Relations of the Thyroid Gland
Relations differ between the lateral lobe (most clinically important) and the isthmus.
Relations of the Lateral Lobe
Anterolateral (Superficial) Surface
Covered by, from superficial to deep:
- Skin
- Superficial fascia — containing platysma
- Deep fascia (investing layer)
- Anterior jugular veins
- Sternohyoid muscle
- Superior belly of omohyoid
- Sternothyroid muscle (directly applied — surgical importance)
The sternothyroid is attached to the oblique line of the thyroid cartilage, which limits the upward extension of the thyroid lobes and explains why thyroid swellings enlarge downward (retrosternal goitre) rather than upward.
Medial Surface
Related to the midline structures of the neck (anterior to posterior):
| Structure | Notes |
|---|---|
| Cricothyroid muscle (upper pole) | Crossed by external branch of superior laryngeal nerve — at risk during ligation of superior thyroid artery |
| Thyroid cartilage | Upper half of lateral lobe |
| Cricoid cartilage | At isthmus level |
| Trachea | 1st–6th rings |
| Cricothyroid joint and cricothyroid muscle | |
| Pharynx (inferior constrictor) | Posteromedially |
| Oesophagus | Below pharynx — tends to be to the left side (explains why left lobe goitre causes more dysphagia) |
| Recurrent laryngeal nerve | Runs in the tracheo-oesophageal groove — most important surgical relation |
Posterolateral Surface
Related to the carotid sheath contents:
- Common carotid artery (medially)
- Internal jugular vein (laterally)
- Vagus nerve (between artery and vein, posteriorly)
Also related to the sympathetic trunk and parathyroid glands (superior and inferior), which lie between the true and false capsules.
Relations of the Isthmus
Anterior Surface (Superficial)
- Skin and superficial fascia
- Deep fascia
- Anterior jugular veins (anastomose across the midline)
- Sternohyoid and sternothyroid muscles
Posterior Surface
- 2nd, 3rd, and 4th tracheal rings
- Anastomotic branch between the two superior thyroid arteries runs along upper border
Upper Border
- Anastomotic vessel between superior thyroid arteries
- Sometimes thyroidea ima artery (from brachiocephalic trunk or aortic arch) — important in tracheostomy
Lower Border
- Inferior thyroid veins descend from here to drain into the brachiocephalic veins
- Thymic tissue may be present here
The Recurrent Laryngeal Nerve — Critical Surgical Relation
The recurrent laryngeal nerve (RLN) is the most important relation of the thyroid gland.
| Side | Course |
|---|---|
| Right RLN | Hooks under the right subclavian artery; ascends in the right tracheo-oesophageal groove |
| Left RLN | Hooks under the aortic arch (posterior to ligamentum arteriosum); ascends in the left tracheo-oesophageal groove |
Relation to inferior thyroid artery: The RLN crosses the inferior thyroid artery at the posteromedial aspect of the lateral lobe. This crossing is variable:
- RLN may pass anterior, posterior, or between branches of the inferior thyroid artery
- The artery must not be ligated at the gland — ligate it laterally away from the nerve
Relation to ligament of Berry: The RLN passes just posterior or lateral to the ligament of Berry before entering the larynx at the lower border of the inferior constrictor muscle.