A refined method for creating saccular aneurysms in the rabbit

Evaluation of the EMBOPIPE flow diverter device: in vivo and in vitro experiments

BACKGROUND

Although flow diverter device (FDD) has brought revolutionized advances in endovascular treatment of intracranial aneurysms, it also presents considerable drawbacks as well, as the innovation for novel device has never stopped. This preclinical research aims to evaluate the safety and efficacy of a newly developed FDD, the EMBOPIPE, through in vivo and in vitro experiments.

METHODS

Aneurysms were induced in 20 New Zealand white rabbits which were randomized to three follow-up groups according to the time elapsed after EMBOPIPE implantation (28, 90, and 180 days). Additional EMBOPIPEs were implanted in the abdominal aorta to cover the renal artery in nine rabbits. Angiography was performed immediately after device placement in all groups. Aneurysm occlusion, patency of renal arteries, and pathological outcomes were assessed. For the in vitro experiments, we measured the thrombogenic potential of EMBOPIPEs (n = 5) compared with bare stents (n = 5) using the Chandler loop model. Evaluation indicators were the platelet counts, macroscopic observations and scanning electron microscopy.

RESULTS

EMBOPIPEs were successfully deployed in 19 of 20 rabbit aneurysms (95.0%). The rates of complete or near-complete aneurysm occlusion were 73.3%, 83.3%, and 100% in the 28-, 90-, and 180-day groups, respectively. All renal arteries covered by EMBOPIPEs remained patent, and the mean difference in renal artery diameter before and after the device placement in the three groups was 0.07 mm, 0.10 mm, and 0.10 mm, respectively (p = 0.77). Renal pathology was normal in all cases. The pathological findings of the aneurysms were as follows: thickened and adequate neointimal coverage at the aneurysm neck, minimal inflammatory response, near-complete smooth muscle cell layer, and endothelialization along the device. In vitro experiments showed that the platelet counts were significantly higher in EMBOPIPE blood samples than in bare stent samples and that platelet adhesion to the device was lower in the EMBOPIPE stent struts compared with bare stent struts through macroscopic observations and scanning electron microscopy.

CONCLUSIONS

The EMBOPIPE can achieve high rates of aneurysm occlusion while maintaining excellent branch artery patency. It exhibited wonderful pathological results. This novel device with phosphorylcholine surface modification could reduce platelet thrombus attached to the stent struts.

Imaging of intracranial aneurysms in animals: a systematic review of modalities

Intracranial aneurysm (IA) animal models are paramount to study IA pathophysiology and to test new endovascular treatments. A number of in vivo imaging modalities are available to characterize IAs at different stages of development in these animal models. This review describes existing in vivo imaging techniques used so far to visualize IAs in animal models. We systematically searched for studies containing in vivo imaging of induced IAs in animal models in PubMed and SPIE Digital library databases between 1 January 1945 and 13 July 2022. A total of 170 studies were retrieved and reviewed in detail, and information on the IA animal model, the objective of the study, and the imaging modality used was collected. A variety of methods to surgically construct or endogenously induce IAs in animals were identified, and 88% of the reviewed studies used surgical methods. The large majority of IA imaging in animals was performed for 4 reasons: basic research for IA models, testing of new IA treatment modalities, research on IA in vivo imaging of IAs, and research on IA pathophysiology. Six different imaging techniques were identified: conventional catheter angiography, computed tomography angiography, magnetic resonance angiography, hemodynamic imaging, optical coherence tomography, and fluorescence imaging. This review presents and discusses the advantages and disadvantages of all in vivo IA imaging techniques used in animal models to help future IA studies finding the most appropriate IA imaging modality and animal model to answer their research question.

Anatomical Variations of the Common Carotid Arteries and Neck Structures of the New Zealand White Rabbit and Their Implications for the Development of Preclinical Extracranial Aneurysm Models

BACKGROUND

Rabbit models involving neck arteries are of growing importance for the development of preclinical aneurysm models. An optimal understanding of the anatomy is primordial to allow the conception of models while minimizing mortality and morbidity. The aim of this study is to give reliable anatomical landmarks to allow a standardized approach to the neck vessels.

METHODS

We performed a necropsy on nine specimens from ongoing experimental studies. We measured the distance between the origins of the right and left common carotid artery (rCCA/lCCA) and between the rCCA and the manubrium sterni (MS). The structures at risk were described.

RESULTS

Female New Zealand White rabbits (NZWR) weighing 3.7 ± 0.3 kg and aged 25 ± 5 weeks were included. The rCCA origin was located 9.6 ± 1.2 mm laterally and 10.1 ± 3.3 mm caudally to the MS. In all specimens, the lCCA originated from the aortic arch, together with the brachiocephalic trunk (BCT), and 6.2 ± 3.1 mm proximally to the rCCA origin. The external and internal jugular veins, trachea and laryngeal nerve were the main structures at risk.

CONCLUSIONS

The data help to localize both CCAs and their origin to guide surgical approaches with the manubrium sterni as a main landmark. Special attention has to be paid to the trachea, jugular veins and laryngeal nerves.

An Improved Surgical Technique to Increase Neck Width of Elastase-Induced Aneurysm Model in Rabbits: A Prospective Study

Background

Rabbit elastase-induced aneurysms have widely been used to test various endovascular materials over the past two decades. However, wide-necked aneurysms cannot be stably constructed.

