Bilateral common carotid artery (CCA) ligation in rabbits is a model for basilar terminus (BT) aneurysm formation.
We asked if this model could be replicated in rats. Fourteen female Sprague Dawley rats underwent bilateral CCA
ligation (n=8) or sham surgery (n=6). After 7 days, 5 ligated and 3 sham rats were euthanized for histological evaluation
of BT aneurysm formation, while the remaining rats were imaged with magnetic resonance angiography, euthanized, and
subjected to corrosion casting of the Circle of Willis (CoW). 3D micro computed tomography images of CoW casts were
used for flow simulations at the rat BT, and electron micrographs of the casts were analyzed for aneurysmal and morphological
changes. Results from these analyses were compared to rabbit model data (n=10 ligated and n=6 sham). Bilateral
CCA ligation did not produce aneurysmal damage at the rat BT. While the surgical manipulation increased rat basilar artery
flow, fluid dynamics simulations showed that the initial hemodynamic stress at the rat BT was significantly less than
in rabbits. Rats also exhibited fewer morphological and pathological changes (minor changes only occurred in the posterior
CoW) than rabbits, which had drastic changes throughout the CoW. A comparison of CoW anatomies demonstrated a
greater number of branching arteries at the BT, larger CoW arteries in relation to basilar artery, and a steeper BT bifurcation
angle in the rat. These differences could account for the lower hemodynamic stress at the BT and in the cerebrovasculature
of the rat. In conclusion, bilateral CCA ligation in rats does not recapitulate the rabbit model of early flow-induced
BT aneurysm. We suspect that the different CoW morphology of the rat lessens hemodynamic insults, thereby diminishing
flow-induced aneurysmal remodeling.