IMMEDIATE AND MIDTERM OUTCOMES OF PATIENTS WITH CEREBRAL ANEURYSMS TREATED WITH MATRIX1 AND MATRIX2 COILS

A review of technological innovations leading to modern endovascular brain aneurysm treatment

Tools and techniques utilized in endovascular brain aneurysm treatment have undergone rapid evolution in recent decades. These technique and device-level innovations have allowed for treatment of highly complex intracranial aneurysms and improved patient outcomes. We review the major innovations within neurointervention that have led to the current state of brain aneurysm treatment.

Histological and Transmission Electron Microscopy Results after Embolization with HydroSoft/HydroFrame Coils in Experimental Swine Aneurysm

Coiling and clipping are standard treatment strategies for cerebral aneurysms. Regardless of the strategy used, recanalization may affect the patient's prognosis. The aim of this study was to histologically and morphologically compare the tissue proliferation after coil embolization using bare platinum coils versus second-generation hydrogel coils (HydroSoft/HydroFrame; MicroVention, Inc., Aliso Viejo, CA, USA). Endothelial-like cell proliferation was seen in both groups at 2 weeks after surgery. Macroscopic findings showed a tighter layer at 4 weeks in the hydrogel coil group, and histological and immunohistochemical findings revealed endothelial cell proliferation. This layer became much thicker and tighter at 4 weeks after surgery. Aneurysms treated with second-generation hydrogel coils may be more stable and have a lower incidence of recanalization than those treated with bare platinum coils because of the tight endothelial layer proliferation.

Autologous adipose-derived mesenchymal stem cells improve healing of coiled experimental saccular aneurysms: an angiographic and histopathological study

PURPOSE

Long-term occlusion of coiled aneurysms frequently fails, probably because of poor intrasaccular healing and inadequate endothelialization across the aneurysm neck. The purpose of this study was to determine if attachment of autologous mesenchymal stem cells (MSCs) to platinum coils would improve the healing response in an elastase-induced aneurysm model in rabbits.

MATERIALS AND METHODS

With approval from the institutional animal care and use committee, aneurysms were created in rabbits and embolized with control platinum coils (Axium; Medtronic) (n=6) or coils seeded ex vivo with autologous adipose-tissue MSCs (n=7). Aneurysmal occlusion after embolization was evaluated at 1 month with angiography. Histological samples were analyzed by gross imaging and graded on the basis of neck and dome healing on H&E staining. Fibrosis was evaluated using a ratio of the total area presenting collagen. Endothelialization of the neck was quantitatively analyzed using CD31 immunohistochemistry. χ² and Student's t-test were used to compare groups.

RESULTS

Healing score (11.5 vs 8.0, p=0.019), fibrosis ratio (10.3 vs 0.13, p=0.006) and endothelialization (902 262 μm² vs 31 810 μm², p=0.041) were significantly greater in the MSC group. The MSC group showed marked cellular proliferation and thrombus organization, with a continuous membrane bridging the neck of the aneurysm. Angiographic stable or progressive occlusion rate was significantly lower in the MSC group (0.00, 95% CI 0.00 to 0.41) compared with controls (0.67, 95% CI 0.22 to 0.96) (p=0.02).

CONCLUSIONS

Autologous MSCs attached to platinum coils significantly improve histological healing, as they result in improved neck endothelialization and collagen matrix formation within the aneurysm sac.

Endovascular coiling of small intracranial aneurysms using a very soft bare platinum coil: A comparison of the packing performance of new and old HyperSoft® helical coils

AIMS

Soft and small coils are known to be appropriate for the treatment of small aneurysms. The purpose of this study was to determine whether the new HyperSoft® helical coil, which is softer and smaller than its predecessors, has any effect on the packing performance in a matched-pair study with an old HyperSoft® helical coil.

