Highly vascular endocrine gland of 2 symmetrical lobes connected by an isthmus.
The isthmus lies in front to 2nd-4th tracheal rings.
The lobes lie on the larynx and trachea, from oblique line of thyroid cartilage down to the 6th tracheal ring.
Its deep to the strap muscles of the neck from the C5 to T1 vertebrae (can remember this easily as brachial plexus roots).
False Capsule: the visceral layer of the pretracheal, deep cervical fascia, easily dissected from gland. It splits to enclose the gland, and is not adherent except to the isthmus and 2nd/3rd/4th tracheal rings.
True Capsule: part of the gland - peirces it to form septa, very difficult to seperate.
Suspensory Ligament of Berry are condensation of fascia and capsule, 'suspending' thyroid from trachea at medial aspect of upper lobes.
Pear shaped Lobes, triangular in cross section.
Lateral surface : under sternothyroid and sternohyoid.
Medial Surface: against lateral larynx and upper trachea.
Posterior surface: overlaps medial carotid sheath; parathyroids usually in contact.
Fixed to trachea by dense pre tracheal fascia.
so the gland moves with swallow.
Two superior thyroid arteries anastomose across it's upper margin.
Tributaries from thyroid veins emerge from lower border.
Small portion generally projecting to the left of midline (very very common (60% of people) ) just above the isthmus
- represents the caudal end of thyroglosal duct.
- may be attached to inferior hyoid by fibrous tissue.
- sometimes there is a muscle (levator glandulae thyroidae) innervated by external laryngeal nerves.
Superior and Inferior Thyroid Arteries.
Superior Thyroid Artery is a branch from the external carotid artery.
Superior Thyroid Artery - Pierces the Thyroid capsule. Then Divides.
Inferior Thyroid Artery - Divides. Then Pierces the thyroid capsule.
3% of people Thyroid Ima Artery - very important surgical variant.
Recurrent laryngeal Nerve
Left more likely to lie behind ITA "L-L-L"
Right about 50%-50% above or behind.
From Middle Cervical Ganglion on inferior thyroid Artery
Upper Pole follows superior thyroid artery - to anterior superior group of deep cervical lymph nodes.
Inferior Pole follows the inferior thyroid artery - posterior inferior deep cervical lymph nodes.
Some go to pre-tracheal nodes.
Superior Thyroid Vein - drains upper pole - enters either internal jugular or facial about 50%.
Middle of the Lobe - Middle Thyroid Vein - enteres into the internal jugular.
Inferior Thyroid Veins form a plexus that lies in the pretracheal fascia in front of cervical trachea - drains into brachiocephalic veins.
follicles are created by
follicular cells that surround them. They secrete colloid, which is then stored in the follicles.
Profileration of cells form the caudal end of the thyroglossal duct.