De novo cerebral aneurysm formation associated with proximal stenosis

BACKGROUND: Hemodynamic insults-high wall shear stress (WSS) combined with high positive WSS gradient (WSSG)-have been proposed to link to cerebral aneurysm initiation. We report 4 cases of aneurysms with proximal stenosis, including 1 de novo aneurysm, that might be associated with hemodynamic insults caused by the proximal stenosis. CLINICAL PRESENTATION: In 4 clinical cases, the diameter stenosis was 37% to 49% (mean, 42%) located 2.7 to 4.7 mm (mean, 3.7 mm) from the apex. We performed computational fluid dynamics simulations for 2 cases: a ruptured basilar terminus aneurysm with proximal stenosis (which had an angiogram taken 15 years previously that showed no aneurysm and no stenosis) and a cavernous carotid artery aneurysm with proximal stenosis. In both cases, the stenosis caused unphysiologically high WSS (> 7 Pa) at the apex, nearly doubling the WSS and WSSG values. To investigate the relationship between stenosis and distal hemodynamic elevation, we created a series of T-shaped vascular models by varying the degree and location of stenosis. We found that stenosis > 40% by diameter located within 10 mm from the apex caused unphysiologically high WSS and WSSG. All 4 clinical cases satisfied these conditions. CONCLUSION: Proximal stenosis could produce high WSS and high positive WSSG at the apex, thus potentially inducing de novo aneurysm formation.