History and Recent Development of Basic Research Using an Experimental Intracranial Aneurysm Model

Since intracranial aneurysm(IA)is a disease that follows an extremely unpredictable course, from initiation to rupture, experimental models have greatly contributed to a better understanding of IA pathophysiology. This article aims to review the history of IA models through the pivotal theme of the ideal IA model. In addition, this article introduces updated findings from the application of these experimental models. Though the first IA model, known as a venous pouch model, was reported in 1954, it mimicked only the shape of the IA, without reproducing its pathological structure or blood-flow characteristics. Currently, two models are generally applied: the "Hashimoto model," produced by unilateral common carotid artery(CCA)ligation followed by systemic hypertension and weakening of the vascular wall, and the "elastase injection model," induced by intraventricular elastase injection and also followed by systemic hypertension. In addition, other models, including a rabbit basilar top IA, developed after bilateral CCA ligation, and an artificial bifurcation model, generated by an anastomosis between the CCAs, have been found to be valuable for computational fluid dynamics analysis. Through this advancement, the IA model has gradually elucidated the pathophysiology of IA as a flow-induced inflammatory disease. Nowadays, vascular inflammation is suggested to be regulated by bacterial flora. Further development of IA models and a better understanding of IA pathophysiology are expected in the future.