Rabbit aneurysm models mimic histologic wall types identified in human intracranial aneurysms

Balloon neck-plasty to create a wide-necked aneurysm in the elastase-induced rabbit model

PURPOSE

The elastase-induced aneurysm (EIA) model in rabbits has been proposed for translational research; however, the adjustment of aneurysm neck size remains challenging. In this study, the technical feasibility and safety of balloon neck-plasty to create a wide-necked aneurysm in rabbit EIA model were investigated.

METHODS

Male New Zealand White rabbits (N = 15) were randomly assigned to three groups: group A, EIA creation without neck-plasty; group B, neck-plasty immediately after EIA creation; group C, neck-plasty 4 weeks after EIA creation. The diameter of balloon used for neck-plasty was determined 1 mm larger than origin carotid artery diameter. All rabbits were euthanized 4 weeks after their final surgery. Aneurysm neck, height, dome-to-neck (D/N) ratio, and histologic parameters were compared among the groups.

RESULTS

Aneurysm creation was technically successful in 14 out of 15 rabbits (93.3%), with one rabbit experiencing mortality due to an adverse anesthetic event during the surgery. Saccular and wide-necked aneurysms were successfully created in all rabbits. Aneurysm neck was significantly greater in groups B and C compared to group A (all P < .05). D/N ratio was significantly lower in groups B and C compared to group A (all P < .05). Additionally, tunica media thickness, vessel area, and luminal area were significantly greater in groups B and C compared to group A (all P < .05). These variables were found to be significantly greater in group B compared to group C (all P < .05).

CONCLUSION

The creation of a wide-necked aneurysm using balloon neck-plasty after elastase induction in rabbits has been determined to be technically feasible and safe.

Targeting myeloperoxidase to stabilize unruptured aneurysm: an imaging-guided approach

Inflammation plays a key role in pathogenesis and rupture of aneurysms. Non-invasively and dynamically monitoring aneurysm inflammation is critical. This study evaluated myeloperoxidase (MPO) as an imaging biomarker and therapeutic target for aneurysm inflammation using an elastase-induced rabbit model treated with or without 4-aminobenzoic acid hydrazide (ABAH), an irreversible inhibitor of MPO. Myeloperoxidase-sensitive magnetic resonance imaging (MRI) using Mn-TyrEDTA, a peroxidase activity-dependent contrast agent, revealed weak contrast enhancement in contralateral arteries and decreased contrast enhancement in aneurysm walls with ABAH treatment, indicating MPO activity decreased and inflammation mitigated. This was supported by reduced immune cell infiltration, matrix metalloproteinases (MMP-2 and - 9) activity, ROS production and arterial wall destruction on histology. Finally, the aneurysm expansion rate remained < 50% throughout the study in the ABAH(+) group, but increased gradually in the ABAH(-) group. Our results suggest that inhibition of MPO attenuated inflammation and expansion of experimental aneurysm and MPO-sensitive MRI showed promise as a noninvasive tool for monitoring aneurysm inflammation.

High-frequency optical coherence tomography predictors of aneurysm occlusion following flow diverter treatment in a preclinical model

BACKGROUND

High-frequency optical coherence tomography (HF-OCT) is an intravascular imaging method that allows for volumetric imaging of flow diverters in vivo.

OBJECTIVE

To examine the hypothesis that a threshold for both volume and area of communicating malapposition can be predictive of early aneurysm occlusion.

METHODS

Fifty-two rabbits underwent elastase aneurysm formation, followed by treatment with a flow diverter. At the time of implant, HF-OCT was acquired to study the rate and degree of communicating malapposition. Treated aneurysms were allowed to heal for either 90 or 180 days and euthanized following catheter angiography. Healing was dichotomized into aneurysm remnant or neck remnant/complete occlusion. Communicating malapposition was measured by HF-OCT using a semi-automatic algorithm able to detect any points where the flow diverter was more than 50 µm from the vessel wall. This was then summed across image slices to either a volume or area. Finally, a subsampled population was used to train a statistical classifier for the larger dataset.

RESULTS

No difference in occlusion rate was found between device type or follow-up time (p=0.28 and p=0.67, respectively). Both volume and area of malapposition were significantly lower in aneurysms with a good outcome (p<0.001, both). From the statistical model, a volume of less than 0.56 mm3 or a normalized area less than 0.69 as quantified by HF-OCT was predictive of occlusion (p<0.001, each).

CONCLUSIONS

HF-OCT allows for measurements of both volume and area of malapposition and, from these measurements, an accurate prediction for early aneurysm occlusion can be made.

