Obliteration of experimental aneurysms in dogs with isobutyl-cyanoacrylate

Interventional Neuroradiology in Thailand: 1989–1997

In 1979 the Siriraj team in Bangkok began exploring a field that was then new in Thailand, i. e. interventional neuroradiology. This first phase consisted mostly in self-training and foreign exposure.

It included experimental work with animal models, as well as early clinical trials designed to assess our skills in particle embolisation and the ligated and detachable balloon techniques. In 1990 a new phase started.

Essential techniques were acquired in collaboration with the neurovascular unit of Bicêtre Hospital in France during a three year training programme. Throughout this period, the support of the Association Médicale Franco-Asiatique (AMFA) and the French foreign affairs department proved vital. Our department progressively became a referral centre for the different techniques used in embolisation (balloons, glue…) and for various vascular lesions of the brain, the head and neck region, and spinal cord diseases.

Within Mahidol University, the Ramathibodi and Prasat Hospital centres started the same interventional neuroradiology training program in 1995; they benefited from the same tutors and connections as Siriraj. In 1996, the newly acquired biplane DSA machines in both centres enabled us to improve the treatment of arteriovenous malformations - using the glue technique –, intracranial aneurysm - using GDC-coils -, clot lysis, angioplasty… etc.

According to international recommendations, the critical mass we reached in 1997 in terms of number of patients and interventions, allows us to offer training in endovascular techniques to junior neuroradiologists at Mahidol university.

A large and giant bifurcation aneurysm model in canines: proof of feasibility

BACKGROUND AND PURPOSE

To our knowledge, no reproducible animal model of a giant bifurcation type aneurysm has been described. It was our aim to develop a 1-stage and reproducible model of a venous pouch giant aneurysm in canines.

MATERIALS AND METHODS

Nine canines were involved. Bilateral CCAs were exposed. The left CCA was divided and its distal segment was swung to the right side. Using the right CCA and the distal segment of the left CCA, either a bifurcation or a terminal arterial structure was constructed. Bilateral external jugular veins were also exposed. A 30-mm vein segment was harvested from each side. Each vein graft was split and unfolded to make 2 venous sheets. These sheets were then joined top-to-bottom so as to form a single cylinder in such a way that original adventitial side of the venous sheets was on the exterior surface. In 2 instances, pieces of polytetrafluoroethylene were employed along with the venous sheets. The combined vein graft was then incorporated into the arterial anastomosis. Lastly, the top of the venous pouch was closed. No medications for anticoagulant or antiplatelet were used throughout the study period. Follow-up imaging studies were performed.

RESULTS

It took 2.5 hours on average for 2 operators to create an aneurysm. Eight of the 9 aneurysms were patent at follow-up. The cause of the spontaneous thrombosis was unclear despite autopsy. All the aneurysms had a maximum diameter >20 mm.

CONCLUSIONS

We demonstrated and illustrated a 1-stage and reproducible procedure to create a model of a venous pouch bifurcation giant aneurysm in canines.

Current status and future prospect of endovascular neurosurgery

Recently, due to the evolution of technology, the field of neurosurgery is receiving spotlight. In particular endovascular neurosurgery has gained a great interest along with the advancement of the modern neurosurgery. The most remarkable advances were made in embolization of the cerebral aneurysms, arteriovenous malformations and intracranial stenosis during the past 10 years. These advances will further change the role of neurosurgeons in treating cerebrovascular disease. Because interventional neuroradiologists have performed most of procedures in the past, neurosurgeons have been deprived of chances to learn endovascular procedure. This article discusses the development of technological aspect of endovascular neurosurgery in chronological order. By understanding the history and current status of the endovascular surgery, the future of neurosurgery will be promising.

Endovascular treatment of experimental cerebral aneurysms using thermoreversible liquid embolic agents

SUMMARY

We have developed a new embolic agent, thermoreversible gelation polymer (TGP). This polymer is unique in that solidification occurs at body temperature. The utility of this new liquid embolic agent for the treatment of large experimental aneurysms was evaluated angiographically. TGP remains liquid at temperatures below the sol-gel transition temperature (TT) and becomes gelatinous above the TT. TGP can also be used to slowly deliver biologically active substances such as growth factors or engineered cells. In this study, TGP was mixed with radiopaque material without solvent. Bilateral common carotid arteries of swine (n=5) were used for surgical creation of lateral aneurysms, then 1 aneurysm in each animal was embolized using TGP without any protection device. The remaining untreated aneurysm in each animal was used as a control. All aneurysms were successfully embolized using TGP. No distal migration of TGP was observed when aneurysms were embolized without using protection devices. TGP can be safely used to embolize experimental aneurysms. Embolization of aneurysms with a protection device needs to be evaluated. Further modifications such as mechanical stability and use as a drug delivery system will be necessary prior to the clinical application of TGP.