MATERIALS AND METHODS

Thirty-six consecutive patients harboring 43 cerebral aneurysms treated with new HyperSofts were included in this study. Forty-one aneurysms treated with old HyperSofts were identified from our database as matched controls based on similar volumes and locations. Packing attenuation, adverse events during the procedures, and angiographic occlusions were observed and compared between the two groups.

RESULTS

The mean packing density was significantly higher in the new HyperSoft® group compared to the control group (35.5% vs. 26.9%), and a larger proportion of the aneurysms embolized with the 1.5 mm size coil, which has higher packing density. There was no difference in immediate and midterm angiographic outcomes. There was no difference in the rate of intraprocedural perforation, but there was no intraprocedural rupture related to the 1.5 mm coil.

CONCLUSIONS

The use of new HyperSoft® helical coils allows higher packing density comparable with the old technology. New HyperSoft® coils, especially those with 1.5 mm loop diameter, can be expected to fill smaller residual spaces in small aneurysms and may be helpful in preventing recanalization.

Differences in tissue proliferation and maturation between Matrix2 and bare platinum coil embolization in experimental swine aneurysms

BACKGROUND AND PURPOSE

Recanalization of post-embolization cerebral aneurysms remains a serious problem that influences treatment outcomes. Matrix2 is a bioactive, bio-absorbable, detachable coil that was developed to reduce the risk of recanalization. We examined the short-term efficacy of the Matrix2 coil system, and evaluated the temporal profile of tissue proliferation in a swine experimental aneurysm model compared with the bare platinum (BP) coil.

MATERIALS AND METHODS

Thirty-six experimental aneurysms were created in 18 swine. All aneurysms were tightly packed with Matrix2 or BP coils. Comparative histologic and morphologic analyses were undertaken 1, 2 and 4 weeks post-embolization.

RESULTS

Endothelial-like cells were observed partially lining the aneurysmal opening one week post-embolization with both coil types. At two and four weeks post-embolization, the aneurysms treated with Matrix2 coils had more extensive areas of organized thrombus than those packed with BP coils, but the numbers of functional proliferating endothelial cells identified by immunohistochemistry in the tissue were broadly comparable between the groups. Moreover, morphological analysis suggested there were more mature endothelial cells in aneurysms treated with bare platinum rather than Matrix2 coils.

CONCLUSIONS

Our results indicate that aneurysms embolized with Matrix2 coils build thicker scaffolds for endothelialization, but this is not necessarily evidence of earlier tissue proliferation and maturation than those embolized with BP coils. Matrix2 coils may not be superior to BP coils for preventing aneurysmal recanalization after endovascular treatment of cerebral aneurysms.

Bioactive versus bare platinum coils in the treatment of intracranial aneurysms: the MAPS (Matrix and Platinum Science) trial

BACKGROUND AND PURPOSE

The ability of polymer-modified coils to promote stable aneurysm occlusion after endovascular treatment is not well-documented. Angiographic aneurysm recurrence is widely used as a surrogate for treatment failure, but studies documenting the correlation of angiographic recurrence with clinical failure are limited. This trial compares the effectiveness of Matrix(2) polyglycolic/polylactic acid biopolymer-modified coils with bare metal coils and correlates the angiographic findings with clinical failure (ie, target aneurysm recurrence), a composite end point that includes any incident of posttreatment aneurysm rupture, retreatment, or unexplained death.

MATERIALS AND METHODS

This was a multicenter randomized noninferiority trial with blinded end point adjudication. We enrolled 626 patients, divided between Matrix(2) and bare metal coil groups. The primary outcome was target aneurysm recurrence at 12 ± 3 months.

