Morphological parameters associated with ruptured posterior communicating aneurysms

Abstract

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.

Figure 1. 3D model of PCoA aneurysm depicting morphological variables previously studied in the literature.

The aspect ratio (AR) is obtained by dividing the perpendicular height by the neck diameter. Size ratio (SR) is calculated by dividing the maximum height (H_max) by the average composite diameter of the all vessels (ICA1_v, PCoA_v, ICA2_v) involved with the aneurysm. Composite diameters are obtained by averaging the initial diameter of the vessel (ICA1₁, PCoA₁, ICA2₁) at the aneurysm neck or branching point with the diameter of the vessel 1.5 away from the initial diameter (ICA1₂, PCoA₂, ICA2₂). Aneurysm angle is defined as the angle between the vector formed by the maximum height of the aneurysm with the aneurysm neck. The vessel angle is defined as the angle between the vector of flow and the neck of the aneurysm. The flow angle is defined as the angle between the vector of flow and the vector formed by the maximum height of the aneurysm.

Figure 2. 3D model of PCoA aneurysm depicting angular variables of the surrounding vasculature.

There were three vessel-to-vessel angles measured. The ICA1 to ICA2 angle refers to the angle between the distal ICA (ICA2) and the proximal ICA (ICA1). The ICA1 to PCoA angle refers to the angle formed between the proximal ICA (ICA1) and PCoA.