The carotid arteries are major blood vessels located on each side of the neck that carry oxygenated blood from the heart to the brain, neck, and face. Understanding the anatomy and location of the carotid arteries is important because blockages in these critical blood vessels can lead to stroke. This article will provide a detailed overview of carotid artery anatomy, including which side of the neck each carotid artery is found.
Carotid Artery Anatomy
The right common carotid artery and left common carotid artery are the two main carotid arteries located on either side of the front of the neck. They each divide into two branches called the internal and external carotid arteries:
- Right common carotid artery
- Left common carotid artery
- Right internal carotid artery
- Left internal carotid artery
- Right external carotid artery
- Left external carotid artery
The internal carotid arteries supply oxygen-rich blood to the brain, while the external carotid arteries supply blood to structures in the face and neck including the thyroid, larynx, pharynx, scalp, forehead, and more.
Right Common Carotid Artery
The right common carotid artery originates from the brachiocephalic trunk on the right side of the body. The brachiocephalic trunk branches directly off the aortic arch, which curves and extends from the heart. After branching from the brachiocephalic trunk, the right common carotid travels up the neck within the carotid sheath, a collection of connective tissue that also houses the internal jugular vein and vagus nerve.
At around the level of the 4th cervical vertebrae in the neck, the right common carotid artery divides into the right internal and external carotid arteries.
Left Common Carotid Artery
The left common carotid artery has a slightly different origin than the right common carotid artery. The left common carotid branches directly from the aortic arch instead of the brachiocephalic trunk. It travels up the left side of the neck within the carotid sheath, similar to the right common carotid artery.
At approximately the level of the 4th cervical vertebrae, the left common carotid artery splits into the left internal and external carotid arteries.
Right vs. Left Carotid Arteries
The main difference between the right and left common carotid arteries is their origin:
- The right common carotid artery branches from the brachiocephalic trunk.
- The left common carotid artery branches directly from the aortic arch.
Aside from different origins, the path of the right and left common carotid arteries is otherwise similar. They both travel up either side of the anterior neck after branching off the brachiocephalic trunk or aortic arch.
Around the level of the 4th cervical vertebrae, both common carotids divide into internal and external branches. The internal and external carotid arteries on each side go on to supply blood to the same respective structures.
Internal Carotid Arteries
The internal carotid arteries are one of the two terminal branches of the common carotid arteries. As mentioned, the internal carotids supply oxygenated blood to the brain and are critically important.
After branching from the right and left common carotids, the internal carotid arteries enter the carotid canal in the skull base. They then continue upwards through the canal until reaching the base of the brain.
Segments of the Internal Carotids
The internal carotid arteries can be divided into 4 segments:
- Cervical segment – From the common carotid bifurcation to entering the carotid canal
- Petrous segment – Within the petrous portion of the temporal bone
- Cavernous segment – Within the cavernous sinus
- Cerebral segment – From the cavernous sinus to the circle of Willis
The cervical segments in the neck are the only portions of the internal carotids that are outside the skull. The remaining segments travel through canals and spaces within the temporal bone and brain.
After reaching the brain, the internal carotids play an important role in supplying the cerebral hemispheres via the circle of Willis. They also provide blood to structures at the brain base including the eyes and pituitary gland. Any blockage of the internal carotids can lead to ipsilateral (on the same side) brain infarction and stroke.
External Carotid Arteries
The external carotid arteries are the other terminal branches of the common carotids beyond the carotid bifurcation. As the name suggests, the external carotids supply blood to numerous external structures located outside the brain.
Branches of the External Carotids
The many branches of the external carotid arteries can be divided into an anterior (front) and posterior (back) group:
Anterior Branches:
- Superior thyroid artery
- Lingual artery
- Facial artery
- Ascending pharyngeal artery
Posterior Branches:
- Occipital artery
- Posterior auricular artery
- Superficial temporal artery
- Maxillary artery
These external carotid artery branches supply blood to structures such as the thyroid, tongue, lips, pharynx, external ear, portions of the skull, face, scalp, upper jaw, and meninges. Blockages of the external carotid arteries or their branches are not as immediately dangerous as internal carotid blockages but can still result in issues like facial paralysis, tongue weakness, and jaw pain depending on the branch affected.
Clinical Significance
Understanding the anatomy of the carotid arterial system is very important from a clinical perspective for many reasons:
- The carotid pulse in the neck can provide vital information about heart rate and rhythm.
- Auscultating the carotids can reveal abnormal sounds indicating obstructed blood flow.
- Doppler ultrasound is used to measure internal and external carotid blood flow velocity and check for blockages.
- Carotid endarterectomy surgery may be done to remove plaque blockages.
- The carotid arteries are vulnerable to traumatic injury from strangulation, hanging, and blunt carotid trauma.
But from a stroke perspective, the most important reason involves the internal carotid arteries. Plaque buildup in these critical blood vessels that supply the brain is a leading cause of ischemic stroke.
Atherosclerotic narrowing of the internal carotids limits oxygen delivery to the brain and increases the risk of artery blockage and clot formation. Carotid stenosis is diagnosed when the internal carotid lumen is 50% stenosed by plaque. Patients with severe carotid stenosis often require surgery (endarterectomy) to help prevent future stroke.
Conclusion
In summary, the right and left common carotid arteries ascend up both sides of the neck and split into the internal and external branches. The internal carotid arteries dive into the skull to supply the brain, while the external carotids provide blood flow to extracranial structures in the face and neck. Blockages of the internal carotids put patients at high risk of stroke, which is why assessing carotid artery health is so important. Understanding carotid artery anatomy and location can help medical professionals better diagnose and treat associated pathology.