Overview
The subclavian arteries lie just below the clavicles, providing blood supply to the bilateral upper extremities with contributions to the head and neck
Origin
Left subclavian artery: Arises as the third major branch of the aortic arch
Right subclavian artery: Arises as the terminal branch of the brachiocephalic (innominate) artery behind the right sternoclavicular articulation
Course & Segments
From its origin, the subclavian artery arches laterally, passing between anterior scalene (anteriorly) and middle scalene (posteriorly) muscles. This course can be divided into three segments:
Left subclavian artery: Ascends in the superior mediastinum, entering root of neck posterior to the left sternoclavicular joint
Right subclavian artery: Posterior to the right sternoclavicular joint
First part – Pre-scalene
- From the origin to medial border of the anterior scalene muscle
- Relations:
- Anteriorly: Vagus nerve, internal jugular vein
- Branches:
- Vertebral artery – ascends until it reaches the transverse foramen of the sixth cervical vertebra
- Internal thoracic artery – gives musculophrenic artery, pericardiocophernic and superior epigastric artery
- Thyrocervical trunk – gives inferior thyroid, suprascapular, transverse cervical, ascending cervical
- Costocervical trunk – givesdeep cervical and superior intercostal artery
Second part – Scalene
- Posterior to the anterior scalene muscle
- Relations:
- Anteriorly: Anterior scalene muscle, subclavian vein, phrenic nerve
- Posteriorly: Scalenus medius
- Superiorly: Three cervical trunks of brachial plexus
- Inferiorly: Pleura
- Branches:
- Costocervical trunk – variable origin with first part
Third part – Post-scalene
- Lateral border of the anterior scalene muscle to lateral border of first rib
- Branches:
- Dorsal scapular artery (Variants)
- Relations:
- Inferiorly: first rib
Termination
Terminates and continues as axillary artery at the lateral border of the first rib
Relations
Right subclavian artery
- It is covered, in front, by the integument, superficial fascia, the platysma muscle, deep fascia, the clavicular origin of the sternocleidomastoid muscle, the sternohyoid muscle, and the sternothyroid muscle, and another layer of the deep fascia.
- It is crossed by the internal jugular vein and the vertebral vein, by the vagus nerve and the cardiac branches of the vagus and sympathetic, and by the subclavian loop of the sympathetic trunk which forms a ring around the vessel. The anterior jugular vein is directed laterally in front of the artery, but is separated from it by the sternohyoid muscle and the sternothyreoid muscle. Below and behind the artery is the pleura, which separates it from the apex of the lung.
- Behind the artery is the sympathetic trunk, the longus colli muscle and the first thoracic vertebra (T1). The right recurrent laryngeal nerve winds around the lower and back part of the vessel.
Left subclavian artery
It is in relation, in front, with the vagus nerve, the cardiac nerves, and the phrenic nerves, which lie parallel with it, the left common carotid artery, left internal jugular and vertebral veins, and the commencement of the left innominate vein. It is covered by the sternothyroid muscle, the sternohyoid muscle, and the sternocleidomastoid muscle. Behind, it is in relation with the esophagus, thoracic duct, left recurrent laryngeal nerve, inferior cervical ganglion of the sympathetic trunk, and the longus colli muscle; higher up, however, the esophagus and thoracic duct lie to its right side; the latter ultimately arching over the vessel to join the angle of union between the subclavian and internal jugular veins. Medial to it are the esophagus, trachea, thoracic duct, and left recurrent laryngeal nerve. Lateral to it are the left pleura and lung.
Development
Embryologically, the left subclavian simply arises from the left 7th intersegmental artery, while the right subclavian arises, proximal to distal:
- Right 4th aortic arch
- Right dorsal aorta
- Right 7th intersegmental artery
Essentially, the 4th aortic arch and dorsal aorta form the aortic arch on the left, but since the right dorsal aorta regresses distal to the right 7th intersegmental artery, on the left they form the proximal portion of the subclavian artery. Since the left subclavian is then a tributary of the left common carotid, they can be thought of as arising from the brachiocephalic trunk.
Variants
- Aberrant right subclavian – originating distal to left subclavian, courses posterior to trachea and oesophagus to the right
- Aberrant left subclavian artery – from right sided aortic arch
- Left vertebral artery originating from aortic arch
- Dorsal scapular artery originating from 3rd part of subclavian artery
- Dorsal scapular artery originating from 2nd part of subclavian artery