The Anatomy of the Thyrocervical Trunk

The thyrocervical trunk is one of the three major branches of the subclavian artery. This branch arises on the anterior (front side) of the lower neck near the scalenus anterior muscle. Ascending upwards, it breaks off into several important branches that supply oxygen-rich blood to the thyroid gland as well as other regions throughout the neck. In some cases, vascular disorders such as peripheral artery disease can affect this region, leading to serious complications.

Anatomy

Emerging from the first portion of the subclavian artery, the thyrocervical trunk is a thick and stout branch that runs between the vertebral artery and the costocervical trunk towards the front and sides of the neck. It arises close to the junction of the scalenus anterior muscle, which helps lift the upper pair of ribs during breathing and aids in lateral movement of the head.

As it ascends, this artery breaks into four major branches.

Inferior Thyroid Artery

The largest and most significant branch, the inferior thyroid artery moves upward in front of the vertebral artery to supply the thyroid gland, the larynx, trachea, esophagus, and surrounding muscles.

Suprascapular Artery

Branching away behind and to the side of the anterior scalene muscle, one of the three major muscles on the sides of the neck, the suprascapular artery crosses the third part of the subclavian artery, as well as the brachial plexus, a network of nerves connecting the spine to areas in the neck and upper arm. After that, it moves behind the clavicle, where it connects with the rich scapular arterial plexus, a bundle of nerves in the shoulder.   

Ascending Cervical Artery

This short artery ascends medial (next to but closer to the middle of the body) to the phrenic nerve, a nerve that extends down between the lung and the heart to access the diaphragm. This artery splits off into smaller branches that supply the neck’s intervertebral foramina, which are the spaces created by the neck’s vertebrae that allow the spinal nerves to pass. In addition, branches from this artery supply the lateral muscles of the upper neck.       

Transverse Cervical Artery

Another short artery, the transverse cervical artery quickly splits into superficial and deep branches that extend towards the side of the body across the phrenic nerve and anterior scalene muscle.

These then pass through or cross the brachial plexus, supplying the vasa nervorum (a series of small arteries that supply peripheral nerves). This artery splits into two major branches: the superficial cervical artery (which runs behind the trapezius muscle, essential for neck and head movement), and the dorsal scapular artery supplies the levator scapulae and rhomboid muscles of the upper back.

Anatomical Variations

A few variations have been seen in the anatomy of the thyrocervical trunk and surrounding areas.

Primarily, these are:

• Alternate origin of the suprascapular artery: Though the suprascapular artery often arises directly from the thyrocervical trunk, in many cases it has been observed branching off directly from the subclavian artery.
• Alternate origin of dorsal scapular artery: Most often seen as a branch of the transverse cervical artery—itself a branch of the thyrocervical trunk—the dorsal scapular artery also sometimes emerges directly from the second or third parts of the subclavian artery.
• Dual origin of ascending cervical artery: Another common variation that’s seen is that the ascending cervical artery has a dual origin in both the thyrocervical trunk as well as the transverse cervical artery.
• Alternate origin of the transverse cervical artery: This artery will sometimes arise from the suprascapular artery or directly from the subclavian artery rather than directly from the thyrocervical trunk.
• Size differences: Another often observed variations are thicker branches on the right side than the left.

Function

The thyrocervical trunk primarily supplies oxygenated blood to the viscera of the neck, which includes the thyroid and parathyroid glands, the trachea and larynx, as well as the pharynx and esophagus in the throat. In addition, this artery supplies the brachial plexus (nerve clusters radiating from the spine), several important muscle groups in the neck, as well as the scapular anastomosis (arteries that supply the scapula and shoulder joint).

Clinical Significance

There are several conditions that can affect the thyrocervical trunk or its branches, leading to symptoms.

• Vascular defects or an injury can lead to the formation of an aneurysm in this artery, which is ballooning in a specific region of the arterial wall. Aneurysms have a risk of rupturing (tearing and leaking).
• Peripheral artery disease leads to plaque build-up in arteries can cause stenosis (narrowing) and impede blood flow.
• Thoracic outlet syndrome is characterized by stenosis that causes insufficient blood supply to certain neck regions. As a result, there’s a weakened pulse and, in more advanced cases, neurological issues as well as weakness or other symptoms in the upper limbs.
• In Takayasu arteritis, a systemic inflammatory vasculitis, inflammation in the region can cause subclavian steal syndrome. This is when the hardening of the artery causes blood to flow backward, impeding proper oxygen flow to parts of the brain.