The fluid-structure instability driving aortic aneurysm formation and growth

Aneurysms are pathological, localized dilations of a blood vessel that may occur throughout the human body. Thoracic aortic aneurysms are estimated to occur with a global prevalence of 2-3%. Rupture of an aneurysm carries high risk of mortality and morbidity for the patient. Growth rates are associated with risk of rupture or dissection, but prospective prediction of growth remains a challenge. The standard of care for assessment of an aneurysm entails surveillance imaging to assess aortic dimensions at intervals of 1 or more years. After clinical follow-up, a backward- looking comparison of sizes is made to identify growth. Over this period, the aneurysm may exhibit significant growth or rupture fatally. Thus, the current standard of care for tracking aneurysm progression can only identify growth after the fact. In this work, we hypothesize that a fluid-structure instability drives aneurysm formation and growth. A single dimensionless parameter is derived from first principles that encapsulate this instability. If the stability parameter at a local cross section of the blood vessel exceeds an analytically derived threshold, an aneurysm is expected to form or grow at the site. Otherwise, the location should remain stable with time. In a retrospective study of 117 patients with thoracic aortopathies, we show that the stability parameter can be used as a diagnostic physiomarker to forecast whether an aortic aneurysm grows or stays stable. The only input to calculate the parameter for each patient is a magnetic resonance imaging (MRI) scan taken at a single time point. This analytical determination is then compared with the clinical outcome reported from a follow-up at least one year after the baseline MRI. The area under the curve for a receiver operating characteristic analysis is 0.91. No training data is necessary to tune the physical parameter.