Ligamentum arteriosum

The ligamentum arteriosum is the fibrous remnant of the fetal ductus arteriosus, a vessel that connects the pulmonary trunk to the aortic arch during fetal life to bypass the non-functioning lungs. After birth, when the lungs begin functioning, the ductus arteriosus undergoes closure and transforms into the ligamentum arteriosum.

The ligamentum arteriosum extends from the bifurcation of the pulmonary trunk (or left pulmonary artery) to the inferior surface of the aortic arch, typically just distal to the origin of the left subclavian artery. This location is clinically significant as it marks the typical site of aortic coarctation and can be involved in vascular ring anomalies.

Histological studies demonstrate that it retains smooth muscle cells and remains innervated and contractile in postnatal life, rather than being a completely obliterated, passive ligament. Histological analysis shows that the majority (80%) of adult specimens contain a duct-like structure, with only 16% showing complete fibrosis. The structure contains α-smooth muscle actin-positive cells that can contract in response to noradrenaline, suggesting it may influence the distensibility of the great vessels to which it attaches. 

The ligamentum arteriosum can calcify, which is seen in approximately 13% of pediatric chest CT scans and represents a normal finding. The site where it attaches to the aorta is also prone to preferential atherosclerosis, which can lead to complications such as saccular aneurysms or ulcerated plaques.