Morphological parameters and anatomical locations associated with rupture status of small intracranial aneurysms

Abstract

Characterization of the rupture risk factors for small intracranial aneurysms (SIAs, ≤5 mm) is clinically valuable. The present study aims to identify image-based morphological parameters and anatomical locations associated with the rupture status of SIAs. Two hundred and sixty-three patients with single SIAs (128 ruptured, 135 unruptured) were included, and six morphological parameters, including size, aspect ratio (AR), size ratio (SR), height-width ratio (H/W), flow angle (FA) and aneurysm width-parent artery diameter ratio, and the aneurysm locations were evaluated using three-dimensional geometry, and were used to identify a correlation with aneurysm rupture. Statistically significant differences were observed between ruptured and unruptured groups for AR, SR, H/W, FA, and aneurysm locations, from univariate analyses. Logistic regression analysis further revealed that AR (p = 0.034), SR (p = 0.004), H/W (p = 0.003), and FA (p < 0.001) had the strongest independent correlation with ruptured SIAs after adjustment for age, gender and other clinical risk factors. A future study on a larger SIA cohort need to establish to what extent the AR, SR, H/W and FA increase the risk of rupture in patients with unruptured SIAs in terms of absolute risks.

Figure 1

Definition of the morphological parameters in end-wall aneurysm (A) and side-wall aneurysm (B). Aneurysm size is defined as the maximum distance of the dome from the aneurysm neck plane (W). Aspect ratio (AR) is defined as the maximum perpendicular height (H1) of the aneurysm divided by the average neck diameter of the aneurysm (N). D1: the diameter of the parent vessel at the edge of the neck, perpendicular to flow; D2: the diameter of the parent vessel perpendicular to flow, measured at 1.5D1 from D1; average diameter: (D1 + D2)/2; size ratio (SR) is defined as the maximum aneurysm height (H2) divided by the average diameter. Height–width (H/W) ratio is defined as the ratio of H2/W. Aneurysm width–parent artery diameter ratio is the ratio between W/D1. Flow angle (FA) is defined as the angle between the maximum height of the aneurysm and the parent vessel (α).