Analysis of Morphological Parameters to Differentiate Rupture Status in Anterior Communicating Artery Aneurysms

In contrast to size, the association of morphological characteristics of intracranial aneurysms with rupture has not been established in a systematic manner. We present an analysis of the morphological variables that are associated with rupture in anterior communicating artery aneurysms to determine site-specific risk variables. One hundred and twenty-four anterior communicating artery aneurysms were treated in a single institution from 2005 to 2010, and CT angiograms (CTAs) or rotational angiography from 79 patients (42 ruptured, 37 unruptured) were analyzed. Vascular imaging was evaluated with 3D Slicer© to generate models of the aneurysms and surrounding vasculature. Morphological parameters were examined using univariate and multivariate analysis and included aneurysm volume, aspect ratio, size ratio, distance to bifurcation, aneurysm angle, vessel angle, flow angle, and parent-daughter angle. Multivariate logistic regression revealed that size ratio, flow angle, and parent-daughter angle were associated with aneurysm rupture after adjustment for age, sex, smoking history, and other clinical risk factors. Simple morphological parameters such as size ratio, flow angle, and parent-daughter angle may thus aid in the evaluation of rupture risk of anterior communicating artery aneurysms

Morphological Parameters Associated with Ruptured Posterior Communicating Aneurysms

The rupture risk of unruptured intracranial aneurysms is known to be dependent on the size of the aneurysm. However, the association of morphological characteristics with ruptured aneurysms has not been established in a systematic and location specific manner for the most common aneurysm locations. We evaluated posterior communicating artery (PCoA) aneurysms for morphological parameters associated with aneurysm rupture in that location. CT angiograms were evaluated to generate 3-D models of the aneurysms and surrounding vasculature. Univariate and multivariate analyses were performed to evaluate morphological parameters including aneurysm volume, aspect ratio, size ratio, distance to ICA bifurcation, aneurysm angle, vessel angles, flow angles, and vessel-to-vessel angles. From 2005–2012, 148 PCoA aneurysms were treated in a single institution. Preoperative CTAs from 63 patients (40 ruptured, 23 unruptured) were available and analyzed. Multivariate logistic regression revealed that smaller volume (p = 0.011), larger aneurysm neck diameter (0.048), and shorter ICA bifurcation to aneurysm distance (p = 0.005) were the most strongly associated with aneurysm rupture after adjusting for all other clinical and morphological variables. Multivariate subgroup analysis for patients with visualized PCoA demonstrated that larger neck diameter (p = 0.018) and shorter ICA bifurcation to aneurysm distance (p = 0.011) were significantly associated with rupture. Intracerebral hemorrhage was associated with smaller volume, larger maximum height, and smaller aneurysm angle, in addition to lateral projection, male sex, and lack of hypertension. We found that shorter ICA bifurcation to aneurysm distance is significantly associated with PCoA aneurysm rupture. This is a new physically intuitive parameter that can be measured easily and therefore be readily applied in clinical practice to aid in the evaluation of patients with PCoA aneurysms

Univariate analyses for the morphological parameters measured for ruptured and unruptured ACoA aneurysms.

<p>P value and odds ratios indicate the level of statistical significance that the value of certain variable differs between the ruptured group and unruptured group (p<0.05 is considered statistically significant).</p

Computed Tomography Angiogram (CTA) and three-dimensional models of anterior communicating aneurysms with a dominant A1 or with co-dominant A1’s.

<p>Coronal MIP images are shown for an ruptured AcoA aneurysm with a dominant left A1 (A) and an unruptured AcoA aneurysm with co-dominant A1’s (C). The corresponding 3-D reconstructed images from Slicer are shown in B and D with definitions of morphological parameters. Solid line (B and D) indicates aneurysm neck.</p

Multivariate analysis after adjustment for clinical and morphological risk factors.

<p>A multivariate logistic regression model was constructed to ascertain morphological parameters that were significant predictors of aneurysm rupture, after adjusting for demographic and clinical risk factors. P value and odds ratios indicate the level of statistical significance for certain parameter in the multivariable regression model (p<0.05 is considered statistically significant).</p

Scatter plots depicting the interaction between size ratio and other morphological parameters.

<p>Linear regression analysis for scatter plot of size ratio and aspect ratio yielded an R² value of 0.75 for the ruptured group and 0.74 for the unruptured group (A), suggesting inter-dependency of the two variables. No clear dependency was observed between size ratio and aneurysm angle (B), flow angle (C), or parent-daughter angle (D).</p

Definition of morphological parameters used in the analysis.

<p>Maximum aneurysm height (H_max) is measured between the center of the aneurysm neck and the greatest distance to the aneurysm dome. Maximal perpendicular height (H) is the largest perpendicular distance from the neck of the aneurysm to the dome of the aneurysm. Aspect ratio is calculated as the ratio of the H and neck diameter of the aneurysm. Size ratio is the ratio between H_max and the mean vessel diameter of all branches associated with the aneurysm (L_A1_v, L_A2_v, R_A1_v, R_A2_v). Aneurysm angle is the angle formed between the neck of the aneurysm and the maximum height of the aneurysm (H_max). Vessel angle is the angle between the parent vessel and the plane of the aneurysm neck. Flow angle is the angle between the maximum height of the aneurysm and the parent vessel.</p

Morphological and hemodynamic parameters evaluated in the literature.

<p>Morphological and hemodynamic parameters evaluated in the literature.</p

Scatter plots depicting the interaction between flow angle and other morphological parameters.

<p>Linear regression analysis for scatter plot of aneurysm angle and flow angle yielded an R² value of 0.76 and 0.56 for the ruptured and unruptured groups, respectively (Figure A). No apparent relationship was found between flow angle and size ratio (B), aspect ratio (C), or parent-daughter angle (D).</p