Table of Contents
The Arteries of the Upper Body
The three major vessels branching off from the arch of the aorta are:
1. The brachiocephalic artery
- The right subclavian artery
- The right common carotid artery
2. The left common carotid artery
3. The left subclavian artery
The brachiocephalic artery is the first branch of the arch of the aorta. It supplies the right side of the body above the heart. This vessel further divides into two: the Right subclavian artery, which supplies the right shoulder and right limb, and the right common carotid artery, which moves upward into the neck and gives off branches.
Both the right and left common carotid arteries divide into two branches at the level of the upper border of the thyroid cartilage:
- Internal carotid artery
- External carotid artery
Since the left common carotid emerges directly from the arch of aorta, it has a thorax part and a cervical part. The thoracic part is the part of this artery found in the chest, and the cervical part is the artery located in the neck.
In the chest, the artery is covered by sternohyoid and sternothyroid muscles, separated from the manubrium sterni by the anterior part of the lungs and pleura, remains of thymus and left brachiocephalic vein.
Posterior to the artery are the trachea, esophagus, left recurrent laryngeal nerve and thoracic duct.
Structures on the right of the left common carotid artery are the brachiocephalic trunk, initially followed by the trachea, thymus and the inferior thyroid veins further up.
On the left, phrenic nerve, left vagus and left pleura are related to the common carotid artery.
Both the common carotids have very similar relations. They move obliquely upwards towards the thyroid cartilage where they divide into various branches. These pass behind the sternoclavicular joint, initially separated from each other by the trachea, and later by the thyroid gland and laryngeal cartilages.
In the neck, a sheath covers the common carotid artery, vagus nerve and internal jugular vein; this is called the carotid sheath.
The vein is the most lateral structure within the sheath, followed by the nerve and then the artery, which is the most medial. Each of these components of the carotid sheath has a separate fibrous compartment.
The common carotid artery is covered by the superficial fascia, the platysma muscle, deep cervical fascia, and the neck muscles like the sternocleidomastoid muscle, the sternohyoid, sternothyroid, the the omohyoid in the lower neck. It is relatively superficial in the rest of the upper part in the neck, covered merely by the superficial fascia, the platysma muscle, deep cervical fascia, and medial margin of the sternocleidomastoid muscle.
Branches of the Carotid Artery
At the level of the 4th cervical vertebra, the common carotid artery divides into two following branches:
- External carotid artery (ECA)
- Internal carotid artery (ICA)
The common carotid artery does not give any other branch during its course in the neck before bifurcating into these two branches. Occasionally, in some people, less common branches like the superior thyroid artery or its laryngeal branch, the ascending pharyngeal artery, the inferior thyroid artery, or the vertebral artery, can originate from the common carotid.
The internal carotid artery, as the name suggests, supplies deeper structures of the neck, and the brain. As it emerges from the common carotid artery, it takes a deeper route and travels until reaching the brain.
The external carotid artery, just as the name suggests, is relatively superficial in its path and also supplies superficial structures and parts of the neck and face.
The Carotid Body
A small oval shaped reddish brown body is present at the bifurcation of the common carotid artery, called the carotid body.
- To measure pulse
This artery is often used in measuring a pulse, especially in patients of shock and in those who do not have a detectable peripheral pulse. Palpation of the common carotid artery is done below the angle of the mandible and at the upper border of the thyroid cartilage, on the anterior border of the sternocleidomastoid muscle.
If a carotid pulse is present, systolic blood pressure can be estimated to be more than 40 mmHg.
This is a syndrome which involves the carotid arteries at the point of division into two terminal branches. It leads to the inflammation of the artery near the bifurcation.
- In patient of a hypercholesterolemia and atherosclerosis, carotid artery stenosis can also occur.
- Marker of atherosclerosis:
The medium layer of the common carotid artery may become thickened in patients. This mostly occurs due to the atherosclerosis in the vessels. The thickness of the intima-media of the carotid artery wall is a marker of subclinical atherosclerosis. This is a normal occurrence in old age.
The External Carotid Artery
The external carotid artery is one of the two branches of the common carotid artery; the other being the internal carotid artery. The internal carotid artery, as mentioned above, supplies the internal structures and brain, while the external carotid artery supplies the superficial structures like the neck, face, jaw, scalp and the coverings of the brain, meninges. The two terminal branches of the external carotid artery are the superficial temporal artery and maxillary artery.
The external carotid artery starts just opposite the upper border of the thyroid cartilage from the common carotid artery; initially, it curves upward and moves forward, later inclining backward to the space just at the back of the neck of the mandible giving terminal branches: the superficial temporal artery and the maxillary artery.
The external carotid artery reduces in size while moving upward in the neck while giving various branches on its way. In children, it is also smaller than the internal carotid artery, but the two vessels are roughly of equal size in adults.
At the origin, the external carotid artery is more superficial, and lies within the carotid triangle of the neck.
Branches of the External Carotid Artery
The branches of the external carotid artery can be subdivided into groups:
1. Branches rising from the carotid triangle
A. Anterior branches
- Superior thyroid artery – supplies the thyroid gland
- Lingual artery – supplies the tongue
- Facial artery – supplies the face
B. Medial or deeper branch
- Ascending pharyngeal artery – supplies the pharynx
C. Posterior branch
- Occipital artery – supplies the occipital part of the scalp
2. Ascending branch
- Posterior auricular artery
3. Muscular branch
- Sternocleidomastoid artery – supplies the sternocleidomastoid muscle
4. Terminal branches
- Maxillary artery
- Superficial temporal artery
Relations of the external carotid artery during its course until the terminal branches
The artery is covered by the skin, superficial fascia, platysma muscle, deep fascia, and anterior margin of the sternocleidomastoid muscle.
The hypoglossal nerve, the lingual, common facial and superior thyroid veins cross this artery in the neck, and the digastric and stylohyoid muscle crosses anteriorly.
As the artery moves upwards, it penetrates deeply into the parotid gland substance, crossing the facial artery and the junction of the temporal and internal maxillary veins posteriorly.
Medial relations include the hyoid bone, the pharynx, the superior laryngeal nerve, and the parotid gland. The internal carotid artery is found laterally.
Posterior to the artery, near its origin, is the superior laryngeal nerve, whereas superiorly, it is separated from the internal carotid artery by the styloglossus and stylopharyngeus muscles, the glossopharyngeal nerve, the pharyngeal branch of the vagus, and the parotid gland.