Fucoidan-coated coils improve healing in a rabbit elastase aneurysm model

BACKGROUND

Recanalization of coiled aneurysms remains unresolved. To limit aneurysm recanalization after embolization with coils, we propose an innovative approach to optimize aneurysm healing using fucoidan-coated coils.

OBJECTIVE

To evaluate the short-term efficacy and long-term safety of the new coil system with conventional angiography, histology, and multiphoton microscopy for follow-up of fibrosis and neointima formation.

METHODS

We conducted a feasibility study on rabbit elastase-induced aneurysms. Embolization was carried out with bare platinum coils, fucoidan-coated coils, or dextran-coated coils. Aneurysms were controlled after 1 month by digital subtraction angiography (DSA). Aneurysm samples were collected and processed for histological analysis. Aneurysm healing and fibrosis were measured by quantifying collagen according to the histological healing score by combining standard light microscopy and multiphoton imaging. We divided 27 rabbits into three groups: bare platinum group, fucoidan group, and dextran group as controls.

RESULTS

Angiographic grading showed a trend toward less recanalization in the fucoidan group, although there were no significant differences among the three groups (P=0.21). Histological healing was significantly different according to the presence of more collagen in the neck area of aneurysms in the fucoidan group versus the bare platinum group (P=0.011), but not in the dextran group. Histological index was significantly better at the aneurysm neck in the fucoidan group than in the bare platinum group (P=0.004). Collagen organization index was also significantly better in the fucoidan group than in the bare platinum group (P=0.007).

CONCLUSION

This proof-of-concept study demonstrated the feasibility and efficacy of treatment with fucoidan-coated coils to improve aneurysm healing. The results in this rabbit in vivo model showed that fucoidan-coated coils have the potential to improve healing following endovascular treatment.

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.

Rabbit Elastase Aneurysm Model Mimics the Recurrence Rate of Human Intracranial Aneurysms following Platinum Coil Embolization

BACKGROUND AND PURPOSE

Intracranial aneurysms treated with coils have been associated with incomplete occlusion, particularly in large or wide-neck aneurysms. This study aimed to validate the accuracy of the rabbit elastase model in predicting aneurysm recurrence in humans treated with platinum coils.

MATERIALS AND METHODS

Elastase-induced saccular aneurysms were induced in rabbits and embolized with conventional platinum coils. The recurrence rates of aneurysms were retrospectively analyzed. Morphologic characteristics of aneurysms, angiographic outcomes, and histologic healing were evaluated.

RESULTS

A total of 28 (15.3%) of 183 aneurysms recurred. The aneurysm recurrence rate observed in this study (15.3%) is similar to those reported in multiple analyses of aneurysm recurrence rates in humans (7%-27%). The rate of recurrence was higher in aneurysms treated without balloon assistance (19/66, 28.8%) compared with those treated with balloon assistance (9/117, 7.7%). Aneurysms treated with balloon-assisted coiling had a lower recurrence rate (OR = 0.17; 95% CI, 0.05-0.47; P = .001) and higher occlusion rate (OR = 6.88; 95% CI, 2.58-20.37; P < .001) compared with those treated without balloon-assisted coiling. In this rabbit elastase-induced aneurysm model, packing density and aneurysm volume were weak predictors of aneurysm recurrence; however, the packing density was a good predictor of the occlusion rate (OR = 1.05; 95% CI, 1.02-1.10; P = .008).

CONCLUSIONS

The rabbit elastase aneurysm model may mimic aneurysm recurrence rates observed in humans after platinum coil embolization. Moreover, balloon assistance and high packing densities were significant predictors of aneurysm recurrence and occlusion.

Disturbed flow's impact on cellular changes indicative of vascular aneurysm initiation, expansion, and rupture: A pathological and methodological review

Aneurysms are malformations within the arterial vasculature brought on by the structural breakdown of the microarchitecture of the vessel wall, with aneurysms posing serious health risks in the event of their rupture. Blood flow within vessels is generally laminar with high, unidirectional wall shear stressors that modulate vascular endothelial cell functionality and regulate vascular smooth muscle cells. However, altered vascular geometry induced by bifurcations, significant curvature, stenosis, or clinical interventions can alter the flow, generating low stressor disturbed flow patterns. Disturbed flow is associated with altered cellular morphology, upregulated expression of proteins modulating inflammation, decreased regulation of vascular permeability, degraded extracellular matrix, and heightened cellular apoptosis. The understanding of the effects disturbed flow has on the cellular cascades which initiate aneurysms and promote their subsequent growth can further elucidate the nature of this complex pathology. This review summarizes the current knowledge about the disturbed flow and its relation to aneurysm pathology, the methods used to investigate these relations, as well as how such knowledge has impacted clinical treatment methodologies. This information can contribute to the understanding of the development, growth, and rupture of aneurysms and help develop novel research and aneurysmal treatment techniques.

