An acute experimental model of saccular aneurysms in the rat

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.

Experimental microaneurysms in rats: I. Model for induction

BACKGROUND

Small aneurysms (lesser than 2 mm) in humans called sessile, baby aneurysms, or microaneurysms, generally are not able to be clipped or to be coil-packed through endovascular route. Among the modalities of treatment that have been used for treating microaneurysms, bipolar coagulation and wrapping of the lesion are outstanding. Nevertheless, demonstration of the efficacy of these treatments is difficult because most reported experimental models for inducting aneurysms are complex and difficult to be reproduced. This study aimed to develop a simple and reproducible model for inducing microaneurysms.

METHODS

Microaneurysms were induced using a mechanical lesion of the bifurcation of the aorta in 72 rats. Three groups of 10 animals were sacrificed 7, 14, and 21 days after the lesion and 2 groups (35 and 7 animals) after 30 days. The aortic bifurcation was macro/microscopically analyzed in the first 4 groups and a resistance test was applied in the fifth group.

RESULTS

Microaneurysms occurred in 77.8% of cases. Microscopically, degenerative changes were observed in the intima, media, and adventitia and in the internal elastic lamina. The bursting pressure ranged from 368 to 1,472 mm Hg during the resistance test in the fifth group.

CONCLUSIONS

The presented model of experimental microaneurysm induction is simple, reproducible and gives a high rate of positivity.

Mouse model of cerebral aneurysm: experimental induction by renal hypertension and local hemodynamic changes

BACKGROUND AND PURPOSE

Rupture of cerebral aneurysm (CA) is the major cause of subarachnoid hemorrhage. Molecular mechanisms of this disease, however, remain unknown. To make possible genetic analysis of CA formation with genetically altered mice, we have successfully established a mouse model of saccular CA that recapitulates the essential features of human saccular CA.

METHODS

In C57black/6 male mice, various stages of CAs were experimentally induced at the right anterior cerebral artery-olfactory artery bifurcations by ligations of left common carotid arteries and posterior branches of bilateral renal arteries with high salt diet. Both light and electron microscopic studies were performed with the longitudinal sections of anterior cerebral artery-olfactory artery bifurcations.

RESULTS

In the treated group, various aneurysmal changes were detected in 14 of 18 mice. On the other hand, in the control group, no aneurysmal changes were found in 15 mice. In microscopic studies, aneurysmal changes were shown to include mainly fragmentation of internal elastic lamina, thinning of the smooth muscle cell layer, and degeneration of adventitial tissue, which were very similar to critical changes in human saccular CA.

CONCLUSIONS

This mouse model of CA will be useful for studying the effects of complex determinants on CA formation and makes it possible to understand the pathogenesis of CA at the molecular level.

Experimental creation of fusiform carotid artery aneurysms using vein grafts in rats

OBJECTIVE

We developed an in vivo model of growing fusiform aneurysms, using vein grafts to the rat carotid artery. This aneurysm model might demonstrate the pathological features of the development and growth of aneurysms to become giant aneurysms.

METHODS

Placement of an interposed femoral vein graft to restore carotid artery flow was performed in Wistar rats. On Day 21, 75% of the grafts (mean diameter, 1.6 mm) were found to be dilated to resemble fusiform aneurysms (mean diameter, 5.82 mm), and 53% of these were giant. Quantitative analysis of the histological findings was performed using image-analyzing software.

RESULTS

Histological findings were similar to those for human intracranial giant aneurysms. The average length of the initial grafts in the aneurysm group was 9.1+/-1.9 mm, and grafts were significantly longer and more tortuous than in the normal graft group (6.4+/-0.8 mm) (P = 0.01). Cross-sectional areas of the aneurysms (mean, 18.9 mm2) were significantly correlated with the following: 1) the area of intra-aneurysmal thrombosis (mean, 11.1 mm2) (P < 0.0001); 2) the number of intrathrombotic vascular channels (P = 0.005); and 3) the area of dissection, with hemorrhage, between the thrombus and the wall of the aneurysm (mean, 0.72 mm2) (P = 0.0013). Scanning electron microscopic examination showed evidence of endothelial damage associated with growth of the aneurysms.

CONCLUSION

Recurrent hemorrhaging from intrathrombotic vascular channels caused dissection between the thrombus and the aneurysm wall, which led to growth of the experimental aneurysms to giant aneurysms. With this model, we demonstrated the growth mechanism of giant fusiform aneurysms.

Rapid saccular aneurysm induction by elastase application in vitro

OBJECTIVE

To develop a new saccular aneurysm model in vitro using elastase to study aneurysm initiation, growth, and rupture and to create a new in vivo aneurysm model to test endovascular therapies.

METHODS

Seventeen common carotid arteries excised from freshly killed pigs and sheep were treated with seven different methods of elastase delivery. The arteries were mounted in a saline-filled flow chamber. They received pulsatile flow for 48 hours, or until the resulting aneurysms ruptured. Changes were continuously monitored with video camera recordings and validated with histological sections.

RESULTS

All eight arteries treated topically, either on the intimal or on the adventitial surface, with elastase concentrations greater than 1 U/mm2, developed saccular aneurysms; five of them ruptured within 48 hours. All four arteries treated with surface concentrations of 0.1 U/mm2 via microcatheter infusion into the lumen developed fusiform aneurysms. None of the arteries that received surface concentrations less than 0.1 U/mm2 developed aneurysms. Histological sections revealed a reduced number of cellular element in a stretched collagen matrix at the dome of the saccular aneurysms.

CONCLUSION

After empirically testing several methods of elastase delivery, we were able to induce saccular, bifurcation-type aneurysms in animal arterial specimens. These aneurysms are histologically similar and more authentic than surgical models. The procedure is easy and reproducible. Our results suggest a possible enzymatic role in aneurysm formation and highlight the dramatic effects of selective arterial elastic damage. Also, the rapid growth of our experimental aneurysms may reflect the speed of the natural process.

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

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