The ligamentum arteriosum is the fibrous remnant of the ductus arteriosus, connecting the superior surface of the left pulmonary artery to the undersurface of the aortic arch at the aortic isthmus. In the fetus, the ductus arteriosus shunted blood from the pulmonary trunk to the systemic circulation, bypassing the unexpanded lungs. After birth it closes within 24-48 hours (functionally) and within weeks (anatomically) to become the ligamentum arteriosum.
A fibrous fetal remnant with no circulatory function in adults; defines the boundary of the aortic isthmus, anchors the left pulmonary artery to the aortic arch, and is a landmark for the recurrent laryngeal nerve loop.
The ligamentum arteriosum is the key surgical landmark for the left recurrent laryngeal nerve, which loops around the aortic arch immediately posterior to it. The ligamentum arteriosum marks the aortic isthmus, the most common site of traumatic aortic injury in deceleration trauma. Patent ductus arteriosus, where the ductus fails to close, produces a left-to-right shunt managed by pharmacological (indomethacin in premature infants), catheter-based, or surgical ligation at this precise location.
Sudden deceleration shears the aorta at the isthmus where the mobile aortic arch meets the fixed descending aorta at the ligamentum arteriosum, producing a contained haematoma and aortic tear managed by endovascular stent grafting in haemodynamically stable patients.
Failure of the ductus arteriosus to close maintains a persistent left-to-right shunt between the aorta and pulmonary artery at the ligamentum arteriosum site, producing a continuous machinery murmur and left heart volume overload, closed by indomethacin, transcatheter device, or surgical ligation.
