Topography and course of the vessel
The artery originates near the origin of the external carotid artery (a. carotis externa), although in some cases it may arise from the bifurcation zone or the common carotid artery. The vessel forms an arch and runs downward and anteriorly toward the upper margin of the thyroid gland.
The artery runs parallel to the external branch of the superior laryngeal nerve (n. laryngeus superior), lying medial to it. At a distance of 1.5–2.0 cm from the upper pole of the lateral lobe of the thyroid gland, the trunk divides into branches.
Branches and areas of blood supply
The artery gives off several branches supplying the thyroid gland, larynx, and soft tissues of the neck:
- Glandular branches (rr. glandulares anterior, posterior, lateralis) — pass toward the lobes of the thyroid gland, supplying the upper margin of the isthmus as well as the outer, anterior, and posterior surfaces of the upper pole of the lateral lobe. They anastomose with branches of the inferior thyroid artery (a. thyroidea inferior), which arises from the thyrocervical trunk.
- Superior laryngeal artery (a. laryngea superior) — passes together with the nerve of the same name through the thyrohyoid membrane (memb. thyrohyoidea) and ramifies within the larynx. It anastomoses with the inferior laryngeal artery (a. laryngea inferior).
- Infrahyoid branch (r. infrahyoideus) — runs toward the infrahyoid muscles.
- Sternocleidomastoid branch (r. sternocleidomastoideus) — runs toward the muscle of the same name.
The superior thyroid artery also participates in the blood supply to the pharynx along with the ascending pharyngeal, facial, and maxillary arteries.
Supplied muscles
The superior thyroid artery participates in the blood supply to the following neck muscles:
- Sternocleidomastoid muscle (m. sternocleidomastoideus) — also receives blood supply from the occipital artery.
- Thyrohyoid muscle (m. thyrohyoideus).
- Sternohyoid muscle (m. sternohyoideus) — also receives blood supply from the superficial cervical artery.
Clinical significance and surgery
Knowledge of the topography of the superior thyroid artery is important when exposing the external carotid artery for its ligation to achieve hemostasis in surgeries involving tumors of the parotid gland and tongue, as well as during maxillary resection.
Access is achieved through an incision along the anterior border of the m. sternocleidomastoideus. After opening the fascial sheaths, the surgeon identifies the artery. The main distinguishing feature of the external carotid artery is the presence of branching vessels, unlike the internal carotid artery, which gives off no branches in the neck. The first branch of the external carotid artery is the a. thyroidea superior. When mobilizing the vascular bundle, the artery is separated from the internal jugular vein (v. jugularis interna) and the vagus nerve (n. vagus), which lie posteriorly.
Class and exam questions
How to distinguish the external carotid artery from the internal during neck surgery?
The main distinguishing feature is the presence of branches. The external carotid artery gives off branches, the first of which is the superior thyroid artery. The internal carotid artery has no branches in the neck.
Which nerve runs adjacent to the superior thyroid artery?
The vessel runs parallel to the external branch of the superior laryngeal nerve (n. laryngeus superior), lying medial to it.
How is the larynx supplied with blood from this arterial system?
The superior laryngeal artery arises from the superior thyroid artery. It passes through the thyrohyoid membrane and ramifies within the larynx.
With which artery do the glandular branches anastomose?
They form an anastomosis with the inferior thyroid artery (a. thyroidea inferior), which arises from the thyrocervical trunk.
What else to study on this topic
- External carotid artery
- Inferior thyroid artery
- Thyroid gland
- Superior laryngeal artery
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