Origin and Pathway of the Vessel
These arteries are asymmetric. The right subclavian artery (a. subclavia dextra) originates from the brachiocephalic trunk. The left subclavian artery (a. subclavia sinistra) branches directly off the aortic arch. Consequently, the left vessel is longer and features an intrathoracic segment hidden behind the left brachiocephalic vein.
Further on, both arteries course upward and laterally, forming a gentle arch. They loop over the pleural dome and the apex of the lung (leaving a characteristic impression there — impressio subclaviae). Having reached the first rib, the vessel settles into its own groove and enters the interscalene triangle (between the anterior and middle scalene muscles), after which it dives beneath the clavicle.
Three Parts of the Subclavian Arteries
Topographically, the trunk is divided into three parts depending on its relation to the interscalene triangle:
| Part | Boundaries | Branches arising |
|---|---|---|
| First | From the origin to the entrance into the interscalene triangle | Vertebral artery, internal thoracic artery, thyrocervical trunk |
| Second | Within the interscalene triangle | Costocervical trunk |
| Third | From the exit of the triangle to the margin of the axillary fossa | Transverse cervical artery |
Key Branches of the First Part
It is precisely before entering the interscalene triangle that the artery gives off its most massive and significant branches:
- Vertebral artery (a. vertebralis). The main vessel supplying the posterior structures of the brain. It ascends, passes through the foramina in the transverse processes of the cervical vertebrae (C6–C2), wraps around the atlas, and enters the cranial cavity through the foramen magnum. There, the two vertebral arteries merge into a single basilar artery (a. basilaris).
- Internal thoracic artery (a. thoracica interna). Runs downwards along the sternum behind the costal cartilages. It supplies blood to the anterior mediastinum, pericardium, bronchi, and mammary gland, and at the level of the seventh rib divides into branches to the diaphragm and the rectus abdominis muscles.
- Thyrocervical trunk (truncus thyrocervicalis). A very short (about 1.5 cm) vessel that rapidly branches out to the thyroid gland, neck muscles, and scapula (e.g., the suprascapular artery).
Clinical Features and Anastomoses
The subclavian artery forms crucial pathways for collateral circulation. The scapular anastomosis (rete scapulare) plays a particularly important role. It is formed by a network of branches from the subclavian and axillary arteries. If the subclavian trunk is ligated or occluded, this very network will save the arm from ischemia.
An interesting clinical manifestation of vascular pathology is subclavian steal syndrome (subclavian steal syndrome). If the artery narrows proximal to the origin of the vertebral branch, vigorous arm activity can reverse the blood flow in a. vertebralis (from the brain to the arm), triggering transient cerebral ischemia.
Briefly: answers to topical questions
What specific branches arise from the thyrocervical trunk?
The thyrocervical trunk gives rise to four main branches supplying the organs of the neck and the shoulder girdle.
- Inferior thyroid artery (a. thyroidea inferior) — runs to the posterior surface of the thyroid gland.
- Superficial cervical artery (a. cervicalis superficialis) — is one of the branches of the trunk.
- Ascending cervical artery (a. cervicalis ascendens) — runs along the anterior surface of the anterior scalene muscle and the levator scapulae muscle.
- Suprascapular artery (a. suprascapularis) — runs laterally and downward behind the clavicle, passing into the supraspinous and infraspinous fossae.
What branches does the costocervical trunk divide into?
The costocervical trunk divides into two main branches.
- Deep cervical artery (a. cervicalis profunda) — heads toward the deep muscles of the posterior neck region, passing between the neck of the 1st rib and the transverse process of the 7th cervical vertebra.
- Supreme intercostal artery (a. intercostalis suprema) — runs downward anterior to the necks of the 1st–2nd ribs and gives off the first and second posterior intercostal arteries.
What terminal arteries does the internal thoracic artery divide into at the level of the seventh rib?
At the level of the seventh rib, the internal thoracic artery divides into two terminal branches.
- Musculophrenic artery (a. musculophrenica) — runs along the costal margin, supplying the diaphragm and the abdominal wall.
- Superior epigastric artery (a. epigastrica superior) — runs toward the rectus abdominis muscle and forms an anastomosis with the inferior epigastric artery.
Which specific vessels participate in the formation of the scapular arterial anastomosis?
The scapular arterial anastomosis (rete scapulare) is formed by vessels from the systems of the subclavian and axillary arteries.
- Suprascapular artery (a. suprascapularis) — a branch of the thyrocervical trunk.
- Transverse cervical artery (a. transversa colli / a. transversa cervicis) — participates via its deep branch (a. dorsalis scapulae).
- Circumflex scapular artery (a. circumflexa scapulae) — a branch of the subscapular artery.
- Thoracodorsal artery (a. thoracodorsalis) — the terminal branch of the subscapular artery.
These vessels provide collateral circulation to the upper extremity.
Class and exam questions
Why is the left subclavian artery longer than the right?
Because it originates directly from the aortic arch and features an additional intrathoracic segment, whereas the right arises from the brachiocephalic trunk at the level of the neck.
Which muscles are bordered by the artery in the second part?
In its second part, the vessel runs through the interscalene triangle, lying between the anterior and middle scalene muscles (m. scalenus anterior and m. scalenus medius).
Which branch of the subclavian artery is used by surgeons for heart bypass surgery?
Internal thoracic artery (a. thoracica interna). In cardiac surgery, this vessel is frequently referred to by the acronym LIMA (left internal mammary artery) and is used for coronary artery bypass grafting.
What else to study on this topic
- Topography and 4 segments of the vertebral artery (a. vertebralis)
- Branches of the basilar artery (a. basilaris) and posterior cerebral arteries
- Basilar territory of the internal thoracic artery (a. thoracica interna)
- Anatomy of the scapular anastomosis (rete scapulare)
- Branches of the costocervical trunk (truncus costocervicalis)
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