Ligamentum Arteriosum and Ductus Arteriosus
Ligamentum Arteriosum
Definition: The ligamentum arteriosum is a short fibrous cord connecting the superior surface of the left pulmonary artery (at its root) to the inferior surface of the arch of the aorta, just distal to the origin of the left subclavian artery.
It is the remnant of the ductus arteriosus — the fetal arterial channel that shunted blood from the pulmonary trunk into the aorta, bypassing the unexpanded fetal lungs.
Position and Relations
| Relation | Structure |
|---|---|
| Posterior to the ligament | Left recurrent laryngeal nerve (hooks under the arch posterior to the ligamentum arteriosum) |
| Anterior to the ligament | Superficial cardiac plexus (lies on its anterior surface, in the concavity of the arch) |
| Superior | Inferior surface of the arch of aorta (just distal to left subclavian origin) |
| Inferior | Root of the left pulmonary artery |
The left recurrent laryngeal nerve loops under the inferior border of the arch of aorta, posterior to the ligamentum arteriosum, and ascends in the left tracheo-oesophageal groove. The ligament thus serves as an important surgical landmark for identifying the recurrent laryngeal nerve.
Ductus Arteriosus — Fetal Function
In fetal life, the ductus arteriosus is a wide, short muscular arterial channel (not fibrous):
- Connects the left pulmonary artery to the arch of aorta just distal to the origin of the left subclavian artery
- Allows most of the right ventricular output to bypass the unexpanded (high-resistance) fetal lungs
- Blood flows from the pulmonary trunk → ductus arteriosus → descending aorta → placenta (for oxygenation)
- Carries mixed blood (neither fully oxygenated nor fully deoxygenated)
Closure of the Ductus Arteriosus
Functional closure:
- Occurs within the first few hours to days after birth
- Triggered by the rise in arterial oxygen tension (PaO₂) following the first breath
- Also stimulated by the fall in circulating prostaglandins (prostaglandin E₂) that were produced by the placenta
- Smooth muscle in the ductus wall contracts → lumen obliterates
Anatomical closure:
- Fibrous obliteration (endarteritis obliterans) takes 4–12 weeks postnatally
- Produces the fibrous ligamentum arteriosum
Developmental Origin
The ductus arteriosus develops from the left 6th aortic arch artery — specifically its proximal part, connecting the pulmonary trunk to the dorsal aorta.
The arch of aorta itself develops from:
- Aortic sac
- Left horn of the aortic sac
- Left 4th aortic arch artery
- Left dorsal aorta (between attachment of the 4th arch artery and the 7th intersegmental artery)
Clinical Significance
See Applied Anatomy of the Arch of Aorta for Patent Ductus Arteriosus (PDA) details.
Surgical landmark: During surgery in the superior mediastinum, division of the ligamentum arteriosum is required to expose the tracheal bifurcation and identify the left recurrent laryngeal nerve safely.