Endovascular Treatment of Cerebral Arteriovenous Malformations

Development of Dual-Crosslinking N-Isopropylacrylamide-Based Injectable Hydrogel for Transcatheter Embolization in Swine Model

For decades, endovascular embolization (EE) has been a common technique for the treatment of several vascular abnormalities where the affected vessel is occluded using biocompatible embolic agents. In this work, we developed a NIPAAm-based temperature responsive, dual-crosslinking biocompatible and non-toxic injectable hydrogel system as a liquid embolic agent for EE. The swelling and mechanical properties of the hydrogel were tuned and optimized for its in vivo application. The in vivo study was carried out with nine swine models, including three animals for exploratory study and six animals for acute confirmatory study for the occlusion of surgically created aneurysm and rete mirabile. The polymer hydrogel was delivered into the vascular malformation sites using a catheter guided by angiography. After the injection, the liquid embolic agent was transformed into a solid implant in situ via cross-linking through chemical and thermal processes. During the exploratory study, it was observed that one of the three aneurysms and all the RMs were occluded. During the acute confirmatory study, all the aneurysms and the RMs of six animals were successfully occluded. Overall, our study presents the construction and characterization of a novel injectable hydrogel system capable of successfully occluding vascular malformation in large animals. In the future, after further modification and validation, this material may be used as a liquid embolic agent in clinical studies.

A case of brain arteriovenous malformation treated by high-pressure cooker technique assisted with anhydrous alcohol embolization: A case report

RATIONALE

Brain arteriovenous malformations (BAVMs) are a relatively rare but very dangerous developmental abnormality of the blood vessels. Intracranial hemorrhage is the most common clinical manifestation of BAVMs, and has a high rate of rebleeding, disability, and mortality, which has a serious impact on patients' quality of life and working ability. Endovascular intervention was a new technique that emerged in recent years. Anhydrous ethanol embolization has been used with satisfactory results in the treatment of peripheral arteriovenous malformations, but there is a lack of practice in the treatment of BAVMs. We tried to treat BAVMs by embolizing malformed vessels with anhydrous alcohol in order to provide a safe and effective treatment for more patients with BAVMs.

PATIENT CONCERNS

The patient was admitted to our hospital in the emergency department with "sudden onset of headache for more than 4 hours." At the time of admission, the patient was clearly conscious, not mentally alert, spoke fluently, and had a normal level of orientations. The direct and indirect responses to light were blunted. The patient's muscle strength, muscle tone, and sensation of the extremities were normal. National Institute of Health stroke scale score was 1. Head computed tomography at the onset suggested a right occipital hemorrhage and hematoma formation.

DIAGNOSES

Brain arteriovenous malformations (BAVMs) were suspected based on preoperative imaging findings.

INTERVENTIONS

After obtaining the consent of the patient and their family members, we performed whole brain angiography to determine the location of the lesion, and then, with the help of high-pressure cooker technology, targeted embolization of interventional BAVM was performed. The high-pressure cooker technology was achieved through spring coils, and the embolic material was anhydrous ethanol.

OUTCOMES

The surgery was successful, and the patient recovered well without recurrence.

LESSON

The successful performance of this surgery illustrates the feasibility of anhydrous ethanol-targeted ablation for BAVMs.

Liquid Embolic Agents for Endovascular Embolization: A Review

Endovascular embolization (EE) has been used for the treatment of blood vessel abnormalities, including aneurysms, AVMs, tumors, etc. The aim of this process is to occlude the affected vessel using biocompatible embolic agents. Two types of embolic agents, solid and liquid, are used for endovascular embolization. Liquid embolic agents are usually injectable and delivered into the vascular malformation sites using a catheter guided by X-ray imaging (i.e., angiography). After injection, the liquid embolic agent transforms into a solid implant in situ based on a variety of mechanisms, including polymerization, precipitation, and cross-linking, through ionic or thermal process. Until now, several polymers have been designed successfully for the development of liquid embolic agents. Both natural and synthetic polymers have been used for this purpose. In this review, we discuss embolization procedures with liquid embolic agents in different clinical applications, as well as in pre-clinical research studies.

