The Anatomy of the Common Carotid Artery

The common carotid artery supplies blood for the head and neck

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A large artery that arises on each side of the neck, the common carotid artery is the primary source of oxygenated blood for the head and neck. While both right and left arteries run the same course in the neck, they have differing origins. These arteries are often used to measure pulse, especially in cases where shock or other factors reduce blood flow to more peripheral parts of the body.

In addition, clots or restriction of blood flow here, a condition called carotid artery stenosis, can lead to stroke. Furthermore, carotid aneurysm—a ballooning of a weak section of the vessel—can result in potentially deadly severe bleeding.

Anatomy

The right and left common carotid arteries have differing origins. The left arises directly from the aortic branch of the heart, whereas the right arises from a higher branch of that artery called the brachiocephalic trunk (which supplies the right arm, head, and neck). Both of these terminate into separate branches at the upper level of the thyroid cartilage, at the level of the fourth neck vertebra.

Only the left carotid artery, which arises directly from the aortic arch, has a thoracic section (corresponding to the upper spine, below the neck). This section travels through the superior mediastinum—a region of the thoracic cavity, which is the space surrounded by the ribs—to the sternoclavicular joint (where the clavicle meets the sternum at the top of the ribcage).

From there, the path of the left carotid artery (called the cervical section) is identical to the right. Moving from the sternoclavicular joint, both sides move upwards along a slanting path to the upper border of the thyroid cartilage in the neck.

In the lower portion of the neck, the two sides are separated by the trachea (windpipe). Working upwards, however, they move further away from each other and are separated by the structures of the throat, including the larynx and pharynx.

These arteries run through the carotid sheath, a structure made up of the three layers of the deep cervical fascia, which are membranes that cradle and protect deeper portions of the neck. This sheath also contains the internal jugular vein (essential in moving blood from the head back down to the heart) and vagus nerve (a nerve whose main function is relaying brain signals that regulate breathing, heart rate, and digestion).   

The only major branches of the common carotid artery are its two terminating ones, which arise at the level of the fourth neck vertebra. These are the internal carotid artery and the external carotid artery.

  • The internal carotid artery: The larger of the two, this artery is primarily tasked with supplying blood to structures in the forebrain, including the hypothalamus and cerebral hemispheres.
  • The external carotid artery: This artery courses upward and to the back and supplies structures in the face and neck, including the teeth and gums, thyroid gland, and others. 

Anatomical Variations

A number of variations are seen in the structure of this artery. In many cases, the vertebral artery, which is one of the larger arteries on each side of the neck, arises as a branch of the common carotid artery rather than the central subclavian artery. This means that it emerges higher up in the neck, rather than at the juncture of the clavicle and upper spine.   

In addition, different pathways are seen at its terminal end, where it splits into the external and carotid branches.

In many cases, the superior thyroid artery, which supplies the thyroid gland as well as some neck muscles, arises directly from the common carotid, rather than from its usual origin at the external carotid artery. In other instances, the bifurcation or position where this artery splits up is located to the side of the vagus nerve, rather than behind it.   

Function

The common carotid artery is a primary source of oxygenated blood to the head and neck. Through its external carotid branch, it supplies the face, scalp, tongue, upper and lower teeth, gums, sinus, external and middle ear, pharynx and larynx in the throat, as well as the thyroid.

The internal carotid artery, meanwhile, is tasked with supplying the forebrain, which houses the cerebral hemispheres (the sight of language and cognition), the thalamus (essential for sensory processing and sleep), and the hypothalamus (which regulates hormones and metabolism).

Clinical Significance

This artery can be used by doctors to check for heart rate and pulse. Doctors rely on this pulse when there is reduced blood flow to outer limbs, and athletes often check it by feeling around at the side of the area where the neck meets the head.

Given its essential role in supplying the head and neck, disorders of or damage to the common carotid arteries can have a serious clinical impact. Most notable of these are:

  • Carotid stenosis: This is a build-up of plaque within the artery, which leads to reduced blood flow to the brain. Over time, this can lead to stroke—rapid brain cell death that can lead to partial paralysis, loss of speech function, and death.
  • Carotid artery aneurysm: A build-up of blood causing ballooning of a section of the carotid artery, this can lead to clots in the brain as well as hemorrhage, severe and potentially deadly bleeding.
  • Carotid sinus hypersensitivity: Usually occurring in seniors, or those with hypertension (high blood pressure) or coronary artery disease, this is when external pressure on the artery leads to dizziness and temporary loss of function.
  • Carotid artery vasculitis: In some cases, autoimmune disorders or infection can cause severe inflammation of the artery. This can restrict proper blood flow and lead to a range of symptoms including headache, neck pain, and others.         
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