Optical coherence tomography for elucidation of flow-diversion phenomena: The concept of endothelized mural thrombus behind reversible in-stent stenosis in flow-diverters

Comprehensive Analysis of Post-Pipeline Endothelialization and Remodeling

BACKGROUND AND PURPOSE

Successful post-flow-diverter endoluminal reconstruction is widely believed to require endothelial overgrowth of the aneurysmal inflow zone. However, endothelialization/neointimal overgrowth is a complex process, over which we currently have very limited influence. Less emphasized is vascular remodeling of the target arterial segment, the dynamic response of the vessel to flow-diverter implantation. This process is distinct from flow modifications in covered branches. It appears that basic angiographic methods allow simple and useful observations. The purpose of this article was to quantitatively evaluate observable postimplantation changes in target vessels following deployment of Pipeline endoluminal constructs.

MATERIALS AND METHODS

One hundred consecutive adults with unruptured, previously untreated, nondissecting aneurysms treated with the Pipeline Embolization Device with Shield Technology and the availability of follow-up conventional angiography were studied with 2D DSA imaging. Target vessel size; Pipeline Embolization Device diameter; endothelial thickness; and various demographic, antiplatelet, and device-related parameters were recorded and analyzed.

RESULTS

The thickness of neointimal overgrowth (mean, 0.3 [SD, 0.1] mm; range, 0.1-0.7 mm) is inversely correlated with age and is independent of vessel size, smoking status, sex, and degree of platelet inhibition. The decrease in lumen diameter caused by neointimal overgrowth, however, appears counteracted by outward remodeling (dilation) of the target arterial segment. This leads to an increase in the diameter with a corresponding decrease in length (foreshortening) of the implanted Pipeline Embolization Device. This physiologic remodeling process affects optimally implanted devices and is not a consequence of stretching, device migration, vasospasm, and so forth. A direct, linear, statistically significant relationship exists between the degree of observed outward remodeling and the diameter of the implanted Pipeline Embolization Device relative to the target vessel. Overall, remodeled arterial diameters were reduced by 15% (SD, 10%) relative to baseline and followed a normal distribution. Clinically relevant stenosis was not observed.

CONCLUSIONS

Vessel healing involves both outward remodeling and neointimal overgrowth. Judicial oversizing could be useful in specific settings to counter the reduction in lumen diameter due to postimplant neointimal overgrowth; however, this overszing needs to be balanced against the decrease in metal coverage accompanying the use of oversized devices. Similar analysis for other devices is essential.

Endovascular Treatment for Complex Vascular Pathologies in the Pediatric Population: Experience from a Center with Dual-Trained Neurosurgeons

OBJECTIVE

Endovascular treatment of complex vascular pathologies in the pediatric population is often performed by nonpediatric subspecialists with adaptation of equipment and techniques developed for adult patients. We aimed to report our center's experience with safety and outcomes of endovascular treatments for pediatric vascular pathologies.

METHODS

We performed a retrospective review of our endovascular database. All patients ≤18 years who underwent endovascular treatment between January 1, 2004 and December 1, 2022 were included.

RESULTS

During the study time frame, 118 cerebral angiograms were performed for interventional purposes in 55 patients. Of these patients, 8(14.5%) had intracranial aneurysms, 21(38.2%) had intracranial arteriovenous malformations, 6(10.9%) had tumors, 5(9.1%) had arterial occlusions (n = 3) or dissections (n = 2), 8(14.5%) had vein of Galen malformations, and 7(12.7%) had other cerebrovascular conditions. Of the total 118 procedures, access-site complications occurred in 2(1.7%), intraprocedural complications occurred in 3(2.5%), and transient neurological deficits were observed after 2(1.7%). Treatment-related mortality occurred in 1(1.8%) patient.

CONCLUSIONS

Neurointervention in pediatric patients was safe and effective in our experience.

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.

Pipeline embolization of complex, wide-necked middle cerebral artery bifurcation aneurysms: A single-center experience

PURPOSE

To evaluate the performance of Pipeline Embolization Device (PED) in complex, wide-necked middle cerebral artery (MCA) bifurcation aneurysms.

