Background and purpose The Penumbra Coil 400 System (PC 400) is the newly introduced platinum coil system designed specifically to enhance filling efficiency by increasing coil diameter. Our goal was to study the packing and treatment advantage of the PC 400's unique geometric configuration compared with conventional coils (controls).
Materials and methods 16 aneurysms embolized with the PC 400 in 2011 were compared with 79 equally matched aneurysms embolized with conventional coils from 2004 to 2011. Primary outcomes assessed were acute packing density, embolization time, and the number of coils required for aneurysm occlusion.
Results Aneurysm embolization with the PC 400 achieved a higher packing density (36.8% vs 28.1%; p<0.005) and with fewer coils (an average of 3.9 vs 6.1 coils per aneurysm; p<0.05). In addition, the total procedural time for the subjects treated with the PC 400 was significantly less (45.7 vs 64.1 min; p<0.05). There were no procedural complications associated with the PC 400.
Conclusions Compared with conventional coils, the PC 400 is more efficient in the embolization of cerebral aneurysms, achieving greater packing density with fewer coils and less time without compromising safety.
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Over the past two decades, endovascular coiling has emerged as a safe and durable alternative to surgical clipping for intracranial aneurysms.1 In the USA, there has been a paradigm shift towards endovascular coiling for both ruptured and unruptured intracranial aneurysms.2 One of the drawbacks of endovascular coiling continues to be aneurysmal recurrence,3 ,4 which has been quoted at approximately 20% in a recent meta-analysis.5 Since the advent of the bare platinum Gugliemi detachable coil (GDC) in the 1990s, there have been a number of attempts to improve coil characteristics and reduce recurrence, with variable results.6 Coil packing density has been studied both in vitro7–11 and in vivo and has been positively associated with improved aneurysm obliteration12–14 and decreased coil compaction.15 ,16
The Penumbra Coil 400 (PC 400) system consists of a new generation of softer platinum coils with a larger diameter than conventional embolic coils (controls). The larger diameter with the inherent softness of the coils should result in a higher packing density of coils within aneurysms treated with embolization. The purpose of this study was to assess the efficiency of the PC 400's filling advantage in the treatment of cerebral aneurysms compared with conventional coils. Particular focus was put on the comparison of packing density, embolization time, and the number of coils required for aneurysm occlusion.
This study was conducted as a single center, retrospective case review of 95 aneurysm cases treated in 94 patients. These 95 aneurysms were treated with either the Penumbra PC 400 coils (n=16) or control coils (n=79). All aneurysm embolizations were performed by two interventionalists (AP and HM) utilizing the same endpoint of maximum safe packing of the aneurysm. The 16 patients coiled with PC 400 were the first to be treated with these coils at the institution; they were compared with equally matched controls. The control group included three different brands of coils: GDC coils, Boston Scientific, Fremont, California, USA; Trufill/Orbit coils, Cordis Neurovascular, Miami Lakes, Florida, USA; and Galaxy coils, DePuy/Codman and Shurtleff, Johnson and Johnson, Warsaw, Indiana, USA.
Institutional review board approval was obtained on site at Mount Sinai School of Medicine (FWA No 00005656, FWA No 00005651). A HIPAA waiver of authorization was granted, which permitted the collection of data without the use of a signed informed consent form as this study involved minimal risk to the participating subjects and could not have been practically conducted without this authorization. Identifying and contacting such a large number of potential subjects would not be feasible for a medical record review for information that would not change the care they would already have received. Patients treated with conventional coils between 2004 and 2011 that met inclusion criteria for this study were included as the control group.
Criteria for inclusion were subjects with cerebral aneurysms treated by coil embolization, including both ruptured and unruptured aneurysms. Excluded were subjects with pseudoaneurysms, dissecting aneurysms, or aneurysms treated with staged embolizations. Those subjects treated initially at an outside facility were excluded as packing density would not have been possible to determine. All subjects had been treated at a single institution from 2004 to 2011. Data were collected by a group of research volunteers, which included neurosurgery residents, medical students, college students, and a high school student with an interest in pursuing medicine. Training of the volunteers on how to review the medical record chart and what data to collect on the case report forms was performed by the research coordinator.