Objective

The purpose of the study was to increase the neck width of the elastase-induced aneurysm model in rabbits via an improved surgical technique with two temporary clips.

Materials and Methods

Fifty-four elastase-induced aneurysms in rabbits were successfully created. Group 1 was (n = 34) composed of cases in which two temporary aneurysm clips were placed closely medially and laterally to the origin of the right common carotid artery (RCCA), respectively. Group 2 (n = 20) included cases in which a single temporary aneurysm clip was placed crossed the origin of RCCA. Digital subtraction angiography (DSA) was performed before and immediately after elastase incubation and 3 weeks later. The diameter of the origin of RCCA before and immediately after elastase incubation and aneurysm sizes of the two groups were measured and compared. Moreover, the correlation analysis was performed between the diameter of the origin of RCCA immediately after elastase incubation and aneurysm neck width.

Results

The mean aneurysm neck and dome width of group 1 were both significantly larger than that of group 2 (p-value < 0.001 and p-value = 0.005, respectively). Moreover, the proportion of wide-necked aneurysms (neck width ≥4 mm) in group 1 was significantly larger than that in group 2 (p-value = 0.004) and the mean dome to neck ratio (D/N) of group 1 was smaller than that of group 2 (p-value = 0.008). Furthermore, there was a positive correlation between the diameter of the origin of RCCA immediately after elastase incubation and aneurysm neck width.

Conclusion

The improved surgical technique with two temporary clips, focusing on the direct contact of elastase with the origin of RCCA, could increase the neck width of elastase-induced aneurysm models in rabbits.

The development and understanding of intracranial aneurysm based on rabbit model

In modern society, intracranial aneurysms have seriously affected people's life. To better study and treat intracranial aneurysm, animal models are ideal candidates to perform biological research and preclinical endovascular device testing. Rabbit aneurysm model is one of the most commonly used animal models, and the rabbit aneurysms share similarities in histology, morphology, and hemodynamic aspects with human intracranial aneurysms, which is an ideal model for intracranial aneurysm pre-clinical and basic research. In this review, we will summarize the main methods of establishing rabbit aneurysms model and will further discuss the current biological mechanisms of intracranial aneurysms based on rabbit model. Further improvements of rabbit aneurysm model and more deep studies based on this model are needed to provide new insights into studying and clinical treating intracranial aneurysm.

Preclinical extracranial aneurysm models for the study and treatment of brain aneurysms: A systematic review

Animal models make an important contribution to our basic understanding of the pathobiology of human brain aneurysms, are indispensable in testing novel treatment approaches, and are essential for training interventional neuroradiologists and neurosurgeons. Researchers are confronted with a broad diversity of models and techniques in various species. This systematic review aims to summarize and categorize extracranial aneurysm models and their characteristics, discuss advantages and disadvantages, and suggest the best use of each model. We searched the electronical Medline/PubMed database between 1950 and 2020 to identify main models and their refinements and technical modifications for creation of extracranial aneurysms. Each study included was assessed for aneurysm-specific characteristics, technical details of aneurysm creation, and histological findings. Among more than 4000 titles and abstracts screened, 473 studies underwent full-text analysis. From those, 68 different techniques/models in five different species were identified, analyzed in detail, and then grouped into one of the five main groups of experimental models as sidewall, terminal, stump, bifurcation, or complex aneurysm models. This systematic review provides a compact guide for investigators in selecting the most appropriate model from a range of techniques to best suit their experimental goals, practical considerations, and laboratory environment.

Carotid artery vein-pouch bifurcation aneurysm in rats: An experimental model for microneurosurgical training

BACKGROUND

In the era of endovascular treatment of intracranial aneurysms, surgical clipping is still a relevant treatment method in some cases. However, it has become harder to teach this skill, as the number of surgical cases has decreased over the past years. We therefore decided to use a previously described experimental aneurysm model for surgical training.

MATERIAL AND METHODS

We operated on 8 rats and constructed a vein-pouch aneurysm at a surgically created carotid bifurcation. Survivors were kept alive for 1 month and operated on to clip the aneurysm.

RESULTS

Only 3 rats had survived at 1 month. All the carotid arteries were permeable. Only 2 aneurysms were circulating at 1 month, as 1 had thrombosed. They were successfully clipped at 1 month.

CONCLUSIONS

These preliminary results enabled our junior surgeon to clip two circulating aneurysms, under an operative microscope reproducing surgical conditions. Although the efficacy of the model could be improved, we believe it could be used as a first step in training neurosurgical residents in the basics of aneurysm clipping and microsurgical techniques in a realistic setting.

In vivo cerebral aneurysm models

Cerebral aneurysm rupture is a devastating event resulting in subarachnoid hemorrhage and is associated with significant morbidity and death. Up to 50% of individuals do not survive aneurysm rupture, with the majority of survivors suffering some degree of neurological deficit. Therefore, prior to aneurysm rupture, a large number of diagnosed patients are treated either microsurgically via clipping or endovascularly to prevent aneurysm filling. With the advancement of endovascular surgical techniques and devices, endovascular treatment of cerebral aneurysms is becoming the first-line therapy at many hospitals. Despite this fact, a large number of endovascularly treated patients will have aneurysm recanalization and progression and will require retreatment. The lack of approved pharmacological interventions for cerebral aneurysms and the need for retreatment have led to a growing interest in understanding the molecular, cellular, and physiological determinants of cerebral aneurysm pathogenesis, maturation, and rupture. To this end, the use of animal cerebral aneurysm models has contributed significantly to our current understanding of cerebral aneurysm biology and to the development of and training in endovascular devices. This review summarizes the small and large animal models of cerebral aneurysm that are being used to explore the pathophysiology of cerebral aneurysms, as well as the development of novel endovascular devices for aneurysm treatment.

