Morphological studies of human arteriovenous malformations. Effects of isobutyl 2-cyanoacrylate embolization

Preclinical study on an animal model of a new non-adhesive cyanoacrylate (Purefill®) for arterial embolization

PURPOSE

The goal of this study was to assess the distal dispersion, the adhesion strength to catheter, the vascular toxicity and the ability in excluding embolized vessels using Purefill^® (α-hexil-cyanoacrylate) as embolic material, which is a new high purity cyanoacrylate and compare these results with those obtained with N-butyl-2-cyanoacrylate (Histoacryl^®) and a mixture of N-butyl-2-cyanoacrylate and methacryloxysulfolane.

MATERIAL AND METHODS

In six pigs, the right rete mirabile (RM) and right renal arteries were embolized with α-hexil-cyanoacrylate, and the left rete mirabile and left renal artery were embolized with N-butyl-2-cyanoacrylate and N-butyl-2-cyanoacrylate+Methacryloxysulfolane for comparison. One minute after glue injection through the microcatheter, displacements of the kidney and the pharyngeal artery were measured on angiographic images, before exercising any traction and during catheter pulling, when the forces were maximal. Displacement was measured in terms of distance (mm) with respect to renal pedicles and in terms of angle (°) with respect to the rete. After acute embolization (4 pigs) or three-month follow-up (2 pigs), the kidneys and the RM were removed and further analysed using computed tomography and histopathological examination.

RESULTS

Similar short and long-term embolic efficacies were observed with the three glues. The mean displacement distances of renal pedicles were 2.6mm for α-hexil-cyanoacrylate, 22.6mm for N-butyl-2-cyanoacrylate and 19.8mm for N-butyl-2-cyanoacrylate+Methacryloxysulfolane (P=0.021). The mean angles of displacement of the ascending pharyngeal arteries were for 12.2° for α-hexil-cyanoacrylate, 23.5° for N-butyl-2-cyanoacrylate and 30° for N-butyl-2-cyanoacrylate+Methacryloxysulfolane (P=0.070). Histopathologically, findings were similar for the three glues, immediately and 90 days after embolization.

CONCLUSION

α-hexil-cyanoacrylate has occlusive efficacy in the short and long term similar to those of N-butyl-2-cyanoacrylate and N-butyl-2-cyanoacrylate+Methacryloxysulfolane. In addition, histopathological changes are similar with the three glues immediately or 90 days after embolization. Conversely, α-hexil-cyanoacrylate results in a reduced angle and distance of displacement compared to the other two glues, assumably reflecting a limited adhesive strength.

Feasibility, Safety, and Efficacy of Flow-Diverting Stent-Assisted Microsphere Embolization of Fusiform and Sidewall Aneurysms

BACKGROUND

Treatment of wide-necked internal carotid artery aneurysms is frequently associated with incomplete occlusion and high recurrence rates. Furthermore, platinum coils cause strong beam-hardening artifacts, hampering subsequent image analyses.

OBJECTIVE

To assess the feasibility, safety, and efficacy of flow-diverting, stent-assisted microsphere embolization of fusiform and sidewall aneurysms in vitro and in vivo.

METHODS

Using a recirculating pulsatile in vitro flow model, 5 different aneurysm geometries (inner/outer curve, narrow/wide neck, and fusiform) were treated (each n = 1) by flow-diverting stent (FDS) implantation and subsequent embolization through a jailed microcatheter using calibrated microspheres (500-900 μm) larger than the pores of the FDS mesh. Treatment effects were analyzed angiographically and by micro computed tomography. The fluid of the in vitro model was filtered to ensure that no microspheres evaded the aneurysm. The experiment was repeated once in vivo.

RESULTS

In vitro, all 5 aneurysms were safely and completely occluded by FDS-assisted microsphere embolization. Virtually complete aneurysm occlusion was confirmed by angiography and micro computed tomography. No microspheres escaped into the circulation. The experiment was successfully repeated in 1 pig with a sidewall aneurysm generated by vessel occlusion. An embolic protection system placed distally of the FDS in vitro and in vivo (each n = 1) contained no microspheres after the embolization. Thus, no microspheres were lost in the circulation, and the use of an embolic protection system seems feasible to provide additional safety.