RESULTS

At 455 days, at least 1 target aneurysm recurrence event had occurred in 14.6% of patients treated with bare metal coils and 13.3% of Matrix(2) (P = .76, log-rank test) patients; 92.8% of target aneurysm recurrence events were re-interventions for aneurysms that had not bled after treatment, and 5.8% of target aneurysm recurrence events resulted from hemorrhage or rehemorrhage, with or without retreatment. Symptomatic re-intervention occurred in only 4 (0.6%) patients. At 455 days, 95.8% of patients with unruptured aneurysms and 90.4% of those with ruptured aneurysms were independent (mRS ≤ 2). Target aneurysm recurrence was associated with incomplete initial angiographic aneurysm obliteration, presentation with rupture, and a larger aneurysmal dome and neck size.

CONCLUSIONS

Tested Matrix(2) coils were not inferior to bare metal coils. Endovascular coiling of intracranial aneurysms was safe, and the rate of technical success was high. Target aneurysm recurrence is a promising clinical outcome measure that correlates well with established angiographic measurements.

Stent-assisted coiling in endovascular treatment of 500 consecutive cerebral aneurysms with long-term follow-up

BACKGROUND AND PURPOSE

Stent-assisted coil embolization has become one of the most preferred techniques in the treatment of wide-neck intracranial aneurysms; however, long-term patency and safety of the self-expanding neurostents and their role in durability of the endovascular treatment has remained ambiguous. We sought to retrospectively examine the long-term results of self-expanding stent usage in conjunction with coil embolization in treatment of wide-neck cerebral aneurysms.

MATERIALS AND METHODS

We coiled 500 wide-neck cerebral aneurysms with different types of self-expanding neurostent assistance in 468 patients. Patient and aneurysm characteristics, pharmacologic therapy protocol, complications, and initial occlusion grades were analyzed. Patients underwent angiographic follow-up at 6 months to 7 years after treatment. DSA or MRA images of all patients were analyzed to assess the occlusion rate of aneurysms and patency of the parent artery.

RESULTS

Enterprise (n = 340), Solitaire (n = 98), Wingspan (n = 41), LEO (n = 16), and Neuroform (n = 5) stent systems were used in this series. Stent-related thromboembolic events occurred in 21 patients and intraoperative rupture occurred in 4 patients. Initially, complete occlusion was achieved in 42.2% of the aneurysms, and, according to the last follow-up data, the rate had progressed to 90.8%. Recanalization rate at 6 months was 8%, whereas the late recanalization rate was 2%.

CONCLUSIONS

The use of stents in endovascular treatment provides high rates of complete occlusion and low rates of recurrence at a long-term follow-up study.

Coil type does not affect angiographic follow-up outcomes of cerebral aneurysm coiling: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Previous studies varied in their conclusions about the superiority of second-generation coils compared with bare platinum. In this systematic review and meta-analysis, we assessed differences in reported unfavorable angiographic outcomes of cerebral aneurysms treated with coil embolization as a function of coil type.

MATERIALS AND METHODS

This systematic review covered 1999-2011 through the use of Ovid MEDLINE and EMBASE. Search terms were "subarachnoid hemorrhage," "intracranial aneurysms," "endovascular treatment," and "coiling." Inclusion criteria were studies reporting >50 aneurysms with imaging follow-up. We defined "unfavorable angiographic outcome" as either "recanalization," <90% occlusion, or "incomplete occlusion" at follow-up. Rates of unfavorable outcomes were pooled through the use of random effects models and compared across various coil types. Multivariate random effects meta-regression models were used to further explore the differences in outcomes related to coil type.

RESULTS

We included 82 studies, comprising 90 patient cohorts, among which, 65 (72%) used bare platinum coils, 8 (8.9%) used Matrix, 11 (12%) used HydroCoil, and 6 (6.7%) used Cerecyte. The overall unfavorable outcome rate was 19% (95% CI: 17%,21%). Unfavorable outcome rates were 20% (95% CI: 17%, 22%) for bare platinum coils, 23% (95% CI: 16%, 29%) for Matrix, 15% (95% CI: 9%, 21%) for HydroCoil, and 15% (95% CI: 7%, 23%) for Cerecyte, respectively. The difference in unfavorable outcome rates among the various coil types was not statistically significant after adjusting for baseline characteristics, including aneurysm size, rupture status, and follow-up duration.