Surgical technique for venous patch aneurysms with no neck in a rabbit model

BACKGROUND

Animal experimental studies are crucial for the development of endovascular devices and embolization techniques for intracranial aneurysms. The aim of the study was to describe the surgical creation technique for an aneurysm with a dilated shape and no definable aneurysm neck. The model should be reproducible in size and shape and stay patent over a long period of time. It should constitute a challenge to endovascular therapy and provide a valuable testing environment for new endovascular devices and techniques.

METHODS

Surgical creation of 30 no-neck aneurysms was attempted in 15 New Zealand White rabbits using a segment of jugular vein, which was transected, longitudinally opened and sutured to the anterior aspect of the common carotid artery. The first 14 aneurysms were used to develop the technique. Once the technique was mastered and the procedure was standardized, 16 consecutive aneurysms were created. For these aneurysms, digital subtraction angiography was employed after a mean of 120 days to confirm size and patency. All aneurysms were evaluated for patency.

RESULTS

Overall aneurysm patency was 93%. Three complications occurred, two of which were related to the vascular anastomosis. Angiographic follow-up showed a median (SD) aneurysm base and height of 6.7 (0.76) mm and 3.2 (0.85) mm), respectively.

CONCLUSIONS

This technique allows creation of aneurysms without a neck which are reproducible in size and shape, and which remain patent. The model contributes to the list of aneurysm models fit for evaluation of embolization devices and techniques. It is particularly useful in exploring treatment options for wide-neck aneurysms and aneurysms which presently do not qualify for conventional coiling.

From bench to bedside: utility of the rabbit elastase aneurysm model in preclinical studies of intracranial aneurysm treatment

Preclinical studies are important in helping practitioners and device developers improve techniques and tools for endovascular treatment of intracranial aneurysms. Thus an understanding of the major animal models used in such studies is important. The New Zealand rabbit elastase induced arterial aneurysm of the common carotid artery is one of the most commonly used models in testing the safety and efficacy of new endovascular devices. In this review we discuss: (1) the various techniques used to create the aneurysm, (2) complications of aneurysm creation, (3) natural history of the arterial aneurysm, (4) histopathologic and hemodynamic features of the aneurysm, (5) devices tested using this model, and (6) weaknesses of the model. We demonstrate how preclinical studies using this model are applied in the treatment of intracranial aneurysms in humans. The model has similar hemodynamic, morphological, and histologic characteristics to human aneurysms, and demonstrates similar healing responses to coiling as human aneurysms. Despite these strengths, however, the model does have many weaknesses, including the fact that the model does not emulate the complex inflammatory processes affecting growing and ruptured aneurysms. Furthermore, the extracranial location of the model affects its ability to be used in preclinical safety assessments of new devices. We conclude that the rabbit elastase model has characteristics that make it a simple and effective model for preclinical studies on the endovascular treatment of intracranial aneurysms, but further work is needed to develop aneurysm models that simulate the histopathologic and morphologic characteristics of growing and ruptured aneurysms.

A New Flow-Diverter (the FloWise): In-Vivo Evaluation in an Elastase-Induced Rabbit Aneurysm Model

OBJECTIVE

We aimed to evaluate the efficacy and safety of a newly developed, partially retrievable flow-diverter (the FloWise) in an elastase-induced rabbit aneurysm model.

MATERIALS AND METHODS

We developed a partially retrievable flow diverter composed of 48 strands of Nitinol and platinum wire. The FloWise is compatible with any microcatheter of 0.027-inch inner diameter, and is retrievable up to 70% deployment. The efficacy and safety of the FloWise were evaluated in the elastase-induced rabbit aneurysm model. The rate of technical success (full coverage of aneurysm neck) and assessment of aneurysm occlusion and stent patency was conducted by angiograms and histologic examinations at the 1-month, 3-month, and 6-month follow-up. The patency of small arterial branches (intercostal or lumbar arteries) covered by the FloWise were also assessed in the 5 subjects.

RESULTS

We attempted FloWise insertion in a total of 32 aneurysm models. FloWise placement was successful in 31 subjects (96.9%). Two stents (6.2%) were occluded at the 3-month follow-up, but there was no evidence of in-stent stenosis in other subjects. All stented aneurysms showed progressive occlusion: grade I (complete aneurysm occlusion) in 44.4% and grade II (aneurysm occlusion > 90%) in 55.6% at 1 month; grade I in 90% and II in 10% at 3 months; and grade I in 90% and II in 10% at 6 months. All small arterial branches covered by the FloWise remained patent.

CONCLUSION

A newly developed, partially retrievable flow-diverter seems to be a safe and effective tool of aneurysm occlusion, as evaluated in the rabbit aneurysm model.

High-flow venous pouch aneurysm in the rabbit carotid artery: A model for large aneurysms

BACKGROUND AND PURPOSE

Currently one of the most widely used models for the development of endovascular techniques and coiling devices for treatment of aneurysm is the elastase-induced aneurysm model in the rabbit carotid artery. Microsurgical techniques for creating an aneurysm with a venous pouch have also been established, although both techniques usually result in aneurysms less than 1 cm in diameter. We investigated whether an increase in blood flow toward the neck would produce larger aneurysms in a microsurgical venous pouch model.

