Arterial Wall Degeneration Plus Hemodynamic Insult Cause Arterial Wall Remodeling and Nascent Aneurysm Formation at Specific Sites in Dogs

Middle cerebral artery bifurcation aneurysms are associated with patient age, sex, bifurcation angle, and vascular diameters

To investigate the relationship of the middle cerebral artery (MCA) bifurcation aneurysms with patients' age and sex, vascular angles at the bifurcation, and diameters of the M1 and two M2 arteries, patients with and without MCA aneurysms were retrospectively enrolled. The lateral angles, MCA bifurcation angle and arterial diameter were measured and analyzed. Totally, 121 (19.0%) patients with and 517 (81.0%) without MCA aneurysms were enrolled. Most (n = 88 or 72.7%) aneurysms were present in the age range of 40-70 years, and significantly (P = 0.01) more women than men had the bifurcation aneurysms. The MCA bifurcation angle was significantly greater (149.2° ± 32.6° vs. 107.2° ± 26.3°; P < 0.0001) while both the smaller and larger lateral (M1/M2) angles were significantly smaller in patients with than without aneurysms (82.0° ± 23.7° vs. 109.1° ± 22.7° with P < 0.001 for the smaller and 123.2° ± 25.2° vs. 139.5° ± 16.9° with P < 0.001 for the larger lateral angle). 109 (90.1%) bifurcation aneurysms deviated towards the smaller lateral angle, and 103 (85.1%) aneurysms deviated towards the thinner M2 branch. The maximal aneurysm diameter ranged 1.6-13.8 (mean 5.4 ± 2.4) mm and was significantly (P < 0.05) positively correlated with the diameter of both M2 arterial branches (R = 0.57 and P = 0.01 for the smaller M2, and R = 0.69 and P = 0.002 for the larger M2) or the MCA bifurcation angle. A significant (P < 0.0001) negative correlation was detected between age and the smaller lateral angle but a significant (P < 0.0001) positive correlation between age and the MCA bifurcation angle in patients without MCA bifurcation aneurysms or in the total patients. MCA bifurcation angle was the only significant (P = 0.0001, odds ratio 2.7, 95% confidence interval 1.6-3.8) independent risk factor for MCA bifurcation aneurysm presence, with the bifurcation angle threshold of 124.1° and an area under the ROC curve of 0.86. In conclusion, significantly more MCA bifurcation aneurysms are present in older patients, females, and patients with a wider MCA bifurcation angle, and deviate towards the smaller lateral angle and the thinner M2 segment. MCA bifurcation angle is the only independent risk factor for presence of MCA bifurcation aneurysms with the threshold of 124.1°.

Imaging of intracranial aneurysms in animals: a systematic review of modalities

Intracranial aneurysm (IA) animal models are paramount to study IA pathophysiology and to test new endovascular treatments. A number of in vivo imaging modalities are available to characterize IAs at different stages of development in these animal models. This review describes existing in vivo imaging techniques used so far to visualize IAs in animal models. We systematically searched for studies containing in vivo imaging of induced IAs in animal models in PubMed and SPIE Digital library databases between 1 January 1945 and 13 July 2022. A total of 170 studies were retrieved and reviewed in detail, and information on the IA animal model, the objective of the study, and the imaging modality used was collected. A variety of methods to surgically construct or endogenously induce IAs in animals were identified, and 88% of the reviewed studies used surgical methods. The large majority of IA imaging in animals was performed for 4 reasons: basic research for IA models, testing of new IA treatment modalities, research on IA in vivo imaging of IAs, and research on IA pathophysiology. Six different imaging techniques were identified: conventional catheter angiography, computed tomography angiography, magnetic resonance angiography, hemodynamic imaging, optical coherence tomography, and fluorescence imaging. This review presents and discusses the advantages and disadvantages of all in vivo IA imaging techniques used in animal models to help future IA studies finding the most appropriate IA imaging modality and animal model to answer their research question.