CONCLUSION

FDS-assisted microsphere embolization of fusiform and sidewall aneurysms is feasible and yields virtually complete aneurysm occlusion while avoiding coil-associated beam-hardening artifacts.

Endovascular and microsurgical treatment of cerebral arteriovenous malformations: Current recommendations

Background:

Cerebral arteriovenous malformations (AVMs) can be a heterogeneous pathological entity whose management requires a complex decision-making process due to the risks associated with their treatment and natural history. Despite the recently published conclusions of the aborted Randomized Trial of Brain Unruptured AVMs (ARUBA) trial, the authors of this article believe multimodality intervention in general and microsurgical resection in particular continue to play a major role in the management of carefully selected ruptured or unruptured AVMs.

Methods:

The authors provide an overview of their methodology for endovascular intervention and microsurgical resection and share their technical nuances for successful embolization and microsurgical resection of AVMs with special emphasis on complication avoidance.

Results:

The authors have achieved successful outcomes in embolization and resection of cerebral AVMs when using their methodology.

Conclusions:

These lesions are among the most technically difficult pathological entities handled by the cerebrovascular specialist, and an overview of technical concepts to help systematize this challenging and variable endeavor can improve the safety of their treatment.

Endovascular treatment of cranial arteriovenous malformations and dural arteriovenous fistulas

Pial arteriovenous malformations (AVMs) and dural arteriovenous fistulas (DAVFs) are high-flow vascular lesions with abnormal communications between the arterial and venous system. AVMs are congenital lesions, whereas DAVFs are considered acquired lesions. Both can cause significant morbidity and mortality if they rupture and result in intracranial hemorrhage. The primary goal of treatment is to eliminate the risk of bleeding or at least decrease it. Because the epidemiology, clinical presentation, and classification of AVMs and DAVFs have been covered in previous articles in this issue, the authors only briefly touch on these subjects as they relate to endovascular treatment.

Arterial distribution characteristics of Embozene particles and comparison with other spherical embolic agents in the porcine acute embolization model

PURPOSE

To determine the arterial distribution pattern of the embolic agent Embozene within the porcine kidney and compare it with those of other spherical embolic agents.

MATERIALS AND METHODS

Embozene, Embosphere, Bead Block, and Contour SE in size classes of 100-300 microm, 500-700 microm, and 700-900 microm and Embozene and Embosphere in the size class of 40-120 microm were used for total arterial occlusion in minipig kidneys. Organs were evaluated microscopically regarding vascular distribution of the different embolic agents and particle sizes.

RESULTS

The following variations of arterial distribution were identified. In the 40-120-microm size class, Embosphere particles penetrated significantly deeper compared with Embozene (P = .04). In the 100-300-microm size class, Bead Block showed a significantly deeper distribution as microscopy identified particles in arteries much smaller than their nominal size. In the 500-700-microm size class, Embosphere and Contour SE showed a deeper distribution. The most uniform arterial distribution was observed in the 700-900 microm size class,. However, few Embosphere and Contour SE particles were found in arcuate arteries, also indicating a distal distribution.

CONCLUSIONS

Throughout the four most-used size classes, from very small (40-120 microm) to large (700-900 microm), the distribution characteristics of the four tested materials vary substantially. Particularly, small Embosphere particles and small Bead Block particles showed a more distal distribution, as did medium-sized Embosphere and Contour SE particles. In the largest investigated size class, the distribution was more uniform. In general, the Embozene particles are very uniform in size, and they seem to reach vessels closely corresponding to their nominal size.

Operation for delayed symptomatic brain oedema after treatment of an arteriovenous malformation by embolization and radiosurgery

A patient with a Spetzler-Martin-grade-III AVM, initially embolized and then stereotactically irradiated, who - with a latency of several months - showed progressive neurological deterioration, is reported. Magnetic resonance imaging revealed enormous ipsilateral brain oedema, which did not respond to dexamethasone. Upon further neurological deterioration the former AVM nidus plus an adjacent rim of brain tissue were removed and the patient recovered considerably. It is concluded that embolization in conjunction with irradiation may impair the blood-brain-barrier with resulting long-term oedema in the surrounding brain, and that surgical treatment should be considered in selected cases.