MATERIALS AND METHODS

Microsurgical operations were performed on 11 New Zealand white rabbits. Both carotid arteries and the right jugular vein were dissected, and the right carotid artery was temporarily clipped followed by an arteriotomy. The left carotid artery was also clipped proximally, ligated distally, and sutured onto the proximal half of the arteriotomy in the right carotid artery. The venous graft was sutured onto the distal half of the arteriotomy. Digital subtraction angiography was also performed.

RESULTS

Angiography showed patent anastomosed vessels and aneurysms in the seven surviving rabbits. Mean aneurysm measurements among surviving rabbits with patent vessels were: 13.9 mm length, 9.3 mm width, and neck diameter 4.7 mm. The resulting mean aspect ratio was 3.35 and the mean bottleneck ratio was 3.05.

CONCLUSION

A large venous graft and increased blood flow toward the base of the aneurysm seem to be key factors in the creation of large venous pouch aneurysms. These large aneurysms allow testing of endovascular devices designed for large and giant aneurysms.

A Model-based Numerical Analysis in the Early Development of Intracranial Aneurysms

Hemodynamic stresses are known to degenerate the arterial wall and be involved in the pathogenesis of intracranial aneurysm formation and development. The present study simulates the formation and growth of aneurysms by focusing on the interplay between the wall shear stress, degeneration of the mechanical wall properties, and the wall deformation. We construct numerical aneurysm models arisen from both straight and curved arteries, and we hypothesize that high local wall shear stress larger than a certain threshold value will lead to a linear decrease in the mechanical property of the vessel wall. The degeneration of vessel wall leads to wall deformation and redistribution of the wall shear stress, which in turn leads to further degeneration of the wall. Development of aneurysm is observed in both the straight and curved models. In the straight model, the growth of aneurysm is small and mainly at the distal neck region, and the aneurysm stops growing after several steps. In contrast, in the curved model, the aneurysm continues to grow in height and width. Our computer simulation shows that even if the wall shear stress inside a saccular aneurysm is low, aneurysm development can occur due to degeneration of the wall distal and proximal to the aneurysm. The interaction between the geometry change and the wall degeneration is key to the development of aneurysms. The method demonstrates the potential utility of model-based numerical methods in the investigation of developmental biology of intracranial aneurysms.

Magnetic microparticles for endovascular aneurysm treatment: in vitro and in vivo experimental results

OBJECTIVE

Endovascular treatment of intracranial aneurysms employing endosaccular coiling can be associated with aneurysm perforation, coil herniation or incomplete obliteration fueling the interest to investigate novel endovascular techniques. We aimed to test a novel embolization material in experimental aneurysms in vitro and in vivo whereby intra-arterially administered magnetic microparticles (MMPs) are navigated into the lumen of vascular aneurysms with assistance from an external magnetic field.

METHODS

MMPs are core-shell particles suspended in saline that have a shell made of a polymeric material and a core made of magnetite (Fe3O4). They have a diameter of 1.4 μm. During MMP administration via a microcatheter, a magnetic field was applied externally to direct the particles with the use of a solid-state neodymium magnet. Experiments were performed in a perfused silicone vessel and aneurysm model to evaluate application techniques and fluid dynamics and in the elastase aneurysm model in rabbits to evaluate in vivo compatibility, including multiorgan histological examinations and long-term stability of aneurysm embolization.

RESULTS

It was possible to steer and hold the MMPs within the aneurismal cavity where they occluded the lumen progressively. After removal of the external magnetic field, the results remained stable in vivo for the remainder of the observational period (30 minutes); after a 12-week observational period, recanalization of the aneurysm occurred.

CONCLUSION

MMPs can be magnetically directed into aneurysms, allowing short-term obliteration. Although the method has yet to show reliable long-term stability, these experiments provide proof of concept, encouraging further investigation of intravascular magnetic compounds.

COMPUTATIONAL MODELING OF FORMATION OF A CEREBRAL ANEURYSM UNDER THE INFLUENCE OF SMOOTH MUSCLE CELL RELAXATION

The mechanics of cerebral aneurysm pathogenesis, evolution and rupture are not yet well understood. This paper presents a numerical analysis of the formation of a saccular cerebral aneurysm in for the first time in a 3D model of the basilar artery bifurcation under normal and hypertensive blood pressure. Due to the excessive endothelium derived nitric oxide produced in high wall shear stress, we assumed that smooth muscle cell relaxation is the origin of the aneurysm formation. Arterial wall remodeling under constant tension was considered to be the other mechanism of disease evolution. The wall was constructed from two elastic and hyperelastic isotropic regions. The flow was considered steady, laminar, Newtonian, and incompressible. The fully coupled fluid and structure models were solved with the finite elements package ADINA 8.5. The wall shear stress, effective stress and deformation distributions under normal and hypertensive blood pressure were compared to a healthy bifurcation. The model shows that although the malfunction of the endothelial cell layer and the corresponding smooth muscle cell-related loss of vascular tone is important to the inception of the disease; A saccular aneurysm may not be formed by this mechanism alone, and also requires the fiber-related arterial wall remodeling for further development.

