Left Common Carotid Artery

The left common carotid artery is the second major branch of the aortic arch and a principal artery supplying the head and neck. Unlike the right common carotid artery, which arises from the brachiocephalic trunk, the left common carotid originates directly from the arch of the aorta, giving it a longer and deeper thoracic course before entering the neck.

Origin and Course

The left common carotid artery arises from the aortic arch, posterior to the manubrium and between the brachiocephalic trunk (on the right) and the left subclavian artery (on the left). From its origin, it ascends through the superior mediastinum and enters the root of the neck posterior to the left sternoclavicular joint.

In the neck, it continues upward within the carotid sheath, medial to the internal jugular vein and anterior to the vagus nerve, and terminates at the level of the upper border of the thyroid cartilage (around C3–C4 vertebral level), where it bifurcates into:

Thoracic (Mediastinal) Portion

In the superior mediastinum, the left common carotid artery has a vertical and relatively deep course. It is initially posterior and slightly to the left of the manubrium. It ascends between the trachea (medially) and the left subclavian artery (laterally). It is also closely related to the thoracic duct, which runs posterior and to its left side.

Cervical Portion

Upon entering the neck, the artery continues within the carotid sheath, an anatomical fascial compartment that also contains the internal jugular vein and vagus nerve. Here, the left common carotid artery is positioned:

Medially: Trachea and esophagus (lower neck)
Laterally: Internal jugular vein
Posteriorly: Vagus nerve
Anteriorly: Sternocleidomastoid muscle and infrahyoid muscles

Termination

The left common carotid artery bifurcates into the internal and external carotid arteries near the level of the upper border of the thyroid cartilage. The bifurcation occurs slightly higher on the left than on the right, and usually near the level of the third or fourth cervical vertebra (C3–C4).

Branches

The left common carotid artery, like the right, gives off no branches in the thorax or the neck before it terminates. All branches to the face, neck, and brain originate from its two terminal divisions:

External carotid artery: Supplies the face, scalp, jaw, neck, and base of the skull.
Internal carotid artery: Supplies the brain and structures within the cranial cavity.

Relations in the Thorax

In the superior mediastinum, the left common carotid artery is surrounded by several important anatomical structures:

Left brachiocephalic vein (crosses anteriorly near the root of the neck)
Thymus (in children)
Manubrium of sternum (separates it from the skin surface)

Posterior

Trachea
Esophagus (posteromedial)
Thoracic duct
Vertebral column (further posterior)

Lateral

Left subclavian artery (laterally and slightly posterior)
Left vagus nerve
Left phrenic nerve

Medial

Brachiocephalic trunk (to the right and slightly anterior)
Trachea (medial and posterior)

Surface Anatomy

In the neck, the left common carotid artery can be approximated along a vertical line from the sternoclavicular joint to a point midway between the mastoid process and the angle of the mandible. While it is not typically palpable like the carotid pulse (which is from the external carotid), its bifurcation marks a key clinical landmark.

Function

The left common carotid artery is responsible for delivering oxygenated blood to the left side of the head and neck, along with the brain and face. It ensures cerebral perfusion through the internal carotid system and supports facial and extracranial circulation through the external carotid system.

The symmetrical branching of the common carotids (left from the arch, right from the brachiocephalic trunk) helps equalize pressure and volume distribution across both sides of the upper body despite the anatomical asymmetry of the aortic arch.

Embryological Origin

Embryologically, the left common carotid artery develops from the left third aortic arch and a portion of the aortic sac. Its distinct origin directly from the aortic arch is due to the asymmetric remodeling of the aortic arches during early vascular development.

This developmental difference explains why the right common carotid arises from the brachiocephalic trunk, whereas the left arises directly from the aortic arch.