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The first part of the left subclavian artery originates in the superior mediastinum as the third branch of the arch of the aorta at the level of T3/T4 intervertebral disc. It passes superiorly and slightly laterally to lie deep to the left sternoclavicular joint. During this course its relations are:
- anteriorly, from deep to superficial:
- left vagus nerve
- left common carotid artery
- left phrenic nerve
- left brachiocephalic vein
- thoracic duct; passes medial to the artery superiorly
- longus coli muscles
- left recurrent laryngeal nerve
- laterally: mediastinal pleura
From the level of the left sternocostal joint it curves more sharply and continues laterally to its termination at the medial border of scalenus anterior. During this course, its relations are similar to those of the first part of the right subclavian artery.
The first part of the left subclavian artery gives off three branches, from proximal to distal:
- vertebral artery; first to arise and passes from the superior margin of the vessel in a superior direction
- thyrocervical trunk; again from the superior surface of the vessel. Passes superiorly.
- right internal thoracic artery; arises from the inferior surface of the subclavian artery just before the medial border of scalenus anterior. Passes inferiorly.
Last reviewed 01/2018