Interval change in size of venous pouch canine bifurcation aneurysms over a 10-month period

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.

Application of a rabbit-elastase aneurysm model for preliminary histology assessment of the PPODA-QT liquid embolic

Background

PPODA-QT is a novel liquid embolic under development for the treatment of cerebral aneurysms. We sought to test the rabbit-elastase aneurysm model to evaluate the tissue response following PPODA-QT embolization.

Methods

Experimental elastase-induced aneurysms were created in fourteen New Zealand White Rabbits. Eight animals were used for aneurysm model and endovascular embolization technique development. Six PPODA-QT-treated animals were enrolled in the study. Control and aneurysm tissues were harvested at acute (n = 2), 1-month (n = 2), and 3-month (n = 2) timepoints and the tissues were prepared for histology assessment.

Results

All fourteen rabbit-elastase aneurysms resulted in small and medium aneurysm heights (<10 mm dome height) with highly variable neck morphologies, small midline dome diameters, and beyond-wide dome-to-neck (d: n) ratios. Histological evaluation of four aneurysms, treated with PPODA-QT, demonstrated reorganization of aneurysm wall elastin into a smooth muscle layer, and observed as early as the 1-month survival timepoint. At the aneurysm neck, a homogenous neointimal layer (200-300 μm) formed at the PPODA-QT interface, sealing off the parent vessel from the aneurysm dome. No adverse immune response was evident at 1- and 3-month survival timepoints.

Conclusion

PPODA-QT successfully embolized the treated aneurysms. Following PPODA-QT embolization, neointimal tissue growth and remodeling were noted with minimal immunological response. The experimental aneurysms created in rabbits were uniformly small with inconsistent neck morphology. Further testing of PPODA-QT will be conducted in larger aneurysm models for device delivery optimization and aneurysm healing assessment before human clinical investigation.

Saccular Aneurysm Models Featuring Growth and Rupture: A Systematic Review

BACKGROUND

Most available large animal extracranial aneurysm models feature healthy non-degenerated aneurysm pouches with stable long-term follow-ups and extensive healing reactions after endovascular treatment. This review focuses on a small subgroup of extracranial aneurysm models that demonstrated growth and potential rupture during follow-up.

METHODS

The literature was searched in Medline/Pubmed to identify extracranial in vivo saccular aneurysm models featuring growth and rupture, using a predefined search strategy in accordance with the PRISMA guidelines. From eligible studies we extracted the following details: technique and location of aneurysm creation, aneurysm pouch characteristics, time for model creation, growth and rupture rate, time course, patency rate, histological findings, and associated morbidity and mortality.

RESULTS

A total of 20 articles were found to describe growth and/or rupture of an experimentally created extracranial saccular aneurysm during follow-up. Most frequent growth was reported in rats (n = 6), followed by rabbits (n = 4), dogs (n = 4), swine (n = 5), and sheep (n = 1). Except for two studies reporting growth and rupture within the abdominal cavity (abdominal aortic artery; n = 2) all other aneurysms were located at the neck of the animal. The largest growth rate, with an up to 10-fold size increase, was found in a rat abdominal aortic sidewall aneurysm model.

CONCLUSIONS

Extracranial saccular aneurysm models with growth and rupture are rare. Degradation of the created aneurysmal outpouch seems to be a prerequisite to allow growth, which may ultimately lead to rupture. Since it has been shown that the aneurysm wall is important for healing after endovascular therapy, it is likely that models featuring growth and rupture will gain in interest for preclinical testing of novel endovascular therapies.

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.

Long-term patency of complex bilobular, bisaccular, and broad-neck aneurysms in the rabbit microsurgical venous pouch bifurcation model

OBJECTIVES

In experimental aneurysm models, long-term patency without spontaneous thrombosis is the most important precondition for analyses of embolization devices. We recently reported the feasibility of creating complex venous pouch bifurcation aneurysms in the rabbit with low morbidity, low mortality, and high short-term aneurysm patency. In order to further evaluate our model, we examined the long-term patency rate.

