Pathophysiology
Clinical meaning
Aortic root dilation refers to progressive enlargement of the aortic root, the segment of the ascending aorta that extends from the aortic annulus to the sinotubular junction, encompassing the sinuses of Valsalva and the coronary artery ostia. The normal aortic root diameter ranges from 2.0 to 3.7 cm, with dilation defined as measurements exceeding the upper limit of normal for age, sex, and body surface area, typically above 4.0 cm. The aortic root wall consists of three layers: the tunica intima (endothelial cells providing a smooth blood-flow surface), the tunica media (smooth muscle cells and elastic lamellae embedded in an extracellular matrix of collagen, elastin, and glycosaminoglycans that provides tensile strength and elasticity), and the tunica adventitia (connective tissue, vasa vasorum, and nerve fibers). Aortic root dilation results from degeneration of the tunica media, a process historically called cystic medial necrosis or cystic medial degeneration. In this process, smooth muscle cell apoptosis occurs alongside fragmentation and loss of elastic fibers, accumulation of mucoid ground substance (pools of basophilic proteoglycans that replace the normal organized lamellar structure), and disorganization of collagen...