A commentary on “The prognostic effects of hemodynamic parameters on rupture of intracranial aneurysm: A systematic review and meta-analysis” (Int J Surg. 2021; 86:15–23)

Dear Editor, Intracranial aneurysms are pathologic outpouchings of the arterial walls. An estimated 5%–8% of the general population harbors intracranial aneurysms, though the exact prevalence is unknown because most of these aneurysms are asymptomatic. Aneurysm rupture is the most common cause of non-traumatic subarachnoid hemorrhage, a devastating event that carries high rates of mortality, morbidity, and disability, as well as high health-care costs. Despite significant improvement in the clinical care of patients with subarachnoid hemorrhage, one-quarter of patients still die, while roughly half of the survivors live with persistent neurologic deficits. Increasing detection of unruptured intracranial aneurysms to prevent, catastrophic outcomes from subarachnoid hemorrhage, and risks and cost of treatment necessitate defining objective predictive parameters of aneurysm rupture risks. Han et al. [1] performed a meta-analysis to evaluate the prognostic effect of hemodynamic parameters on rupture of intracranial aneurysm. They identified wall shear stress (WSS), oscillatory shear index (OSI) and low shear index (LSA) as influential hemodynamic parameters on rupture of intracranial aneurysm. A number of engineering and computational researchers have published computational fluid dynamics (CFD) studies on specific hemodynamic parameters which were associated with intracranial aneurysm growth and rupture [2,3]. While clinicians welcome such effort, the growing number of proposed parameters remains inconsistent and confusing. The most highlighted and controversial parameter has been WSS, the frictional force exerted by the flowing blood tangentially in the vessel lumen. Both high and low aneurysmal WSS have been separately correlated with intracranial aneurysm growth and rupture [4]. Presently, it is unclear whether the “high-versus-low WSS” controversy stems purely from study limitations such as skewness due to small sample sizes, inconsistent parameter definitions, flawed experimental design, variability in assumptions and compromises in CFD, or from the inherent complexity and heterogeneity of intracranial aneurysm growth and rupture mechanisms [5]. In the future, we expect that large, multicenter, global studies will be needed to obtain a more comprehensive picture of intracranial aneurysm hemodynamic pathophysiology and to develop more reliable risk-prediction models. This effort will likely to require better classification of aneurysms (eg, based on aneurysm size, location, phenotype, perienvironment, and patient population), rather than treating them as a conglomeration. Different predictive models could be extracted from different classes of datasets and be applied to intracranial aneurysms that belong to specific categories. For example, statistical analyses of small aneurysms may produce a different set of predictive parameters from that of large aneurysms. There is a need to study the role of hemodynamic-biologic interactions in the natural history and rupture propensity of intracranial aneurysms in experimental models. Animal models commonly used for clinical studies are good for testing medical devices and investigating hemodynamics but are generally biologically deficient. Therefore, improved animal models, aided by advancements in in vivo and molecular imaging, are needed to elucidate the hemodynamic-biologic mechanisms driving aneurysm growth, and models of aneurysm rupture must be developed to study the hemodynamic and biologic mechanisms involved in rupture. Ethical approval None. Sources of funding The fifth "333" project of scientific research of Jiangsu Province. NO. BRA2020265. Author contributions Bimei Hu: writing. Guanghui Zhang: study design and data collection. Trial registry number None. Trial registry number – ISRCTN None. Guarantor Bimei Hu. Provenance and peer review Not commissioned, Editor reviewed. Declaration of competing interest None.