METHODS

Various sizes of complex bilobular, bisaccular, and broad-neck venous pouch aneurysms were surgically formed at an artificially created bifurcation of both common carotid arteries in 17 rabbits. Early aggressive anticoagulation was continued for 1 month. The rabbits were followed up using contrast-enhanced three-dimensional 1.5-T magnetic resonance angiography (CE-3D-MRA) at 1 month and up to 1 year after creation of the bifurcation.

RESULTS

At 1-month follow-up, all but one of the created aneurysms and all parent vessels proved to be patent. Three animals (18%) were lost during follow-up for reasons unrelated to aneurysm surgery. At 1-year follow-up, one animal showed partial and one complete spontaneous aneurysm thrombosis (aneurysm patency rate: 86%). Six out of 42 parent vessels were occluded at that time (vessel patency rate: 86%).

CONCLUSIONS

Complex bilobular, bisaccular, and broad-neck microsurgical aneurysm formation in the rabbit bifurcation model demonstrates a high long-term patency rate but is complicated by high rates of unrelated procedural mortality and morbidity. There is no need for prolonged (>4 weeks) anticoagulation to achieve good long-term patency in complex venous pouch bifurcation aneurysms.

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.

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.

Symptomatic perianeurysmal edema following bare platinum embolization of a small unruptured cerebral aneurysm

There is considerable interest in the development of symptomatic inflammatory reactions following coil embolization of cerebral aneurysms. Patients have experienced a range of adverse events, usually after treatment of moderately large aneurysms with modified "bioactive" coils. More recently, it has been recognized that adverse inflammatory reactions can be associated with the use of "nonbioactive" coils, and we present a case of symptomatic perianeurysmal edema after treatment of a small unruptured aneurysm with bare platinum coils.

Evaluation of the new HydroSoft coil in a canine model of bifurcation aneurysm

Object

The present study was designed to evaluate the new HydroSoft coil as a finishing coil in a canine model of a wide-necked, high-flow bifurcation aneurysm.

Methods

Nine experimental aneurysms were created. The aneurysm dome was first embolized with bare platinum coils and HydroCoils, and then the remaining neck portion was embolized with HydroSoft coils to obtain maximum aneurysm occlusion. Follow-up angiography was performed at 1 and 3 months, and histopathological analysis was performed after the 3-month follow-up angiography.

Results

One hundred twenty-five HydroSoft coils were deployed into 9 aneurysms without any technical problem. The mean volume % of the bare platinum coils, HydroCoils, and HydroSoft coils were 23.0 ± 15.9, 63.0 ± 23.5, and 13.9 ± 8.9%, respectively. The mean aneurysm volumetric occlusion rate was 45.9%. At the 3-month follow-up angiography, 8 of 9 aneurysms remained stable and had not recanalized. Microscopically, most aneurysms showed complete endothelialization and thick neointima formation at the neck surface with no thrombus present.

Conclusions

The HydroSoft coil appears feasible as a finishing coil based on the results of this animal study. HydroSoft coils inserted at the neck of the aneurysm may help induce neointima formation, which may lead to less coil compaction and aneurysm recanalization in clinical practice.

Dangerous advances in measurements from digital subtraction angiography: when is a millimeter not a millimeter?

Aneurysms need accurate millimeters (mm). Direct millimeters were lost with digital subtraction angiography (DSA) years ago, with measurements in pixels. Advances in DSA can now give inherent millimeters. The Cerecyte aneurysm coiling trial's angiographic core lab assesses images from compact disc (CD). External fiducials for millimeter calibration are required. Of 25 cases with two 10 mm fiducials, near and far from the intensifier, the midline mean is between 9 "mm" to 15 "mm". Yet 10 mm must be 10 mm. This variance is potentially dangerous. Proprietary software seems to prohibit calibration transfer via CD to another vendor's system.