Endovascular treatment of cerebral aneurysms: An in vitro study with detachable platinum coils and tricellulose acetate polymer

OBJECTIVE

The purpose of our experimental study was to determine the effectiveness of filling the cavity of in vitro aneurysms with detachable platinum coils and the combination of detachable platinum coils and liquid embolic agent.

MATERIALS AND METHODS

Silicone aneurysm models were connected to a circulatory system to simulate arterial flow. A microcatheter was used to introduce detachable coils into the aneurysm cavities. First, platinum coils were introduced until the point of minimal dense packing, indicated by aneurysmal circulatory exclusion. Packing was continued up to maximal dense packing, indicated by protrusion of the coil into the parent artery. Volumetric ratios (coil volume-aneurysm volume) were calculated for minimal and maximal dense packing. Then, after purposeful undercoiling of aneurysm models, a micropump system was used to fill the aneurysm by stepwise injection of tricellulose acetate polymer through the coil mesh until angiographic aneurysm exclusion was completed. The volumetric ratios of maximal packing with coils and tricellulose acetate polymer in relation to the aneurysm volume were calculated.

RESULTS

Maximal dense packing ratios with coils (mean, 32.5%; standard deviation [SD], 3%) were slightly higher than those with the minimal dense packing (mean, 28. 2%; SD, 3%) but were always less than 37%. The ratios of packing with the combined use of coils and tricellulose acetate polymer were greater than 100% (mean, 124.4%; SD, 15%).

CONCLUSION

Knowledge of the volumetric ratio of maximal dense packing was useful for effective filling with coils and tricellulose acetate polymer. The combined use of coils and liquid polymer appeared more effective than the use of coils alone for the complete occlusion of the aneurysm lumen.

Radiopaque polymeric materials for medical applications. Current aspects of biomaterial research

The aim of this review is to give an overview and some insight into different radiopaque polymeric materials that are currently used as medical implants or inserts. The advantages and limitations of each radiopaque polymeric material are summarized. The main method used to make medical implants radiologically visible is based on blending polymers with conventional radiopaque agents, blends which usually are a physical mixture of acrylic derivatives and inorganic salts. Other methods reported involve either the formation of single-phase radiopaque polymer salt complexes somehow preventing the release of the radiopacifying element by entrapment of the complex in a crosslinked network, or radiopaque polymerized monomers characterized by a radiopacifying element associated with the monomer unit prior to polymerization. In the near future, research will certainly concentrate on biocompatible radiopaque polymers with covalently bound opaque elements leading to stable polymers with properties equivalent to the nonopaque, parent polymer.

Acute human histopathology of an intracranial aneurysm treated using Guglielmi detachable coils: case report and review of the literature

OBJECTIVE AND IMPORTANCE

This case study provided us with the opportunity to explore the histopathological effects of Guglielmi detachable coil (GDC) therapy on the aneurysm orifice and parent vessel-aneurysm neck interface. This type of study is important to the understanding of the mechanisms of obliteration of aneurysms by GDCs.

CLINICAL PRESENTATION

The patient presented with a Hunt and Hess Grade III subarachnoid hemorrhage that occurred secondary to the rupture of a small anterior communicating artery aneurysm.

INTERVENTION

The aneurysm was successfully coiled without complication, but the patient died 36 hours later. We examined the gross and microscopic pathological findings of this GDC-treated anterior communicating artery aneurysm 36 hours after coiling. A discrete membrane composed of fibrin had formed completely across the aneurysm orifice, excluding the aneurysm sac from the circulation. This membrane was contiguous with the parent vessel.

CONCLUSION

This case represents one of the first examples in humans of the formation of a membrane over the aneurysm orifice after GDC therapy. The formation of this membrane, shown to be composed of fibrin, was found at 36 hours after coiling, which is the earliest time frame at which membrane formation has been noted in either humans or animal models. This fibrin membrane may function both as a scaffold for subsequent endothelialization across the aneurysm neck as well as to isolate the aneurysm from the parent circulation, permitting thrombus within the aneurysm sac to mature to an endovascular scar. The factors contributing to the formation of this membrane and its clinical implications are discussed.

