Origin and Course
These arteries are asymmetrical. The right subclavian artery (a. subclavia dextra) originates from the brachiocephalic trunk. The left subclavian artery (a. subclavia sinistra) branches directly from the aortic arch. Consequently, the left vessel is longer and features an intrathoracic segment hidden behind the left brachiocephalic vein.
Both arteries then course upward and laterally, forming a gentle arch. They arch over the cervical pleura and the apex of the lung (leaving a distinct groove, the impressio subclaviae). Reaching the first rib, the vessel occupies its own groove and enters the interscalene triangle (between the anterior and middle scalene muscles), after which it passes beneath the clavicle.
Three Parts of the Subclavian Artery
Topographically, the main trunk is divided into three parts based on its relation to the interscalene interval:
| Part | Boundaries | Branches Given Off |
|---|---|---|
| First part | From origin to the medial border of the scalenus anterior muscle | Vertebral artery, internal thoracic artery, thyrocervical trunk |
| Second part | Posterior to the scalenus anterior muscle (interscalene space) | Costocervical trunk |
| Third part | From lateral border of scalenus anterior to the outer border of the first rib | Transverse cervical artery |
Key Branches of the First Part
Prior to entering the interscalene interval, the artery gives off its largest and most significant branches:
- Vertebral artery (a. vertebralis). The primary vessel supplying posterior brain structures. It ascends, passes through the transverse foramina of the cervical vertebrae (C6–C2), curves around the atlas, and enters the cranial cavity through the foramen magnum. There, the two vertebral arteries unite to form the single basilar artery (a. basilaris).
- Internal thoracic artery (a. thoracica interna). Descends vertically down the chest wall behind the costal cartilages. It supplies the anterior mediastinum, pericardium, bronchi, and mammary gland, and at the level of the seventh intercostal space, it terminates into musculophrenic and superior epigastric branches.
- Thyrocervical trunk (truncus thyrocervicalis). A very short (about 1.5 cm) vessel that rapidly divides into branches supplying the thyroid gland, neck muscles, and scapula (e.g., suprascapular artery).
Clinical Features and Anastomoses
The subclavian artery forms critical collateral pathways. The scapular anastomosis (rete scapulare) plays a particularly vital role. It is formed by an interconnection of branches from the subclavian and axillary arteries. If the subclavian trunk is ligated or occluded, this network prevents upper limb ischemia.
A notable clinical manifestation of vascular pathology is subclavian steal syndrome. If the subclavian artery narrows proximal to the origin of the vertebral artery, active use of the upper limb can reverse blood flow within the ipsilateral a. vertebralis (drawing blood from the brain to the arm), causing transient focal neurological symptoms or brainstem ischemia.