The ligamentum arteriosum is a fibrous remnant in the adult human chest, connecting two major blood vessels near the heart: the underside of the aortic arch and the left pulmonary artery. It is the final form of a temporary structure present during fetal development.
From Fetal Lifeline to Adult Structure
The ligamentum arteriosum originates from a crucial fetal blood vessel known as the ductus arteriosus. During gestation, a fetus does not use its lungs for gas exchange, as oxygen and nutrients are supplied by the mother through the placenta. The ductus arteriosus acts as a shunt, diverting blood away from the non-functional fetal lungs. This connection allows blood pumped from the right ventricle, which would normally go to the lungs, to flow directly into the aorta, bypassing the pulmonary circulation.
At birth, a shift in circulation occurs as the newborn takes its first breaths. The lungs expand and begin to function, leading to a rapid increase in oxygen levels in the blood. Concurrently, the placenta is removed, causing a drop in prostaglandin levels, which had previously helped keep the ductus arteriosus open. These combined physiological changes trigger the ductus arteriosus to constrict and functionally close within hours to days after birth. Over weeks and months, this functional closure is followed by anatomical closure, where the vessel transforms into the fibrous ligamentum arteriosum.
Anatomy and Adult Function
In adults, the ligamentum arteriosum is a small, non-functional band of tissue. It connects the underside of the aortic arch to the left pulmonary artery and no longer carries blood.
Despite its lack of circulatory function, the ligamentum arteriosum serves as an anatomical landmark for surgeons operating in the thoracic region. It also anchors the aorta and pulmonary artery, influencing their movement. Additionally, the left recurrent laryngeal nerve, which controls voice box muscles, loops around the aortic arch near the ligamentum arteriosum.
Clinical Relevance
Patent Ductus Arteriosus (PDA) occurs when the ductus arteriosus fails to close after birth. In PDA, blood shunts from the aorta to the pulmonary artery, increasing blood flow to the lungs. Small PDAs may cause no symptoms other than a heart murmur, but larger ones can lead to symptoms like rapid breathing, shortness of breath, poor feeding, and fatigue. If left untreated, a large PDA can result in pulmonary hypertension and heart failure.
Diagnosis often involves listening for a characteristic heart murmur, followed by imaging tests like an echocardiogram. Treatment depends on the PDA’s size and the baby’s symptoms. In premature infants, medications like ibuprofen or indomethacin can be used to block prostaglandins and encourage closure.
For larger or symptomatic PDAs, or when medication is ineffective, interventional procedures like cardiac catheterization or surgical closure may be necessary. During catheterization, a device or coil is inserted to block the opening, while surgical ligation involves tying off or clipping the vessel. The ligamentum arteriosum can also be involved in rare cases of aortic aneurysms or dissections, where its tethering effect might contribute to stress on the aortic wall.