Improved microsurgical creation of venous pouch arterial bifurcation aneurysms in rabbits

BACKGROUND AND PURPOSE

The choice of the experimental aneurysm model is essential for valid embolization-device evaluations. So far, the use of the rabbit venous pouch arterial bifurcation aneurysm model has been limited by demanding microsurgery, low aneurysm patency rates, and high mortality. This study aimed to facilitate microsurgery and to reduce mortality by optimized peri-/postoperative management.

MATERIALS AND METHODS

Aneurysms were created in 16 New Zealand white rabbits under general intravenous anesthesia. Using modified microsurgical techniques, we sutured a jugular vein pouch into a bifurcation created between both CCAs. Aggressive anticoagulation (intraoperative intravenous: 1000-IU heparin, 10-mg acetylsalicylic acid/kg; postoperative subcutaneous: 14 days, 250-IU/kg /day heparin) and prolonged postoperative anesthesia (fentanyl patches: 12.5 μg/h for 72 hours) were applied. Angiographic characteristics of created experimental aneurysms were assessed.

RESULTS

The reduced number of interrupted sutures and aggressive anticoagulation caused no intra-/postoperative bleeding, resulting in 0% mortality. Four weeks postoperation, angiography showed patency in 14 of 16 aneurysms (87.5%) and Ohshima type B bifurcation geometry. Mean values of parent-artery diameters (2.3 mm), aneurysm lengths (7.9 mm), and neck widths (4.1 mm) resulted in a mean 1.9 aspect ratio.

CONCLUSIONS

Compared with historical controls, the use of modified microsurgical techniques, aggressive anticoagulation, and anesthesia resulted in higher aneurysm patency rates and lower mortality rates in the venous pouch arterial bifurcation aneurysm model. Gross morphologic features of these aneurysms were similar to those of most human intracranial aneurysms.

Bare, bio-active and hydrogel-coated coils for endovascular treatment of experimentally induced aneurysms. Long-term histological and scanning electron microscopy results

Endovascular treatments of cerebral aneurysms with bare platinum coils have a higher rate of recurrence compared to surgical clipping. This may be related to failed vessel wall reconstruction since histological and scanning electron microscopy results following embolization failed to demonstrate neoendothelialization over the aneurysm neck. The present study tried to elucidate whether the use of modified coils resulted in a better rate of reconstructing the vessel wall over the aneurysm neck in experimental aneurysms. Aneurysms were created in 20 rabbits by intraluminal elastase incubation of the common carotid artery. Five animals each were assigned to the following groups: untreated, bare platinum coils, bioactive coils with polyglycolic/polylactic acid coating, and hydrogel-coated platinum coils. After 12 months, angiography, histology and scanning electron microscopy was performed. No neoendothelial layer was visualized in the bioactive and bare coil groups with a tendency to an increased layering of fibroblasts along the bioactive coils at the aneurysm fundus. However, at the aneurysm neck perfused clefts were present and although a thin fibrinous layer was present over some coils, no bridging neointimal or neoendothial layer was noted over different coils. Following loose Hydrogel coiling, a complete obliteration of the aneurysm was present with neoendothelialization present over different coil loops. The study demonstrates that with surface coil modifications complete and stable aneurysm obliteration may become possible. A smooth and dense surface over the aneurysm neck may be necessary for endothelial cells to bridge the aneurysm neck and to lead to vessel wall reconstruction.

In vivo experimental intracranial aneurysm models: a systematic review

Animal models are necessary to develop and test innovations in aneurysm therapy before clinical introduction. This review aims at identifying the most likely candidates for standardizing preclinical testing of aneurysm devices. We systematically searched electronic databases for publications on animal aneurysm models from 1961-2008 to assess the methodologic quality of the studies and collect data on the patency and angiographic and pathologic outcomes of treatments. There has been a steady increase in the annual number of publications with time. Species that were most frequently used were dogs, rabbits, and rodents, followed by swine. Most publications are single-laboratory studies with variables and poorly validated outcome measures, a small number of subjects, and limited standardization of techniques. The most appropriate models to test for recurrences after endovascular occlusion were the surgical bifurcation model in dogs, and the elastase-induced aneurysm model in rabbits. A standardized multicenter study is needed to improve the preclinical evaluation of endovascular devices in aneurysm therapy.

Neurological deficits associated with the elastase-induced aneurysm model in rabbits

OBJECTIVE

Although the rabbit elastase-induced aneurysm model is currently used widely for endovascular research and device testing, procedural causes leading to animal morbidity and mortality have not yet been clearly described. We conducted a retrospective study to analyse factors contributing to neurological deficits in rabbits that underwent the elastase-induced aneurysm creation procedure at our research center from 2002 to 2005 in order to improve the technique and reduce procedure-related morbidity and mortality.

METHODS

A total sample of 38 animals that underwent the procedure under the same conditions was analysed in two groups: animals that presented neurological deficits (ND, n=15) and animals that were neurological deficit free (NDF, n=23). Data were collected by reviewing the animal records and radiographic images from the procedures. Statistical analyses using the Mann-Whitney test, unpaired t-test with Welch correction and Fisher's exact tests were performed to compare the two groups based on variables associated with endothelial injury and activation of the coagulation cascade.

RESULTS

The variables of animal weight (signifying state of health of the animal), total procedure time, total balloon occlusion time and clot formation were found to be significantly and/or very significantly correlated to ND presentation.