Endovascular Treatment of Cerebral Arteriovenous Malformations

The modern management of cerebral arteriovenous malformations (AVMs) is based on three therapeutic modalities: microneurosurgery, endovascular embolization, and stereotactic radiosurgery. Embolization facilitates subsequent radiosurgery by reducing the volume of the nidus, prepares the resection of surgically accessible AVMs, and immediately addresses the risks related to associated intra/extranidal aneurysms and arteriovenous fistulas. We discuss in this article the current state of AVM endovascular therapy.

Effects of a mixture of a low concentration of n-butylcyanoacrylate and ethiodol on tissue reactions and the permanence of arterial occlusion after embolization

OBJECTIVE

Cyanoacrylates are the most commonly used liquid embolic agents. For embolization of arteriovenous malformations, a mixture of a low concentration of n-butylcyanoacrylate (NBCA) and Ethiodol (Savage Laboratories, Melville, NY) has been recommended for deeper penetration of the nidus. Dilution of NBCA, however, might result in different degrees of tissue reaction and might influence the permanence of vessel occlusion, with an increased risk of vessel recanalization. We compared tissue reactions induced by different NBCA/Ethiodol mixtures and analyzed the permanence of their embolic effects.

METHODS

NBCA was diluted with Ethiodol to prepare the following standard solutions: Mixture A, low concentration (NBCA/Ethiodol ratio of 20:80); Mixture B, high concentration (50:50). The study was designed in two parts, because tissue reactions after embolization are considered to be a combination of foreign body reactions to solidified material and reactions to the injured blood vessel. Foreign body reactions were studied by intramuscularly injecting both glue mixtures into the backs of 18 rats. Specimens were obtained at various times after implantation. Immunohistochemical analysis and esterase staining were used to detect macrophages and neutrophils, respectively. The densities of these inflammatory cells were calculated and statistically compared. To study the degree of vascular wall injury and the permanence of embolic effects, the renal arteries in 48 rabbits were embolized with NBCA Mixture A or B. Six specimens for each group were obtained at various times after embolization.

RESULTS

There was no significant difference in foreign body reactions between groups treated with Mixtures A and B, at any time. However, the macrophage density was larger for both groups at 3 months versus 3 days and for the group treated with Mixture B at 3 months versus 2 weeks. There was no difference in the degree of vessel wall injury. None of the embolized vessels demonstrated evidence of recanalization.

CONCLUSION

The low concentration of NBCA induced a tissue response similar to that of the high-concentration form. Embolized vessels exhibited no greater incidence of recanalization. Therefore, embolization of arteriovenous malformations with diluted NBCA may be safe.

Nontoxic embolic liquids for treatment of arteriovenous malformations

Interventional radiology is becoming one of the standard treatments of arteriovenous malformation (AVM). Cyanoacrylate derivatives and polymer solutions are widely used to occlude the AVM nidus by their injection through a catheter, but they are far from satisfactory embolic liquids. For instance, cyanoacrylate derivatives sometimes glue the catheter to the artery, resulting in serious complications; in addition, the organic solvents used to dissolve polymers cause damage to the surrounding brain tissue of the AVM. Therefore, we attempted to develop embolic liquids by dissolving poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) in Iopamiron with an addition of a small amount of ethyl alcohol. This new embolic liquid is not cytotoxic and is easily injected into the AVM through a thin, long catheter to effectively occlude the AVM.

