Effect of Siphon Morphology on the Risk of C7 Segment Aneurysm Formation

Tortuosity of the internal carotid artery (ICA) is associated with intracranial aneurysms (IAs). The siphon is the most curved segment of the ICA, but its morphology has controversial effects on IAs. This study aimed to explore the morphometric features of the siphon and the potential hemodynamic mechanisms that may affect C7 aneurysm formation.

In this study 32 patients with C7 aneurysms diagnosed at Xiangya Hospital between 2019 and 2021 and 32 control subjects were enrolled after propensity score matching. Computed tomography angiography (CTA) images were acquired to measure morphologic features, and then, by combining clinical data, simplified carotid siphon models were constructed, and computational fluid dynamics (CFD) analysis was performed.

The presence of C7 aneurysms was associated with the height of the C4–C6 curved arteries (odds ratio [OR] 0.028, 95% confidence interval [CI] 0.003–0.201; P < 0.001). The heights of the C4–C6 curved arteries in the aneurysm group were significantly shorter than those in the control group. The CFD analysis revealed that shorter C4–C6 bends led to greater blood velocity and pressure in the C7 segment arteries.

A shorter C4–C6 bend was associated with distal C7 aneurysm formation, and an elaborate hemodynamic mechanism may underlie this association.