Dosimetric effects of Onyx embolization on Gamma Knife arteriovenous malformation dose distributions

OBJECTIVE

Patients with arteriovenous malformations (AVMs) treated with Gamma Knife radiosurgery (GKRS) subsequent to embolization suffer from elevated local failure rates and differences in adverse radiation effects. Onyx is a common embolic material for AVMs. Onyx is formulated with tantalum, a high atomic number (Z = 73) element that has been investigated as a source of dosimetric uncertainty contributing to the less favorable clinical results. However, prior studies have not modeled the complicated anatomical and beam geometries characteristic of GKRS. This study investigated the magnitude of dose perturbation that can occur due to Onyx embolization using clinically realistic anatomical and Gamma Knife beam models.

METHODS

Leksell GammaPlan (LGP) was used to segment the AVM nidus and areas of Onyx from postcontrast stereotactic MRI for 7 patients treated with GKRS postembolization. The resulting contours, skull surface, and clinically selected dose distributions were exported from LGP in DICOM-RT (Digital Imaging and Communications in Medicine–radiotherapy) format. Isocenter locations and dwell times were recorded from the LGP database. Contours were converted into 3D mesh representations using commercial and in-house mesh-editing software. The resulting data were imported into a Monte Carlo (MC) dose calculation engine (Pegasos, Elekta Instruments AB) with a beam geometry for the Gamma Knife Perfexion. The MC-predicted dose distributions were calculated with Onyx assigned manufacturer-reported physical constants (MC-Onyx), and then compared with corresponding distributions in which Onyx was reassigned constants for water (MC-water). Differences in dose metrics were determined, including minimum, maximum, and mean dose to the AVM nidus; selectivity index; and target coverage. Combined differences in dose magnitude and distance to agreement were calculated as 3D Gamma analysis passing rates using tolerance criteria of 0.5%/0.5 mm, 1.0%/1.0 mm, and 3.0%/3.0 mm.

RESULTS

Overall, the mean percentage differences in dose metrics for MC-Onyx relative to MC-water were as follows; all data are reported as mean (SD): minimum dose to AVM = −0.7% (1.4%), mean dose to AVM = 0.1% (0.2%), maximum dose to AVM = 2.9% (5.0%), selectivity = 0.1% (0.2%), and coverage = −0.0% (0.2%). The mean percentage of voxels passing at each Gamma tolerance were as follows: 99.7% (0.1%) for 3.0%/3.0 mm, 98.2% (0.7%) for 1.0%/1.0 mm, and 52.1% (4.4%) for 0.5%/0.5 mm.

CONCLUSIONS

Onyx embolization appears to have a detectable effect on the delivered dose distribution. However, the small changes in dose metrics and high Gamma passing rates at 1.0%/1.0 mm tolerance suggest that these changes are unlikely to be clinically significant. Additional sources of delivery and biological uncertainty should be investigated to determine the root cause of the observed less favorable postembolization GKRS outcomes.

Magnetic Resonance Angiography in the Diagnosis of Cerebral Arteriovenous Malformation and Dural Arteriovenous Fistulas: Comparison of Time-Resolved Magnetic Resonance Angiography and Three Dimensional Time-of-Flight Magnetic Resonance Angiography

Background

Traditional digital subtraction angiography (DSA) is currently the gold standard diagnostic method for the diagnosis and evaluation of cerebral arteriovenous malformation (AVM) and dural arteriovenous fistulas (dAVF).

Objectives

The aim of this study was to analyze different less invasive magnetic resonance angiography (MRA) images, time-resolved MRA (TR-MRA) and three-dimensional time-of-flight MRA (3D TOF MRA) to identify their diagnostic accuracy and to determine which approach is most similar to DSA.

Patients and Methods

A total of 41 patients with AVM and dAVF at their initial evaluation or follow-up after treatment were recruited in this study. We applied time-resolved angiography using keyhole (4D-TRAK) MRA to perform TR-MRA and 3D TOF MRA examinations simultaneously followed by DSA, which was considered as a standard reference. Two experienced neuroradiologists reviewed the images to compare the diagnostic accuracy, arterial feeder and venous drainage between these two MRA images. Inter-observer agreement for different MRA images was assessed by Kappa coefficient and the differences of diagnostic accuracy between MRA images were evaluated by the Wilcoxon rank sum test.