Embolic materials for endovascular treatment of cerebral lesions

Recently developed soft microcatheters can be maneuvered endovascularly into the brain, permitting treatment of lesions without conventional neurosurgery. Progress in biomaterial science has contributed significantly to the development of this new therapeutic modality termed intravascular neurosurgery or interventional neuroradiology. Although embolic materials play an important role, ideal materials have yet to be devised. Various embolic materials in clinical use are reviewed, such as cyanoacrylates, ethylene-vinyl alcohol copolymer mixtures, Ethibloc, ethanol, estrogen, poly(vinyl acetate), cellulose acetate polymer, poly(vinyl alcohol), gelatin sponges, microfibrillar collagen, surgical silk sutures, detachable balloons, and coils. The materials are reviewed in the context of treatment application for various brain lesions, such as arteriovenous malformations, cerebral aneurysms, and head and neck tumors. Further developments in biomaterial polymer science can bring about progress against brain diseases.

Application of thermosensitive polymers as a new embolic material for intravascular neurosurgery

Application of thermosensitive polymers as an embolic material for intravascular neurosurgery was investigated. We intended to use thermosensitive polymers to occlude vessels by precipitation in response to body temperature. Copolymers of N-isopropylacrylamide (NIPAM) and N-n-propylacrylamide (NPAM) were selected as thermosensitive polymers. To determine the optimal lower critical soluble temperature (LCST) for the embolic material, we developed an in vitro flow model. In this study the copolymers with an LCST of 24-26 degrees C showed appropriate precipitation. To prove the occlusion of vessels in vivo, we injected the copolymers into a rabbit kidney through a microcatheter. The extent of embolization was judged by angiography and histological examination. An acute toxicity test of the copolymer of NIPAM and NPAM was performed in comparison with that of the NIPAM monomer. The copolymer used in this paper showed no acute toxicity in mice. Water solubility, non-adhesiveness, and non-toxicity are the advantages of the use of thermosensitive polymers as an embolic material. By changing the LCST, various embolic materials can be designed. Based on our results, we believe that the application of thermosensitive polymers as a new embolic material is very promising.

Cure, morbidity, and mortality associated with embolization of brain arteriovenous malformations: a review of 1246 patients in 32 series over a 35-year period

Published reports of cure, morbidity, and mortality associated with the embolization of 1246 brain arteriovenous malformations during the last 35 years were reviewed. Embolization resulted in cure in 5% of arteriovenous malformations. The cure rates of embolization were 4% in reports of 708 patients published before 1990 and 5% in reports of 538 patients published since 1990 (P = not significant). Temporary morbidity from embolization was 10%, and permanent morbidity was 8%. Permanent morbidity was 9% before 1990 and 8% since 1990 (P = not significant). Death after embolization of brain arteriovenous malformations occurred in 1% of patients. Mortality associated with the embolization was 2% before 1990 and 1% since 1990 (P = not significant). Long-term morbidity associated with the use of neurotoxic embolization materials is worrisome but has never been proven.

Persistent feeding arteries to angiographically completely embolized arteriovenous malformation demonstrated by intraoperative color-flow Doppler testing: report of two cases

Two cases of arteriovenous malformation (AVM) treated preoperatively by endovascular embolization that appeared to be completely occluded after embolization are presented. Seven and 12 days later, respectively, these patients underwent resection of their AVM. At the time of surgery, intraoperative color-flow Doppler studies revealed persistent feeding arteries to an active residual nidus of the AVM. The significance of this finding is presented in light of previous published literature.

The combined management of cerebral arteriovenous malformations. Experience with 100 cases and review of the literature

