The inferior thyroid artery, through its branches, supplies the inferior half of the thyroid lobe, and in addition the inferior larynx as well as trachea, cervical portion of esophagus and the parathyroid glands.
Origin: Normally from the Thyrocervical Trunk.
Course and Relations:
- Arises form the thyrocervical trunk.
- Travels up the prevertebral fascia of the anterior scalene muscle to then arch medially, behind the carotid sheath.
- Arches over the vertebral artery, with the highest point of its arch at c6.
- Turns medially and runs under the sympathetic cervical chain (middle cervical ganglia) Here it's running across the prevertebral fascia over the longus colli muscle.
- Approaches the posterior surface of the thyroid capsule (not the inferior surface) at the midpolar level (not inferior pole (superior thyroid does peirce superior pole)
- Around the junction of the lower and middle thirds of the thyroid gland it's associated with the recurrent laryngeal nerve.
- It divides into 4-5 branches before piercing the pretracheal fascia
4-5 branches piercing pretracheal fascia to enter gland
3 tracheoesophageal branches. Lower branch for anteriolateral trachea in superior mediastinum. Middle branch lateral tracheal wall. Superior Supplies the uppermost part of the trachea.
Inferior Parathyroid Branch
Superior Parathryoid Branch (equally arises from the superior thyroid artery).
Ascending Cervical Artery ascends on the anterior scalene muscle with the phrenic nerve (more often comes off thyrocervical trunk)
Inferior laryngeal artery, accompanies the inferior laryngeal nerve (terminal part of the recurrent laryngeal nerve) and supplies the mucous membrane and muscles in the inferior part of the larynx.
It gives off the inferior laryngeal and esophgeal branches before its terminal distribution of thyroid branches.
Original Image from greys anatomy, sourced from wikipedia under a creative commons license
Relationship to the recurrent laryngeal nerve:
You can see from the summary of dissections below that the recurrent laryngeal nerve most frequently passes posterior to the Inferior Thyroid Artery. It may however also pass anteriorly or between branches of the ITA.
The artery has been reported both doubled and absent (2-5%) - if absent may be supplement by a thyroid ima artery.
In about 10-15% of individuals, it arises from the subclavian.
It may pass anterior, posterior or have branches going around the recurrent laryngeal nerve.