Are superabsorbers useful for endovascular embolization of saccular aneurysms? An in vitro study

RATIONALE AND OBJECTIVES

The authors conducted in vitro evaluation of superabsorber for endovascular embolization of saccular aneurysms.

METHODS

The swelling properties of the superabsorber Sanwet IM-7000 were investigated in various solvents. The material used was granulate (group A: particle size approximately 459 microm; group B: particle size approximately 20 microm) as well as cubes with an edge length of 1 mm prepared from a block. With ascending concentrations of Sanwet IM-7000 held in suspensions made of Lipiodol and 96% ethanol, the injectability was determined using microcatheters (2.1 F/3 F). The behavior of Sanwet IM-7000 as occlusion material for aneurysms was examined in a sacciform glass-model aneurysm.

RESULTS

The granule showed no significant increase in size in Lipiodol and in 96% ethanol, so that they were chosen for catheter measurement. In Lipiodol suspension the maximum fraction of the granulate suitable for injection through a 3 F catheter was 3.2%. In 96% ethanol suspension the maximum fraction of granulate suitable for injection through a 3 F catheter was 0.8%. Suspended in Lipiodol Sanwet IM-7000 showed a moderate swelling in the aneurysm model, whereas the use of 96% ethanol resulted in a pronounced swelling of the granulate (100 vol%) after the 96% ethanol was washed off. Irrespective of the granulate size used, a rinse-off process of the granulate occurred in the model aneurysm at a flow rate above 200 mL x min(-1). Cubes prepared from a block of the base polymerisate of Sanwet IM-7000 showed a delayed increase in size. The final size in 0.9% NaCl solution was reached in the cubes after 220 min, in the granulate already after 20 mins. The cubes displayed a high form stability.

CONCLUSIONS

Due to the substance-related absence of intercorporeal cross-linking and the unpredictable increase in size, embolization of aneurysms using Sanwet IM-7000 granulate is inadvisable at present. In spite of a longer swelling time and because of its form consistency, the use of prepared cubes could provide a reasonable alternative.

Partial thrombosis of canine carotid bifurcation aneurysms with cellulose acetate polymer

OBJECTIVE

To investigate the usefulness of a cellulose acetate polymer (CAP) solution for partial thrombosis of aneurysms.

METHODS

We created 14 canine cervical carotid bifurcation aneurysms, 11 of which were subsequently thrombosed partially with CAP solution. We then conducted angiographic and histological investigations.

RESULTS

Nine aneurysms were thrombosed 50 to 70% by volume, although a significant crescent crevice between the aneurysmal sac and the CAP mass was left in four of the aneurysms. In the remaining two aneurysms in which a crescent crevice had been seen in the initial stage of CAP injection, 80% and more than 95% thrombosis were needed to occlude the crevice, respectively. Follow-up angiograms of the seven aneurysms with no crescent crevice revealed no shifts of position of the CAP mass toward the bottom of the aneurysm sac, but slight ballooning of the remnants was observed in two of them. The angiograms of the other four aneurysms with significant crescent crevices demonstrated rupture with a massive hematoma in one and shifts of the CAP mass with marked enlargement of remnants in three. Histologically, the seven aneurysms with no enlarged remnants had newly developed membranes consisting of endothelium, infiltrated spindle-shaped cells, collagen, and elastic fibers. In contrast, in the three markedly enlarged aneurysms, there were only recent clots between the CAP mass and the aneurysm lumen and no development of endothelium.

CONCLUSION

Partial thrombosis with CAP solution is useful to keep aneurysms in a stable configuration, unless a crescent crevice has been left.

Direct thrombosis of experimental aneurysms with cellulose acetate polymer (CAP): technical aspects, angiographic follow up, and histological study

