Objective To discuss the morphological characteristics of three types of clinically rare cerebral aneurysms and arterial bifurcations.Methods A total of 17 patients with clinically rare cerebral aneurysms,including anterior cerebral artery-pericallosal artery aneurysms(ACA-PA aneurysms,n=8),internal carotid artery-anterior choroidal artery bifurcation aneurysms(ICA-AChA aneurysms,n=5)and vertebral artery-posterior inferior cerebellar artery bifurcation aneurysms(VA-PICA aneurysms,n=4),who received treatment in the Shijiazhuang People's Hospital between January 2017 and April 2020 were enrolled in this study.The clinical baseline data were recorded,and the morphological parameters of the aneurysms were determined.The bifurcation angle,small lateral angle and large lateral angle were defined as φ1,φ2 and φ3,respectively.D1,S1 and T1 represented the diameter,cross-sectional area and tortuosity of the main blood vessel,respectively.D2,S2 and T2 were defined as the corresponding parameters of the branch vessel forming small lateral angle with the main vessel.D3,S3 and T3 were the corresponding morphological parameters of the contralateral branch vessel.Results All of the ICA-AChA and VA-PICA bifurcation aneurysms were type D aneurysms and oriented towards the small lateral angle.Six ACA-PA bifurcation aneurysms were type C aneurysm,and 5 of them were oriented toward the small lateral angle.The S2 and φ2 of the ACA-PA and ICA-AChA bifurcations harboring aneurysms were significantly smaller than S3 and φ3(P＜0.05),while T2 was remarkably largerthan T3(P＜0.05).The VA-PICA bifurcations also showed a similar manifestations.Conclusion These three types of clinically rare cerebral aneurysms are mostly oriented towards the small lateral angle,and the diameter and cross-section area of the branch forming small lateral angle with parent artery were smaller than those of the contralateral branch vessel,while the tortuosity was greater than that of the contralateral branch.

Objective:To investigate the asymmetric geometry of middle cerebral artery (MCA) bifurcations and aneurysm formation.Methods:From January 2017 to April 2020, 65 patients with MCA aneurysm underwent 3D-digital subtraction angiography (DSA) in our hospital were recruited in this study; 170 patients without arterial stenosis or cerebral aneurysm at the same time period were selected as normal control group; their corresponding morphological parameters of MCA bifurcations in the imaging data were analyzed. Bifurcation angle was termed as φ1, while small and large lateral angles were termed as φ2 and φ3, respectively. D2, S2, C2, T2 and E2 represented diameter, sectional area, circumference, tortuosity and ellipticity of the branch forming angle φ2 with parent vessel, respectively; whereas D3, S3, C3, T3 and E3 represented diameter, sectional area, circumference, tortuosity and ellipticity of the branch forming angle φ2 with parent vessel on the contralateral branch, respectively. The independent factors affecting the formation of MCA aneurysm were screened by binary Logistic regression, and the predictive value of independent factors affecting the formation of MCA aneurysm was evaluated by receiver operating characteristic (ROC) curve.Results:(1) The aneurysmal group had significantly larger φ1, significantly smaller φ2 and φ3 than the normal control group ( P<0.05); D3, S3, C3, T2, T3 and E2 in the aneurysmal group were significantly higher/larger than those in the normal control group ( P<0.05). In terms of the symmetry of bilateral branches of blood vessels, the difference of φ3/φ2 ratio between the normal control group and aneurysm group was statistically significant ( P<0.05). (2) Binary Logistic regression results showed that φ2 was the protective factor for aneurysm formation ( OR=0.880, 9 5%CI: 0.844-0.918, P=0.000), while D3 and φ3/φ2 ratio were the risk factors for aneurysm formation ( OR=4.493, 9 5%CI: 1.414-14.278, P=0.011; OR=30.676, 95%CI: 9.884-95.202, P=0.000). (3) The ROC curve showed that the area under the curve of φ2 was the largest, reaching 0.93, and the optimal cut-off point was 104.59°, enjoying sensitivity and specificity of 87.7% and 85.9%, respectively. Conclusion:Normal MCA bifurcations almost show symmetrical morphology, whereas aneurysmal MCA bifurcations show asymmetrical morphology in both lateral angles and daughter branches; φ2 is the best morphological parameter to predict the aneurysm formation of MCA bifurcations.