CONCLUSIONS

The rate of unfavorable angiographic outcomes was not statistically different across the major approved coil types. The quality of the evidence, however, remains low because of high heterogeneity, small sample size, and potential publication bias.

Initial experience with an extremely soft bare platinum coil, ED coil-10 Extra Soft, for endovascular treatment of cerebral aneurysms

BACKGROUND AND PURPOSE

The ED coil-10 Extra Soft (EDC-10 ES) is an extremely soft coil with excellent operability for embolization of cerebral aneurysms and is frequently used as a 'finishing coil'. The aim of this study was to evaluate the efficacy and safety of this coil.

METHODS

Clinical data were analyzed retrospectively for 92 consecutive aneurysms for which at least one EDC-10 ES was used. Follow-up angiography at 6 months was available for 69 aneurysms. Initial and follow-up outcomes were evaluated using three-category occlusion grading. Factors that affect the packing density were also investigated.

RESULTS

Of the 92 aneurysms, 63 (68.5%) were classified as complete occlusion, 11 (12.0%) as having a neck remnant and 18 (19.6%) with dome filling immediately after the embolization procedure. The mean ± SD packing density was 29.5 ± 10.6%. Periprocedural complications were observed in three cases (3.3%). At 6 months the rate of completely occluded cases increased to 78.3% (54/69) and those for neck remnant and dome filling decreased to 11.8% (8/69) and 10.1% (7/69), respectively. Recanalization occurred in six aneurysms and one aneurysm was retreated during the follow-up period, giving an overall recurrence rate of 10.0% (7/70). Linear regression analysis showed a significant association of packing density with the percentage EDC-10 ES volume (p<0.001) and with the maximum aneurysm size (p<0.001).

CONCLUSIONS

Use of the EDC-10 ES permits safe and effective embolization of a cerebral aneurysm and contributes to a reduction in the rate of recanalization.

Endovascular Embolization of Intracranial Aneurysms Using Bare Platinum Axium™ Detachable Coils: Immediate and Short-Term Follow-up Results from a Multicenter Registry

Purpose

Axium™ coils were developed to improve the durability of coil-embolized cerebral aneurysms by increasing packing density. The purpose of this prospective multicenter registry was to evaluate the safety and durability of Axium™ coils.

Materials and Methods

One hundred twenty-six patients with 135 aneurysms of ≤ 15 mm in size underwent coil embolization using bare platinum coils, with Axium™ coils constituting over 50% of the total coil length. Immediate and short-term follow-up results were prospectively registered and retrospectively evaluated.

Results

Of the 135 aneurysms (83 unruptured and 52 ruptured), immediate post-embolization angiography revealed complete occlusion in 80 aneurysms (59.3%), neck remnants in 47 (34.8%), and incomplete occlusion in 8 (5.9%). The mean packing density was 42.8% (range, 9.5 - 90%) with Axium™ coil length constituting a mean of 87.9% of total coil length. The rate of procedure-related complications was 16.3%. Procedure-related permanent morbidity and mortality rates were 3.2% and 0.8%, respectively. Follow-up catheter or MR angiography, which was available in 101 aneurysms at 6 - 15 months (mean, 7.7 months), revealed stable or improved occlusion in 95 aneurysms and worsening in 6 aneurysms (5.9%). Lower packing density (< 30%) remained the only predictor for anatomical worsening on multivariable logistic regression analysis (P < 0.05).

Conclusion

In this registry, Axium™ coils showed a relatively low rate of anatomical worsening on short-term follow-up imaging with an acceptable periprocedural safety profile compared to reports of other platinum coils. These results may warrant further study of long-term durability with Axium™ coils in larger populations.

Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association

PURPOSE

The aim of this guideline is to present current and comprehensive recommendations for the diagnosis and treatment of aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

A formal literature search of MEDLINE (November 1, 2006, through May 1, 2010) was performed. Data were synthesized with the use of evidence tables. Writing group members met by teleconference to discuss data-derived recommendations. The American Heart Association Stroke Council's Levels of Evidence grading algorithm was used to grade each recommendation. The guideline draft was reviewed by 7 expert peer reviewers and by the members of the Stroke Council Leadership and Manuscript Oversight Committees. It is intended that this guideline be fully updated every 3 years.

RESULTS

Evidence-based guidelines are presented for the care of patients presenting with aSAH. The focus of the guideline was subdivided into incidence, risk factors, prevention, natural history and outcome, diagnosis, prevention of rebleeding, surgical and endovascular repair of ruptured aneurysms, systems of care, anesthetic management during repair, management of vasospasm and delayed cerebral ischemia, management of hydrocephalus, management of seizures, and management of medical complications.

CONCLUSIONS

aSAH is a serious medical condition in which outcome can be dramatically impacted by early, aggressive, expert care. The guidelines offer a framework for goal-directed treatment of the patient with aSAH.

Bare platinum vs matrix detachable coils for the endovascular treatment of intracranial aneurysms: a multivariate logistic regression analysis and review of the literature

BACKGROUND

Despite increasing acceptance of endovascular coiling for treating intracranial aneurysms, incomplete occlusion remains a limitation. Attempts to reduce recanalization have prompted creation of polyglycolic/polylactic acid-coated (Matrix) coils shown to improve neointima formation; however, previous publications demonstrate conflicting results regarding their efficacy. Few studies account for factors influencing recurrence, and only 4 studies include bare platinum (BP) coil control groups.

OBJECTIVE

To compare initial and short- and mid-term occlusion as well as retreatment rates using Matrix compared with BP coils.

METHODS

Retrospective review of patients undergoing coiling of cerebral aneurysms from 2001 to 2005 was performed. Analysis included a multivariate logistic regression model designed to detect a 35% absolute difference in initial occlusion between coil treatment groups with 80% power.

RESULTS

Complete initial occlusion was achieved in 64% of BP (n = 45) and 63% of Matrix (n = 56) cases (P = 1.0). Follow-up occlusion rates in the short term and mid term were 52% and 60%, respectively, for BP cases and 42% and 67%, respectively, for Matrix cases (P = .24 and P = .38, respectively). After adjusting for size, morphology, volumetric packing density, location, rupture, and balloon remodeling, no difference in initial and subsequent occlusion or retreatment rates for BP coils versus Matrix coils was appreciated.

CONCLUSION

After controlling for factors influencing recanalization, this investigation failed to show a significant difference between coil groups.

Matrix² coils in embolization of intracranial aneurysms: 1-year outcome and comparison with bare platinum coil group in a single institution

BACKGROUND AND PURPOSE

The endosaccular occlusion by using BPC has been useful in the treatment of intracranial aneurysms, but its limited durability remains a deep-seated drawback. The Matrix² coil, one of the bioactive-coated coils, had been developed to improve this limited durability. To evaluate durability of Matrix² coils after embolization of intracranial aneurysms, we retrospectively compared 1-year outcomes with that of BPC groups.

MATERIALS AND METHODS

A group of 121 aneurysms in 114 patients were embolized by using Matrix² coils between April 2006 and September 2008. The BPC group consisted of 151 aneurysms in 137 patients embolized by using BPCs alone between October 2007 and October 2008. The initial outcomes including packing densities, occlusion grades, and periprocedural complications, and the 1-year outcomes on MR angiography were retrospectively compared between the 2 groups.

