Comparison of coil types in aneurysm recurrence
Article Outline
- Abstract
- 1. Introduction
- 2. Clinical materials and methods
- 3. Statistical analysis
- 4. Results
- 5. Discussion
- 6. Conclusions
- Acknowledgments
- References
- Copyright
Abstract
Objective
Coiling of saccular aneurysms may result in recurrence requiring retreatment. Aneurysm recanalization may depend on coil type. Coil variations include bare platinum, polymer coated (Matrix), and hydrophylic gel coated (HydroCoil) coils. The effect of coil type on aneurysm recurrence was evaluated.
Methods
Retrospective analysis of prospectively collected database of 100 consecutive, 4–15
mm, coiled, ruptured aneurysms. There were 3 groups based on coil type: (1) bare platinum, (2) HydroCoil, and (3) Matrix. Data collected included age, gender, aneurysm location, follow-up, retreatments and angiographic occlusion and recanalization.
Results
There were 42.4% (n=14) anterior and 57.5% (n=19) posterior circulation aneurysms in the bare platinum, 61.5% (n=16) and 38.45% (n=10) in HydroCoil, and 43.9% (n=18) and 56.1% (n=23) in the Matrix groups. Retreatment was required in 4 (12.1%) bare platinum, 9 (21.9%) Matrix, and 3 (11.5%) HydroCoil groups. On follow-up angiography HydroCoil group had the most number of completely occluded and least number of residual aneurysms (P=0.01), HydroCoils showed the least (n=4), bare platinum an intermediate (n=7), and matrix group the greatest tendency (n=15) to recanalize.
Conclusions
Matrix coils were most likely to need retreatment. Retreatment rates were comparable for bare platinum and HydroCoils. Follow-up angiography demonstrated statistically significant attenuation of residual aneurysms for HydroCoils. Matrix group had the greatest and HydroCoils the least tendency to recanalize. Factors other than coil surface-coating may attenuate aneurysm recurrence.
Keywords: Aneurysm recurrence, Coil compaction, Bare platinum coils, Hydrocoils, Matrix coils
1. Introduction
Recurrence of aneurysms occurs in approximately one-third of patients after coil embolization [19], [21]. This recurrence may be due to incomplete aneurysm occlusion [8], translation of coils into endoaneurysmal thrombus [28], and coil compaction [8], [13], [18]. Aneurysm-specific features, e.g., neck diameter >4mm [9] also contribute to recurrence, as may patient-specific factors, e.g., connective tissue disorders [26], [27]. Coil embolization obliterates aneurysms by resulting in an unorganized thrombus 1 week following treatment, granulation tissue formation after 2 weeks and coil incorporation and endothelial overgrowth at 4 years or more [1]. In an attempt to address aneurysm recurrence, different coil types have been introduced into the market since the original bare platinum GDC coil. These include, polymer coated coils that incite tissue response across the aneurysm neck (Matrix), and coils coated with a hydrophylic gel that expands on exposure to blood, reducing dead space (HydroCoil). Matrix and HydroCoil are proposed as improvements over bare platinum. This study analyzed the role of different coil types in attenuating aneurysm recurrence.
2. Clinical materials and methods
A hundred consecutive ruptured aneurysms ranging in size from 4 to 15mm treated by endovascular coiling, by a single operator, during a period from 04/16/2002 through 12/31/2007 were identified from the senior author's (AJR) prospectively collected database and analyzed retrospectively. The patients were divided into three groups based on the type of coil used: (1) bare platinum including GDC® (Boston Scientific, Fremont, CA), DCS® (Cordis, Miami Lakes, FL), Micrus ACT Microcoil delivery system (Micrus Endovascular Corporation, San Jose, CA); (2) HydroCoil® embolic system (MicroVention, Inc., Aliso Viejo, CA); and (3) Matrix® (Boston Scientific, Fremont, CA). Patient profile including age, gender, and location of aneurysms were recorded for each group. All patients were treated by the same operator (AJR) under standard conditions using systemic heparinization. The type of coils used for each treatment and the frequency of retreatment were determined. The follow-up for each group was also compared. A blinded reviewer (TAA) determined the occlusion and recanalization status of each aneurysm on angiography for each patient using the modified Raymond scale [4]. According to this scale, occlusion status was graded as 1=complete occlusion, 2=residual neck or dog ear, 3=residual aneurysm (fig. 1, Fig. 2). The recanalization status of aneurysms was graded as 1=same, 2=better, and 3=worse when compared to angiography immediately after treatment completion (Table 1).
fig. 1.
