Simple measurement of aneurysm residual after treatment: the SMART scale for evaluation of intracranial aneurysms treated with flow diverters

Evaluation of flow diverters for cerebral aneurysm therapy: recommendations for imaging analyses in clinical studies, endorsed by ESMINT, ESNR, OCIN, SILAN, SNIS, and WFITN

BACKGROUND

Multiple studies and meta-analyses have described the technical and clinical outcomes in large cohorts of aneurysm patients treated with flow diverters (FDs). Variations in evaluation methodology complicate making comparisons among studies, hinder understanding of the device behavior, and pose an obstacle in the assessment of further advances in FD therapy.

METHODS

A multidisciplinary panel of neurointerventionalists, imaging experts, and neuroradiologists convened with the goal of establishing consensus recommendations for the standardization of image analyses in FD studies.

RESULTS

A standardized methodology is proposed for evaluating and reporting radiological outcomes of FD treatment of intracranial aneurysms. The recommendations include general imaging considerations for clinical studies and evaluations of longitudinal changes, such as neointimal lining and stenosis. They cover standards for classification of aneurysm location, morphology, measurements, as well as the assessment of aneurysm occlusion, wall apposition, and neck coverage. These reporting standards further define four specific braid deformation patterns: foreshortening, fish-mouthing, braid bump deformation, and braid collapse, collectively termed 'F2B2'.

CONCLUSIONS

When widely applied, standardization of methods of measuring and reporting outcomes will help to harmonize the assessment of treatment outcomes in clinical studies, help facilitate communication of results among specialists, and help enable research and development to focus on specific aspects of FD techniques and technology.

Evaluation of the Significance of Persistent Remnant Filling and Enlargement After Flow Diversion for Intracranial Aneurysms

BACKGROUND

This study aimed to evaluate the clinical course after flow diversion (FD) treatment with a focus on aneurysms with remnant sac filling, by analyzing angiographic outcomes, aneurysm volume, and clinical events.

METHODS

We retrospectively reviewed the medical records of 61 patients who underwent FD for intracranial aneurysms between July 2014 and June 2021.

RESULTS

The majority of aneurysms (52.5%) were located in the internal carotid artery, with a median diameter of 16.6 mm and neck size of 9.3 mm. Remnant filling was observed in 17 aneurysms (27.9%) more than 18 months after FD, 10 (16.4%) of these aneurysms underwent enlargement, which occurred only in cases with subtotal filling or entry remnant states. Eleven patients experienced major adverse events, and three exhibited unfavorable functional outcomes. The incidence of major adverse events and unfavorable functional outcomes was significantly higher in the aneurysm enlargement group than that in the no-filling or stable remnant filling groups (P < 0.001). Aneurysmal diameter and the presence of incorporated branches were independent predictors of aneurysm enlargement, while the presence of incorporated branches was the only independent predictor of persistent remnant filling.

CONCLUSIONS

Aneurysm enlargement after FD is not uncommon, particularly when the aneurysm is large, has incorporated vessels, or does not undergo occlusion within 12 months, often culminating in major adverse events and unfavorable functional outcomes. In addition to investigating angiographic results, it is necessary to evaluate the changes in aneurysm size and clinical events when assessing the efficacy of FD.

Imaging Intracranial Aneurysms in the Endovascular Era: Surveillance and Posttreatment Follow-up