Results

Almost all vascular lesions (92.68%) were correctly diagnosed using 4D-TRAK MRA. However, 3D TOF MRA only diagnosed 26 patients (63.41%) accurately. There were statistically significant differences regarding lesion diagnostic accuracy (P = 0.008) and venous drainage identification (P < 0.0001) between 4D-TRAK MRA and 3D TOF MRA. The results indicate that 4D-TRAK MRA is superior to 3D TOF MRA in the assessment of lesions.

Conclusion

Compared with 3D TOF MRA, 4D-TRAK MRA proved to be a more reliable screening modality and follow-up method for the diagnosis of cerebral AVM and dAVF.

Comparing monomodality treatments of low-grade intracranial arteriovenous malformation at Hospital Kuala Lumpur between 2008 and 2011: A retrospective study

Introduction:

Intracranial arteriovenous malformations (AVMs) of Spetzler-Martin grades (SMGs) I-III are treated using either monomodality treatments of microsurgical excision, embolization or stereotactic radiosurgery (SRS), or a combination of two or more of these treatment options. At Hospital Kuala Lumpur, we still practice monomodality treatments for AVMs of these three grades. In this study, we wanted to achieve an understanding whether monomodality treatments can achieve a satisfactory outcome of AVM nidi for patients, for up to 3 years, and to gather an objective data for AVM treatment for the Malaysian population.

Subjects and Methods:

This is a retrospective review of records study. The data are acquired from case notes of patients with intracranial AVM of SMGs I to III who underwent monomodality treatment at Hospital Kuala Lumpur between 2008 and 2011. The patients were followed up with imaging for up to 3 years from the date of treatment. A total of 81 patients were recruited in this study, where 30 underwent microsurgical treatment, 27 underwent embolization, and 24 underwent SRS.

Results:

Total obliteration of AVM nidus was achieved in 96.7% of patients who underwent microsurgery, 8.7% of patients who underwent embolization, and 79.2% of patients who underwent SRS. The modified Rankin scale (mRS) for all three groups showed an improving trend, with the microsurgery group showing the best improvement (from 70% at 3 months to 92.3% at 3 years showing favorable mRS scores).

Conclusions:

The AVM nidus obliteration for each treatment group is comparable to the meta-analysis published in 2011. Each modality had its own set of complications; however, most of the patients in all three groups had either static or improved mRS at the end of the 3-year follow-up.

Segmentation and reconstruction of cerebral vessels from 3D rotational angiography for AVM embolization planning

Diagnosis and computer-guided therapy of cerebral Arterio-Venous Malformations (AVM) require an accurate understanding of the cerebral vascular network both from structural and biomechanical point of view. We propose to obtain such information by analyzing three Dimensional Rotational Angiography (3DRA) images. In this paper, we describe a two-step process allowing 1) the 3D automatic segmentation of cerebral vessels from 3DRA images using a region-growing based algorithm and 2) the reconstruction of the segmented vessels using the 3D constrained Delaunay Triangulation method. The proposed algorithm was successfully applied to reconstruct cerebral blood vessels from ten datasets of 3DRA images. This software allows the neuroradiologist to separately analyze cerebral vessels for pre-operative interventions planning and therapeutic decision making.

Hemorrhage risk after partial endovascular NBCA and ONYX embolization for brain arteriovenous malformation

OBJECTIVE

To estimate for hemorrhage risk of partially endovascularly embolized brain arteriovenous malformation (BAVM).

METHODS

We retrospectively reviewed 147 consecutive patients with BAVM-treated mainly with endovascular N-butyl cyanoacrylate (NBCA) and ONYX embolization. In Kaplan-Meier survival analysis, the index date was the dated of initial endovascular embolization; cases were censored at time of subsequent intracranial hemorrhage (ICH), or loss to follow-up, and multivariate proportional-hazards regression models included age of presentation (≤30 years old), clinical presentations, and other potential confounders.

