Configuration of intracranial arteries and development of aneurysms - A follow-up study

Background: The reasons for development of intracranial aneurysms are unknown; hemodynamic factors may play an important role in this process. We performed a cohort study to further elicit the role of intracranial arterial geometry. Methods: We compared the original CTA/MRA of the circle of Willis of 26 patients who developed an aneurysm during follow-up with those of 78 controls with no aneurysm development who were matched for gender, age, and period of follow-up. We assessed hypoplasia of the arteries of the circle of Willis and measured bifurcation angles within and beyond the circle of Willis on three-dimensional CTA/MRA. Bifurcation angles were classified in tertiles for analysis. We used Student t test for comparison of bifurcation angles and calculated OR with corresponding 95% Cl for presence of hypoplasia and bifurcation angles in tertiles. Results: A hypoplastic branch was found in 5 of 7 (71%) sites with aneurysm development and in 6 of 21 corresponding sites (29%) without aneurysm development ( OR 6; 95% Cl 0.9 to 42). The branch angle was sharp (lowest tertile) in 10 of 14 (71%) sites with aneurysm development and in 8 of 42 (19%) sites without aneurysm development (OR 11.3; 95% Cl 2.0 to 64). Conclusions: Bifurcations with a hypoplastic branch and bifurcations with sharper bifurcation angles are risk factors for development of aneurysms. Analysis of the geometry of intracranial arteries might be helpful in detecting persons with increased risk for developing aneurysms.