Structural Remodeling of the Extracellular Matrix in Arteriogenesis: A Review

Lower extremity arterial occlusive disease (AOD) results in significant morbidity and mortality for the population, with up to 10% of patients ultimately requiring amputation. An alternative method for non-surgical revascularization which is yet to be fully understood is the optimization of the body's own natural collateral arterial network in a process known as arteriogenesis. Under conditions of conductance vessel stenosis or occlusion resulting in increased flow, shear forces, and pressure gradients within collaterals, positive remodeling occurs to increase the diameter and capacity of these vessels. The creation of a distal arteriovenous fistula (AVF) will drive increased arteriogenesis as compared to collateral formation with the occlusion of a conductance vessel alone by further increasing flow through these arterioles, demonstrating the capacity for arteriogenesis to form larger, more efficient collaterals beyond what is spontaneously achieved after arterial occlusion. Arteries rely on an extracellular matrix (ECM) composed of elastic fibers and collagens that provide stability under hemodynamic stress, and ECM remodeling is necessary to allow for increased diameter and flow conductance in mature arterial structures. When positive remodeling occurs, digestion of lamella and the internal elastic lamina (IEL) by matrix metalloproteinases (MMPs) and other elastases results in the rearrangement and thinning of elastic structures and may be replaced with disordered elastin synthesis without recovery of elastic function. This results in transmission of wall strain to collagen and potential for aneurysmal degeneration along collateral networks, as is seen in the pancreaticoduodenal artery (PDA) after celiac occlusion and inferior mesenteric artery (IMA) with concurrent celiac and superior mesenteric artery (SMA) occlusions. Further understanding into the development of collaterals is required to both better understand aneurysmal degeneration and optimize collateral formation in AOD.

Creating Clinically Relevant Aneurysm Sizes in the Rabbit Surgical Elastase Model

BACKGROUND

Creating aneurysm sizes in animal models that resemble human aneurysms is essential to study and test neuroendovascular devices. The commonly used rabbit surgical elastase model, however, produces saccular aneurysms that are smaller than those typically treated in humans. The goal of this study was to determine whether an increased vessel stump length and the addition of calcium chloride to the incubation solution has an effect on the resulting aneurysm size.

METHODS

Using a modified aneurysm creation method, 32 female New Zealand White rabbits underwent aneurysm creation procedures. Subjects were equally allocated into 4 different groups based on vessel stump length (2 cm controls vs. 3 cm) and incubation solution (elastase alone controls vs. a 1:1 mixture of elastase and calcium chloride). At 4 weeks, all animals underwent angiography to determine the resulting aneurysm size by a neurointerventionalist who was blinded to treatment group.

RESULTS

An increase in stump length from 2 cm to 3 cm resulted in a significant increase in the height of aneurysm (P < 0.05). Compared with control animals, the combination of a 3-cm stump length and the addition of calcium chloride to the incubation solution resulted in a significant increase in aneurysm height, width, and volume (P < 0.05).

CONCLUSIONS

Creating larger aneurysms is necessary for the rabbit model to be more clinically relevant. Our study demonstrated that the utilization of a 3-cm vessel stump as well as both calcium chloride and elastase in the incubation solution results in aneurysm sizes that more closely resemble the population of aneurysms treated in humans.

Rabbit Elastase Aneurysm: Imaging and Histology Correlates for Inflammation and Healing

OBJECTIVE

Aneurysmal subarachnoid hemorrhage remains a devastating event with poorly understood pathophysiology. Previous studies have suggested that aneurysm wall inflammation may play a part in the development and potential rupture of aneurysms. The rabbit elastase aneurysm model is a well-established model, which produces aneurysms closely mimicking human cerebral aneurysms in flow dynamics and histopathology. The primary aim of this study was to correlate inflammatory changes after aneurysm formation using sequential vessel wall imaging with histopathologic analysis. A secondary aim was to evaluate the potential effect of gender and anti-inflammatory treatment with aspirin on this inflammatory response.

METHODS

Twenty-seven New Zealand rabbits underwent surgery to create an aneurysm using elastase infusion at the right common carotid artery origin. Vessel wall imaging and histopathologic analysis was obtained at different time points after aneurysm creation. The rabbits were also randomized by gender and to treatment groups with or without aspirin.