RESULTS

The Matrix² coil group and BPC group with similar baseline demographic characteristics revealed comparable initial outcomes. The rates of overall recurrence, major recanalization, and retreatment were 17.4%, 14.0%, and 10.7% versus 7.3%, 5.3%, and 4.6%, respectively (P = .066). However, the rates of subgroups with aneurysm volumes between 50 and 200 mm³ were 23.7%, 13.1%, and 10.5% versus 2.2%, 0%, and 0% (P = .022), respectively. The rates of subgroups with packing attenuation <30% were 38.3%, 31.9%, and 23.4% versus 13.3%, 11.7%, and 10% (P = .025), respectively. There were no differences in packing attenuation (P = .152), initial occlusion grade (P = .098), and 1-year outcomes (P = .209) according to the length of Matrix² coils used.

CONCLUSIONS

Overall, initial and 1-year outcomes of the Matrix² coil group were comparable to those of the BPC group. However, in certain subgroups of aneurysm volume and packing attenuation, the 1-year durability of Matrix² coils was inferior to that of the BPC group.

Comparison of cerebral aneurysm volumes as determined by digitally measured 3D rotational angiography and approximation from three diameters

This study compared digital measurement of aneurysm volume by 3D rotational angiography (3D-RA) with an approximation technique using three diameters of an aneurysm to re-interpret previously reported optimal packing densities (volume embolization ratio, VER) in coil embolization of intracranial aneurysms. Estimation of the volume of saccular aneurysms is important for calculation of the VER, which is in turn reported to be useful for prediction of coil compaction. The conventional formula for the volume estimation is V=4/3 π(A/2) (B/2) (C/2), where A, B, and C are the aneurysmal height, length, and width measured on 3D-RA image respectively. Using 3D rotational angiography data from 74 aneurysms, the approximated volume generated using the conventional formula was directly compared with the digitally measured volume. The digitally measured volume varied from 0.003 ml to 7.935 ml, and the dome-to-neck ratio (D/N) from 0.79 up to 4.62. We found that the conventional formula almost systematically underestimated the volume by up to 50 %, particularly when the neck was large relative to the dome (D/N<2). On average, digitally measured volume was 1.26~1.29 times larger than the approximated volume obtained using the conventional formula.Conventional 2D angiography based aneurysm volume calculation tends to underestimate an aneurysm volume, so the so-called VER (volume embolization ratio) could be overestimated.

Evaluation of the characteristics of various types of coils for the embolization of intracranial aneurysms with an optical pressure sensor system

INTRODUCTION

In coil embolization for an intracranial aneurysm, it is important to appropriately choose the coil most suitable for coping with various unforeseen situations. Additionally, because dense coil packing of the aneurysm sac is the most important factor to avoid a recurrence, properly selecting the coil is essential. In this article, the authors measured the coil insertion pressure of various types of coils with a newly developed sensor system, and coil characteristics were investigated.

METHODS

The sensor consists of a hemostatic valve connected to the proximal end of a microcatheter. The sensor principle is based on an optical system. Using this, an experimental silicone aneurysm embolization was performed automatically at constant speed. The pattern of the insertion pressure and the maximum insertion pressure (MIP) were analyzed for the various types of coils. The sensor continuously monitored the mechanical force during the insertions.

RESULTS

The sensor adequately recorded the coil insertion pressure during embolization in each coil. MIP was generally ranked in order of the coil type. The soft type coils required relatively less insertion pressure than standard/helical and 3D type. As for the patterns of coil insertion pressure, each coil presented a saw-like pressure pattern, though we observed some slight differences. 3D type coils showed peak pressure at the moment of "painting". Coil loop diameters barely affected MIP. However, as to the patterns of pressure, larger size coils more often presented the peak.

CONCLUSIONS

Coil characteristics were well evaluated. The results obtained here reflected some actual clinical experience. Furthermore, collecting the in vivo study is mandatory, which may provide clinically useful data.

The effect of aneurysm geometry on the intra-aneurysmal flow condition

Introduction

Various anatomical parameters affect on intra-aneurysmal hemodynamics. Nevertheless, how the shapes of real patient aneurysms affect on their intra-aneurysmal hemodynamics remains unanswered.