DISCUSSION

Successful creation of the rabbit elastase-induced aneurysm model depends on careful control over several technical details. Important variables governing outcome have been identified here. A specific, improved endovascular arrangement that facilitates maneuvering of the devices and reduces the risk of air emboli is presented.

A novel arterial pouch model of saccular aneurysm by concomitant elastase and collagenase digestion

BACKGROUND

An ideal aneurysm model of cerebral aneurysm is of great importance for studying the pathogenesis of the lesion and testing new techniques for diagnosis and treatment. Several models have been created in rabbits and are now widely used in experimental studies; however, every model has certain intrinsic limitations. Here we report the development of a novel saccular aneurysm model in rabbits using an arterial pouch that is subject to in vitro pre-digestion with combined elastase and collagenase.

METHODS

A segment of right common carotid artery (CCA) was dissected out and treated with elastase (60 U/ml, 20 min) followed by type I collagenase (1 mg/ml, 15 min) in vitro. The graft was anastomosed to an arterial arch built with the left CCA and the remaining right CCA, while the other end of the graft was ligated. The dimension and tissue structure of the pouch were analysed immediately, 2 or 8 weeks after operation.

FINDINGS

Ten terminal aneurysms were produced. The gross morphology of the aneurysm resembles the human cerebral terminal aneurysms. We have observed the following pathological changes: (1) growth of the aneurysm (mean diameter increased from (2.0+/-0.1) to (3.2+/-0.3) mm at 2 weeks, P<0.001, n=7-10); (2) thinning of the aneurysmal wall (the mean wall thickness decreased to 44% at 2 weeks), which was accompanied by significant losses of elastic fibres, collagen and the cellular component; and (3) spontaneous rupture (3 out of 9, one aneurysm ruptured 24 h after operation with the other two at 2 and 4 weeks respectively).

CONCLUSION

This rabbit arterial pouch model mimics human cerebral aneurysms in relation to morphology and histology. In particular, this model exhibited an increased tendency of spontaneous rupture.

Transauricular Arterial or Venous Access for Cardiovascular Experimental Protocols in Animals

PURPOSE

To describe a safe percutaneous method of transauricular endovascular access in small and large animals that uses basic catheter-based interventional skills and renders surgery and general anesthesia with intubation unnecessary.

MATERIALS AND METHODS

Twenty New Zealand White rabbits and five domestic juvenile swine were used in the experiments. Animals were restrained in the supine position after induction of dissociative anesthesia. Transauricular endovascular access was accomplished by percutaneous catheterization of the auricular artery or vein, roadmap imaging, introduction of a 0.018-inch hydrophilic guide wire, and over-the-wire vascular sheath insertion after serial tract dilations.

RESULTS

Technical success rates were 90% and 100% for intraarterial and endovenous access in the rabbit, respectively, and 100% for both routes in the pig. The largest sheaths inserted were 5 F in the rabbits' aortae, 7 F in the rabbits' venae cavae, 6 F in the pigs' aortae, and 8 F in the pigs' venae cavae. Animal recovery was uneventful, and 48-hour necropsy detected only minor perivascular hematoma in cases of transauricular intraarterial access. Peripheral, intracoronary, intrapulmonary, and intracerebral selective vascular access was safe and feasible. A method of reserving the transauricular endovascular access for future interventions or follow-up by placement of indwelling hydrophilic catheters was also established.

CONCLUSIONS

Transauricular endovascular access is a successful technique for establishing and maintaining intraarterial or endovenous vascular access. It obviates surgical cutdown and sacrifice of the femoral and cervical vessels and might considerably improve and expedite cardiovascular experimental protocols in small and large animals.

Long-term histological and scanning electron microscopy results of endovascular and operative treatments of experimentally induced aneurysms in the rabbit

OBJECTIVE

Treatment strategies of cerebral aneurysms include surgical clipping and endovascular therapies. To determine the long-term results of these therapeutic strategies, the vessel wall reaction close to the former aneurysm was studied according to the assumption that an intact endothelial layer over the former aneurysm neck constitutes complete vessel wall reconstruction and stable aneurysm obliteration.

METHODS

Aneurysms were created in 40 rabbits by intraluminal elastase incubation of the common carotid artery. Five animals each were assigned to the following groups: untreated, porous stents, polyurethane covered stentgrafts, porous stents with subsequent coiling. Ten animals were treated with coils alone, 10 with clips. After 6 months, angiography, histology, and scanning electron microscopy was performed.

RESULTS

Porous stents did not obliterate the aneurysm, whereas stentgrafts did; in-stent stenosis of up to 60% was present because of neointimal multilayer proliferation. After coiling, the aneurysm dome was occluded with fibrinous and collagenous material, whereas the aneurysm neck was not covered by an endothelial lining. Coil loops lay bare within the vessel, with fresh thrombus material on their surface. After clipping, a thin layer of endothelial lining bridging the two attached vessel walls was present, thereby completely obliterating the aneurysm and reconstructing the vessel wall.

CONCLUSION

This study demonstrates complete and stable aneurysm obliteration with vessel wall reconstruction after clipping, a sufficient obliteration of the aneurysm dome using endovascular techniques, but a failed healing response of the aneurysm neck that might correlate to its associated higher risk of rebleed. Whether or not this is counterbalanced by the better immediate outcome after endovascular treatment remains a matter of debate.

Vascular Anatomic Variation in Rabbits

PURPOSE

To explore the vascular anatomic variation along the aortic arch in New Zealand White rabbits with the goal of highlighting potential anatomic configurations that might be encountered in the performance of preclinical endovascular research in rabbits.