A series of 100 patients treated for a cerebral arteriovenous malformation (AVM) is presented. Patients were admitted between 1985 and April 1992. Two groups are considered: the first group including 52 patients treated before the availability of radiosurgery (1985-1988), and the second group including 48 patients treated after the availability of radiosurgery (1989-1992). AVM's were classified in five grades according to the Spetzler's Grading System. Three techniques of treatment were used: surgical resection, intravascular embolization (with cyanoacrylate), and radiosurgery (linear accelerator). These three techniques were used either alone or in association, giving four types of management: surgical resection alone, embolization and resection, embolization alone, and radiosurgery (alone, or after embolization, or after surgical resection). From 1989 on, the availability of radiosurgery was responsible for the decrease of the "embolization and resection" group, which until then was predominantly used as well for low-grade (I, II, III) as for high-grade AVM's (IV, V). Overall, for the low-grade AVM's, the treatment of choice was surgical resection (79% of cases), with pre-operative embolization in one-half of these cases; the other low-grade AVM's were irradiated, with various combinations. For the high-grade AVM's, the treatment of choice was intravascular embolization (95% of cases), either alone, or followed by resection (45%) or radiosurgery (9%). Results were evaluated in terms of deterioration following treatment, in five groups: no deterioration (59%), minor deterioration (20%), long-lasting deficit (10%), major deterioration (5%), and death (6%). Overall, results improved after 1989: favourable outcome (no deterioration and minor deterioration) increased from 67% to 90%. Results were not related to the patients' age. More favourable results were obtained for low-grade AVM's (93%) than for high-grade AVM's (60%). For the low-grade AVM's the evolution from 1989 on (favourable outcomes increasing from 89% to 96%) occurred with the lowering of the mortality rate. For the high-grade AVM's, the evolution from 1989 onwards (favourable outcome increasing from 46% to 78%) occurred with the decrease of the cases with deficits. The angiographic results were strongly related to the management: 95% of complete eradication after surgical resection and 5% only after embolization alone. Concerning the results in irradiated cases, the follow-up is not long enough. The review of the neurosurgical literature since 1972 demonstrates progressive modifications in the therapeutic attitude as regards AVM's. The surgical management which was predominantly used at the beginning gave way progressively to a combined management, with a combination of embolization, surgery, and lately radiosurgery.(ABSTRACT TRUNCATED AT 400 WORDS)

Arteriovenous malformations of the brain: choosing embolic materials to enhance safety and ease of excision

The authors report their experience with surgical resection of 108 previously embolized arteriovenous malformations (AVM's). Embolization was performed via only transfemoral catheterization in 70 lesions and via the surgical exposure of feeding vessels in 32. The remaining six patients were referred for resection following silicone sphere embolization elsewhere. Materials used included polyvinyl alcohol (PVA) foam, platinum microcoils, detachable silicone balloons, surgical silk, a mixture of 33% ethanol and microfibrillar collagen, and isobutyl cyanoacrylate (IBCA). It is believed that proximal arterial occlusion with balloons is an inferior choice for preresection embolization, because the technical difficulty of placement is high and the nidus of the AVM is unaffected. Vascular coagulation and section and AVM retraction are more difficult with IBCA; therefore, this is also considered an inferior choice. Among the materials studied, the combination of PVA for distal occlusion and microcoils for proximal occlusion appears to be the superior choice. Fewer complications (stroke or hemorrhage) are seen when intraarterial Amytal (amobarbital) testing is used to guide the embolization. Data regarding toxicity, oncogenicity, and vascular metabolism or recanalization associated with PVA, IBCA, and n-butyl cyanoacrylate are reviewed.

Increased superoxide anion production in polymorphonuclear leucocytes on exposure to isobutyl-2-cyanoacrylate

Alkyl-2-cyanoacrylates have been employed in a variety of surgical procedures, although the pathophysiological basis for their cytotoxicity has not been resolved. Previous reports indicated that leucocytes infiltrate the site of cyanoacrylate application in situ. Consequently, human polymorphonuclear leucocytes were treated with 0-200 mM cyanoacrylate isobutyl-2- and superoxide anion radical production, lactate dehydrogenase release, and intracellular reduced glutathione content were quantitated following this treatment. In addition, some cells were also treated with 0-20 mM ascorbic acid before exposure to the adhesive. Pretreatment with ascorbic acid resulted in a statistically significant decrease in superoxide production (up to 111%), decrease in lactate dehydrogenase release (up to 26.4%) and a like increase in glutathione content (up to 26.6%). These results indicated that the cytotoxic properties of isobutyl-2-cyanoacrylate were diminished in a dose-dependent manner with addition of ascorbic acid, a free radical trapping agent. Moreover, isobutyl-2-cyanoacrylate appeared to increase specifically the production of superoxide anion. These findings suggested that the cytotoxicity of this class of adhesives may be associated with the formation of reactive oxygen intermediates.