RESULTS

Histopathologic analysis revealed 3 distinct phases after aneurysm formation. These phases were an initial inflammatory phase, followed by a regeneration phase, and finally a connective tissue deposition phase. Vessel wall imaging demonstrated 2 distinct imaging patterns. No appreciable differences were seen in histology or imaging when comparing gender or treatment with aspirin.

CONCLUSIONS

Inflammatory changes induced by the rabbit elastase aneurysm model can be correlated with histopathologic findings and observed on noninvasive vessel wall imaging. This may provide a method to study the inflammatory pathway as it pertains to aneurysmal development and subsequent rupture.

Adaptive Remodeling in the Elastase-induced Rabbit Aneurysms

BACKGROUND

Rupture of brain aneurysms is associated with high fatality and morbidity rates. Through remodeling of the collagen matrix, many aneurysms can remain unruptured for decades, despite an enlarging and evolving geometry.

OBJECTIVE

Our objective was to explore this adaptive remodeling for the first time in an elastase induced aneurysm model in rabbits.

METHODS

Saccular aneurysms were created in 22 New Zealand white rabbits and remodeling was assessed in tissue harvested 2, 4, 8 and 12 weeks after creation.

RESULTS

The intramural principal stress ratio doubled after aneurysm creation due to increased longitudinal loads, triggering a remodeling response. A distinct wall layer with multi-directional collagen fibers developed between the media and adventitia as early as 2 weeks, and in all cases by 4 weeks with an average thickness of 50.6 ± 14.3 μm. Collagen fibers in this layer were multi-directional (AI = 0.56 ± 0.15) with low tortuosity (1.08 ± 0.02) compared with adjacent circumferentially aligned medial fibers (AI = 0.78 ± 0.12) and highly tortuous adventitial fibers (1.22 ± 0.03). A second phase of remodeling replaced circumferentially aligned fibers in the inner media with longitudinal fibers. A structurally motivated constitutive model with both remodeling modes was introduced along with methodology for determining material parameters from mechanical testing and multiphoton imaging.

CONCLUSIONS

A new mechanism was identified by which aneurysm walls can rapidly adapt to changes in load, ensuring the structural integrity of the aneurysm until a slower process of medial reorganization occurs. The rabbit model can be used to evaluate therapies to increase aneurysm wall stability.

In situ decellularization of a large animal saccular aneurysm model: sustained inflammation and active aneurysm wall remodeling

OBJECTIVE

To investigate in situ decellularization of a large animal model of saccular aneurysm as a strategy for achieving aneurysmal growth and lasting inflammation.

METHODS

18 New Zealand White rabbits were randomized 2:1 to receive endoluminal sodium dodecyl sulfate infusion (SDS, 1% solution, 45 min) following elastase or elastase-only treatment (control). All aneurysms were measured by digital subtraction angiography every 2 weeks. Every 2 weeks, three of the rabbits (two elastase + SDS, one control) underwent MRI, followed by contrast injection with myeloperoxidase (MPO)-sensing contrast agent. MRI was repeated 3 hours after contrast injection and the enhancement ratio (ER) was calculated. Following MRI, aneurysms were explanted and subjected to immunohistopathology.

RESULTS

During follow-up MRI, the average ER for SDS-treated animals was 1.63±0.20, compared with 1.01±0.06 for controls (p<0.001). The width of SDS-treated aneurysms increased significantly in comparison with the elastase aneurysms (47% vs 20%, p<0.001). Image analysis of thin sections showed infiltration of MPO-positive cells in decellularized aneurysms and surroundings through the 12-week observation period while control tissue had 5-6 times fewer cells present 2 weeks after aneurysm creation. Immunohistochemistry demonstrated the presence of MPO-positive cells surrounding decellularized lesions at early time points. MPO-positive cells were found in the adventitia and in the thrombi adherent to the aneurysm wall at later time points.

CONCLUSIONS

In situ decellularization of a large animal model of saccular aneurysms reproduces features of unstable aneurysms, such as chronic inflammation (up to 12 weeks) and active aneurysm wall remodeling, leading to continued growth over 8 weeks.

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.

Ruptured Fisher grade 3 blister aneurysms have a higher incidence of delayed cerebral ischemia than ruptured Fisher grade 3 saccular aneurysms

BACKGROUND

Blister aneurysms are a rare subclass of aneurysms, which remain challenging to treat both with open cerebrovascular and endovascular techniques, and clinicians continue to see poor outcomes in some cases despite improvements in technology. Based on our clinical observations, we hypothesized that patients with a Fisher grade 3 subarachnoid hemorrhage (SAH) from a ruptured anterior circulation blister aneurysm are significantly more likely to develop poor outcome due to delayed cerebral ischemia than patients with a Fisher grade 3 SAH from a ruptured anterior circulation saccular aneurysm.