While most intracranial aneurysms (IAs) remain asymptomatic over a patient's lifetime, those that rupture can cause devastating outcomes. The increased usage and quality of neuroimaging has increased detection of unruptured IAs and driven an increase in surveillance and treatment of these lesions. Standard practice is to treat incidentally discovered unruptured IAs that confer high rupture risk as well as ruptured IAs to prevent rehemorrhage. IAs are increasingly treated with coil embolization instead of microsurgical clipping; more recently, flow diversion and intrasaccular flow disruption have further expanded the versatility and utility of endovascular IA treatment. Imaging is increasingly used for posttreatment IA follow-up in the endovascular era. While cerebral angiography remains the standard for IA characterization and treatment planning, advances in CT and CT angiography and MR angiography have improved the diagnostic accuracy of noninvasive imaging for initial diagnosis and surveillance. IA features including size, dome-to-neck ratio, location, and orientation allow rupture risk stratification and determination of optimal treatment strategy and timing. The radiologist should be familiar with the imaging appearance of common IA treatment devices and the expected imaging findings following treatment. In distinction to clipping and coil embolization, flow diversion and intrasaccular flow disruption induce progressive aneurysm obliteration over months to years. Careful assessment of the device; the treated IA; adjacent brain, bone, meninges; and involved extracranial and intracranial vasculature is crucial at posttreatment follow-up imaging to confirm aneurysm obliteration and identify short-term and long-term posttreatment complications. An invited commentary by Chatterjee is available online. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article. ^©RSNA, 2022.

Use of Surpass Streamline Flow Diverter for the Endovascular Treatment of Craniocervical Aneurysms: a Single-Institution Experience

INTRODUCTION

Flow diversion has revolutionized endovascular treatment for cerebral aneurysms. Surpass Streamline flow-diverter (SSFD) has shown promise for expanding flow diversion device options for aneurysm treatment. The SSFD differs from earlier stents by maintaining high porosity with increased pore density to ensure appropriate flow disruption. Given the delivery system's increased dimension options, and potential greater flow diverting properties, the SSFD is poised to extend the anatomic/pathologic reaches of flow diversion therapy.

METHODS

Data pertaining to SSFD-treated aneurysms were gathered retrospectively from 2019 to 2020. Collected information included aneurysm location, size, symptoms, complications, and occlusions rates at follow-up. Size was categorized as small (<10 mm), large (10-25 mm), and giant (>25 mm) according to SCENT trial criteria. Aneurysm occlusion on follow-up imaging was characterized by SMART grading with adequate occlusion defined as grades 3 and 4. Imaging was performed at time of treatment, six-month, and one-year follow-up.

RESULTS

42 SSFD-treated aneurysms were treated throughout the cerebrovascular system; 3 cervical, 4 posterior, and 35 intracranial anterior circulation. Complete occlusion rates at six months and one year were 48% and 57% with adequate occlusion achieved in 89.6% and 85.7% respectively. Rates of complete occlusion were higher for small aneurysms (69%) compared to large aneurysms (38%).

CONCLUSIONS

Our data suggests comparable complete occlusion rates compared to the SCENT trial (66.1% vs 57% in our center) and adequate occlusion rates. Similar occlusion rates to prior studies despite broadened inclusion criteria/diversity of aneurysms treated demonstrates favorable generalizability of flow-diverting technology to a wide array of aneurysmal pathology.

Flow Diverter Devices for the Treatment of Unruptured Vertebral Artery Dissecting Aneurysm

Objective

Vertebral artery dissecting aneurysm (VADA) is a very rare subtype of intracranial aneurysms; when ruptured, it is associated with significantly high rates of morbidity and mortality. Despite several discussions and debates, the optimal treatment for VADA has not yet been established. In the last 10 years, flow diverter devices (FDD) have emerged as a challenging and new treatment method, and various clinical and radiological results have been reported about their safety and effectiveness. The aim of our study was to evaluate the clinical and radiological results with the use of FDD in the treatment of unruptured VADA.

Methods

We retrospectively evaluated the data of all patients with unruptured VADA treated with FDD between January 2018 and February 2021 at our hybrid operating room. Nine patients with unruptured VADA, deemed hemodynamically unstable, were treated with FDD. Among other parameters, the technical feasibility of the procedure, procedure-related complications, angiographic results, and clinical outcomes were evaluated.

