm device performs better in flow diversion of a middle cerebral artery (MCA) aneurysm than a 3 mm device with the same wire size and wire number, but thicker wires do not lead to better flow diversion.

Virtual endovascular treatment of intracranial aneurysms: models and uncertainty

Virtual endovascular treatment models (VETMs) have been developed with the view to aid interventional neuroradiologists and neurosurgeons to pre-operatively analyze the comparative efficacy and safety of endovascular treatments for intracranial aneurysms. Based on the current state of VETMs in aneurysm rupture risk stratification and in patient-specific prediction of treatment outcomes, we argue there is a need to go beyond personalized biomechanical flow modeling assuming deterministic parameters and error-free measurements. The mechanobiological effects associated with blood clot formation are important factors in therapeutic decision making and models of post-treatment intra-aneurysmal biology and biochemistry should be linked to the purely hemodynamic models to improve the predictive power of current VETMs. The influence of model and parameter uncertainties associated to each component of a VETM is, where feasible, quantified via a random-effects meta-analysis of the literature. This allows estimating the pooled effect size of these uncertainties on aneurysmal wall shear stress. From such meta-analyses, two main sources of uncertainty emerge where research efforts have so far been limited: (1) vascular wall distensibility, and (2) intra/intersubject systemic flow variations. In the future, we suggest that current deterministic computational simulations need to be extended with strategies for uncertainty mitigation, uncertainty exploration, and sensitivity reduction techniques. WIREs Syst Biol Med 2017, 9:e1385. doi: 10.1002/wsbm.1385 For further resources related to this article, please visit the WIREs website.

Flow Diversion for Intracranial Aneurysm Management: A New Standard of Care

Endovascular treatment of intracranial aneurysms with complex morphologies such as giant, wide-necked, or fusiform aneurysms is challenging. Stent-assisted coiling and balloon-assisted coiling are alternative techniques to treat such complex aneurysms, but studies have shown less-than-expected efficacy, as suggested by their high rate of recanalization. The management of complex aneurysms via microsurgery or conventional neuroendovascular strategies has traditionally been poor. However, over the last few years, flow-diverting stents (FDS) have revolutionized the treatment of such aneurysms. FDS are implanted within the parent artery rather than the aneurysm sac. By modifying intra-aneurysmal and parent-vessel flow dynamics at the aneurysm/parent vessel interface, FDS trigger a cascade of gradual intra-aneurysmal thrombosis. As endothelialization of the FDS is complete, the parent vessel reconstructs while preserving the patency of normal perforators and side branch vessels. As with any intervention, the practice and application of flow-diversion technology is inherent, with risks that include vessel rupture or perforation, in-stent thrombosis, perforator occlusion, procedural and delayed hemorrhages, and perianeurysmal edema. Herein, we review the devices, their mechanisms of actions, clinical applications, complications, and ongoing studies.

The expanding realm of endovascular neurosurgery: flow diversion for cerebral aneurysm management

The worldwide prevalence of intracranial aneurysms is estimated to be between 5% and 10%, with some demographic variance. Subarachnoid hemorrhage secondary to ruptured intracranial aneurysm results in devastating neurological outcomes, leaving the majority of victims dead or disabled. Surgical clipping of intracranial aneurysms remained the definitive mode of treatment until Guglielmi detachable coils were introduced in the 1990s. This revolutionary innovation led to the recognition of neurointervention/neuroendovascular surgery as a bona fide option for intracranial aneurysms. Constant evolution of endovascular devices and techniques supported by several prospective randomized trials has catapulted the endovascular treatment of intracranial aneurysms to its current status as the preferred treatment modality for most ruptured and unruptured intracranial aneurysms. We are slowly transitioning from the era of coils to the era of flow diverters. Flow-diversion technology and techniques have revolutionized the treatment of wide-necked, giant, and fusiform aneurysms, where the results of microsurgery or conventional neuroendovascular strategies have traditionally been dismal. Although the Pipeline Embolization Device (ev3-Covidien, Irvine, CA) is the only flow-diversion device approved by the Food and Drug Administration for use in the United States, others are commercially available in Europe and South America, including the Silk (Balt Extrusion, Montmorency, France), Flow-Redirection Endoluminal Device (FRED; MicroVention, Tustin, CA), Surpass (Stryker, Kalamazoo, MI), and p64 (Phenox, Bochum, Germany). Improvements in technology and operator experience and the encouraging results of clinical trials have led to broader acceptance for the use of these devices in cerebral aneurysm management. Continued innovation and refinement of endovascular devices and techniques will inevitably improve technical success rates, reduce procedure-related complications, and broaden the endovascular therapeutic spectrum for varied aneurysm morphology.

