Collagen in dissecting aneurysms of the human thoracic aorta. Increased collagen content and decreased collagen concentration may be predisposing factors in dissecting aneurysms

Biochemical investigations were made into dissecting aneurysms of the thoracic aorta by taking samples at 12 specific sites from aortas of 10 patients who had dissected with fatal results in comparison with samples from 10 matched controls. When sites actually involved in dissection were compared with corresponding sites in controls, there were highly significant increases in dry weight, amount of collagen, and total protein (all p less than 0.001) and a significant decrease in collagen concentration (p = 0.016). In contrast, when samples from sites within dissected aortas, but not involved in dissection, were compared with corresponding sites in controls, there were no significant differences. We therefore conclude that in dissecting aneurysms of the thoracic aorta, there is localized expansion of the aortic matrix, due to deposition of collagen and other proteins, which decreases the concentration of matrix constituents, including collagen. Clearly, the deposition of collagen could be a cause but not a consequence of dissection. The altered composition means that the aortic wall becomes weaker and less able to withstand the mechanical stresses constantly imposed upon it.