Results

Successful FDD deployment was achieved in all cases, and the immediate follow-up angiography showed intra-aneurysmal contrast stasis with parent artery preservation. A temporary episode of facial numbness and palsy was noted in one patient; however, the symptoms had completely disappeared when followed up at the outpatient clinic 2 weeks after the procedure. The 3–6 months follow-up angiography (n=9) demonstrated complete/near-complete obliteration of the aneurysm in seven patients, and partial obliteration and segmental occlusion in one patient each. In the patient who achieved only partial obliteration, there was a sac 13 mm in size, and there was no change in the 1-year follow-up angiography. In the patient with segmental occlusion, the cause could not be determined. The clinical outcome was modified Rankin Scale 0 in all patients.

Conclusion

Our preliminary study using FDD to treat hemodynamically unstable unruptured VADA showed that FDD is safe and effective. Our study has limitations in that the number of cases is small, and it is not a prospective study. However, we believe that the study contributes to evidence regarding the safety and effectiveness of FDD in the treatment of unruptured VADA.

A novel score for evaluating cerebral aneurysms treated with flow diversion: 4F-flow diversion predictive score

Background and purpose

Although grading scales for angiography outcomes following cerebral aneurysm treatment with flow diversion have been published, physicians have not widely adopted these scales in practice. The aim of this study is to propose and validate a novel Flow diversion Predictive Score (4F-FPS) grading scale based on previously established scales that is simple and reliable.

Methods

We retrospectively analyzed consecutive patients who underwent endovascular treatment for cerebral aneurysms with flow diversion between January 2014 and September 2019. The included patients were randomly divided into the derivation and validation group in a 70/30 ratio, respectively. Aneurysms were classified as incomplete or complete occlusion based on final angiography outcomes. 4F-FPS was derived to predict aneurysm occlusion from multivariate logistic regression analyses in the derivation group and validated with previously published grading scales in the validation group.

Results

Overall, 662 patients [mean age, 53.8 years; 72.5% (480/662) female] with 662 aneurysms treated with the Pipeline^TM flow diverter were included [69.9% (463/662) derivation group, 30.1% (199/662) validation group]. The incidence of aneurysm occlusion was 82.7%. 4F-FPS demonstrated significant discrimination in 10-fold cross validation [mean receiver operating characteristic (ROC) area, 0.862 ± 0.055] and calibration (Cox & Snell R ², 0.251; Nagelkerke R ², 0.413) in the derivation group. The ROC area of 4F-FPS score in both the derivation and validation groups is the largest compared with previously published grading scales/scores (p < 0.05), which shows better sensitivity and specificity. The 4F-FPS score showed excellent prediction, discrimination, and calibration properties.

Conclusion

The 4F-FPS score is a simple and reliable tool to predict angiography outcome after flow diversion treatment. If widely adopted, it may provide a common language to be used in future reporting of flow diversion results for clinical trials and daily practice.

Clinical trial registration

http://www.clinicaltrials.gov. Unique identifier: NCT03831672.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Predictive score for complete occlusion of intracranial aneurysms treated by flow-diverter stents using machine learning

BACKGROUND

Complete occlusion of an intracranial aneurysm (IA) after the deployment of a flow-diverter stent is currently unpredictable. The aim of this study was to develop a predictive occlusion score based on pretreatment clinical and angiographic criteria.

METHODS

Consecutive patients with ≥6 months follow-up were included from 2008 to 2019 and retrospectively analyzed. Each IA was evaluated using the Raymond-Roy occlusion classification (RROC) and dichotomized as occluded (A) or residual (B/C); 80% of patients were randomly assigned to the training sample. Feature selection and binary outcome prediction relied on logistic regression and threshold maximizing class separation selected by a CART tree algorithm. The feature selection was addressed by a genetic algorithm selected from the 30 pretreatment available variables.

RESULTS

The study included 146 patients with 154 IAs. Feature selection yielded a combination of six variables with a good cross-validated accuracy on the test sample, a combination we labeled DIANES score (IA diameter, indication, parent artery diameter ratio, neck ratio, side-branch artery, and sex). A score of more than -6 maximized the ability to predict RROC=A with sensitivity of 87% (95% CI 79% to 95%) and specificity of 82% (95% CI 64% to 96%) in the training sample. Accuracy was 86% (95% CI 79% to 94%). In the test sample, sensitivity and specificity were 89% (95% CI 77% to 98%) and 60% (95% CI 33% to 86%), respectively. Accuracy was 81% (95% CI 69% to 91%).

