A review of the anatomy of extracranial arteries

Carotid, vertebral, and subclavian ultrasound scans are key in the assessment of arterial disease. In this video, from our Ultrasound Masterclass: Carotid Artery course, we'll review some essential cerebrovascular anatomy so we can learn how to perform these scans with confidence.

In this course, you’ll learn how to optimize the scanner controls as well as recognize and identify normal and atypical carotid, subclavian, and vertebral arteries using ultrasound images and flow patterns. You’ll learn how to make key measurements and use these to categorize disease and write a report.

A carotid, vertebral and subclavian ultrasound scan plays an important role in the assessment of arterial disease. Before we learn how to image these arteries, we need to review some essential cerebrovascular anatomy. So let's start with the brain. The brain receives blood from four arteries, including the left and right internal carotid arteries, and the left and right vertebral arteries.

Other arteries such as the innominate artery, subclavian arteries, common carotid arteries, and external carotid arteries supply blood to the head, neck and upper extremities. The term extracranial cerebral arteries refers to all of the arteries carrying blood up from the heart to the base of the skull.

During a carotid ultrasound investigation, you will image and report on the extracranial cerebral arteries. The origin of all of these arteries are found at the base of the neck, but their anatomy is not symmetrical. On the right side of the body, the innominate artery, also known as the brachiocephalic artery, arises directly from the aortic arch, and then divides into the right subclavian artery and common carotid artery.

However, on the left side of the body, the common carotid artery and subclavian artery both extend directly from the aortic arch. The main arteries of the neck of the carotid, which serve as the anterior supply of the brain. The common carotid artery, or CCA, has no branches and widens at the bifurcation, which is known as the carotid bulb.

The bulb usually includes the origin of the internal carotid artery, or ICA, which lies posterior and lateral to the external carotid artery, or ECA, and is larger in caliber. The ECA is typically anterior and medial to the ICA at its origin and has multiple extracranial branches. It is important to know that the level of the carotid bifurcation is variable, but it is typically located at the angle of the mandible, or lower jaw.

The other main arteries of the neck are the vertebral arteries, which supply most of the posterior circulation to the brain. These usually arise from subclavian arteries, and then ascend vertically through the transverse processes. The left vertebral artery is typically larger in caliber than the right, and the vertebral arteries lie lateral and posterior to the carotid arteries at their origin.

There are a few anatomical variations in this territory for you to be aware of. In rare cases, the left common carotid artery and subclavian artery may actually share a common origin instead of both arising from aortic arch. In addition, the left vertebral artery can arise directly from the aortic arch, instead of from the subclavian artery, but this is particularly rare on the right side.

Lastly, the right vertebral artery may be at the distal end of the innominate artery instead of arising from the subclavian artery. As you can see the anatomy here is complex. Therefore having a good understanding of the cerebral vascular anatomy, and possible anatomical variations is important when performing extracranial ultrasound investigations.