subclavian artery

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The subclavian arteries are asymmetric paired arteries that supply blood to the posterior cerebrum, cerebellum, posterior neck, upper limbs and the superior and anterior chest wall.

Gross anatomy

Origin

Right and left subclavian arteries classically have different origins:

right subclavian artery (RSA) is one of the terminal branches of the brachiocephalic artery
left subclavian artery (LSA) arises as the third branch of the aortic arch after the left common carotid artery

Course

The subclavian artery exits the thorax via the superior thoracic aperture between the anterior and middle scalene muscles before passing between the first rib and clavicle. At the lateral border of the first rib it continues as the axillary artery.

Parts

The vessel can be split into three parts (first, second, third) depending on the position of the vessel in relation to scalenus anterior:

first part: from its origin to the medial border of scalenus anterior
second part: posterior to scalenus anterior
third part: from the lateral border of scalenus anterior to the lateral border of the first rib

Branches

The vessel branches relate to the part of the vessel :

first part
- vertebral artery: courses cranially to supply the posterior cerebral circulation
- internal thoracic artery: courses caudally
- thyrocervical trunk: very short trunk that soon divides into 4 branches
second part
- costocervical trunk: courses cranially before bifurcating
third part
- dorsal scapular artery: courses posteriorly (less commonly, it branches from the second part); some authors describe this branch as arising from the thyrocervical trunk

Memorable mnemonics for these branches include:

Very Indignant Tired Individuals Sip Strong Coffee Served Double Daily
VIT C, D (as in vitamins C and D).

Relations

first part
- anterior
  - common carotid artery
  - internal jugular and vertebral vein
  - vagus and phrenic (left side only) nerve, cardiac branches of vagus and sympathetic trunk, and ansa cervicalis (encircling)
  - sternocleidomastoid, sternohyoid and sternothyroid muscles
  - thoracic duct (left)
- posterior
  - apex of lung
  - lower trunk of the brachial plexus
  - scalenus medius muscle
second part
- anterior:
  - scalenus anterior
  - phrenic nerve (right side only)
  - sternocleidomastoid
- posterior:
  - apex of lung
  - lower trunk of the brachial plexus
  - scalenus medius muscle
third part
- anterior:
  - suprascapular and transverse cervical vessels
  - subclavian and anterior jugular vein
- posterior:
  - apex of lung
  - lower trunk of the brachial plexus
  - scalenus medius muscle

Variant anatomy

The subclavian vessels may arise from aberrant locations if there is failure of the normal embryological aortic arch development.

The most common variant is the aberrant right subclavian artery which results in a vessel that arises distal to the left subclavian artery and courses posteriorly between the trachea and esophagus where it may cause compression resulting in breathing difficulties or dysphagia. An aberrant left subclavian artery may arise with a right aortic arch.

Other variations occur with branching patterns. If the inferior thyroid artery arises from it (instead of the normal origin of from the thyrocervical trunk), it is known as the accessory inferior thyroid artery.