Evaluation of the morphology of internal carotid artery in patients with intracranial aneurysms

Objective: The purpose of this study is to analyze the properties and differences in the geometry of internal carotid artery (ICA) as well as qualitative evaluation of the cervical segment of internal carotid artery and carotid siphon between genders and disease-control groups to investigate the possiple effect of anatomical features in the formation of aneurysms in cerebral circulation. Additonally it is aimed to survey the pedictive values of morphological aneurysmal parameters in rupture risk assesment. Materials and Methods: In this study DSA images of 130 patients harbouring intracranial aneurysms and 75 subjects without an aneurysm screened between 2015 and 2020 were obtained. Three dimensional (3D) models of ICA was segmented using 3D Slicer (www.slicer.org) software. Acquired 3D models were trimmed and cleansed of artifacts in Oculus Medium (Oculus Software). Measurements of the diameters of respective segments in accordance with Bouthillier were carried out using Autodesk Meshmixer 3.5.474 (Autodesk, Inc) software. Segment angle measurements were conducted using ImageJ software (U. S. National Institutes of Health, Bethesda, Maryland, USA). Cervical segments and carotid siphons were classified into categories. Several morphological parameters were calculated between ruptured and unruptured aneurysms using the measured values. Findings were statistically analyzed with SPSS 20.0 package program (IBM Corp. Armonk, New York, USA). Results: Differences in distribution of aneurysm between genders is statistically significant, men are prone to have aneurysms in anterior cerebral artery (ACA) (43.3%) whereas women are prone to have aneurysms in last two segments of internal carotid artery(45%) (p=0.005). Segment diameters of C1, C2, C3, C4, C5, C6, C7 and angle of C6 segment is larger in men compared to women (p<0.05). Segment diameters of C1, C3, C5, C6, ACA and angle of ACA are larger in ACA aneurysm group compared to control, in the same assesment, angles of C6 and middle cerebral artery (MCA) were larger in control group (p<0.05). Segment diameters of C1, C3, C4, C5, C7 and ACA, angle of ACA are larger in patients with ACA aneurysms, ACM angles are larger in patients with ACM aneurysms (p<0.05). Angles of C2, C4 and ACA are larger in patients with communicating (C7) segment aneurysms compared to control group (p<0.05). Segment diameter of C5 angles is larger in patients with aneurysms before terminal bifurcation compared to patients with aneurysms after terminal bifurcation (p<0.05). Evaluation of cervical segments among age groups revealed statistically signficant differences. in earlier decades (2nd and 3rd) straight type is the common type, by progression of decades, frequency of tortuosity type is increased, dominating later (4.≥) decades (p=0.028). Distributions of carotid siphon types was more homogenous among age groups compared to cervical types, yet statistical signigificance was present as well, C and S type siphons are more frequent after 4th decade. Evaluation of aneurysmal morphological parameters demonstrated that ruptured aneurysms in our study has narrower necks, has higher Aspect Ratios (AR) and Height Width (H/W) ratios than the ones that are not ruptured. Conclusion: Anatomical properties of internal carotid differentiate both between genders and patients with or without aneurysms. Breadth of bifurcation angles of ACA and MCA and presence of an aneurysm in the respected branch demonstrates significant relationship. Tortuosity and therefore variations in cervical segment of internal carotid artery increase with age increment and more common in women. Same mechanisms underlying the increase of variations seems to be effective in carotid siphon as well. Among the parameters investigated in our study, AR and H/W ratios indicate importance in terms of assesing the risk of rupture.