The effect of clinical, bifurcation, and aneurysm morphological characteristics on the risk of rupture in internal carotid artery bifurcation aneurysms

BACKGROUND: This study aimed to examine the clinical and morphological characteristics associated with the risk of rupture of internal carotid artery (ICA) bifurcation aneurysms (ICAbifAn) by comparing ruptured and unruptured aneurysms. METHODS: The two-center observational study included 66 patients with ICAbifAn (4.3%) identified from a database of 1,512 patients with intracranial aneurysms. The following data were collected and evaluated for their association with rupture risk: demo-graphic data, medical history, aneurysm neck and dome size, bottleneck factor, aspect ratio (AR), size ratio, dome projection and localization, ICA (D1), M1, and A1 diameters, and ICA-M1 (beta), ICA-A1 (gamma), and M1-A1 (alpha) angles. RESULTS: Sixty ICAbifAn cases were included in the study. Of these, 26 (43.3%) were ruptured aneurysms, and 34 (56.7%) were un-ruptured aneurysms. Patients in the ruptured group were younger than those in the unruptured group (p=0.017). The ruptured group had a smaller alpha angle (p=0.018) and significantly narrower A1 (p=0.004) and M1 (p=0.005) vessel diameters compared to the unruptured group. Irregular shape (p=0.001), AR>1.7, and a narrow neck (p=0.007) were significant predictors of rupture. Logistic regression analysis revealed that AR, alpha angle, and M1 and A1 diameters were significant predictors of aneurysm rupture. In receiver operating characteristic (ROC) analysis, an alpha angle cutoff of 126.2 degrees exhibited a sensitivity of 61.5% and a specificity of 67.7% (area under the curve [AUC]=0.67). A cutoff M1 diameter of 2 mm exhibited a sensitivity and specificity of 61.5% and 76.4%, respectively (AUC=0.71). Additionally, a cutoff A1 diameter of 1.5 mm exhibited a sensitivity and specificity of 73.1% and 71.1%, respectively (AUC=0.75). CONCLUSION: This study provided insights into the impact of aneurysm and bifurcation geometry on the risk of ICAbifAn rupture, which may also be applicable to more common bifurcation site aneurysms. Simple morphological measurements at the bifurcation region, where instability prevails, may serve as useful indicators for clinicians evaluating the likelihood of ICAbifAn rupture.