Configuration of the circle of Willis, direction of flow, and shape of the aneurysm as risk factors for rupture of intracranial aneurysms

Improved knowledge on risk factors for rupture of intracranial aneurysms may lead to more tailored aneurysm management. We studied whether configuration of the circle of Willis, direction of flow towards the aneurysm, and shape of the aneurysm are risk factors for rupture. We reviewed CT angiograms of 126 patients with 75 ruptured and 75 unruptured aneurysms, matched for site of the aneurysm, gender and age of the patient, and year of CT angiogram. For the characteristics studied, we calculated odd ratios (ORs) with corresponding 95 % confidence intervals (CIs) for risk of rupture. Configuration of the circle of Willis (incompleteness, asymmetry or dominance) was analyzed on a per site basis. Non-spherical shape was subdivided into elliptical (oval and oblong) and multilobed. In additional analyses, we adjusted for size by means of multivariable logistic regression. Flow straight into the aneurysm (OR 2.0; 95 % CI 1.0-4.1) and non-spherical shape (OR 2.8; 95 % CI 1.5-5.5) were associated with rupture. Both elliptical shape, with increasing ORs for oval (OR 1.8; 95 % CI 0.8-4.0) to oblong shape (OR 6.2; 95 % CI 1.9-21), and multilobed shape (OR 4.1; 95 % CI 1.2-14) were associated with rupture. These ORs decreased after adjustment for size. Configuration of the circle of Willis was not associated with a strong risk of rupture; moderate risk could not be excluded. Direction of flow into the aneurysm and nonspherical (both elliptical and multilobed) shape may contribute to the risk of rupture, but are related to aneurysm size and may warrant more frequent follow-up.