Experimental aneurysms were created using a microsurgical technique to produce anastomosed venous pouches in the bilateral common carotid arteries of 12 dogs. The 24 aneurysms were then thrombosed via an endovascular approach with injection of a cellulose acetate polymer (CAP) solution that the authors have developed for use as a liquid thrombotic material. Angiography performed 1 to 4 weeks after CAP injection revealed complete thrombosis of the aneurysm with patency of the parent artery in 16 aneurysms. Histological analysis disclosed that the aneurysmal orifice in these cases was completely covered with newly formed endothelial cells 2 weeks after CAP thrombosis. Three other aneurysms exhibited parent artery occlusion caused by protrusion of the CAP mass through the aneurysmal orifice into the parent artery; this was thought to be caused by over-injection of the CAP solution. Histological analysis of the remaining five aneurysms, initially shown to have incomplete occlusion, revealed that they each possessed a residual neck that was partially covered with endothelial cells. No rupture of the aneurysms or migration of CAP into the distal arteries was observed. These results suggest that using an endovascular approach, direct thrombosis of cerebral aneurysms with CAP is safe and effective. This technique may prove to be an alternative treatment for such aneurysms. However, there is a potential risk of regrowth or rupture of aneurysms that retain a residual neck and long-term follow-up studies will be required to evaluate this issue.

Experimental saccular aneurysms. I. Review of surgically-constructed models and their laboratory applications

Experimental models of intracranial saccular aneurysms are a useful contribution to our basic understanding of these lesions. Currently, the commonest in use are those constructed surgically in laboratory animals. We review the numerous surgical techniques available since the 1950s, and the research applications and uses of experimental aneurysms. Further development and use of such models is greatly encouraged in future pathophysiological, hemodynamic, and therapeutic investigations of intracranial saccular aneurysms.

Histopathological study of balloon embolization: silicone versus latex

Bilateral, symmetrical, experimental aneurysms were produced with anastomosed vein flap in the carotid arteries of 24 mongrel dogs. Aneurysms were occluded with latex or silicone balloons on each side and observed angiographically from 2 weeks to 2 months. A histopathological study was performed subsequently using light and scanning electron microscopy. Rupture after balloon embolization occurred in five aneurysms; all of which were incompletely occluded by a silicone balloon. On subsequent angiograms, four silicone balloons and one latex balloon were found to have migrated into the aneurysm, resulting in aneurysmal expansion. Parent artery occlusion was more common with latex balloons than silicone balloons. Histopathologically, residual fresh thrombi, decreased proliferation of fibroblasts within the aneurysmal cavity, and poor endothelialization were present around the silicone balloon. These results suggest that the intra-aneurysmal organization, as seen in the aneurysm occluded by the silicone balloon, will be delayed because the balloon is not fixed within the aneurysm, and that this free-floating and rotating balloon causes repeated trauma to the aneurysm wall, contributing to subsequent enlargement and rupture of the aneurysm. The superior antithrombogenic nature of silicone may be responsible for the bias of such phenomena toward the silicone balloon.

One-stage construction of giant experimental aneurysms in dogs

In an attempt to find safe and effective methods of treating giant intracranial aneurysms, we have developed a one-step construction of giant experimental aneurysms in dogs with a yield of 100% patency of the parent artery and the experimental aneurysm without intraaneurysmal thrombus. Giant aneurysms were produced in the right thrombus. Giant aneurysms were produced in the right common carotid artery of nine mongrel dogs. Key features concerning the procedure were: (1) proximal placement of the aneurysmal neck, (2) 1 cm length as the aneurysmal ostea, and (3) postoperative aspirin therapy. This one-step construction of giant experimental aneurysms in dogs should prove helpful in evaluating a wide variety of treatment modalities of giant aneurysms in the laboratory. It also may be of additional value in investigative studies relative to catheters, balloons, and other similar techniques.

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.

Experimental aneurysms in the rabbit: occlusion by intrasaccular injection of fibrin sealant

Experimental aneurysms of the carotid artery were produced using the microsurgical technique of grafting a venous sack onto the artery in the neck of rabbits after the removal of an elliptical piece of arterial wall. Twenty-five aneurysms were occluded with the fibrin sealant Tissucol. Microscopic examination showed complete resorption of the fibrin clot and the formation of dense granulation tissue within the aneurysm, which was covered with a layer of endothelial cells after 2 weeks. The results are only tentative and require further experimental studies.

Artificial embolization with isobutyl-2-cyanoacrylate for the treatment of carotid-ophthalmic aneurysm

A large carotid-ophthalmic aneurysm was successfully obliterated by the combined treatment of clipping the aneurysmal neck and intraaneurysmal injection of isobutyl-2-cyanoacrylate. Reflux of the glue into the artery was prevented by temporary trapping of the carotid artery. The obliteration of an aneurysm with isobutyl-2-cyanoacrylate is an effective procedure in cases where clipping of the aneurysmal neck is not completed due to technical difficulties.