Deep structures of the neck: Root of the neck
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
The neck has both superficial and deep structures. But before you stick your neck out and try to guess what the deep structures are, we will just tell you. The deep structures consist of paravertebral muscles and the viscera extending through the superior thoracic aperture at the root of the neck.
When looking at the root of the neck specifically, it joins the neck and thorax, and acts like a passageway for neurovascular structures going from the thorax to the head or upper limb and vice versa.
It’s located on the cervical side of the superior thoracic aperture, which is formed laterally by the first pair of ribs and their costal cartilages, anteriorly by the manubrium of the sternum and posteriorly by the body of T1 vertebra.
The root of the neck contains neurovascular structures like the brachiocephalic trunk and the subclavian arteries, as well as veins such as the external and anterior jugular veins and the subclavian vein, and nerves such as the vagus nerve, phrenic nerves and the sympathetic trunks.
Let’s look at the arteries first. The brachiocephalic trunk is the largest branch of the aorta which arises in the midline from the beginning of the arch of aorta, posterior to the sternal manubrium.
It’s covered anteriorly by the right sternohyoid and sternothyroid muscles and passes superolaterally to the right and bifurcates posterior to the sternoclavicular joint into the right common carotid artery and right subclavian artery. Now, the right and left subclavian arteries supply each upper limb and also send branches to the neck and brain.
Now, while the right subclavian artery arises from the brachiocephalic trunk, the left subclavian artery arises from the arch of the aorta directly, about 1 centimeter distal to the origin of the left common carotid artery.
Although the two subclavian arteries have different origins, they have the same course in the neck. So, they start posterior to the sternoclavicular joints on either side, and they ascend through the superior thoracic aperture and enter the root of the neck. Here, they arch superolaterally, reaching an apex as they pass posterior to the anterior scalene muscles.
Then they begin to descend until they disappear posterior to the middle of the clavicles. When they cross the outer margin of the first ribs, their name changes and they become the axillary arteries.
Now, each subclavian artery has three parts which are described relative to the anterior scalene muscle. So, the first part is medial to the anterior scalene, the second part is posterior to the muscle and the third part is lateral to the anterior scalene.
The first part of the artery gives three branches: the vertebral artery, the internal thoracic artery and the thyrocervical trunk. The second part gives the costocervical trunk and the third part gives the dorsal scapular artery.
The vertebral artery ascends in the neck and passes through the foramina transversaria of C1-C6 vertebrae. Then, it enters the cranial cavity through the foramen magnum, also known as “the big hole in the occipital bone” to its friends.
Here, the vertebral artery supplies the medulla and spinal cord, parts of the cerebellum and the dura of the posterior cranial fossa. The internal thoracic artery arises from the anteroinferior aspect of the first part of the subclavian artery and passes inferomedially into the thorax, and goes on to supply the anterior thoracic wall.
The thyrocervical trunk arises from the anterosuperior aspect of the first part of the subclavian artery, near the medial border of the anterior scalene muscle, and it has four branches: the inferior thyroid artery, the suprascapular artery, the ascending cervical artery and the transverse cervical artery.
The inferior thyroid artery supplies the larynx, trachea, esophagus, thyroid and parathyroid glands and the adjacent muscles. The ascending cervical artery supplies the lateral muscles of the upper neck.
The suprascapular artery passes through the posterior triangle then posterior to the clavicle to supply the supraspinatus and infraspinatus.
Finally the cervicodorsal trunk or the transverse cervical artery passes through the posterior triangle and supplies the trapezius muscle.
Next, the costocervical trunk arises from the posterior aspect of the second part of the subclavian artery behind the anterior scalene, and it passes posterosuperiorly to divide into the superior intercostal and deep cervical arteries which supply the first two intercostal spaces and the posterior deep cervical muscles, respectively.
Finally, the dorsal scapular artery typically branches off of the third part of the subclavian artery. However, sometimes the dorsal scapular artery arises as a deep branch of the transverse cervical artery. Regardless of its origin, it supplies the levator scapulae and rhomboids.
So far so good! Take a quick break and try to recognize the branches of the subclavian artery.
Next, let’s take a look at the veins in the root of the neck. There are two large veins that terminate in the root of neck: the external jugular vein which mostly drains blood from the scalp and face, and the anterior jugular vein which arises near the hyoid from the union of the superficial submandibular veins, and drains blood from the anterior aspect of the neck.
The anterior jugular vein descends into the root of the neck where it drains into the external jugular vein or the subclavian vein. Now, the subclavian vein is a continuation of the axillary vein, that begins at the lateral border of the first rib.
It passes over the first rib anterior to the scalene tubercle and parallel to the subclavian artery from which is separated by the anterior scalene muscle. The subclavian vein has only one tributary which is the external jugular vein, and ends when it joins with the internal jugular vein to form the brachiocephalic vein.
This union is called either the right or left venous angle, which is located posterior to the medial end of the clavicle. The left venous angle is where the thoracic duct drains lymph, and the right venous angle is where the right lymphatic duct drains lymph.