A Methodology to Quantify the Geometrical Complexity of the Abdominal Aortic Aneurysm

Abstract

The abdominal aortic aneurysm (AAA) anatomy influences the technical success of the endovascular aneurysm repair (EVAR), yet very few data regarding the aortic tree angles exist in the literature. This poses great limitations in the numerical analyses of endografts, constraining their design improvement as well as the identification of their operational limitations. In this study, a matrix Φ of 10 angles was constructed for the description of the pathological region and was implemented on a large dataset of anatomies. More specifically, computed tomography angiographies from 258 patients were analysed and 10 aortic angles were calculated per case, able to adequately describe the overall AAA shape. 9 dimensional variables (i.e. diameters and lengths) were also recorded. The median and extreme values of these variables were computed providing a detailed quantification of the geometrical landscape of the AAA. Moreover, statistical analysis showed that the identified angles presented no strong correlation with each other while no lateral or anterior/posterior symmetry of the AAA was identified. These findings suggest that endograft designers are free to construct any extreme case-studies with the values provided in a mix-and-match manner. This strategy can have a powerful effect in EVAR stent graft designing, as well as EVAR planning.

Figure 1

3D reconstruction of the aortic geometry from 2D CTA scans in the m2s Preview. The blood lumen (red), the calcified regions (white) and the thrombus (transparent yellow) are visible. The dot at the top left corner corresponds to the (0,0,0) point of the coordinate system, used for all measurements. It is located at the posterior right corner of the 1st CTA scan.

Figure 2

Schematic of the front view of an AAA. XZ-plane. 14 points are identified on the centreline of the aneurysm that allow the definition of 10 angles. Positive angles are illustrated with green.

Figure 3

Schematic of the left (a) and right (b) view of an AAA. YZ-plane. Positive angles are illustrated with green.

Figure 4

Schematic of the top view of an AAA. XY-plane. Positive angles are illustrated with green.

Figure 5

Schematic of the front view of an AAA. XZ-plane. 5 points are identified on the centreline of the aneurysm (dotted line). The maximum diameter is also illustrated.

Figure 6

Boxplots of the angles investigated, in their 3D and 2D manifestations.