What is the thyroid gland?
An endocrine structure
Where is the thyroid gland located?
In the anterior neck, spanning between C5 and T1 vertebrae
What is the thyroid gland divided into?
What connects the two lobes of the thyroid gland?
Where does the thyroid gland lie in the neck?
- Behind the sternohyoid and sternothyroid muscles
- Wraps around the criocoid cartilage and superior tracheal rings
- Inferior to thryoid cartilage of larynx
What compartment of the neck is the thyroid gland in?
Other than the thyroid gland, what else is in the visceral compartment of the neck?
What is the visceral compartment of the neck bound by?
Where does the thyroid gland form during development?
In the floor of the primitive pharynx, near the base of the tongue
What happens to the thyroid gland during development?
It descends down the neck to lie in its adult anatomical position
What does the thyroid gland move through during developmental descent?
A duct called the thyroglossal duct
What normally happens to the thyroglossal duct?
It fuses and regresses in the adult
What may happen if the thyroglossal duct does not regress?
- Continuation as pyramidal lobe
- Persist as thryoglossal cysts
What portion of the thryoglossal duct continues as a pyramidal lobe?
In what % of individuals does the distal portion of the thyroglossal duct continue as a pyramidal lobe?
Effectively, what is the pyramidal lobe?
An extra piece of thyroid tissue
What are the clinical consequences of the thyroglossal duct continuing as a pyramidal lobe?
There are none
How may thyroglossal cysts present?
As a mass in the midline of the neck, and can be excised surgically
Why does the thyroid gland need to be highly vascularised?
Because it secretes hormones directly into the blood
How is blood supply to the thyroid gland achieved?
Two main arteries; superior and inferior thyroid arteries
Where does the superior thyroid artery arise from?
External carotid artery, it is the first branch
What course does the superior thyroid artery take after arising?
Descends towards the thyroid gland
What does the superior thyroid artery supply?
Superior and anterior portions of the gland
Where does the inferior thyroid artery arise from?
The thyrocervical trunk
What is the thyrocervical trunk a branch of?
The subclavian arter y
What course does the inferior thyroid artery take?
Travels superomedially to reach the inferior pole of the thyroid
What does the inferior thyroid artery supply?
The postero-inferior aspect
What artery supplying the thyroid gland is present in some people?
The thyroid ima artery
What % of people is the thyroid ima artery present in?
The brachiocephalic trunk of the arch of the aorta
What does the thryroid ima artery supply?
The anterior surface and isthmus
What is the venous drainage of the thyroid gland?
- Superior thyroid
- Middle thyroid
- Inferior thyroid
What do the superior and middle thyroid veins drain into?
The internal jugular veins
Where does the inferior thyroid vein drain into?
The brachiocephalic vein
What is the innervation of the thyroid gland?
Branches derived from the sympathetic trunk
What regulates the release of hormones from the thyroid gland?
Where do the left and right recurrent laryngeal nerves arise from?
Their respective vagus nerves
What course to the recurrent laryngeal nerves take?
The descend into the chest, and then hook around the subclavian artery (right) or arch of aorta (left). The nerve then ascends back up the neck, running between the trachea and oesophagus. They pass under the thyroid gland to innervate the thyroid
What is the clinical relevance of the close proximity between the thyroid gland and recurrent laryngeal nerves?
During surgety on the thyroid gland, care must be taken not to ligate or damage the recurrent laryngeal nerves