RESULTS

We reviewed 147 patients with BAVM (58.8% male; mean age±SD at treatment: 27.5±11.1 years) treated with endovascular embolization. One hundred and forty-four NBCA and 76 ONYX embolizations were performed. Complete obliteration of BAVMs was achieved in 29 patients (19.7%). Thirty-two (21.8%) patients were treated with additional Gamma-knife radiosurgery. During 499.5 years of follow-up, 15 partially treated patients suffered a further hemorrhage, which caused four deaths. The crude annual risk of hemorrhage was 3.0% and the annual death rate was 0.8%. Among partially treated patients with hemorrhage at initial presentation, the risk of hemorrhage was 3.8%, while the risk of hemorrhage for patients without hemorrhage at initial presentation was 2.5%. The annual rate of subsequent hemorrhage was 2.6% for non-ICH and 4.2% for ICH in the partial NBCA embolization group compared with 2.4% for non-ICH and 2.4% for ICH in the partial ONYX embolization group.

CONCLUSIONS

The effect of partial AVM embolization with liquid embolic agents may still be unclear as for risk reduction of annual hemorrhage rate of cerebral AVM.

Onyx pulmonary artery embolization after treatment of a low-flow dural arteriovenous fistula: case report

BACKGROUND AND IMPORTANCE

Endovascular management of dural arteriovenous fistulas (DAVFs) has become an accepted primary and often definitive therapy. We present the first documented case of Onyx pulmonary embolism after embolization of a low-flow DAVF.

CLINICAL PRESENTATION

A 63-year-old man presented with subarachnoid hemorrhage secondary to a DAVF. Computed tomographic angiography, magnetic resonance imaging, and initial conventional angiogram were negative. A repeat angiogram demonstrated a DAVF, which was cured with Onyx embolization. A routine chest computed tomography after intervention revealed an asymptomatic Onyx embolization cast in a subsegmental pulmonary artery.

CONCLUSION

Endovascular treatment options include transarterial embolization with microcoils, polyvinyl alcohol particles, n-butyl-2cyanoacrylate, and Onyx (ev3 Neurovascular, Irvine, California). Complications associated with the use of Onyx are low but include embolizate pulmonary embolism. Patients often remain asymptomatic, but for symptomatic patients, conservative treatment options usually result in resolution of symptoms.

Pediatric stroke

INTRODUCTION

Pediatric stroke, while increasingly recognized among practitioners as a clinically significant, albeit infrequent entity, remains challenging from the viewpoint of clinicians and researchers.

DISCUSSION

Advances in neuroimaging have revealed a higher prevalence of pediatric stroke while also provided a safer method for evaluating the child's nervous system and vasculature. An understanding of pathogenic mechanisms for pediatric stroke requires a division of ages (perinatal and childhood) and a separation of mechanism (ischemic and hemorrhagic). This article presents a review of the current literature with the recommended divisions of age and mechanism.

CONCLUSION

Guidelines for treatment, though limited, are also discussed.

Assessment of EmboGel--a selectively dissolvable radiopaque hydrogel for embolic applications

PURPOSE

To evaluate the embolic properties of an alginate-based embolic biomaterial (EmboGel) and its solvent (EmboClear) in treatment of aneurysms.

MATERIALS AND METHODS

EmboGel is a mixture of iohexol and alginate that polymerizes into a hydrocoil when delivered through a coaxial catheter with a distal mixing tip, exposing alginate to a calcium chloride solution. In contrast to previously reported embolic agents, EmboGel can be selectively dissolved by EmboClear, a mixture of the enzyme alginate lyase and ethylenediaminetetraacetic acid (EDTA). The embolic and contrast properties of EmboGel were assessed in in vitro models of saccular aneurysm and an aortic aneurysm endoleak. The dissolvability of EmboGel with EmboClear was assessed further after endovascular delivery in the New Zealand white rabbit in the native aortoiliofemoral territory, a created saccular aneurysm, and the native carotid arteries.

RESULTS

EmboGel effectively filled aneurysm cavities in the case of stent excluded saccular and fusiform aneurysms. EmboGel was readily dissolved by EmboClear in vitro and after in vivo embolization. When the distal abdominal aorta and pelvic arteries were occluded with EmboGel, within 1 minute of EmboClear infusion, patency of the aorta and most of the pelvic circulation was regained as noted by angiography. Embolization in the subclavian artery and numerous distal branches was rapidly dissolved by EmboClear. Finally, the carotid artery occluded with EmboGel regained patency after administration of EmboClear.