MATERIALS AND METHODS

Digital subtraction angiography images of the brachiocephalic artery (BCA) and aortic arch in New Zealand White rabbits were obtained after creation of elastase-induced aneurysms at the origin of the right common carotid artery (RCCA) in 214 animals. The patterns of origin of the RCCA and left common carotid artery (LCCA), right subclavian artery (RSCA) and left subclavian artery (LSCA), and right vertebral artery (RVA) and left vertebral artery (LVA) were analyzed.

RESULTS

Five predominant variations of vessel origin were identified. In 200 of 214 cases (93%), the LCCA originated from the bifurcation of the BCA and aorta. In eight cases (4%), the LCCA directly originated from the aorta. In two cases (1%), the LCCA originated from the BCA. Aberrant RSCA anatomy in which the RSCA originated from the aortic arch instead of the BCA was found in three cases (1.5%). In a single case (0.5%), aberrant RSCA anatomy with the RVA originating from the BCA was encountered.

CONCLUSIONS

Anatomic variation of the BCA in New Zealand White rabbits is similar to that seen in humans. Understanding of the normal and variant anatomy of the rabbit will aid investigators who use the rabbit model for endovascular research.

Modified technique to create morphologically reproducible elastase-induced aneurysms in rabbits

INTRODUCTION

The purpose of this study was to create morphologically reproducible elastase-induced model aneurysms in rabbits.

METHODS

We created 120 elastase-induced aneurysms in rabbits using two different methods: the standard technique (group 1, n=62) and a modified technique (group 2, n=58). In the standard technique a small cutdown with a focal area of exposure of the mid-right common carotid artery (RCCA) was employed, while in the modified technique the RCCA was completely exposed to its origin. We measured aneurysm sizes (neck diameter, width and height) in the two groups. The aneurysm sizes were compared between the two groups using Student's t test, and the standard deviations of the aneurysm sizes were compared between the groups using the F test.

RESULTS

The mean aneurysm neck size, width and height in group 1 were 3.4+/-1.2 mm, 3.8+/-1.0 mm and 8.0+/-1.7 mm, respectively, and in group 2, were 3.2+/-0.9 mm, 3.7+/-0.6 mm and 9.1+/-1.8 mm, respectively. The differences in mean aneurysm neck and width between the two groups were not significant (P>0.05). However, there were significant differences in the standard deviation of these two parameters between the two groups (P<0.05 and P<0.01, respectively). The mean aneurysm height in group 2 was larger than in group 1 (P<0.001), but no significant difference in the standard deviation of this parameter between the two groups was found (P>0.05).

CONCLUSION

The results indicate that more consistent aneurysm diameters can be created using the modified technique.

Magnetic versus manual guidewire manipulation in neuroradiology: in vitro results

INTRODUCTION

Standard microguidewires used in interventional neuroradiology have a predefined shape of the tip that cannot be changed while the guidewire is in the vessel. We evaluated a novel magnetic navigation system (MNS) that generates a magnetic field to control the deflection of a microguidewire that can be used to reshape the guidewire tip in vivo without removing the wire from the body, thereby potentially facilitating navigation along tortuous paths or multiple acute curves.

METHOD

The MNS consists of two permanent magnets positioned on either side of the fluoroscopy table that create a constant precisely controlled magnetic field in the defined region of interest. This field enables omnidirectional rotation of a 0.014-inch magnetic microguidewire (MG). Speed of navigation, accuracy in a tortuous vessel anatomy and the potential for navigating into in vitro aneurysms were tested by four investigators with differing experience in neurointervention and compared to navigation with a standard, manually controlled microguidewire (SG).

RESULTS

Navigation using MG was faster (P=0.0056) and more accurate (0.2 mistakes per trial vs. 2.6 mistakes per trial) only in less-experienced investigators. There were no statistically significant differences between the MG and the SG in the hands of experienced investigators. One aneurysm with an acute angulation from the carrier vessel could be navigated only with the MG while the SG failed, even after multiple reshaping manoeuvres.

CONCLUSION

Our findings suggest that magnetic navigation seems to be easier, more accurate and faster in the hands of less-experienced investigators. We consider that the features of the MNS may improve the efficacy and safety of challenging neurointerventional procedures.

Coil embolization training using a rabbit saccular aneurysm model

SUMMARY

We developed a rabbit saccular aneurysm model for coil embolization training. Elastaseinduced aneurysms were created successfully in about 80% of the rabbits. The aneurysms were usually broad in the neck and lengthy. At the 28(th) postoperative day, the aneurysms were about 1.5 times larger in both width and height than they had been at the 14(th) day. All aneurysms were successfully embolized with 18-sized electrically detachable (ED) platinum coils. After embolization, almost all aneurysms had a neck remnant. In conclusion, this model is useful not only for learning the technique of coil embolization but also for testing new embolic materials. The rabbit aneurysm model proved to be an efficacious training modality for endovascular coil embolization.

A triple bifurcation aneurysm model for evaluating complex endovascular therapies in dogs

OBJECT

Animal aneurysm models are required for the study of the hemodynamics and pathophysiology of intracranial aneurysms in humans and so that experimental treatments can be tested prior to clinical trials. The authors developed a canine model that consistently produces up to three bifurcation aneurysms similar in morphological features and hemodynamics to human intracranial aneurysms.