CONCLUSION

A score was developed as a grading scale for prediction of the final occlusion status of IAs treated with a flow-diverter stent.

2D parametric contrast time-density analysis for the prediction of complete aneurysm occlusion at six months' post-flow diversion stent

OBJECTIVE

Indications for the treatment of cerebral aneurysms with flow diversion stents are expanding. The current aneurysm occlusion rate at six months ranges between 60 and 80%. Predictability of complete vs. partial aneurysm occlusion is poorly defined. Here, we evaluate the angiographic contrast time-density as a predictor of aneurysm occlusion rate at six months' post-flow diversion stents.

METHODS

Patients with unruptured cerebral aneurysms proximal to the internal carotid artery terminus treated with single flow diversion stents were included. 2D parametric parenchymal blood flow software (Siemens-Healthineers, Forchheim, Germany) was used to calculate contrast time-density within the aneurysm and in the proximal adjacent internal carotid artery. The area under the curve ratio between the two regions of interests was assessed at baseline and after flow diversion stents deployment. The area under the curve ratio between completely vs. partially occluded aneurysms at six months' follow-up was compared.

RESULTS

Thirty patients with 31 aneurysms were included. Mean aneurysm diameter was 8 mm (range 2-28 mm). Complete occlusion was obtained in 19 aneurysms. Younger patients (P = 0.006) and smaller aneurysms (P = 0.046) presented higher chance of complete obliteration. Incomplete occlusion of the aneurysm was more likely if the area under the curve contrast time-density ratio showed absolute (P = 0.001) and relative percentage (P = 0.001) decrease after flow diversion stents deployment. Area under ROC curve was 0.85.

CONCLUSION

Negative change in the area under the curve ratio indicates less contrast stagnation in the aneurysm and lower chance of occlusion. These data provide a real-time analysis after aneurysm treatment. If validated in larger datasets, this can prompt input to the surgeon to place a second flow diversion stents.

Preliminary in vitro angiographic comparison of the flow diversion behavior of Evolve and Pipeline devices

Background and purpose

Flow diverters are increasingly used to treat a broad category of cerebral aneurysms. We conducted an in vitro study to angiographically compare the flow diversion effect of Surpass Evolve from Stryker Neurovascular with the Pipeline Shield Embolization Device from Medtronic Neurovascular.

Methods

Three copies each of three carotid aneurysm geometries were manufactured from silicone. Evolve and Pipeline flow diverters were deployed in one copy of each geometry; the third copy was used as Control. High-speed angiography was acquired under pulsatile flow in each replica, contrast concentration-time curves within the aneurysms were recorded, and the curves were quantified with six parameters. The parameters were statistically evaluated to compare the flow diversion effect of both devices.

Results

The Evolve showed greater flow diversion trends in almost all intra-geometry comparisons than the Pipeline. When aggregated over the three geometries, the Evolve was statistically significantly better than the Pipeline in four of the six parameters, and about the same or better (not statistically significant) than the Pipeline in the other two parameters.

Conclusions

The Evolve device demonstrated greater in vitro flow diversion effects than Pipeline. Comparative efficacy of the devices will need to be adjudicated based on clinical outcomes.

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.

Predicting Outcomes for Cerebral Aneurysms Treated with Flow Diversion: A Comparison Between 4 Grading Scales

OBJECTIVE

Despite the development of 4 grading scales of angiographic outcome after flow diversion for cerebral aneurysms, none have been widely adopted in the neurosurgical literature, nor have any been validated in an independent dataset. We evaluated the reported grading scales for their ability to predict aneurysm occlusion at follow-up.

METHODS

Four reported grading scales were applied in a retrospective analysis of our prospectively maintained institutional database of patients with intracranial aneurysms treated with flow-diverting stents. Analysis of patient factors, aneurysm factors, and outcomes was made to compare the grading scales' ability to predict aneurysm occlusion.