Aneurysmal and subject characteristics were determined by review of both chart and angiographic data. The angiographic reports were used to report the number and types of coils placed within the aneurysm. Three-dimensional angiographic data were used to calculate the maximum length, width and height of the aneurysm. Aneurysmal volume was then measured using these dimensions in AngioCalc (http://www.angiocalc.com), a web based open source calculator endorsed by all of the major coil manufacturers. Coil length and packing density were also calculated in AngioCalc, drawing from the data on aneurysm volume and the coil device placed within the aneurysm. Procedure time was determined by analysis of the imaging, defined as time from establishment of working angiographic view to the end of the procedure.
Baseline demographic, aneurysm characteristics, and procedural information were summarized using descriptive summary statistics. The statistics for continuous variables included sample size, mean, median, SD, minimum, and maximum. Categorical variables were described using counts and percentages. The PC 400 and control groups were compared using Fisher's exact test for categorical variables and the Wilcoxon rank sums test for continuous variables. All p values reported are two sided. All analyses were performed using SAS V.9.2 (SAS Institute Inc, Cary, North Carolina, USA).
Subject demographics and aneurysm characteristics preprocedure did not differ significantly between the PC 400 and control groups. The data indicate that the PC 400 coils achieved a higher packing density (36.8% vs 28.1%; p<0.005) with fewer coils (3.9 vs 6.1 coils per aneurysm; p<0.05). In addition, the procedural time for the subjects treated with PC 400 was significantly less (45.7 vs 64.1 min; p<0.05). The results are shown in table 1.
There were no procedural complications in the study group. In the control group, there were six procedural complications, including a perioperative left middle cerebral artery acute infarction, an aneurysm re-rupture, an in-stent thrombosis, a femoral artery pseudoaneurysm formation, and two retroperitoneal bleeds. Only the left middle cerebral artery infarction led to a permanent deficit.
The first example herein is a 4.28 mm by 4.57 mm by 5.95 mm posterior communicating artery aneurysm treated with three PC 400 coils in a patient who presented with subarachnoid hemorrhage. The packing density was 46.55% and the operational time was 19 min. Pretreatment (figure 1A, B) and post-treatment (figure 1C, D) angiographic images are shown. The second example is a 9.8 mm by 7.9 mm by 7.8 mm unruptured internal carotid artery aneurysm that was treated with three PC 400 coils with stent assistance. The packing density was 28.84% and the operational time was 56 min. Pretreatment (figure 2A) and post-treatment (figure 2B, C) angiographic images are shown.
Because aneurysm recanalization carries with it a risk of aneurysm re-rupture,17 there have been many innovations to improve endovascular embolization, including using three-dimensional and coated coils, stent assisted coiling, and liquid embolization.18 Three-dimensional and complex shaped coil configurations have been developed to improve packing density and aneurysm obliteration.19–21 Coils with bioactive coatings (Matrix) have been developed to enhance inflammation and induce aneurysm thrombosis, but have been shown to be equivalent22 ,23 and sometimes inferior6 ,12 ,24 to standard GDC coils. Coils with an expandable hydrophilic coat (Hydrocoil) have been developed to expand within the aneurysm, fill deadspace, and effectively increase the packing density.6 Hydrocoils have generally been found to have similar25 or improved6 ,26 ,27 recanalization rates compared with standard GDC coils. Despite some positive results, these second generation coils have also been associated with rare complications, such as cerebral edema, inflammation, aseptic meningitis, and hydrocephalus following uncomplicated coil embolization.28–31
The PC 400 coils are softer platinum coils with a larger diameter than conventional embolic coils. The PC 400 was specifically designed to address aneurysm recanalization and operational time. The PC 400 is a bare platinum coil with stretch resistant nitinol wire that is marketed as having up to 400% more volume per unit length than conventional embolic coils, tight breaks during all stages of packing because of an inherently softer larger diameter coil, complete coverage and neck to dome stability with multiple shapes, and exceptionally soft curve finishing coils for treatment of the aneurysm neck or for complete treatment of small aneurysms.32 Together, these properties allow for more rapid aneurysm packing and improved packing density.33