Combined Effects of Flow Diverting Strategies and Parent Artery Curvature on Aneurysmal Hemodynamics: A CFD Study

PURPOSE

Flow diverters (FD) are increasingly being considered for treating large or giant wide-neck aneurysms. Clinical outcome is highly variable and depends on the type of aneurysm, the flow diverting device and treatment strategies. The objective of this study was to analyze the effect of different flow diverting strategies together with parent artery curvature variations on altering intra-aneurysmal hemodynamics.

METHODS

Four ideal intracranial aneurysm models with different parent artery curvature were constructed. Computational fluid dynamics (CFD) simulations of the hemodynamics before and after applying five types of flow diverting strategies (single FD, single FD with 5% and 10% packing density of coils, two FDs with 25% and 50% overlapping rate) were performed. Changes in pressure, wall shear stress (WSS), relative residence time (RRT), inflow velocity and inflow volume rate were calculated and compared.

RESULTS

Each flow diverting strategy resulted in enhancement of RRT and reduction of normalized mean WSS, inflow volume rate and inflow velocity in various levels. Among them, 50% overlapped FD induced most effective hemodynamic changes in RRT and inflow volume rate. The mean pressure only slightly decreased after treatment. Regardless of the kind of implantation of FD, the mean pressure, inflow volume rate and inflow velocity increased and the RRT decreased as the curvature of the parent artery increased.

CONCLUSIONS

Of all flow diverting strategies, overlapping FDs induced most favorable hemodynamic changes. Hemodynamics alterations post treatment were substantially influenced by parent artery curvature. Our results indicate the need of an individualized flow diverting strategy that is tailored for a specific aneurysm.

Computational Fluid Dynamics Study of Bifurcation Aneurysms Treated with Pipeline Embolization Device: Side Branch Diameter Study

An intracranial aneurysm, abnormal swelling of the cerebral artery, may lead to undesirable rates of mortality and morbidity upon rupture. Endovascular treatment involves the deployment of a flow-diverting stent that covers the aneurysm orifice, thereby reducing the blood flow into the aneurysm and mitigating the risk of rupture. In this study, computational fluid dynamics analysis is performed on a bifurcation model to investigate the change in hemodynamics with various side branch diameters. The condition after the deployment of a pipeline embolization device is also simulated. Hemodynamic factors such as flow velocity, pressure, and wall shear stress are studied. Aneurysms with a larger side branch vessel might have greater risk after treatment in terms of hemodynamics. Although a stent could lead to flow reduction entering the aneurysm, it would drastically alter the flow rate inside the side branch vessel. This may result in side-branch hypoperfusion subsequent to stenting. In addition, two patient-specific bifurcation aneurysms are tested, and the results show good agreement with the idealized models. Furthermore, the peripheral resistance of downstream vessels is investigated by varying the outlet pressure conditions. This quantitative analysis can assist in treatment planning and therapeutic decision-making.

Repression of wall shear stress inside cerebral aneurysm at bifurcation of anterior cerebral artery by stents

The effect of a simple bare metal stent on repression of wall shear stress inside a model cerebral aneurysm was experimentally investigated by two-dimensional particle image velocimetry in vitro. The flow model simulated a cerebral aneurysm induced at the apex of bifurcation between the anterior cerebral artery and the anterior communicating artery. Wall shear stress was investigated using both stented and non-stented models to assess the simple stent characteristics. The flow behavior inside the stented aneurysm sac was unusual and wall shear stress was much smaller inside the aneurysm sac. Stent placement effectively repressed the temporal and spatial variations and the magnitude of wall shear stress. Hence, there is an effective possibility that would retard the progress of cerebral aneurysms by even simple stent.

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

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

Management of complicated aortic aneurysms using multiple overlapping uncovered stents: mid-term outcome from a cohort study