METHODS

In this consecutive case series, we reviewed management, outcomes, and rates of delayed cerebral ischemia for all ruptured anterior circulation blister aneurysms from 2012 to 2018 at our institution and compared them to a concurrent cohort of ruptured saccular anterior circulation aneurysms. A blister aneurysm was defined as an aneurysm that arises from a nonbranching point and demonstrates hemispherical anatomy on diagnostic angiography.

RESULTS

We identified 14 consecutive ruptured anterior circulation blister aneurysms. Thirteen aneurysms were treated operatively- 5 with clip remodeling and 8 with flow diversion embolization. While clip remodeling had a high intraoperative rupture rate (80%), there was only one (12.5%) intraoperative rupture with flow diversion embolization. Outcomes were worsened by delayed cerebral ischemia from vasospasm in patients with Fisher 3 hemorrhages from blister aneurysms (86%). The rate of delayed cerebral ischemia from vasospasm was significantly higher for ruptured blister aneurysms than for a concurrent cohort of ruptured saccular aneurysms (8.6%, P = 0.0001).

CONCLUSION

Ruptured Fisher grade 3 anterior circulation blister aneurysms have a significantly higher incidence of delayed cerebral ischemia from vasospasm compared to saccular aneurysms, regardless of the treatment modality.

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.

Comparison of Aneurysm Patency and Mural Inflammation in an Arterial Rabbit Sidewall and Bifurcation Aneurysm Model under Consideration of Different Wall Conditions

Background: Biological processes that lead to aneurysm formation, growth and rupture are insufficiently understood. Vessel wall inflammation and degeneration are suggested to be the driving factors. In this study, we aimed to investigate the natural course of vital (non-decellularized) and decellularized aneurysms in a rabbit sidewall and bifurcation model. Methods: Arterial pouches were sutured end-to-side on the carotid artery of New Zealand White rabbits (vital [n = 6] or decellularized [n = 6]), and into an end-to-side common carotid artery bifurcation (vital [n = 6] and decellularized [n = 6]). Patency was confirmed by fluorescence angiography. After 28 days, all animals underwent magnetic resonance and fluorescence angiography followed by aneurysm harvesting for macroscopic and histological evaluation. Results: None of the aneurysms ruptured during follow-up. All sidewall aneurysms thrombosed with histological inferior thrombus organization observed in decellularized compared to vital aneurysms. In the bifurcation model, half of all decellularized aneurysms thrombosed whereas the non-decellularized aneurysms remained patent with relevant increase in size compared to baseline. Conclusions: Poor thrombus organization in decellularized sidewall aneurysms confirmed the important role of mural cells in aneurysm healing after thrombus formation. Several factors such as restriction by neck tissue, small dimensions and hemodynamics may have prevented aneurysm growth despite pronounced inflammation in decellularized aneurysms. In the bifurcation model, rarefication of mural cells did not increase the risk of aneurysm growth but tendency to spontaneous thrombosis.

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.

Assessment of endothelialization of aneurysm wall over time in a rabbit model through CD31 scoring

BACKGROUND

Intracranial aneurysms represent a significant health concern and are poorly understood despite decades of research. Our study focused on understanding temporal patterns of endothelial cell distribution in different spatial locations within the aneurysm early after creation in a rabbit model.

METHODS

Elastase induced saccular aneurysms were created in rabbits and harvested on day 1 (n=3) and after 2 (n=5), 4 (n=4), 8 (n=5), and 12 (n=6) weeks. Sham operated controls (n=3) were harvested on the same day. Aneurysm and control tissue samples were subjected to en face whole mount CD31 staining for endothelial cells. Semiquantitative scoring was performed on the basis of endothelial coverage of the vessel wall (proximal, middle, and distal portions of the aneurysm dome). Mixed effects models were used to assess the effect of time and aneurysm section on endothelial coverage.

RESULTS

Aneurysmal segments were near completely de-endothelialized at 4 and 8 weeks but had re-endothelialized by 12 weeks. Compared with controls, aneurysms at all time points showed decreased endothelialization, but the difference was only significant compared with the 4 and 8 week groups. Both time (P=0.03) and aneurysm section (P=0.07) were significantly associated with the degree of endothelialization. Proximal locations showed increased endothelialization compared with distal locations (P=0.03).

CONCLUSION

In experimental aneurysms of rabbits, endothelial cells regress during the first month after creation, followed by ascending re-endothelialization that stays incomplete. These findings suggest that re-population of endothelial cells comes from resident cells in the adjacent parent artery and that deranged hemodynamics may affect full reconstitution of endothelial cells long term.