Methods

Quantitative computational fluid dynamics simulation was conducted using eight patients’ angiograms of internal carotid artery–ophthalmic artery aneurysms. The mean size of the intracranial aneurysms was 11.5 mm (range 5.8 to 19.9 mm). Intra-aneurysmal blood flow velocity and wall shear stress (WSS) were collected from three measurement planes in each aneurysm dome. The correlation coefficients (r) were obtained between hemodynamic values (flow velocity and WSS) and the following anatomical parameters: averaged dimension of aneurysm dome, the largest aneurysm dome dimension, aspect ratio, and dome–neck ratio.

Results

Negative linear correlations were observed between the averaged dimension of aneurysm dome and intra-aneurysmal flow velocity (r = −0.735) and also WSS (r = −0.736). The largest dome diameter showed a negative correlation with intra-aneurysmal flow velocity (r = −0.731) and WSS (r = −0.496). The aspect ratio demonstrated a weak negative correlation with the intra-aneurysmal flow velocity (r = −0.381) and WSS (r = −0.501). A clear negative correlation was seen between the intra-aneurysmal flow velocity and the dome–neck ratio (r = −0.708). A weak negative correlation is observed between the intra-aneurysmal WSS and the dome–neck ratio (r = −0.392).

Conclusion

The aneurysm dome size showed a negative linear correlation with intra-aneurysmal flow velocity and WSS. Wide-necked aneurysm geometry was associated with faster intra-aneurysmal flow velocity.

Intravascular tissue reactions induced by various types of bioabsorbable polymeric materials: correlation between the degradation profiles and corresponding tissue reactions

Introduction

Several different bioabsorbable polymeric coil materials are currently used with the goal of improving treatment outcomes of endovascular embolization of intracranial aneurysms. However, little is known about the correlation between polymer degradation profiles and concomitant tissue responses in a blood vessel. The authors describe in vitro degradation characteristics of nine different polymeric materials and their corresponding tissue responses induced in rabbit carotid arteries.

Methods

Mass loss and molecular weight loss of nine commercially available bioabsorbable sutures were evaluated in vitro up to16 weeks. The same nine materials, as well as platinum coils, were implanted into blind-end carotid arteries (n = 44) in rabbits, and their tissue reactions were evaluated histologically 14 days after the implantation.

Results

Five of the nine polymers elicited moderate to strong tissue reactions relative to the remaining materials. While polymer mass loss did not correlate with their histologic findings, polymers that showed a faster rate of molecular weight loss had a tendency to present more active tissue reactions such as strong fibrocellular response around the implanted material with a moderate inflammatory cell infiltration. Maxon exhibited the fastest rate of molecular weight loss and poly-l-lactic acid the slowest.

Conclusions

The rate of molecular weight loss may be an important factor that is associated with the degree of bioactivity when bioabsorbable polymers are implanted into blood vessels. For further quantitative analysis, additional experiments utilizing established aneurysm models need to be conducted.

Advances in Interventional Neuroradiology

In 2008 we witnessed a rapid advancement in stent technology, which is reflected in the high number of case reports, publications of case series, and randomized trials. Stents not only served for a combined intrasaccular and extrasaccular treatment of challenging aneurysms but also assisted the revascularization in acute and chronic ischemic conditions of the neurovascular system. Although a self-expanding nitinol semiopen cell stent is currently used for intracranial occlusive disease, a new retrievable closed-cell designed stent is widely used for aneurysms because of its easy delivery through a microcatheter in frequently tortuous head and neck as well as cerebrovascular circulation ( Figure 1 ). However, despite numerous publications in the field, the widespread acceptance of the use of stents to routinely treat carotid stenosis awaits the results of the multicenter randomized clinical trials that should be available in 2009. The role of interventional neuroradiology in the treatment of acute ischemic stroke continues to expand and excite interest.