RESULTS

Ninety-nine aneurysms in 90 patients treated at our institution between 2011 and 2018 were included in the analysis. Lower Flow-Diverting Stent Score (FDSS) scores were associated with higher rates of aneurysm occlusion at final follow-up (P=0.004). The OKM, Kamran-Byrne, and SMART scales scores were not associated with aneurysm occlusion at final follow-up even after adjustments for baseline differences. Area under the receiver operating characteristic curve for the FDSS was 0.675 (0.534-0.816).

CONCLUSIONS

Although the FDSS was the only reported grading scale that was significantly associated with occlusion at follow-up, its ability to predict occlusion fell below the typical level for widespread clinical utility. The high rate of eventual occlusion of most aneurysms after flow diversion likely limits the clinical utility of a grading score for this application.

Stent and flow diverter assisted treatment of acutely ruptured brain aneurysms

OBJECTIVE

We present our experience with stent techniques in the management of acutely ruptured aneurysms, focusing on aneurysm occlusion rates, intraprocedural complications, and late outcomes.

METHODS

We retrospectively reviewed the clinical records of patients treated by stent techniques during the early acute phase of aneurysmal rupture, from June 2011 to June 2016. Patients who underwent stenting for the management of unruptured aneurysms, or in a delayed fashion for a ruptured lesion, were excluded.

RESULTS

47 patients met inclusion criteria, including 46 with subarachnoid hemorrhage (SAH). There were 27 men and 20 women, mean age 38 years (range 23-73). They harbored 71 aneurysms, including 56 treated in the acute phase. Aneurysmal dome and neck width averaged 4.7 mm (range 1.7-12.1) and 3.2 mm (range 1.5-7.1), respectively. Single stent techniques were used in 39 patients and dual stent techniques in 17. External ventricular drains (EVDs) were placed before embolization in 35 patients (92%) and after in 3. Intraprocedure thromboembolic complications due to a hyporesponse to antiplatlets in 4 patients (8.5%) were successfully managed with intra-arterial antiplatelet agents. In 45 surviving patients (96%), there was complete aneurysm occlusion at the 9-12 month follow-up in 26/29 aneurysms treated by stent-assisted coiling (90%), in 2/3 aneurysms treated by flow diverter-assisted coiling (66%), and in 19/22 aneurysms treated by flow diverter alone (86%); 42/45 patients (93%) presented with a modified Rankin Scale score of 0-2.

CONCLUSION

Stenting techniques in ruptured aneurysms can be performed with good technical success; however, procedural thromboembolic complications related to the antiplatelet strategy merit investigation. EVD placement before stenting must be considered.

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.

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.

Does Arterial Flow Rate Affect the Assessment of Flow-Diverter Stent Performance?

BACKGROUND AND PURPOSE

Our aim was to assess the performance of flow-diverter stents. The pre- and end-of-treatment angiographies are commonly compared. However, the arterial flow rate may change between acquisitions; therefore, a better understanding of its influence on the local intra-aneurysmal hemodynamics before and after flow-diverter stent use is required.

MATERIALS AND METHODS

Twenty-five image-based aneurysm models extracted from 3D rotational angiograms were conditioned for computational fluid dynamics simulations. Pulsatile simulations were performed at different arterial flow rates, covering a wide possible range of physiologic flows among 1-5 mL/s. The effect of flow-diverter stents on intra-aneurysmal hemodynamics was numerically simulated with a porous medium model. Spatiotemporal-averaged intra-aneurysmal flow velocity and flow rate were calculated for each case to quantify the hemodynamics after treatment. The short-term flow-diverter stent performance was characterized by the relative velocity reduction inside the aneurysm.

RESULTS

Spatiotemporal-averaged intra-aneurysmal flow velocity before and after flow-diverter stent use is linearly proportional to the mean arterial flow rate (minimum R² > 0.983 of the linear regression models for untreated and stented models). Relative velocity reduction asymptotically decreases with increasing mean arterial flow rate. When the most probable range of arterial flow rate was considered (3-5 mL/s), instead of the wide possible flow range, the mean SD of relative velocity reduction was reduced from 3.6% to 0.48%.