Higher packing densities were observed in the PC 400 group in the present study. Improved coil packing density has been shown to be associated with reduced aneurysm recurrence and has therefore been a focus of many studies. Packing density is defined as the coil volume divided by the aneurysm volume. Although the exact mechanism of aneurysm thrombosis is not known, some of the explanations for why there is a decreased recanalization rate with increased packing density include reduced intra-aneurysmal blood flow and reduced wall stress,34 and improved neck coverage and biomechanical stability.14 In general, traditional coils can achieve approximately 30% packing density and complex shaped coils can achieve approximately 40% packing density.11 Sluzewski et al evaluated 145 aneurysms treated with coil embolization and found that coil compaction could be avoided by achieving a packing density of 25% or greater.15
Tamatani et al evaluated 100 aneurysms treated with coil embolization and found on follow-up that aneurysms that remained obliterated had an average packing density of 31% and aneurysms that recanalized had an average packing density of 20%.13 Sadasivian and Lieber were able to achieve large packing densities with complex coil configurations in an in vitro model and concluded that coil configurations that allow for ordered filling of cerebral aneurysms can potentially provide packing densities that are twice those currently achieved.11 Wakhloo et al evaluated 77 aneurysms coiled with complex coils alone, and found favorable packing densities (37%) and recanalization rates (13%).14 Slob et al evaluated 115 aneurysms treated with complex shaped Cordis Trufill coils and found improved packing density (absolute difference of 6.8%), re-opening rates (16% vs 22%), and retreatment rates (8% vs 13%) compared with GDC coils.21 Gaba et al evaluated 50 aneurysms treated with Hydrocoils and found very high packing densities (85%) and lower recurrence rates at 1 year compared with bare platinum coils (17% vs 24%).26
Fewer coils and decreased operational time were also observed in the PC 400 group in the present study. Although risks are small, some of the potential complications of endovascular treatment include stroke, aneurysm rupture, technical failure, and groin hematoma.35 Of these complications, the stroke rate has been shown to increase with longer fluoroscopic time.36 Decreased operational time utilizing PC 400 coils may contribute to an improved safety profile.
There are some limitations of this current study. First, it was retrospective in nature. Second, there were only a small number of cases in the study group. Third, the study group was only being compared with bare platinum coils and not with other types of coils, such as the second generation coated coils. Fourth, although the overall embolization experience of the operators was longer at the time of the PC 400 cohort, there was still a learning curve related to a new larger diameter catheter and coils with the PC 400 system.
Aneurysm embolization with PC 400 achieved statistically significant greater packing density compared with conventional coils. This was achieved with significantly less procedure time and less total number of coils, with a trend towards less total coil length for similar aneurysm volume. In addition, there were no procedure related neurological events. Our data confirm that when compared with conventional coils, the PC 400 is more efficient in the embolization of cerebral aneurysm. Overall, our data show that the PC 400 system can be used to safely embolize cerebral aneurysms with higher packing densities. Follow-up studies will be required to confirm the durability of these treatment results.
The authors would like to thank Simon Buttrick, Eric Sussman, and Sadev Parikh for their valuable contribution to the data collection for this study. Support in the data analysis was provided by a statistician at Penumbra Inc.
Contributors All authors are justifiably credited with authorship, according to the authorship criteria. JRM: acquisition of the data, drafting of the manuscript, critical revision of the manuscript, and final approval. MFP: design, acquisition of the data, drafting of the manuscript, and critical revision of the manuscript. AAP: acquisition of the data, and drafting of the manuscript. AAK: acquisition of the data, and analysis of data. HM: design, acquisition of the data, interpretation of the data, critical revision of the manuscript, and final approval. ABP: conception, design, acquisition of the data, analysis and interpretation of the data, and final approval.
Competing interests ABP (the principal investigator in this study) receives financial compensation as a consultant and lecturer for Penumbra Inc and Codman and Shurtleff Inc, manufacturers of coils used for the treatment of carotid artery aneurysms.
Ethics approval Institutional review board approval was obtained from Mount Sinai School of Medicine.
Provenance and peer review Not commissioned; externally peer reviewed.