METHODS

We performed a retrospective review of patients treated with PED for complex, wide-necked MCA bifurcation aneurysms between August 2016 and March 2021. In addition to demographic data, we collected aneurysmal neck width, dome-to-neck ratio, complications, and clinical and angiographic follow-up. The embolization degree of aneurysms was evaluated by O'Kelly-Marotta (OKM) grading scale, and the prognosis was assessed with the modified Rankin Scale (mRS).

RESULTS

From August 2016 to March 2021, a total of 46 patients with 49 MCA bifurcation aneurysms in our center were enrolled, of whom all received PEDs successfully. The O'Kelly-Marotta (OKM) grading showed that post-procedure 15 patients (32.6%) were grade C, another 8 patients (17.4%) were grade D. Aneurysms with small remnant or complete occlusion were 50%, symptomatic ischemic events occurred in 3 (6.5%), and bleeding events in 1 (2.2%). 41 patients underwent a 6-month angiography follow-up, in which 7 patients (17.1%) remained OKM grade C and 30 patients (73.2%) achieved OKM grade D. Complete occlusion and small remnant aneurysms were up to 90.3%. 40 (97.6%) patients' mRS scores were 0, and 1 (2.4%) patient was 2. No new bleeding and ischemic events occurred during the 6-month.

CONCLUSIONS

The Pipeline Embolization Device provides a safe and effective treatment alternative for complex, wide-necked MCA aneurysms. A larger number with longer-term follow-up data is needed for further verification.

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.

Recurrent reversible in-stent-stenosis after flow diverter treatment

Flow diverter stents (FDS) are well established in the treatment of intracranial aneurysms which are difficult to treat with conventional endovascular techniques. However, they carry a relatively high risk of specific complications compared to conventional stents. A minor but frequent finding is the occurrence of reversible in-stent-stenosis (ISS) that tend to resolve spontaneously over time. Here, we report the case of a patient in their 30s who was treated with FDS for bilateral paraophthalmic internal carotid artery (ICA) aneurysms. ISS were found at the respective early follow-up examinations on both sides and had resolved at the 1-year follow-up examinations. Surprisingly ISS reoccurred at both sides in later follow-up examinations and again resolved spontaneously. The recurrence of ISS after resolution is a finding that has not been described previously. Its incidence and further development should be investigated systematically. This might contribute to our understanding of the mechanisms underlying the effect of FDS.

Optical Coherence Tomography in Cerebrovascular Disease: Open up New Horizons

Optical coherence tomography (OCT), based on the backscattering or reflection of near-infrared light, enables an ultra-high resolution of up to 10 μm. The successful application of OCT in coronary artery diseases has sparked increasing interest in its implementation in cerebrovascular diseases. OCT has shown promising potential in the atherosclerotic plaque structure characterization, plaque rupture risk stratification, pre-stenting and post-stenting evaluation, and long-term follow-up in extracranial and intracranial atherosclerotic stenosis (ICAS). In hemorrhagic cerebrovascular diseases, OCT plays an important role in the structure evaluation, rupture risk stratification, and healing and occlusion evaluation following initial treatment in intracranial aneurysms (IAs). In this study, we summarized the applications of OCT in the diagnosis, treatment, and follow-up of cerebrovascular diseases, especially in ICAS and IAs. The current limitations and future directions of OCT in the endovascular treatment of cerebrovascular diseases were also discussed.

Machine learning to predict in-stent stenosis after Pipeline embolization device placement

Background

The Pipeline embolization device (PED) is a flow diverter used to treat intracranial aneurysms. In-stent stenosis (ISS) is a common complication of PED placement that can affect long-term outcome. This study aimed to establish a feasible, effective, and reliable model to predict ISS using machine learning methodology.