CONCLUSIONS

EmboGel is a dissolvable alginate-based biomaterial that can be used for numerous embolic applications. EmboGel can be selectively dissolved with EmboClear, a solution of alginate lyase and EDTA.

Treatment of arteriovenous malformations with hydrocoils in a Swine model

SUMMARY

Arteriovenous malformations (AVM) of the brain are the most common symptomatic congenital vascular malformation of the central nervous system, with significant associated morbidity and mortality. This study compared the feasibility and efficacy of treating AVMs by embolization with hydrocoils with similar treatment with bare platinum coils, using the swine rete mirabile as a model. A right carotid-jugular fistula was created in ten swine.A microcatheter was positioned into the rete mirabile, which was unilaterally (contralateral to the fistula) embolized with hydrocoils in six and bare platinum coils in four swine. Angiograms were evaluated during and immediately after embolization. Embolization with complete cessation of bloodf low in the unilateral rete mirabile was achieved in all animals treated with hydrocoils. The number of coils needed varied from four to seven (diameter 2-4 mm; mean coil length 22.3 cm). Embolization with platinum coils of similar number (seven) and slightly longer length (mean 37.75 cm) had a minimal effect on blood flow, resulting in occlusion of only small compartments. No immediate complications were noted with either coil. Hydrocoils are more effective in achieving embolization than bare platinum coils. Expansion of the hydrocoil over only a few minutes allows precise placement and stabilization of the coil before detachment. Hydrocoilscan be safely placed into small vessels. This approach may be particularly useful to decrease the flow rate, as a first stage of AVM embolizationin high flow AVMs that contain arteriovenous fistulae.

[Failure of transverse sinus dural fistula embolization using ethanol injection]

This is a case report of successful arterial embolization of a dural fistula using absolute alcohol. In this two-part embolization of a dural fistula of the left sagittal venous sinus, the use of n-BCA (n-butyl-cyanoacrylate) was followed by 1 ml of absolute alcohol four months later. The first procedure, using n-BCA via the external carotid, permitted exclusion of the arterial supply coming from the medial meningeal and occipital arteries. Persistence of the blood supply through the internal carotid prompted us to perform the second procedure, to occlude the tentorium marginalis artery, using 1 ml of 95% ethanol. This was followed by a cranial nerve (III) palsy that was reversible. The three-month follow-up was satisfactory, although arteriography after one year showed revascularization of the fistula, which was successfully treated by Onyx. Routinely used in the treatment of superficial vascular malformations, the use of absolute alcohol intracerebrally appears to be unreliable, with results that were only temporary.

Brain aneurysms and arteriovenous malformations: advancements and emerging treatments in endovascular embolization

BACKGROUND AND PURPOSE

Brain aneurysms and vascular malformations can cause cerebral hemorrhages, with devastating consequences for the patients and their families. Since the development of microcatheters and materials used for endovascular embolization, we have witnessed a rapid advancement in the technology and in the number or patients treated with this approach. The aim of this review is to survey recent data relevant to new technologies and emerging treatment strategies in these areas.

SUMMARY OF REVIEW

Clinical trials assessing the safety and efficacy of coil embolization for cerebral aneurysms were based on the use of bare platinum, helical coils. Since then, endovascular operators have been testing and using new materials such as bioactive coils, expandable coils, and complex-shaped coils. Based on the data so far obtained, third and fourth generation coil designs are rapidly emerging and will be ready for clinical application in the near future. Balloon- and stent-assisted coil embolization is enabling the treatment of complex, large-neck aneurysms and the vascular reconstruction of lesions previously considered not treatable. New open- and closed-cell designs allow the navigation and deployment of stents in extremely tortuous vessels. With regards to the embolization of vascular malformations, it is possible to safely navigate microcatheters and microwires through very small arteries previously considered not accessible. In addition, embolization materials such as n-butyl cyanoacrylate and ethylene-vinyl alcohol copolymer are now routinely injected to safely reduce or obliterate large and complex arteriovenous malformations and fistulae.

CONCLUSIONS

Advancements in technology are rapidly improving the endovascular approach to the treatment of cerebral aneurysms and arteriovenous malformations.