Branches of the Arch of Aorta
Overview
The arch of aorta gives off three branches from its convex (superior) surface, from right to left:
- Brachiocephalic trunk (innominate artery)
- Left common carotid artery
- Left subclavian artery
All three branches ascend from the arch into the root of the neck. All three are crossed anteriorly by the left brachiocephalic vein.
1. Brachiocephalic Trunk (Innominate Artery)
Largest branch of the arch. The only unpaired great vessel arising directly from the arch on the right side.
| Feature | Detail |
|---|---|
| Origin | From the arch behind the centre of the manubrium sterni — first and most anterior branch |
| Course | Passes superolaterally to the right, anterior to the trachea |
| Termination | Posterior to the right sternoclavicular joint (anterior to the dome of the right pleura) by dividing into: right subclavian artery + right common carotid artery |
| Relations at origin | Anterior: left brachiocephalic vein; Posterior: trachea |
Variation: The thyroidea ima artery occasionally arises from the brachiocephalic trunk (or directly from the arch) — supplies the isthmus of the thyroid gland. Surgically important during tracheostomy/thyroidectomy.
2. Left Common Carotid Artery
| Feature | Detail |
|---|---|
| Origin | From the arch, immediately to the left of the brachiocephalic trunk — second branch |
| Course | Ascends on the left side of the trachea |
| Termination | Enters the neck posterior to the left sternoclavicular joint |
| Relations | The left vagus and phrenic nerves lie between the left CCA and left subclavian artery |
The left CCA has a thoracic course (unlike the right CCA, which arises in the neck from the brachiocephalic trunk and has no thoracic course).
3. Left Subclavian Artery
| Feature | Detail |
|---|---|
| Origin | From the arch, most posterior and to the left — third and most posterior branch |
| Course | Ascends vertically, closely applied to the left mediastinal pleura; passes obliquely across the trachea, oesophagus, thoracic duct, and left recurrent laryngeal nerve |
| Termination | Enters the neck behind the left sternoclavicular joint; arches laterally grooving the anterior surface of the cervical pleura |
| Relations | Immediately posterior: trachea, oesophagus, thoracic duct; Anterior: left phrenic and vagus nerves |
The left subclavian artery has the longest thoracic course of the three branches.
Relative Position of the Three Branches
From anterior to posterior (right to left):
| Position | Branch |
|---|---|
| Most anterior / right | Brachiocephalic trunk |
| Middle | Left common carotid artery |
| Most posterior / left | Left subclavian artery |
Common Variations
| Variation | Incidence | Significance |
|---|---|---|
| Left CCA arises from brachiocephalic trunk (common origin) | ~10–20% | Most common variation in arch branching |
| Aberrant right subclavian artery (arteria lusoria) | ~0.5–1% | Arises as 4th branch; passes behind oesophagus → dysphagia lusoria |
| Bovine arch (common trunk for left CCA and brachiocephalic) | ~15% | Common, usually asymptomatic |
| Thyroidea ima artery | ~3% | Arises from arch or brachiocephalic trunk; at risk in tracheostomy |
Right vs Left Sided Branching Pattern
| Side | Proximal Arterial Chain |
|---|---|
| Right | Brachiocephalic trunk → Right subclavian + Right CCA (arise in neck) |
| Left | Left CCA + Left subclavian arise directly from arch (no brachiocephalic equivalent) |
This asymmetry results from the embryological obliteration of the right-sided portion of the dorsal aorta between the 4th and 7th segmental arteries.