Cerebral Arterial Bifurcations Harboring D Type Aneurysm are more Asymmetrical than those with C Type Aneurysm

This study was designed to determine aneurysm deviation and to compare anatomical differences of bifurcations harboring C and D-type aneurysms.

A total of 198 arterial bifurcations harboring aneurysms were enrolled in this study, including 58 anterior cerebral arteries (ACAs), 64 middle cerebral arteries (MCAs), 19 basilar arteries (BAs), and 57 internal carotid artery-posterior communicating arteries (ICA-PComAs). Aneurysms were defined as C type if the neck was located on the extension of the parent artery midline and D type if it was not, then, aneurysm deviation was examined. The angles forming between bilateral branching arteries and the main artery were lateral angles, and smaller one named φ2, larger one termed φ3, respectively, D2, S2, C2 and T2 representing the diameter, cross-sectional area, circumference, and tortuosity of the branch forming angle φ2 with the parent vessel, respectively, and D3, S3, C3 and T3 representing the corresponding values of the contralateral branch. The lateral angle ratio (LA ratio; larger lateral angle/smaller lateral angle), daughter artery ratio (DA ratio; the diameter of branch forming larger lateral angle with parent artery/ the diameter of contralateral branch), SA (S3/S2), CA (C3/C2) and TA (T3/T2) ratios were used to describe bifurcation symmetry.

The angle φ2 of the main cerebral bifurcations was significantly smaller than the angle φ3, whereas T2 was significantly larger than T3. Most of the C-type and 100% of the D-type aneurysms deviated toward the angle φ2. The LA, DA, SA and CA ratios of ACA, MCA bifurcations and ICA-PComAs harboring D-type aneurysms were all significantly larger than those harboring C-type aneurysms; moreover, the LA, DA and SA ratios demonstrated significant differences between the bifurcations with C and D-type aneurysms, as determined by ROC analysis.

The majority of C-type and all of the D-type aneurysms deviated toward the smaller lateral angle, and bifurcations harboring D-type aneurysms were more asymmetrical than those harboring C-type aneurysms.