A Modified Method for Creating Elastase-Induced Aneurysms by Ligation of Common Carotid Arteries in Rabbits and Its Effect on Surrounding Arteries

Abstract

Background and purpose: Rabbit models of intracranial aneurysms are frequently used in pre-clinical settings. This study aimed to demonstrate an alternative, extravascular method for creating elastase-induced aneurysms, and how ligation of the right common carotid arteries (RCCA) can impact flow redistribution into left CCA (LCCA).

Methods: Elastase-induced aneurysms in 18 New Zealand rabbits (4.14 ± 0.314 kg) were created by applying 3-5 U of concentrated elastase solution to the exterior of the right and left CCA roots (RCCA and LCCA). After the induction of the aneurysm, the aneurysm was either kept intact to the rest of the corresponding CCA, severed from the rest of the CCA to allow for a free standing aneurysm, or was anchored to nearby tissue to influence the angle and orientation of the aneurysm with respect to the parent vessel. Ultrasound studies were performed before and after creation of aneurysms to collect blood flow measurements inside the aneurysm pouch and surrounding arteries. Prior to sacrificing the animals, computed tomography angiography studies were performed. Harvested aneurysmal tissues were used for histological analysis.

Results: Elastase-induced aneurysms were successfully created by the extravascular approach. Histological studies showed that the biological response was similar to human cerebral aneurysms and previously published elastase-induced rabbit aneurysm models. Ultrasound measurements indicated that after the RCCA was ligated, blood flow significantly increased in the LCCA at one-month follow-up.

Conclusion: An alternate method for creating elastase-induced aneurysms has been demonstrated. The novel aspects of our method allow for ligation of one or both common carotid arteries to create a single or bilateral aneurysm with an ability to control the orientation of the induced aneurysm.

Keywords: aneurysm model; angiography; elastase; flow diverter; rabbit model; ultrasound.

Figure 1. (A) Resin vascular model of rabbit (1: aortic arch, 2: CCAs, 3: SCAs, 4: VAs, and arrows: location of aneurysms). (B) Example of the induced aneurysm after ligating the RCCA.

Figure 2. Sample ultrasound studies. (A) Doppler mode: used to measure blood flow in arteries. (B) Doppler mode: used to visualize flow inside the aneurysm. (C) B-mode: used to measure the diameters.

Figure 3. CTA scans displaying vasculature of affected areas. (A) RCCA aneurysm with anchored orientation. (B) RCCA aneurysm with severed orientation. (C) LCCA aneurysm with severed orientation. (D) RCCA and LCCA double aneurysms.

Figure 4. Measured aneurysm sizes. (A) Median, interquartile range, and minimum/maximum values of all measurements. (B) Mean ± SE values for single aneurysms (n = 16) and dual aneurysms (n = 4).

Figure 5. Panels A, B, and C: mean changes in diameter, velocity, and blood flow for LCCA, LSCA, and RSCA before and after creation of RCCA aneurysm. Panels D, E, and F: average changes for combined LCCA, LSCA, and RSCA diameters, velocities, and blood flows.

Figure 6. Histologic changes in an elastase-induced aneurysm. (A) Saccular aneurysm of the RCCA sampled immediately proximal to area of maximum injury (sac) within the aneurysm. The uninvolved portion of parent vessel (longer arrow) demonstrates full elastin thickness staining with VVG. Approaching the aneurysm sac (square), the neck of the aneurysm (shorter arrow) shows an abrupt transition to a markedly thinned tunica media with fewer layers of elastin staining. (B) Cross section of LCCA (control). (C) Magnified aneurysm segment of RCCA (20X). (D) Magnified LCCA segment (20X). When compared with the LCCA (control) in panels B and D, VVG staining of the aneurysm sac (panels A and C) illustrates fewer distinct layers of medial elastin.