CONCLUSIONS

Both intra-aneurysmal aneurysm velocity and flow-diverter stent performance depend on the arterial flow rate. The performance could be considered independent of the arterial flow rates within the most probable range of physiologic flows.

In vitro investigation of contrast flow jet timing in patient-specific intracranial aneurysms

BACKGROUND

The direction and magnitude of intra-aneurysmal flow jet are significant risk factors of subarachnoid hemorrhage, and the change of flow jet during an endovascular procedure has been used for prediction of aneurysm occlusion or whether an additional flow diverter (FD) is warranted. However, evaluation of flow jets is often unreliable due to a large variation of flow jet on the digital subtraction angiograms, and this flow pattern variation may result in incorrect clinical diagnosis Therefore, factors contributing to the variation in flow jet are examined at an in vitro setting, and the findings can help us to understand the nature of flow jet and devise a better plan to quantify the aneurysmal hemodynamics accurately.

METHODS

Intra-aneurysmal flows in three patient-specific aneurysms between 11 and 25 mm were investigated in vitro, and a FD was deployed in each aneurysm model. X-ray imaging of these models were performed at injection rates between 0.2 and 2 mL/s. Pulsatile blood pump and aneurysm model were imaged together to determine the timing of flow jet.

RESULTS

The contrast bolus arrives at the aneurysm early at high contrast injection rates. The flow patterns with slow injection rates exhibit strong inertia that is associated with the systole flow. Flow jets arrive at the aneurysms at the peak systole when the bolus is injected at 0.2 mL/s. The contrast-to-signal ratio is the highest at the injection rate of 0.5 mL/s. Effect of flow diversion can only be assessed at an injection rate greater than 0.5 mL/s.

CONCLUSIONS

Intra-aneurysmal flow jet is highly dependent on the injection rate of the contrast agent. For the internal carotid artery (ICA) aneurysms, the systolic flows can be visualized at slow injection rates (<0.5 mL/s), while the diastolic flow jets are visible at higher injection rates (>1 mL/s). Dependence of flow jet on the contrast injection rate has serious clinical implications and needs to be considered during diagnostic procedures; a protocol with a consistent injection rate is highly recommended.

Inter-rater reliability of published flow diversion occlusion scales

Background

With increasing use of flow-diverting stents for the treatment of intracranial aneurysms, standardized methods and a common language to evaluate angiographic outcomes are needed. Multiple grading scales have been developed for this purpose but none has been widely adopted.

Objective

To analyze these scales to determine interobserver reliability.

Methods

Four independent assessors scored the intraprocedural angiograms of patients who underwent flow-diverting stent deployment for an intracranial saccular or fusiform aneurysm at our institution between October 2012 and June 2015. Angiographic outcome immediately after flow-diverting stent deployment was scored using three grading scales (Kamran–Byrne (KB), Simple Measurement of Aneurysm Residual after Treatment (SMART), and O'Kelley, Krings, Marotta (OKM)). Statistical analysis was performed using Light's κ for multiple raters (κ), Kendall's coefficient of concordance (W), and intraclass correlation (ICC).

Results

We included the angiograms of 50 consecutive patients (mean age 58 years, range 30–79) who underwent flow-diverting stent deployment for an intracranial aneurysm (40 saccular, 10 fusiform). Six aneurysms were located in the posterior circulation. The inter-rater reliability was typically poor or fair: SMART aneurysm filling (κ=0.30, W=0.36, ICC=0.12), SMART parent vessel stenosis (κ=0.07, W=0.33, ICC=0.12), KB axis I (κ=0.24, W=0.50, ICC=0.25), KB axis II (κ=0.07, W=0.30, ICC=0.06), OKM aneurysm filling (κ=0.23, W=0.45, ICC=0.13), OKM contrast stasis (κ=0.36,W=0.71, ICC=0.54).