This study sought to report the mid-term outcome of a modified flow-diverting strategy in the treatment of complicated aortic aneurysms of different morphology. Historical data suggested aortic aneurysm expansion and rupture after endovascular treatment with current commercial flow-diverters, indicating the essentiality of further investigation of this technique prior to its large-scale clinical application. An alternative flow-diverting strategy using layer-by-layer assembled multiple overlapping uncovered stents was employed in this study. The treatment outcome in aneurysms of different morphology (saccular, fusiform, and dissecting) was assessed during a mid-term follow-up period.Of 42 patients enrolled in this study (30 male, mean age: 63.3 years), technical success was achieved in 40 cases. During an average follow-up period of 20.9 months, mean aneurysm diameter shrunk from 53.4 ± 13.6 mm to 48.8 ± 13.9 mm (P < 0.001), while stent-induced sac thrombosis ratio increased significantly (18.1 ± 14.9% to 93.6 ± 9.5%, P < 0.001). The majority of side branches (74/76 major visceral branches, 237/244 minor segmental arteries), covered by 3.3 stents on average, maintained their patency after stenting. Saccular aneurysms manifested the highest thrombus deposition speed (18/20 were totally thrombosed within 12 months) and most significant shrinkage (51.4 ± 13.3 mm pre-operatively vs 43.5 ± 10.2 mm during follow-up, P < 0.001) compared with fusiform and dissecting aneurysms. This modified flow-diverting strategy could be a feasible alternative in the management of complicated aortic aneurysms where vital branches need to be preserved. The treatment outcome may depend on the aneurysm type. Further studies with larger patient cohort and longer follow-up are required to substantiate these results.

Small pipes: preliminary experience with 3-mm or smaller pipeline flow-diverting stents for aneurysm repair prior to regulatory approval

Flow diversion has become an established treatment option for challenging intracranial aneurysms. The use of small devices of ≤3-mm diameter remains unapproved by major regulatory bodies. A retrospective review of patients treated with Pipeline Embolization Devices of ≤3-mm diameter at 3 Canadian institutions was conducted. Clinical and radiologic follow-up data were collected and reported. Twelve cases were treated with ≥1 Pipeline Embolization Device of ≤3-mm diameter, including 2 with adjunctive coiling, with a median follow-up of 18 months (range, 4-42 months). One patient experienced a posttreatment minor complication (8%) due to an embolic infarct. No posttreatment hemorrhage or delayed complications such as in-stent stenosis/thrombosis were observed. Radiologic occlusion was seen in 9/12 cases (75%) and near-occlusion in 2/12 cases (17%). Intracranial aneurysm treatment with small-diameter flow-diverting stents provided safe and effective aneurysm closure in this small selected sample. These devices should be further studied and considered for regulatory approval.

Cerebrovascular neurosurgery in evolution: the endovascular paradigm

Endovascular technique represents an important, minimally invasive approach to treating cerebrovascular disease. In this article, we discuss the origins of endovascular neurosurgery as a discipline in the context of important technical milestones, evidence-based medicine, and future cerebrovascular neurosurgical training. Cerebrovascular neurosurgery has seen a steady, convergent evolution toward the surgeon capable of seamless incorporation of open and endovascular approaches to any complex vascular disease affecting the central nervous system. Neurosurgery must assume the leadership role in the multidisciplinary neurovascular team.

Multiple overlapping uncovered stents as an alternative flow-diverting strategy in the management of peripheral and visceral aneurysms

OBJECTIVE

In this study we aimed to report on the midterm outcome of multiple overlapping uncovered stents in the treatment of peripheral and visceral aneurysms, and analyze the possible factors affecting the treatment efficacy.

METHODS

Data of patients who were regularly followed up over 24 months were retrospectively reviewed. Descriptive statistics were applied to present aneurysm thrombosis process and diameter change at each follow-up point, and a comparison with the baseline level was performed. Patients were divided into a totally thrombosed (TT) group and a residual perfusion (RP) group according to the sac thrombosis ratio (thrombus volume to sac volume ratio) at 3, 6, and 12 months of follow-up. Aneurysm shrinkage in the two groups was compared to explore the effect of the initial RP on the treatment outcome. Patients were also grouped based on their aneurysm morphology (saccular/fusiform). The aneurysm sac thrombosis speed (time to thrombosis) and diameter decrease (DD) ratio (percentage of DD) were compared between the two groups to understand the influence of aneurysm shape on the treatment efficacy.

