The inferior thyroid artery runs up through your neck and throat. It is considered one of the main vessels that supply blood to the thyroid gland, which is situated in the front of your neck and produces hormones that keep your body functioning, along with the superior thyroid artery. It also supplies the four parathyroid glands, which regulate calcium levels in the body, and some neck muscles and structures that help you breathe, speak, and swallow.
You have two inferior 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.
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Anatomy
Arteries are large blood vessels in your vascular system. As they travel away from your heart and throughout your body, they branch off into smaller arteries and eventually veins and smaller blood vessels.
The subclavian arteries originate at your heart. Their job is to supply blood to the chest, shoulders, arms, neck, and head. Along with other branches, they divide into three arteries:
- Vertebral artery
- Internal thoracic artery
- Thyrocervical trunk
As the thyrocervical trunk moves up and away from the heart, it gives off four branches:
- Ascending cervical artery
- Transverse cervical artery
- Superficial branch
- Inferior thyroid artery
Structure
The inferior thyroid artery is the largest and most significant branch of the thyrocervical trunk. It divides into the inferior and superior branches near the base of the thyroid gland, which supply the thyroid gland’s inferior and posterior surfaces. The superior branch also supply the parathyroid glands.
After leaving the trunk, the inferior thyroid artery branches off into arteries that serve the larynx (voice box), thyroid gland, parathyroid glands, and other structures and muscles in the neck and throat. These branches are:
- Glandular branches: Along with the superior thyroid artery, supplies the thyroid gland; divides into two parts, one of which supplies both the thyroid and the parathyroid glands
- Muscular branches: Supply muscles of the neck or throat, including the infrahyoid, longus colli, scalenus anterior, and inferior pharyngeal constrictor
- Inferior laryngeal artery: Supplies the muscles and mucous membrane of the larynx
- Tracheal branches: Supply the trachea (windpipe)
- Esophageal branches: Supply the esophagus (tube connecting your throat to your stomach)
- Ascending cervical artery: Supplies the muscles of the neck and connects to branches of the vertebral arteries
- Pharyngeal branches: Supply the pharynx (throat)
Location
The inferior thyroid artery branches off from the thyrocervical trunk just above the collarbone. It moves upward, passing in front of the vertebral artery, then turns inward, running behind the carotid sheath and sympathetic trunk.
It then moves toward the back of the thyroid gland, where it splits into two portions that deliver blood to the thyroid and parathyroid glands. In this area, it encounters the recurrent laryngeal nerve, which is vital to the function of your larynx and therefore vital to speech.
Other branches continue up or toward the structures they supply, including the throat, pharynx, and esophagus.
Locations of the muscles supplied by the muscular branch are:
- Infrahyoid: Down the front and sides of the neck
- Longus colli: Down the front of the neck
- Scalenus anterior: Down the sides of the neck
- Inferior pharyngeal constrictor: Low in the throat
Anatomical Variations
Anatomical variations are common, and it’s important for doctors to understand the different paths structures in your body can take. Known variations may influence diagnosis and treatment, especially surgery.
Recurrent Laryngeal Nerve
The inferior thyroid artery’s relationship with the recurrent laryngeal nerve can vary considerably from one person to the next. Research shows that about 50% of the time, the nerve runs behind the artery, while it runs between branches of the artery in 25% of cases, and it runs in front of it in the other 25%.
One study classified this relationship into seven different types while another described 28 configurations. These alternative placements make it vulnerable to injury during surgical procedures on the artery or the thyroid gland.
Odd Number of Arteries
In about 1% of people, the left inferior thyroid artery is missing and the artery on the right side changes in order to compensate for it.
Some people also have a third artery supplying the thyroid gland, along with the inferior and superior thyroid arteries. It’s called the thyroid ima artery. In people without a left inferior thyroid artery, the ima artery may help compensate for its absence.
Differing Origin
In some people, the inferior thyroid artery arises from a different location than usual. Instead of the thyrocervical trunk, it may come from the subclavian artery or, less often, the vertebral artery or common carotid artery.
Vital for Surgeons
To protect all of the structures and the functions they allow, it’s important for surgeons to know about anatomical variations and, when possible, to use imaging tests to identify abnormalities before surgery.
Function
The inferior thyroid artery and its branches carry oxygen-rich blood from your heart to various tissues that are essential for several basic functions in your body:
- The thyroid gland produces hormones that regulate vital functions such as metabolism and growth.
- The parathyroid glands deal with calcium regulation and help keep your bones healthy.
- The larynx allows you to speak.
- The pharynx allows you to breathe and swallow.
- The esophagus allows you to swallow.
- The trachea allows you to breathe.
- The neck muscles allow you to move your head in some ways and aid in swallowing.
Clinical Significance
Inadequate blood supply to any of the structures supplied by the inferior thyroid artery can impair function. Trauma to the neck, surgical error, or diseases of the blood vessels can all cause damage to the artery.
Depending on the location and extent of the damage, you may have problems speaking, breathing, swallowing, and moving your head.
Accidental severing during surgery, such as thyroidectomy, can cause hypoparathyroidism, which causes abnormally low levels of calcium in your blood, along with abnormally high levels of phosphorous. Symptoms include:
- Tingling or burning in the extremities
- Cramping and twitching muscles in the limbs, stomach, or face
- Fatigue
- Weakness
- Hair loss, including the eyebrows
- Brittle nails and dry skin
- Hoarse voice or other voice changes
- Wheezing and difficulty breathing
- Depression
- Anxiety
- In severe cases, seizures
Accidental severing of the recurrent laryngeal nerve during surgery in the area can lead to:
- Weak or hoarse voice
- Loss of voice
- Breathing difficulties
As a diagnostic tool in Graves’ disease (overactive thyroid), doctors can measure the blood flow to the thyroid via the inferior thyroid artery. Higher pressures are associated with Graves’ disease.