Conclusions

Existing flow-diverting stent grading scales have low inter-rater reliability for most categories.

Endovascular reconstruction of unruptured intradural vertebral artery dissecting aneurysms with the Pipeline embolization device

Background

Dissecting aneurysms of the vertebral artery (VA) are difficult to treat using current surgical and endovascular techniques.

Objective

To analyze retrospectively the efficacy and safety of flow diverters in the treatment of dissecting aneurysms of the vertebral artery.

Methods

We identified six patients with six unruptured VA dissecting aneurysms either arising from the V4 or V3–V4 junction that were treated with the Pipeline embolization device (PED) at our institution between July 2012 and February 2015. Among other parameters, technical feasibility of the procedure, procedure-related complications, angiographic results, and clinical outcome were evaluated.

Results

PED placement was achieved in all cases and immediate angiography follow-up demonstrated intra-aneurysmal contrast stasis with parent artery preservation. A temporary episode of dysarthria was noted in one patient. Major procedure-related complications were not observed. The 6-month follow-up (n=6) demonstrated complete/near-complete aneurysm obliteration in five patients and partial obliteration in one. At the 1-year follow-up (n=5) stable complete aneurysm occlusion was seen in two patients. Two cases showed progression from near complete occlusion and partial occlusion at 6 months to complete occlusion and near complete occlusion. One cases showed unchanged near complete occlusion. No aneurysmal bleeding, in-stent stenosis or thromboembolic complication was seen. National Institutes of Health Stroke Scale and modified Rankin scale scores remained unchanged from admission to discharge.

Conclusions

Our preliminary experience with the use of PED for the treatment of intradural VA dissecting aneurysms shows promising short-term results, making this technique a feasible and safe treatment option in patients suitable for this approach. However, long-term and larger cohort studies are needed to validate these results.

A New Aneurysm Occlusion Classification after the Impact of Flow Modification

A new classification is proposed for cerebral aneurysms treated with any endovascular technique, for example, coiling with or without adjunctive devices, flow diversion, intrasaccular flow modifiers, or any combination of the above. Raymond-Roy Occlusion Classification is expanded with novel subgroups such as class 1 represents complete occlusion and is subdivided if a branch is integrated to, or originated from, the aneurysm sac; class 2 represents neck filling; class 3 represents incomplete occlusion with aneurysm filling as in the previous classification; and class 4 describes the immediate postoperative status after extra- or intrasaccular flow modification treatment. A new concept, "stable remodeling," is included as class 5, which represents filling in the neck region that stays unchanged or reduced, as shown with at least 2 consecutive control angiographies, at least 6 months apart, for not <1 year, or the remodeled appearance of a dilated and/or tortuous vessel in continuation with the parent artery without sac filling.

Follow-up of intracranial aneurysms treated by flow diverter: comparison of three-dimensional time-of-flight MR angiography (3D-TOF-MRA) and contrast-enhanced MR angiography (CE-MRA) sequences with digital subtraction angiography as the gold standard

Background and purpose

Follow-up of intracranial aneurysms treated by flow diverter with MRI is complicated by imaging artifacts produced by these devices. This study compares the diagnostic accuracy of three-dimensional time-of-flight MR angiography (3D-TOF-MRA) and contrast-enhanced MRA (CE-MRA) at 3 T for the evaluation of aneurysm occlusion and parent artery patency after flow diversion treatment, with digital subtraction angiography (DSA) as the gold standard.

Materials and methods

Patients treated with flow diverters between January 2009 and January 2013 followed by MRA at 3 T (3D-TOF-MRA and CE-MRA) and DSA within a 48 h period were included in a prospective single-center study. Aneurysm occlusion was assessed with full and simplified Montreal scales and parent artery patency with three-grade and two-grade scales.