Methods

We retrospectively examined clinical, laboratory, and imaging data obtained from 435 patients with intracranial aneurysms who underwent PED placement in our center. Aneurysm morphological measurements were manually measured on pre- and posttreatment imaging studies by three experienced neurointerventionalists. ISS was defined as stenosis rate >50% within the PED. We compared the performance of five machine learning algorithms (elastic net (ENT), support vector machine, Xgboost, Gaussian Naïve Bayes, and random forest) in predicting ISS. Shapley additive explanation was applied to provide an explanation for the predictions.

Results

A total of 69 ISS cases (15.2%) were identified. Six predictors of ISS (age, obesity, balloon angioplasty, internal carotid artery location, neck ratio, and coefficient of variation of red cell volume distribution width) were identified. The ENT model had the best predictive performance with a mean area under the receiver operating characteristic curve of 0.709 (95% confidence interval [CI], 0.697–0.721), mean sensitivity of 77.9% (95% CI, 75.1–80.6%), and mean specificity of 63.4% (95% CI, 60.8–65.9%) in Monte Carlo cross-validation. Shapley additive explanation analysis showed that internal carotid artery location was the most important predictor of ISS.

Conclusion

Our machine learning model can predict ISS after PED placement for treatment of intracranial aneurysms and has the potential to improve patient outcomes.

First U.S. Experience Using the Pipeline Flex Embolization Device with Shield Technology for Treatment of Intracranial Aneurysms

BACKGROUND

The Pipeline Flex Embolization Device with Shield technology (PED-Shield [Medtronic, Dublin, Ireland]) is a third-generation flow diverter. Surface modification of the mesh with phosphorylcholine covalently bound to the metal struts aims to reduce thrombogenicity. In the present study, we report the results from the first U.S. series of patients with intracranial aneurysms treated with the PED-Shield and a comprehensive systematic literature review.

METHODS

We retrospectively collected the patient demographics, aneurysm characteristics, procedural details, and periprocedural complications from our prospectively maintained endovascular database (April 2021 to July 2021). Our literature review encompassed 3 databases (PubMed, Embase, and MEDLINE).

RESULTS

Ten patients with 11 anterior circulation unruptured wide-necked aneurysms (10 saccular, 1 fusiform) were included. The average patient age was 64.7 years (range, 45-86 years), and 9 were women. One device demonstrated insufficient distal opening. No other technical issues or intraprocedural complications had occurred. After the procedure, 1 patient had developed a groin hematoma and 1 had experienced a small intracranial hemorrhage, with no clinical repercussions. All patients were discharged with dual-antiplatelet therapy. In the review, we identified 15 studies. Most had been conducted in Europe and South America and 3 were U.S. case reports of compassionate use of the device.

CONCLUSIONS

In our initial periprocedural experience with the PED-Shield for intracranial aneurysm treatment, the device demonstrated an excellent performance and no major complications. Further studies are required to evaluate the long-term follow-up results and the safety of different antiplatelet regimens.

Predictors of incomplete aneurysm occlusion after treatment with the Pipeline Embolization Device: PREMIER trial 1 year analysis

BACKGROUND

Flow diverters have revolutionized the treatment of intracranial aneurysms. Nevertheless, some aneurysms fail to occlude with flow diversion. The Prospective Study on Embolization of Intracranial Aneurysms with the Pipeline Device (PREMIER) was a prospective, multicenter and single-arm trial of small and medium wide-necked unruptured aneurysms. In the current study, we evaluate the predictors of treatment failure in the PREMIER cohort.

METHODS

We analyzed PREMIER patients who had incomplete occlusion (Raymond-Roy >1) at 1 year angiographic follow-up and compared them with those who achieved Raymond-Roy 1, aiming to identify predictors of treatment failure.

RESULTS

25 aneurysms demonstrated incomplete occlusion at 1 year. There was a median reduction of 0.9 mm (IQR 0.41-2.43) in maximum diameter between pre-procedure and 1 year measurements, with no aneurysmal hemorrhage. Patients with incomplete occlusion were significantly older than those with complete occlusion (p=0.011). Smoking (p=0.045) and C6 segment location (p=0.005) were significantly associated with complete occlusion, while location at V4 (p=0.01) and C7 (p=0.007) and involvement of a side branch (p<0.001) were significantly associated with incomplete occlusion. In multivariable logistic regression, significant predictors of incomplete occlusion were non-smoker status (adjusted OR 4.49, 95% CI 1.11 to 18.09; p=0.03) and side branch involvement (adjusted OR 11.68, 95% CI 3.84 to 35.50; p<0.0001), while C6 location had reduced odds of incomplete occlusion (adjusted OR 0.29, 95% CI 0.10 to 0.84; p=0.02).