Diagrammatic representation of modified Raymond scale demonstrating complete post-treatment aneurysm occlusion (I), dog ear (II) and definite residual aneurysm (III) (with permission from Mayfield Clinic).
Fig. 2.
Anterior communicating artery aneurysm (A) which was deemed completely coiled (B). At follow-up angiography it was graded 1 for recanalization (unchanged).
Table 1. Grading of aneurysm coil occlusion and recanalization using the modified Raymond scale.
| Status | I | II | III |
|---|---|---|---|
| Occlusion | Complete occlusion | Residual neck/dog ear | Residual aneurysm |
| Recanalization | Same | Better | Worse |
3. Statistical analysis
Analysis of variance was performed using JMP® software (SAS Institute, Cary, NC) to assess age and aneurysmal size for each group. Statistically significant variables were further tested by Tukey-Kramer HSD test. Contingency analysis including Pearson test, likelihood ratio, and correspondence analysis were performed for gender, aneurysm location, treatment, recurrence requiring retreatment, and angiographic data. Statistically significant variables were further tested by regression analysis. A P-value of <0.05 was considered significant.
4. Results
There were 100 consecutive coil embolization treatments for ruptured aneurysms in 97 patients. One patient from each group had two aneurysms, either of which could have been responsible for the subarachnoid hemorrhage. Therefore, both aneurysms were treated within days of each other. The patients included 74 women and 23 men with a mean age of 56.7 years (median 55; range 27–91 years). The mean age in each group was 55.1 (bare platinum), 61.5 (HydroCoil) and 54.9 (Matrix). The mean age of women was 56.7 (median 55; range 27–91 years), while the mean age of men was 56.3 (median 56; range 30–79 years). The distribution of treatments was bare platinum 33 (1 with Neuroform stent), HydroCoil 26 (2 with Neuroform stents), and Matrix 41 (1 with Neuroform stent). The mean aneurysm size (mm) for each treatment group was 7.6 (bare platinum), 7.6 (HydroCoil), 6.9 (Matrix). The groups were statistically comparable. A majority of aneurysms were distributed at the anterior communicating artery (n=35), posterior communicating artery (n=27), and basilar artery (n=15) (Table 2). Using the International Study of Unruptured Intracranial Aneurysms system [12] to classify the aneurysms into anterior and posterior, there were 42.4% (n=14) anterior and 57.5% (n=19) posterior circulation aneurysms in the bare platinum group, 61.5% (n=16) and 38.4% (n=10) in HydroCoil, and 43.9% (n=18) and 56.1% (n=23) in Matrix groups. Aneurysmal recurrence requiring retreatment was 21.9% (n=9) for Matrix, 11.5% (n=3) for HydroCoil, and 12.1% (n=4) for bare platinum. Eighty-three aneurysms in 82 patients were treated at least 1 year, and 96 aneurysms in 94 patients were treated at least 6 months prior to the close of the study. Three aneurysms in 2 patients were not due for any follow-up angiography prior to the close of the study according to our routine. No angiographic follow-up was obtained for an additional 33 aneurysms in 33 patients. At least one follow-up angiogram was performed for 64 aneurysms. Angiographic follow-up was available for 58 aneurysms at 6 months: 51.5% (n=17) bare platinum-treated aneurysms, 65.9% (n=27) Matrix, and 53.8% (n=14) HydroCoil. A follow-up of 1 year or more was available for 51 aneurysms: 56.6% (n=17) bare platinum, 44% (n=11) HydroCoil, and 58.9% (n=23) Matrix coils. Correspondence analysis demonstrated a proportionately larger number of males, anterior circulation aneurysms, and a follow-up of less than 1 year in the HydroCoil group, and far greater recurrence requiring retreatment in the Matrix group. However, all four variables were statistically insignificant.