Results

Twenty-two patients harboring 23 treated aneurysms were included. Interobserver agreement using simplified scales for occlusion (Montreal) and parent artery patency were higher for DSA (0.88 and 0.61) and CE-MRA (0.74 and 0.55) than for 3D-TOF-MRA (0.51 and 0.02). Intermodality agreement was higher for CE-MRA (0.88 and 0.32) than for 3D-TOF-MRA (0.59 and 0.11). CE-MRA yielded better accuracy than 3D-TOF-MRA for aneurysm remnant detection (sensitivity 83% vs 50%; specificity 100% vs 100%) and for the status of the parent artery (specificity 63% vs 32%; sensitivity 100% vs 100%).

Conclusions

At 3 T, CE-MRA is superior to 3D-TOF-MRA for the evaluation of aneurysm occlusion and parent artery patency after flow diversion treatment. However, intraluminal evaluation remains difficult with MRA regardless of the sequence used.

A Fourier-based approach to the angiographic assessment of flow diverter efficacy in the treatment of cerebral aneurysms

Flow diversion is an emerging endovascular treatment option for cerebral aneurysms. Quantitative assessment of hemodynamic changes induced by flow diversion can aid clinical decision making in the treatment of cerebral aneurysms. In this article, besides summarizing past key research efforts, we propose a novel metric for the angiographic assessment of flow diverter deployments in the treatment of cerebral aneurysms. By analyzing the frequency spectra of signals derived from digital subtraction angiography (DSA) series, the metric aims to quantify the prevalence of frequency components that correspond to the patient-specific heart rate. Indicating the decoupling of aneurysms from healthy blood circulation, our proposed metric could advance clinical guidelines for treatment success prediction. The very promising results of a retrospective feasibility study on 26 DSA series warrant future efforts to study the validity of the proposed metric within a clinical setting.

Intrasaccular flow-diversion for treatment of intracranial aneurysms: the Woven EndoBridge

Endovascular approach is now the first option for the treatment of most intracranial aneurysms (IA). However, remaining limitations are the suboptimal stability of aneurysm occlusion and the treatment of complex IA. The use of conventional and flow diverter stents has partially addressed these limitations. Nevertheless, as intraluminal devices, stents require aggressive antiplatelet therapy and are associated with higher thromboembolic (TE) complication rates. Intrasaccular flow disrupters (IFD) are newly developed braided-wire devices designed to achieve flow disruption at the neck without placing material in the parent vessel and without the need of antiplatelet therapy. First clinical series have shown promising anatomical and clinical results. Our purpose is to describe the available IFD and to review the literature about their efficacy, safety, limitations, and developments.

Frequency and predictors of endoleaks and long-term patency after covered stent placement for the treatment of intracranial aneurysms: a prospective, non-randomised multicentre experience

OBJECTIVE

We investigated immediate/late endoleaks and long-term patency following stent-graft placement for treatment of intracranial aneurysms located within the distal internal carotid artery (ICA) or vertebral artery (VA).

METHODS

Forty-five aneurysms in 41 patients receiving covered stents in three centres were followed. Outcome measures included aneurysm occlusion rate, endoleaks, late in-stent stenosis rate, clinical improvement, neurological deficiencies and death.

RESULTS

Total aneurysm exclusion was achieved in 69.2% (n = 27), with 30.8% (n = 12) experiencing immediate residual endoleaks. Angiographic follow-up (mean 43.5 ± 14.3 months) revealed that 87.2% (n = 34) were completely occluded with only 12.8% (n = 5) showing residual endoleaks. Predictors of immediate endoleaks in our patient group were stent number (P = 0.023) and stent diameter (P = 0.022), while predictors of late endoleaks in our patient group were stent diameter (P = 0.035) and stent angulation (P = 0.021). Late in-stent stenosis rates were 18.0 ± 13.3 and 29.0 ± 18.5% compared with the period immediately following implantation at 2- and 6-year follow-ups respectively. Smoking (P = 0.017) and stent angulation (P = 0.020) were predictors of late in-stent stenosis.

CONCLUSION

Treating intracranial aneurysms with Willis stent-grafts has an acceptable immediate and late occlusion rate and long-term stented artery patency rate.