METHODS

In 10 mongrel dogs, a harvested segment of the external jugular vein was anastamosed to an external carotid artery (CA)-lingual artery bifurcation arteriotomy site to create a lateral bifurcation aneurysm. The surgery was repeated on the contralateral side in each animal to form a second lateral bifurcation aneurysm and, in five dogs, a CA-CA crossover anastomosis was also performed to create a terminal bifurcation aneurysm. Nineteen of 20 lateral bifurcation aneurysms were confirmed in 10 dogs by diagnostic angiography 7 to 14 days after surgery. Aneurysm fundus-to-neck ratios ranged from 1 to 2, depending on the size of the arteriotomy. The terminal bifurcation aneurysms were confirmed in all five dogs by diagnostic angiography 7 to 14 days after the procedure. The authors later tested endovascular techniques for embolizing the aneurysms.

CONCLUSIONS

Three bifurcation aneurysms of sufficient size for endovascular access can be created in a reproducible fashion in the same animal. This model is useful for studying complex endovascular procedures in aneurysms that mimic the human condition and for testing new devices and techniques.

Treatment of Experimentally Induced Aneurysms with Stents

OBJECTIVE

Although Guglielmi detachable coil systems have been widely accepted for treatment of intracranial aneurysms, primary stenting of aneurysms using porous stents, stent grafts, or implantation of coils after stent placement constitute emerging techniques in endovascular treatment. The aim of the present study was to use an animal model to investigate these different approaches to treat cerebral aneurysms with regard to the rate of closure and the histopathological changes within the aneurysm cavity and the parent vessel after stent placement.

METHODS

We created aneurysms in 30 rabbits by distal ligation and intraluminal incubation of the right common carotid artery with elastase. Ten animals were treated with porous stents alone, 10 animals with stent grafts (covered stents), and 10 animals with stents and additional coiling via the interstices of the stent, which enabled dense packing of the coils. Five animals in each group were observed for 1 month and the other animals for 3 months. Histological analyses were performed, including immunohistochemical investigations for estimating the proliferation of the intima and possible inflammatory infiltration.

RESULTS

Covered stents led to a complete and stable aneurysm occlusion with only minimal proliferative carrier vessel wall changes. One covered stent was completely occluded with old thrombus, and the other 9 remained patent. Porous stents occluded two of five aneurysms in the 1-month follow-up group and four of five after 3 months. However, progressive sprouting of neointima inside the carrier vessel that resulted in a stenosis of up to 40% was present. In the Stent + Coil group, one aneurysm showed recanalization after 1 month, and three of five aneurysms were recanalized after 3 months after coil compaction. Moreover, in-stent stenosis of up to 30% was present.

CONCLUSION

This study demonstrates the possible shortcomings and problems of emerging stent techniques to treat intracerebral aneurysms, shows where technical advances have to be made, and describes in which cases of aneurysm morphology caution has to be exercised when considering an endovascular approach using stents.

Are the configuration and neck morphology of experimental aneurysms predictable? A technical approach

Aneurysm configuration and neck morphology are important factors in the decision for cerebral aneurysm therapy, i.e., clipping versus coiling. The aim of our study was to create various aneurysm configurations in a predictable and reproducible way in an animal model. In our recently proposed endovascular approach to produce bifurcation aneurysms in the rabbit, the right common carotid artery (CCA) is surgically exposed and distally ligated, and a sheath is advanced retrogradely into the CCA, the base of which is proximally occluded using a Fogarty balloon. Subsequently, elastase is injected via a microcatheter that is placed directly distal to the balloon and allowed to incubate for 20 min. After removal of the sheath, saccular aneurysms begin to form within 2 weeks. For greater variability in aneurysm size and neck morphology, we modified two parameters of this formerly established elastase-induced aneurysm model--the distance between the balloon and sheath and the level of balloon position--before the elastase was endoluminally incubated in 15 rabbits. Three weeks after aneurysm induction, the size and configuration of the aneurysms were controlled using DSA. Our results confirm that balloon occlusion in the brachiocephalic trunk results in broad-based aneurysms, whereas balloon occlusion in the CCA gives rise to circumscribed aneurysm necks. By increasing the distance between the balloon and sheath, the rabbits developed significantly larger aneurysms. The balloon-sheath distance and the level of balloon occlusion proved to be parameters whose modifications result in predictable and reproducible aneurysm variants that can be used for the testing of endovascular devices.

Endovascular treatment of experimentally induced aneurysms in rabbits using stents: a feasibility study

Although Guglielmi detachable coil (GDC) systems have been generally accepted for treatment of intracranial aneurysms, primary stenting of aneurysms using porous stents or implantation of coils after stent placement remains experimental. Testing of these new methods requires an animal model which imitates human aneurysms in size, configuration and neck morphology. We assessed in detail the technical requirements of and steps for transfemoral stent treatment of experimentally induced aneurysms at the top of the brachiocephalic trunk in rabbits. We created aneurysms in ten rabbits by distal ligation and intraluminal digestion of the right common carotid artery with elastase. We treated five animals with porous stents alone, and five with stents plus coiling via the meshes of the stent, which permitted dense packing of coils. No complications related to the procedures occurred. In all animals, even in those treated solely with porous stents, total occlusion of the aneurysm was achieved. Our animal model can be suitable for testing the biocompatibility and occlusion rate of new methods and devices for the treatment of experimental aneurysms.