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.

In vitro measurement of the permeability of endovascular coils deployed in cerebral aneurysms

Background and purposeAneurysm recurrence is the primary limitation of endovascular coiling treatment for cerebral aneurysms. Coiling is currently quantified by a volumetric porosity measure called packing density (pd). Blood flow through a coil mass depends on the permeability of the coil mass, and not just its pd. The permeability of coil masses has not yet been quantified. Here we measure coil permeability with a traditional falling-head permeameter modified to incorporate idealized aneurysms.MethodsSilicone replicas of idealized aneurysms were manufactured with three different aneurysm diameters (4, 5, and 8 mm). Four different coil types (Codman Trufill Orbit, Covidien Axium, Microvention Microplex 10, and Penumbra 400) were deployed into the aneurysms with a target pd of 35%. Coiled replicas were installed on a falling-head permeameter setup and the time taken for a column of fluid above the aneurysm to drop a certain height was recorded. Permeability of the samples was calculated based on a simple modification of the traditional permeameter equation to incorporate a spherical aneurysm.ResultsThe targeted 35% pd was achieved for all samples (35%±1%, P=0.91). Coil permeabilities were significantly different from each other (P<0.001) at constant pd. Microplex 10 coils had the lowest permeability of all coil types. Data suggest a trend of increasing permeability with thicker coil wire diameter (not statistically significant).ConclusionsA simple in vitro setup was developed to measure the permeabilities of coil masses based on traditional permeametry. Coil permeability should be considered when evaluating the hemodynamic efficacy of coiling instead of just packing density. Coils made of thicker wires may be more permeable, and thus less effective, than coils made from thinner wires. Whether aneurysm recurrence is affected by coil wire diameter or permeability needs to be confirmed with clinical trials.

Thrombogenicity of flow diverters in an ex vivo shunt model: effect of phosphorylcholine surface modification

BackgroundFlow diverters offer a promising treatment for cerebral aneurysms. However, they have associated thromboembolic risks, mandating chronic dual antiplatelet therapy (DAPT). Shield Technology is a phosphorylcholine surface modification of the Pipeline Embolization Device (PED) flow diverter, which has shown significant reductions in material thrombogenicity in vitro.ObjectiveTo compare the thrombogenicity of PED, PED with Shield Technology (PED+Shield), and the Flow-Redirection Endoluminal Device (FRED)—with and without single antiplatelet therapy and DAPT—under physiological flow.MethodsAn established non-human primate ex vivo arteriovenous shunt model of stent thrombosis was used. PED, PED+Shield, and FRED were tested without antiplatelet therapy, with acetylsalicylic acid (ASA) monotherapy, and with DAPT. Radiolabeled platelet deposition was quantified over 1 hour for each device and total fibrin deposition was also quantified.ResultsCumulative statistical analysis showed significantly lower platelet deposition on PED compared with FRED. The same statistical model showed significant decreases in platelet deposition when ASA, clopidogrel, or Shield Technology was used. Direct comparisons of device performances within antiplatelet conditions showed consistent significant decreases in platelet accumulation on PED+Shield relative to FRED. PED+Shield showed significant reductions in platelet deposition compared with unmodified PED without antiplatelet therapy and with DAPT. PED accumulated minimal fibrin with and without Shield Technology.ConclusionsIn this preclinical model, we have shown that the Shield Technology phosphorylcholine modification reduces the platelet-specific thrombogenicity of a flow diverter under physiologically relevant flow with and without DAPT. We have further identified increased fibrin-driven thrombogenicity associated with FRED relative to PED.

Treatment of experimental aneurysms with a new liquid embolic agent and a retrievable stent: proof of concept and feasibility study

BackgroundOcclusion of canine bifurcation and sidewall aneurysms was undertaken with a new liquid embolic agent (PHIL 35) assisted by a high-density partially retrievable stent (FRED) with preservation of the carotid artery.MethodsThree dogs were used as acute preparations for development of the technique and two were used for chronic studies lasting 90 days. In one animal we intentionally did not completely fill the aneurysm to determine the long-term results of incomplete treatment. The degree of occlusion, carotid artery compromise, and dislodgement and/or migration of embolic material in treated aneurysms were assessed.ResultsAll aneurysms planned for complete obliteration were totally occluded successfully. By design, we partially occluded one aneurysm. In this aneurysm, angiography performed at 30 days revealed less filling, but at 90 days it had persistent small residual filling. We did not detect any distal embolization during the injection and no angiographic occlusions, change in configuration, or delayed migration of the embolic material were found. In the inspected stent, no foreign material was noted. In four animals we successfully removed the stent with preservation of the integrity of the carotid artery. In the fifth we intentionally left both stents deployed.ConclusionsWe have developed a new treatment for cerebral aneurysms using a combination of a retrievable stent and a new liquid embolic agent.

A Novel Neck-Sealing Balloon Technique for Distal Access Through a Giant Aneurysm

BACKGROUND AND IMPORTANCE: In endovascular treatment for cerebral aneurysms using balloons, stents, or flow diverters, a microguidewire or microcatheter needs to be navigated distally across the neck of the aneurysm. However, this is sometimes difficult when there is a wide-neck or large aneurysm with a tortuous or atherosclerotic parent vessel. In this case report, we describe a new technique for navigating a microcatheter into a distal vessel. CLINICAL PRESENTATION: An 81-year-old woman presented with trigeminal neuralgia and diplopia due to abducens nerve palsy because of a giant cavernous carotid artery aneurysm. We planned stent-assisted coil embolization of the aneurysm and tried to advance a microcatheter into a distal vessel across the neck of the aneurysm. Although we attempted several previously reported techniques, these were unsuccessful. We then navigated a balloon into the aneurysm, slowly inflated it within the aneurysm, pulled it back gently, and sealed the neck orifice of the aneurysm with the balloon. We easily navigated a microcatheter into the distal vessel. The stent-assisted coil embolization was completed with no complications. CONCLUSION: This novel neck-sealing technique with a balloon for distal access may be useful in cases in which other methods are unsuccessful. In addition, this technique offers the advantages of not producing a loop in the microcatheter within an aneurysm and not requiring retraction of the microcatheter to reduce the loop.

Flow Diverted Aneurysmal Hemodynamic Simulations and Validation With Experiments

Brain aneurysms occur due to abnormal ballooning of cerebral arteries. Rupture of the cerebral aneurysms can result in subarachnoid hemorrhage and may prove fatal for patients [1]. Surgical clipping is a highly invasive option for treatment of aneurysms. Endovascular flow diverting stents have recently emerged as a less invasive treatment for cerebral aneurysms. Flow diverters for intracranial aneurysms, are porous metallic mesh tubes deployed across the neck of the aneurysm to exclude the aneurysm from the circulation [2–4]. By producing a substantial reduction of flow inside the aneurysm and by promoting activation of platelets that cross the device into the aneurysm, intra-aneurysmal thrombus is generated and the aneurysm is eventually excluded from the circulation.