CONCLUSIONS

The results of our study are consistent with previous retrospective series and warrant consideration for technique adaptations to achieve higher occlusion rates. Further follow-up is needed to assess progression of aneurysm occlusion and clinical behavior in these cases.

First Experience of Three Neurovascular Centers With the p64MW-HPC, a Low-Profile Flow Diverter Designed for Proximal Cerebral Vessels With Antithrombotic Coating

Background: In the last decade, flow diversion (FD) has been established as hemodynamic treatment for cerebral aneurysms arising from proximal and distal cerebral arteries. However, two significant limitations remain—the need for 0.027” microcatheters required for delivery of most flow diverting stents (FDS), and long-term dual anti-platelet therapy (DAPT) in order to prevent FDS-associated thromboembolism, at the cost of increasing the risk for hemorrhage. This study reports the experience of three neurovascular centers with the p64MW-HPC, a FDS with anti-thrombotic coating that is implantable via a 0.021” microcatheter.

Materials and methods: Three neurovascular centers contributed to this retrospective analysis of patients that had been treated with the p64MW-HPC between March 2020 and March 2021. Clinical data, aneurysm characteristics, and follow-up results, including procedural and post-procedural complications, were recorded. The hemodynamic effect was assessed using the O'Kelly–Marotta Scale (OKM).

Results: Thirty-two patients (22 female, mean age 57.1 years) with 33 aneurysms (27 anterior circulation and six posterior circulation) were successfully treated with the p64MW-HPC. In 30/32 patients (93.75%), aneurysmal perfusion was significantly reduced immediately post implantation. Follow-up imaging was available for 23 aneurysms. Delayed aneurysm perfusion (OKM A3: 8.7%), reduction in aneurysm size (OKM B1-3: 26.1%), or sufficient separation from the parent vessel (OKM C1-3 and D1: 65.2%) was demonstrated at the last available follow-up after a mean of 5.9 months. In two cases, device thrombosis after early discontinuation of DAPT occurred. One delayed rupture caused a caroticocavernous fistula. The complications were treated sufficiently and all patients recovered without permanent significant morbidity.

Conclusion: Treatment with the p64MW-HPC is safe and feasible and achieves good early aneurysm occlusion rates in the proximal intracranial circulation, which are comparable to those of well-established FDS. Sudden interruption of DAPT in the early post-interventional phase can cause in-stent thrombosis despite the HPC surface modification. Deliverability via the 0.021” microcatheter facilitates treatment in challenging vascular anatomies.

Treatment of In-Stent Stenosis Following Flow Diversion of Intracranial Aneurysms with Cilostazol and Clopidogrel

In-stent stenosis is a feared complication of flow diversion treatment for cerebral aneurysms. We present 2 cases of patients treated with pipeline flow diversion for unruptured cerebral aneurysms. Initial perioperative dual antiplatelet therapy (DAPT) consisted of standard aspirin plus clopidogrel. At 6-month follow-up cerebral angiography, the patients were noted to have developed significant in-stent stenosis (63% and 53%). The patients were treated with cilostazol and clopidogrel for at least 6 months. Subsequent angiography at 1-year post-treatment showed significant improvement of the in-stent stenosis from 63% to 34% and 53% to 21%. The role of cilostazol as treatment of intracranial in-stent stenosis has not been previously described. Cilostazol’s vasodilatory effect and suppression of vascular smooth muscle proliferation provides ideal benefits in this setting. Cilostazol plus clopidogrel may be a safe and effective alternative to standard DAPT for treatment of in-stent stenosis following flow diversion and warrants further consideration and investigation.