You have two superior thyroid arteries—one on either side with generally symmetrical courses. Unless one side needs to be distinguished from the other, the pair of arteries is usually referred to in the singular.
The superior thyroid artery is a branch of the external carotid artery.
Anatomy
Arteries are large vessels that carry blood to and from the heart. As they move away from the heart and to all areas of your body, they branch out, forming other arteries, and then veins and smaller blood vessels.
The common carotid artery carries blood through the head and neck. It splits into two parts:
Internal carotid artery External carotid artery
The external carotid artery then divides into numerous branches:
Ascending pharyngeal artery Lingual artery Facial artery Occipital artery Posterior auricular artery Superior thyroid artery
Structure
The superior thyroid artery is closely related to the superior laryngeal nerve’s external branch and continues through the thyroid fascia. It divides into the posterior and anterior branches after this point. The anterior branch supplies the anterior (toward the front) surface of the thyroid, while the posterior branch supplies the gland’s side and middle surfaces.
The artery gives off several branches that connect to glands, muscles, and other structures inside of the neck and jaw:
Hyoid arterySuperior laryngeal arterySternocleidomastoid arteryCricothyroid artery
Location
The superior thyroid artery branches off of the external carotid artery just below the chin. From there, it runs upward inside of a structure called the carotid triangle.
Then it turns downward and runs beneath the muscles along the front of the neck. There, it comes into close contact with the inferior pharyngeal constrictor muscle and a branch of the superior laryngeal nerve.
Anatomical Variations
The superior thyroid artery has several known variations that are especially important for preventing nerve damage and blood loss during surgeries on the thyroid gland and other structures in the neck.
In some people, the superior thyroid artery arises from the common carotid artery instead of the external carotid artery. This alters its relationship to the superior laryngeal nerve, which is important for speech. In one study, only about 44% of people had the “standard” configuration, with the arteries of 28% of people coming from one place on the common carotid and almost 27% of arteries coming from another place on the common carotid.
Another study suggested far different rates, though, with more than 88% having the “standard” branching pattern. In that study, researchers also found one case of the external laryngeal nerve running parallel to the artery instead of crossing over its stem.
Other known variations include:
The superior thyroid, lingual, and facial arteries arising together as the thyrolingual trunk, rather than branching off from the external carotid one at a timeThe sternocleidomastoid branches sometimes arising directly from the external carotid rather than from the superior thyroid arteryAn abnormal branching pattern of the superior thyroid artery at its origin and also of its five branches on the right side only, while the left follows the most common pattern
Doctors often perform computed tomography (CT) scans before neck surgery to identify any anatomic variations like these.
Function
The several branches of the superior thyroid artery aid in the function of numerous structures and muscles:
Hyoid artery (aka infrahyoid branch): Runs along the underside of the hyoid bone (behind the jaw) and beneath the thyrohyoid muscle to connect with the same branch on the other side; supplies omohyoid, sternohyoid, sternothyroid, and thyrohyoid muscles, which are used to speak and swallow Sternocleidomastoid artery: Runs downward to partially supply the sternocleidomastoid (SCM) (in the jaw) as well as the muscles and skin around it; the SCM helps with head movements Superior laryngeal artery: Supplies blood to the muscles, mucous membrane, and glands of the upper part of the larynx, thus aiding in speech; also connects with the same branch on the other side Cricothyroid artery: Sometimes contributes to the blood supply of the larynx; may also connect with the same artery on the opposite side or with the laryngeal arteries; supplies blood to the cricothyroid muscle, which stretches and tenses ligaments used for forceful speech and singing
Clinical Significance
Doctors can come into contact with the superior thyroid artery during several procedures involving the head and neck.
During a thyroidectomy (surgical removal of the thyroid gland), this artery needs to be tied off (ligated) in case it’s accidentally severed since that can cause severe bleeding that is difficult to control.
The artery also needs to be ligated during surgery on the larynx. During that surgery, injury to a branch of the external laryngeal nerve is possible.
If the superior laryngeal nerve is severed while working on the artery or in close proximity to it, the ability to speak can be compromised, especially when it comes to yelling or creating high-pitched sounds.