Table 2. . Distribution of aneurysms by location and type of coil used for treatment.
| Location | Treatment | ||
|---|---|---|---|
| Bare platinum % (n) | HydroCoil % (n) | Matrix % (n) | |
| Anterior communicating (n=35) | 30.3 (10) | 42.3 (11) | 34.1 (14) |
| Posterior communicating (n=27) | 27.2 (9) | 26.9 (7) | 26.8 (11) |
| Basilar artery (n=15) | 15.1 (5) | 11.5 (3) | 17.0 (7) |
| Internal carotid (n=2) | 4.8 (2) | ||
| Middle cerebral (n=6) | 9.09 (3) | 11.5 (3) | |
| Opthalmic (n=4) | 3.0 (1) | 3.8 (1) | 4.8 (2) |
| Superior cerebellar (n=4) | 6.0 (2) | 4.8 (2) | |
| Anterior inferior cerebellar (n=3) | 3.0 (1) | 4.8 (2) | |
| Anterior choroidal (n=1) | 3.0 (1) | ||
| Pericallosal (n=1) | 3.8 (1) | ||
| Posterior inferior cerebellar (n=1) | 2.4 (1) | ||
| Vertebral (n=1) | 3.0 (1) | ||
Angiography from the day of treatment was available for blinded radiographic review for 57 treatments and for follow-up angiography for 54 treatments (Table 3). There was a statistically significant difference in the follow-up modified Raymond scale (P=0.01), where the HydroCoil group had the most (60%) completely occluded aneurysms and the least residual aneurysms (13.3%) (Table 3). When assessed for recanalization, the HydroCoil group showed the least (26.6%), bare platinum intermediate (43.7%), and Matrix group showed the greatest (65.2%) trend to recanalize (Table 3). The difference between the three groups, however, remained statistically insignificant (P=0.08).
Table 3. Outcome of endovascular treatment for three types of coils by grading angiographic occlusion and recanalization.
| Treatment | |||
|---|---|---|---|
| Bare platinum % (n) | HydroCoil % (n) | Matrix % (n) | |
| Immediate MRS (n=57) | |||
| Grade I % (n) | 44.4 (8) | 50 (8) | 34.7 (8) |
| Grade II % (n) | 22.2 (4) | 25 (4) | 30.4 (7) |
| Grade III % (n) | 33.3 (6) | 25 (4) | 34.7 (8) |
| Follow-up MRS (n=54) | |||
| Grade I % (n) | 25 (4) | 60 (9) | 21.7 (5) |
| Grade II % (n) | 31.2 (5) | 26.6 (4) | 26 (6) |
| Grade III % (n) | 43.7 (7) | 13.3 (2) | 52.1 (12) |
| Recanalization (n=54) | |||
| Grade I % (n) | 37.5 (6) | 60 (9) | 30.4 (7) |
| Grade II % (n) | 18.7 (3) | 13.3 (2) | 4.3 (1) |
| Grade III % (n) | 43.7(7) | 26.6 (4) | 65.2 (15) |
5. Discussion
Several different factors may be implicated in the pathogenesis of aneurysm recurrence including genetic predisposition [14], [20], [24], [25], connective tissue disorders [11], [25], [30], morphology of the aneurysm [5], [9], [32], as well as coil compaction [5], [8]. The phenomenon of coil compaction can be defined as a decrease in the volume of coil mesh that leads to more contrast material filling aneurysm at follow-up angiography as compared with the immediate post-embolization angiogram [29]. The entrance of contrast into a previously well-coiled aneurysm sac indicates its re-exposure to the circulation. Consequently, there is a risk of re-rupture, albeit at a lesser rate [2], [7]. Of all the factors considered in aneurysmal recurrence, coils are unique to endovascular procedures. Therefore, they become the obvious targets for modification in an attempt to improve the treatment results of aneurysm coil embolization. This study focused on aneurysmal recurrence associated with the type of coils used. Therefore, the rationale for the three groups was based on the differences in their mechanism of action.
Bare platinum coils, such as GDC, induce aneurysmal thrombosis by virtue of their presence as a foreign body and the electrolytic reaction induced at the time of detachment [15]. However, a significant degree of aneurysmal recurrence has been noted with GDC treatment, when compared to surgical clipping [19], [21].
In Matrix coils the inflammatory response is enhanced in an attempt to attenuate aneurysm recurrence. To this effect, Matrix coils have a coating of bioabsorbable copolymer on the inner platinum coil. The hydrolysis of this copolymer at 3 months produces an inflammatory response that is greater than with platinum alone. The inflammatory reaction is believed to induce an accelerated smooth muscle cell migration leading to enhanced thrombogenesis and scar retraction [16]. However, the data available in literature do not support an attenuation in recurrence rate with the use of Matrix coils [6], [10], [23], [31], [33]. Our study found the rate of recurrence to be highest in the aneurysms treated with Matrix coils. Additionally, Matrix coils have a higher price, are stiffer and have a greater friction compared to bare platinum coils [3]. The stiffness may contribute to recurrence when Matrix coils are used alone because, without the addition of the relatively more pliant bare platinum coils, aneurysm filling may remain incomplete [17].
