Risk of Rupture of Aneurysms of the Thoracic Ascending Aorta (ATA) From the Dynamic Imaging

Aneurysms of the thoracic ascending aorta are a serious pathology which may threatens life by rupture or dissection. Their incidence is estimated at 10.4 per 100,000 people. At present, the only parameter for assessing the risk of complication is the maximum diameter of the aneurysm. The only way to avoid a complication is a surgical replacement of the aneurysmal aorta by a prosthetic tube. This procedure is performed by sternotomy and with extracorporeal circulation and its death rate ranges between 3% and 5%. Surgical repair is indicated when the diameter of the aneurysm exceeds 5.5 cm for degenerative atheromatous aneurysms or 5 cm in a patient with genetic disorder of connective tissue (Marfan disease or Ehlers-Danlos syndrome). However, there are aneurysms with diameter greater than the surgical threshold which remain stable. Conversely, complications have been described for aneurysms less than 4.5 cm in diameter. The criterion of diameter appears therefore as inadequate to assess the risk of complication of an aneurysm of the ascending aorta.Multiple methods have been described in the literature. One of them relies on in vitro mechanical testing on healthy or aneurysmal tissue. Another method is the vivo analysis from imaging (CT, MRI or ultrasound). So far, no algorithm is robust enough for predicting the risk of complication better than the universally used criterion of diameter. The pathophysiology of these aneurysms has also been explored from histological studies. The investigators know that the microstructure of the aortic wall of an aneurysm is deteriorated with a degradation of elastin fibers and collagen that determine to a large extent its biomechanical behavior. Histological analysis appears inseparable from biomechanical analysis.