Left subclavian artery

At a glance

English

Left subclavian artery

Latin (TA2)

Arteria subclavia sinistra

System

Artery

Region

Trunk

Side

Single, on the midline

About the left subclavian artery

The left subclavian artery is the last of the three great branches of the aortic arch, leaving it just behind the left common carotid at about the T4 level. Unlike its right-hand partner, which comes from the brachiocephalic trunk, it leaves the aorta directly, so it starts deeper in the chest and is longer, around 9 cm in adults. It carries most of the blood for the left arm and also supplies parts of the neck, brain and chest wall. Once past the first rib's outer edge it takes the name axillary artery.

For description it is split into three parts by scalenus anterior. The first part climbs from its origin through the superior mediastinum into the base of the neck, then bends outwards to reach the inner edge of that muscle. In front of it lie the left common carotid artery, the vagus and phrenic nerves, the cardiac nerves, the left internal jugular vein, the vertebral vein and the beginning of the left brachiocephalic vein, all under cover of the strap muscles and sternocleidomastoid. Behind and medial to it are the oesophagus, the trachea, the left recurrent laryngeal nerve, the sympathetic trunk and longus colli; the thoracic duct climbs on its right and then arches over it to join the venous angle. The left pleura and lung lie lateral to it.

The second part is short and lies behind scalenus anterior, in front of scalenus medius, at the top of the vessel's arch. The brachial plexus lies above it and the pleura below. The third part, lying in the subclavian triangle between the outer edge of scalenus anterior and the first rib, is the most superficial and accessible part. The subclavian vein lies in front of the artery and slightly lower, separated from it by scalenus anterior.

Its branches are the vertebral and internal thoracic arteries, the thyrocervical and costocervical trunks and, often, the dorsal scapular artery. A narrowing before the vertebral origin can cause subclavian steal, in which blood runs backwards down the vertebral artery to the arm. The artery can also be compressed at the thoracic outlet, as in cervical rib or scalene crowding, and can develop an aneurysm.

Course and supply

Arises from

Leaves the aortic arch directly, just behind the left common carotid, at about the T4 level.

Ends in

Becomes the axillary artery once it passes the lateral edge of the first rib.

Supplies

Supplies the left upper limb, and through its branches part of the brain and spinal cord, the neck, the thyroid region, the shoulder and the chest wall.