RESULTS

Of the 64 patients treated, the initial 37 patients (25 male; average age, 55.5 ± 13.0 years) were enrolled into this study. Technical success rate was 100%. All patients were regularly followed up. At 24 months, 94.6% aneurysms (35/37) were TT, and the maximum aneurysm diameter decreased from 36.5 ± 9.7 mm preoperatively to 23.6 ± 7.7 mm (P < .001). Overall clinical success rate (complete thrombosis and shrinkage/stabilization of the aneurysm without aneurysm-related mortality) reached 94.6% in the study cohort. Most side branches (31/33) covered by the bare stent stayed patent during follow-up. Initial sac RP at 3, 6, and 12 months might not fully affect the final aneurysm DD ratio (TT group: 0.37 ± 0.09, 0.35 ± 0.09, and 0.35 ± 0.09; compared with the RP group: 0.33 ± 0.09, 0.36 ± 0.11, and 0.36 ± 0.13; P = .153, .964, and .418, respectively). At 3 and 6 months follow-up, saccular aneurysms (n = 29) seemed to have a faster thrombosis speed compared with fusiform aneurysms (78.1 ± 26.8% and 83.9 ± 21.8% vs 47.0 ± 24.4% and 63.9 ± 22.6%; P = .004 and .013, respectively), but there was no significant difference in aneurysm shrinkage ratio at 24 months between the two groups (0.36 ± 0.10 vs 0.33 ± 0.06; P = .357).

CONCLUSIONS

Multiple overlapping uncovered stents could be a feasible option for the endovascular treatment of peripheral and visceral aneurysms. Neither the aneurysm shape nor the initial sac RP would affect the midterm treatment outcome. Further validation of this technique is required to substantiate these results.

Hemodynamic impact of cerebral aneurysm endovascular treatment devices: coils and flow diverters

Coils and flow diverters or stents are devices successfully used to treat cerebral aneurysms. Treatment aims to reduce intra-aneurysmal flow, thereby separating the aneurysmal sac from the blood circulation. The focus and this manuscript combining literature review and our original research is an analysis of changes in aneurysmal hemodynamics caused by endovascular treatment devices. Knowledge of post-treatment hemodynamics is a path to successful long-term treatment. Summarizing findings on hemodynamic impact of treatment devices, we conclude: coiling and stenting do not affect post-treatment intra-aneurysmal pressure, but significantly alter aneurysmal hemodynamics through flow reduction and a change in flow structure. The impact of treatment devices on aneurysmal flow depends, however, on a set of parameters including device geometry, course of placement, parent vessel and aneurysm geometry.

Advances in Endovascular Approaches to Cerebral Aneurysms

Recent advancements in all phases of endovascular aneurysm treatment, including medical therapy, diagnostics, devices, and implants, abound. Advancements in endovascular technologies and techniques have enabled treatment of a wide variety of intracranial aneurysms. In this article, technical advances in endovascular treatment of cerebral aneurysms are discussed, with an effort to incorporate a clinically relevant perspective. Advancements in diagnostic tools, medical therapy, and implants are reviewed and discussed.

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

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

[Flow diverter: a new therapy option for intracranial aneurysms]

The principle of flow diversion is the newest endovascular concept for the treatment of intracranial aneurysms. These flow-diverting devices have a narrow mesh system and lead to aneurysm occlusion by reconstructing the vessel wall and by changing the hemodynamic blood flow within the aneurysm. The aim of flow diverting devices is the treatment of complex intracranial aneurysms, such as wide-necked, fusiform and giant aneurysms, which in the past could only be treated interventionally with a relatively high risk. The purpose of this article is to give an overview of this new alternative in the treatment of intracranial aneurysms.

Sole stenting technique for the treatment of uncoilable very small aneurysms in the intracranial internal carotid artery

The treatment of very small aneurysms with diameter of less than 3 mm remains a challenge for both endovascular and surgical treatment. Endovascular treatment of these lesions may be difficult and is associated with a high risk of complications because of their small size. The present study evaluated the safety, feasibility, and efficacy of the endovascular treatment using sole stenting technique for uncoilable very small aneurysms of the intracranial internal carotid artery (ICA). From August 2004 through January 2010, eight very small aneurysms of intracranial ICA in eight patients were treated with endovascular sole stenting technique. All very small aneurysms were ruptured (n = 3) or aneurysms associated with another ruptured (n = 2) and unruptured aneurysms (n = 3) in the same artery. Stents were Neuroform and balloon expandable coronary stents. Stent deployment was carried out without difficulty in all patients. Single stent deployment was done for six aneurysms, and double stents in two aneurysms. The immediate angiographic results were partial occlusion in one case and no occlusion in seven cases. One direct carotid-cavernous fistula occurred during coronary stenting without permanent neurological deficit. No neurological deterioration or hemorrhagic complication was seen during the follow-up period in seven patients. Follow-up angiography (mean 9 months) was available in six patients and revealed complete occlusion in four and no occlusion in two cases. Sole stenting technique may be a feasible and effective therapeutic alternative for uncoilable very small aneurysms. The long-term efficacy and durability of stenting for these lesions remains to be determined in a large series.