Topography and Course
The artery originates near the origin of the external carotid artery (a. carotis externa), although in some cases it may arise from the bifurcation area or the common carotid artery. The vessel forms an arch and courses 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 its terminal branches.
Branches and Areas of 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) — travel to the lobes of the thyroid gland, supply the superior margin of the isthmus, as well as the external, 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 corresponding nerve 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) — courses 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.
Muscles Supplied
The superior thyroid artery participates in the blood supply to the following neck muscles:
- Sternocleidomastoid muscle (m. sternocleidomastoideus) — also receives blood from the occipital artery.
- Thyrohyoid muscle (m. thyrohyoideus).
- Sternohyoid muscle (m. sternohyoideus) — also receives blood from the superficial cervical artery.
Clinical Significance and Surgery
Knowledge of the topography of the superior thyroid artery is essential when exposing the external carotid artery for ligation to achieve hemostasis during surgeries involving parotid gland and tongue tumors, as well as during maxillectomy.
Surgical access is achieved via an incision along the anterior border of the m. sternocleidomastoideus. After opening the fascial sheaths, the surgeon identifies the artery. The main identifying 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 superior thyroid artery is the first branch of the external carotid. During mobilization of the vascular bundle, the artery is separated from the internal jugular vein (v. jugularis interna) and the vagus nerve (n. vagus), which lie posteriorly.