By comparison to the other two types, HydroCoil embolic system targets dead space, which is present even in the very well-packed aneurysm. This space occurs because of the irregular shape of the aneurysm and is also present interstitially between the coils and their loops. Therefore, in a HydroCoil, the platinum coil is coated with an expanding gel. The gel is activated when it comes in contact with blood after which the coil should be placed in the aneurysm within 5min. The gel expands within a 20-min period in a “space-seeking” fashion to take up a greater volume than a bare platinum coil would. Due to the trait of expanding only into the available space, the coils are believed to avoid exerting excessive expansile force on the aneurysm wall [16]. In our study, HydroCoils did require less retreatments compared to Matrix coils and a comparable number of retreatments as bare platinum. Angiographic data demonstrated superior results with HydroCoils (fewer residual and recanalized aneurysms) compared to bare platinum- and Matrix-treated aneurysms.
It is recognized that the experience and technical skills of the operator may also be significant, impacting factors in aneurysmal recurrence. These factors were neutralized for all three groups by using the data from a single operator. Additionally, by limiting the study to a single operator, no confounding factors consequent to procedure variability or different treatment protocols occurred. By confining the treatment of each aneurysm to a particular coil type rather than using combinations, another confounding factor was eliminated.
It is also recognized that the decision to treat recurrent aneurysms is not based solely on recurrence. The risks associated with treatment, the patient's clinical condition and prognosis are taken into account. This particular situation did not arise in the study population.
Small aneurysms (less than 4mm) were excluded from the study because in the senior author's experience, the morbidity associated with treating these by endovascular intervention is high [22]. Aneurysms larger than 15mm were excluded from the study because of the potential mass effect from the coils.
The subjectivity of the grading system for angiographic data must be emphasized. Based on the evaluators’ experience and biases, the grading may be too rigid (Fig. 3) or liberal, and both trends may confound interpretation and correlation of clinical and angiographic data. In the absence of a better grading system, one solution when resources permit, may be to have multiple blinded evaluators grade the angiograms and then accept the grade given by the majority.
Fig. 3.
An anterior communicating aneurysm prior to (A) and immediately following coil embolization (B). This immediate post-treatment result was graded as 3 (definite residual aneurysm). Typically this appearance would be scored as 1. The stringent grade application reflects the subjectivity of the grading system. At follow-up (C) the aneurysm occlusion was graded 1 (complete occlusion) and recanalization was scored as 2 (improved angiographic appearance).
While this study clinically and angiographically has more favorable results for HydroCoils over the other two coil types, the treatment results with the other two coil types may be improved by using a combination of coil types, rather than confining oneself to a single type [3]. However, such a strategy would require anticipatory preplanning to ensure the appropriate type and size of microcatheter is selected that is able to handle the different coil types. Using a combination of coils may be more expensive, e.g., two different types of detachment devices may need to be employed, where a single device suffices when confined to a particular type of coils. Additionally, our setup for the HydroCoil embolic system involves placement of a one-way stopcock between the hub of the catheter and the touhy. This is to prevent blood from accumulating in the microcatheter system during the introduction of coil into the touhy, causing the coil to inadvertently expand within the microcatheter. The same becomes a redundant step for the other two coil types.
6. Conclusions
Clinically, the rates of retreatment were comparable in patients with bare platinum and HydroCoils. Matrix coils were more likely than GDCs and HydroCoils to need re-treatment. The difference, however, was statistically insignificant.
Angiographically, there was a statistically significant attenuation in residual aneurysms in the HydroCoil group on follow-up imaging. The bare platinum and Matrix groups were comparable. The Matrix group manifested the greatest tendency, bare platinum intermediate, and HydroCoil the least tendency to recanalyze. The angiographic data, however, is subjective and prone to individual variation. Clinical and angiographic data concurrently indicate that factors other than coil surface-coating may attenuate aneurysm recurrence. No clear advantage in preventing recurrence requiring retreatment was demonstrated by coating platinum coils.
Acknowledgments
We thank Marshfield Clinic Research Foundation for its support through the assistance of Alice Stargardt in the preparation of this manuscript.
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PII: S0303-8467(11)00218-6
doi:10.1016/j.clineuro.2011.07.017
© 2011 Elsevier B.V. All rights reserved.
