Mechanical properties of intracranial aneurysm wall in vivo – PRAnevrisme

PRAnévrisme (Prediction of Aneurysm Rupture) is involved in the development of a larger project aimed at providing clinicians with a quantitative tool to aid in the management of unruptured intracranial aneurysms. This tool will be based on knowledge of the vascular wall's degradation state in relation to its mechanical state of stress. The idea is to estimate the mechanical fragility of the vascular wall and relate it to a potential rupture criterion based on an anatomical image of the cerebral aneurysm.

Several steps and validations are necessary to achieve this goal. As the degradation state of the aneurysmal wall is correlated with its biomechanical characteristics, it is essential to be able to measure them in vivo and in situ. In this context, PRAnévrisme addresses a fundamental question for evaluating the risk of rupture of unruptured intracranial aneurysms: the estimation of the state of stress of the aneurysmal wall in relation to its physiological degradation. To achieve this, it proposes a) accessing the biomechanical behaviour of the aneurysmal wall by measuring its in situ and in vivo properties (experimentation performed on an animal model), and b) developing a predictive model of the rheological behavior of unruptured intracranial aneurysms based on experimental observations (phantoms and animal models) and tools developed within the framework of artificial intelligence (AI).

Stroke is the third leading cause of death in France (the first in women), the leading cause of acquired adult disability, and the second leading cause of intellectual decline. Every year, about 130,000 strokes are recorded, of which 20% result in death. In this project, the studied strokes are those that lead to hemorrhagic rupture. It is estimated that between 2% and 5% of the population has a cerebral aneurysm, and the annual risk of rupture varies between 1% and 4%. In fact, it is generally at the time of rupture that they are discovered, which leads, in about one in four cases, to the patient's death even before arriving at the hospital. When an unruptured cerebral aneurysm is detected, usually incidentally during a cerebral imaging examination, the practitioner must evaluate and predict the potential risk of rupture to decide on the best management: surgical intervention or "doing nothing." This evaluation is based on morphological criteria (size, shape, etc.) and the aneurysm's location, as well as epidemiological factors such as the patient's hypertension, alcohol, and tobacco consumption. Although this information provides an initial assessment of the potential risk of aneurysm rupture, it does not provide any information on the biomechanical quality of its wall, which remains the predominant parameter for rupture probability. Indeed, the formation of an aneurysm can be interpreted as a local degradation of the mechanical properties of the arterial tissue. This weakening of the vascular wall structure is mainly linked to a deterioration/disorganisation of the biomechanical properties of the elastic and collagen fibers that compose it. The shear stresses exerted by the blood flow in these weakened areas can then, in certain cases, cause aneurysm rupture. In this context, knowledge of the biomechanical properties of the vascular tissue in vivo and in situ seems to be one of the keys for practitioners to improve the quantitative diagnosis of the risk of rupture of unruptured aneurysms.