Histopathological studies of a new liquid embolization method using estrogen-alcohol and polyvinyl acetate. Experimental evaluations with a model of cortical arterial cannulation in the canine brain

This experimental report evaluates the histopathological effects of a new embolization method using estrogen-alcohol (E-A) and polyvinyl acetate solution (PVac) as tested on 21 mongrel dogs. Three other animals treated with normal saline served as controls. All agents were introduced through an isolated cortical artery. Estrogen-alcohol induced immediate occlusion of small vessels (less than 20 microns), and then progressive obstruction of larger ones (200-300 microns) within several days. Animals treated with PVac showed vascular obliteration (greater than 100 microns) and moderate chronic fibrosis. The effects of embolization using E-A followed by PVac were found to have the combined advantages of both materials, showing diffuse occlusion of the vascular network with less tissue reaction. Hyalinization of embolized vessels with extensive fibrosis occurred afterward. For 6 weeks there was no evidence of recanalization or foreign body giant cell reaction. This study shows that E-A and PVac are capable of producing vascular occlusions with only mild tissue reaction. Because they are easily controllable and have no adverse effects, they may be suitable for intravascular application in the central nervous system.

Neurovascular lesions and endovascular therapy: the role of MR

Magnetic resonance imaging (MRI) studies were performed on 27 patients with vascular lesions of the central nervous system before and after embolization with either IBCA, polyvinyl alcohol foam particles, Avitene (microfibrillar collagen) or balloons. Thirteen pial brain arteriovenous malformations (AVMs), 3 brain AV fistulas, 2 giant aneurysms, 5 dural AVMs, 1 vertebro-vertebral fistula and 3 meningiomas were studied. The pre-embolization MR demonstrated the nidus and venous drainage of all pial AVMs. MR failed to detect 3 out of 5 dural AVMs using only spin echo sequences. A draining vein alone was seen in the remaining two cases. MR was superior to CT in detecting contiguous parenchymal changes such as atrophy, reversible ischemia, and mass effect in the pre-embolization studies. Following embolization, MR demonstrated partial or complete obliteration of the vascular nidus in all 13 pial AVMs. The embolized area was seen as an area of increased signal consistent with thrombus where previously there had been signal void. Ischemic or edematous changes in the brain parenchyma following embolization were seen on MR more easily than on CT scans. MR was accurate in the assessment of aneurysm patency, degree of thrombosis and balloon position in both giant aneurysms, and AV fistulae. These MR findings had an impact on patient management. MR will be an increasingly useful tool in the diagnosis and management of a number of neurovascular diseases requiring endovascular intervention.

Occlusion of experimental artery aneurysms by intrasaccular injection of fibrin sealant

Aneurysms were produced by grafting a vein pouch onto the cervical carotid artery of rabbits following the removal of an elliptical piece of the arterial wall. The diameter of the opening was 3-4 mm and the maximum height 8 mm. Through direct puncture of the aneurysm a clot of the fibrin sealant Tissucol was injected into the aneurysm. The sequential morphological changes were studied by light microscopy. One case was examined after 3 weeks by scanning electron microscopy. Complete resorption of the fibrin sealant was observed. The aneurysm cavity was filled with a dense connective tissue covered by a layer of newly formed endothelial cells.

Long-term pathological follow-up of cerebral arteriovenous malformations treated by embolization with bucrylate

We examined 17 intracranial arteriovenous malformations that were resected after treatment by embolization using bucrylate (isobutyl-2-cyanoacrylate). In nine specimens removed 5 days to 16 months after embolization therapy, a series of pathologic changes was seen, including patchy mural angionecrosis (adjacent to bucrylate fragments) up to six weeks after embolization, the presence of bucrylate in vessel walls and fibromuscular intimal cushions, and the occurrence (after several months) of entirely extravascular bucrylate. Occasional parts of recanalized vascular malformations were identified. Bucrylate was present within arteriovenous malformations as late as 16 months after embolization, although the amount appeared to be diminished. These findings suggest a specific sequence of events in the interaction between bucrylate and mural components within the malformations and may explain some important complications of embolization therapy (e.g., delayed hemorrhage after embolization).