Thyrocervical trunk

Course

The thyrocervical trunk is a short and wide branch originating from the proximal part of the first segment of the subclavian artery. It originates near the medial border of the anterior scalene muscle, between the origins of the vertebral artery and the costocervical trunk. After its relatively short path through the posterior neck triangle, it usually divides into several branches.

Branches and supply

The inferior thyroid artery crosses the common carotid artery posteriorly. It supplies the inferior portion of the thyroid gland and the parathyroid glands.

The ascending cervical artery is a small branch that arises from either the inferior thyroid artery (in about 60% of people) or the thyrocervical trunk (30%). It gives off numerous small branches that supply the spinal cord, vertebral bodies and muscles of the neck.

The suprascapular artery runs inferolaterally towards the superior border of scapula, posterior to the internal jugular vein and sternocleidomastoid muscle. On its course, it gives off small muscular branches that supply the sternocleidomastoid, subclavius and infraspinatus muscles. Additionally, it provides small branches that supply the skin of the upper thoracic cage and shoulder.

The transverse cervical artery is a branch that runs transversely, in a lateral direction towards the shoulder. It supplies the brachial plexus, the middle part of the trapezius muscle and the adjacent skin.

Sometimes (30% of cases) the dorsal scapular artery arises also from the thyrocervical trunk. Along its course, it passes between the upper and middle trunks of the brachial plexus. It supplies the levator scapulae and rhomboid muscles. Additionally, it anastomoses with the suprascapular artery, contributing to the formation of the scapular anastomosis. In the 2/3 of the cases though, the dorsal scapular artery is a branch of the subclavian artery.

The thyrocervical trunk can have up to five branches, but in most cases, it has two to four. These branches usually include: inferior thyroid artery, suprascapular artery, ascending cervical artery and the transverse cervical artery.

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Anatomical variations

In the most anatomical textbooks, the thyrocervical trunk is described as the artery that gives rise to three branches (inferior thyroid, suprascapular and transverse cervical). But according to more recent research, this is the case only in about 30% of the population. Equally common is a two-branch trunk, consisting of only the inferior thyroid and suprascapular branches. In about 10% of people, the internal thoracic artery can also arise from this trunk.

The branches of the thyrocervical trunk show a significant amount of variability in terms of their origin, number or course.

• The inferior thyroid artery can be absent or can have an accessory vessel on each side. In about 15% of the population, this branch arises directly from the subclavian artery.
• The ascending cervical artery is also variable in terms of its point of origin. Usually, it originates from the inferior thyroid artery or thyrocervical trunk, but it is also reported to occasionally branch from the superficial cervical artery.
• The suprascapular artery can arise from the subclavian, axillary, accessory inferior thyroid, subscapular arteries, or the costocervical trunk. It can originate independently or it can share a common origin with inferior thyroid or internal thoracic artery. It can also appear as a unilateral vessel or it can have an accessory artery on either side.
• The transverse cervical artery arises directly from the subclavian artery in 30-40% of cases, and from the thyrocervical trunk in about 60-70%. It can branch as a single vessel or it can arise together with other branches of the subclavian artery. It is absent in about 6% of cases.