Medial Gap: A Structural Factor at the Arterial Bifurcation Aggravating Hemodynamic Insult

Previous studies have reported that intracranial aneurysms frequently occur adjacent to the medial gap. However, the role of the medial gap in aneurysm formation is controversial. We designed this study to explore the potential role of the medial gap in aneurysm formation. Widened artery bifurcations with or without medial gaps were microsurgically created and pathologically stained in the carotid arteries of 30 rats. Numerical artery bifurcation models were constructed, and bidirectional fluid-solid interaction analyses were performed. Animal experiments showed that the apexes of widened bifurcations with a medial gap were prone to being insulted by blood flow compared to those without a medial gap. The bidirectional fluid-solid interaction analyses indicated that artery bifurcations with the medial gap exhibited higher wall shear stress (WSS) and von Mises stress (VMS) at the apex of the bifurcation. The disparity of stress between the gap and no-gap model was larger for widened bifurcations, peaking at 180° with a maximum of 1.9 folds. The maximum VMS and relatively high WSS were located at the junction between the medial gap and the adjacent arterial wall. Our results suggest that the medial gap at the widened arterial bifurcation may promote aneurysm formation.

Roles of inflammation in the natural history of intracranial saccular aneurysms

Aneurysmal subarachnoid hemorrhage is caused by intracranial aneurysm (IA) rupture and results in high rates of mortality and morbidity. Factors contributing to IA generation, growth and rupture can involve genetics, injury, hemodynamics, environmental factors, and inflammation, in which inflammatory factors are believed to play central roles in the whole natural history. Inflammatory reactions that contribute to IA development may involve synthesis of many functional proteins and expression of genes induced by changes of blood flow, external stimuli such as smoking, internal balance such as hormonal status changes, and blood pressure. Meanwhile, inflammatory reactions itself can evoke inflammatory cytokines release and aggregation such as MMPs, MCP-1, TNF-α and ZO-1, directly or indirectly promoting aneurysm growth and rupture. However, the details of these inflammatory reactions and their action on inflammatory chemokines are still unknown. Moreover, some agents with the function of anti-inflammation, lipid-lowering, antihypertension or inflammatory factor inhibition may have the potential benefit to reduce the risk of aneurysm development or rupture in a group of population despite the underlying mechanism remains unclear. Consequently, we reviewed the potential inflammatory responses and their mechanisms contributing to aneurysm development and rupture and sought intervention targets that may prevent IA rupture or generation.

Hemodynamic characteristics associated with thinner regions of intracranial aneurysm wall

Aneurysm wall thickness is an important determinant of aneurysm progression and intra-procedural rupture. Several previous studies have evaluated the association between hemodynamic stress and aneurysm wall thickness, but conflicting results were obtained and no consensus has been achieved. According to the intraoperative findings, twenty-eight unruptured middle cerebral artery (MCA) aneurysms presented with thin-walled regions were enrolled in our study. Patient-specific 3D aneurysm models were constructed from preoperative computed tomography angiography (CTA) data and computational fluid dynamics (CFD) analyses were performed under pulsatile-flow conditions. Thin-walled regions of aneurysm dome were recognized by two experienced reviewers based on the intraoperative microscopy findings. Hemodynamic parameters derived from CFD analysis, including normalized wall shear stress (NWSS), normalized pressure (NP), the oscillatory shear index (OSI) and relative residence time (RRT), were compared between thin-walled regions and surrounding normal-thickness areas. Of the included aneurysms, twenty-eight pairs of thin-walled and normal surrounding regions were determined. Compared with surrounding tissues, thin-walled regions of aneurysm wall tended to present with higher pressure (1.232 vs 1.043, p < 0.05) and lower wall shear stress (0.693 vs 0.868, p < 0.05). Multivariate analysis revealed that elevated NP was significantly associated with thinning of the local aneurysm wall. Higher pressure and lower WSS were characteristic hemodynamic features associated with thinner regions of the aneurysm wall, elevated NP was an independent risk factor for local aneurysm wall thinning. CFD seems to be a useful method to estimate the location of thin-walled region, which will be helpful in reducing the risk of intraoperative rupture.