Experience with Microaneurysm Formation at the Basilar Terminus in the Rabbit Elastase Aneurysm Model

BACKGROUND AND PURPOSE: Intracranial aneurysms have been induced in mice, rats, rabbits, and primates through carotid artery ligation. We reviewed our experience with RCCA ligation to quantify the rate of aneurysm formation in rabbits.

MATERIALS AND METHODS: In 30 consecutive New Zealand white rabbits, the RCCA was ligated during surgery to create elastase-induced aneurysms. The basilar artery and its bifurcation were harvested at various time points after surgery, including 8 weeks (n = 5), 13 weeks (n = 3), 14 weeks (n = 2), 16 weeks (n = 4), 17 weeks (n = 4), 30 weeks (n = 6), and 33 weeks (n = 6). All specimens were embedded in paraffin and sectioned at 5 μm in a coronal orientation, to show the basilar bifurcation and its branches. All sections were stained with HE. After the sections were evaluated and the photomicrographs were taken, the sections were de-stained and re-stained with VVG staining for elastin.

RESULTS: The IEL was intact and continuous at the BT in all 30 rabbits, as was the medial layer. No bulge-like localized dilation, to suggest microaneurysm or nascent aneurysm formation, was observed at the BT in any subject. There were small (0.08 ± 0.02 mm in diameter) concave structures along the P1 segments in 5 (16.7%) of 30 rabbits. On adjacent tissue sections, each of these 5 structures was shown to be branch vessels with intact IELs.

CONCLUSIONS: In our rabbit model, unilateral RCCA ligation does not induce microaneurysm formation.