Anatomy of the Thyroid Gland Flashcards
What other structures is the thyroid closely related to?
Larynx and the trachea in the anterior neck
What make up the thyroid gland?
Usually consists of two lateral lobes (right and left) and an isthmus (narrow connecting band)
Where do the lobes of the thyroid attach?
Later aspects of the thyroid and cricoid cartilages, and to the trachea
Where is the isthmus located?
Lies anterior to the second and third cartilages of the trachea
How does a lump in the thyroid/enlarged thyroid gland move when swallowing?
Moves superiorly then inferiorly with the larynx = due to its relationship with the larynx and the trachea
Where are the four parathyroid glands located?
Located on the posterior surfaces of the thyroid gland’s lateral lobes (superior and inferior on each side)
What are some features of the pyramidal lobe?
Mean prevalence of 44.6%, most commonly originates from the left lateral lobe, < 10% aren’t connected to main thyroid gland, most attach superiorly to thyroid cartilage, may extend as far superiorly as the hyoid bone
What does the thyroid gland begin its development as?
Midline epithelial proliferation at the junction between the anterior 2/3 and the posterior 1/3 of the tongue (foramen caecum in adult)
Where does the thyroid gland migrate to during its development?
Migrates inferiorly whilst remaining attached to the tongue via the thyroglossal duct
When does the thyroid gland reach its final position in relation to the larynx and trachea?
In the seventh week of development = thyroid is at C7 vertebral level
What can block the migratory path of the thyroid during its development?
Thyroglossal duct cysts or ectopic thyroid tissue
Where are the platysmal muscles located?
Immediately deep to the skin within the superficial fascia of the neck
What group of muscles do the platysmal muscles belong to?
Muscles of facial expression = innervated by facial nerve (CN VII)
What are the different fascial compartments of the neck?
Prevertebral (deep) fascia, investing fascia, carotid sheaths (x2), pretracheal fascia
Where is the prevertebral (deep) fascia located?
Located posteriorly = encloses postural neck muscles and cervical vertebrae
What does the investing fascia envelope?
All the other neck fascial compartments, also encloses trapezius and sternocleidomastoid muscles
What are the contents of the carotid sheaths?
Located anterolaterally = encloses deep vagus nerves, deep cervical lymph nodes, common then internal carotid arteries, internal jugular vein
What does the pretracheal fascia enclose?
Located anteriorly = oesophagus, trachea, thyroid gland, strap muscles, recurrent laryngeal nerves
Where does the descending part of the trapezius muscle attach?
Attaches inferiorly to the spine of the scapula and the lateral end of the clavicle
What are the attachments of the sternocleidomastoid muscle?
Sternal head = attaches to manubrium of sternum
Clavicular head = attaches to medial end of clavicle
Where do both heads of the sternocleidomastoid muscle pass?
Pass superiorly to attach to the mastoid process of the temporal bone
What are the carotid sheaths?
Bilateral tubes of deep fascia = located deep to the investing fascia and located anterolaterally in the neck on either side of the thyroid gland
What are the attachments of the carotid sheaths?
Superior = attaches to base of the skull (around jugular foramen and entrance to carotid canal) Inferiorly = blends with mediastinal fascia
What is the lymphatic drainage of the thyroid gland?
Drains from superior deep cervical lymph nodes into inferior deep cervical lymph nodes (left and right)
Where is lymph on the right side of the body returned to?
Right venous angle via the right lymphatic duct
Where is lymph from the left side of the body returned to?
Left venous angle via the thoracic duct
What nodes make up the tracheal lymph nodes?
Pretracheal and paratracheal nodes
Where do the vagus nerves arise from?
Branch from the medulla oblongata = exit skull via jugular foramen and descend through in carotid sheath
Where are the vagus nerves located in the chest?
Right is lateral to trachea
Left is on left side of aortic arch
Both are posterior to lung hilum and on the oesophagus
What do the vagus nerves pass through the diaphragm with?
The oesophagus
Where do the vagus nerves divide into their terminal branches?
On surface of the stomach = supply the abdominal organs with parasympathetic axons to the distal midgut
What does recurrent mean when applied to nerves?
They turn back in the opposite direction
Where do the recurrent laryngeal nerves recur?
Right = recurs under subclavian artery Left = recurs under arch of the aorta
What is the embryological origin shared by the arch of the aorta and right subclavian artery?
The fourth aortic arch artery
What are the strap muscles?
Thyrohyoid, sternothyroid, sternohyoid and omohyoid muscles
Where do the thyrohyoid and sternohyoid muscles attach?
Thyrohyoid = attaches from hyoid to thyroid Sternohyoid = attaches from hyoid to sternum
Where do the sternothyroid and omohyoid muscles attach?
Sternothyroid = attaches from thyroid to sternum Omohyoid = attaches from hyoid to shoulder (has superior and inferior bellies)
What attaches the intermediate tendon of the omohyoid to the clavicle?
The fascial sling
What are some surgical methods used to operate on the thyroid gland?
Classical thyroidectomy, endoscopically assisted thyroidectomy, endoscopic trans-axillary approach, endoscopic trans-breast approach
What is the classical thyroidectomy incision?
A collar incision is made within the natural skin crease or in the direction of Langer’s lines
What are some requirements of the incision made during a classical thyroidectomy?
Incision should be just superior to the clavicles and jugular notch, and should be made through the skin and platysma
What can cause paralysis of the vocal cord?
Injury to the recurrent laryngeal nerve
What does unilateral injury to the recurrent laryngeal nerve cause?
Hoarseness or weakness of the voice and a weak cough
What does bilateral injury to the recurrent laryngeal nerve cause?
Aphonia = inability to produce sound
Inability to close the rima glottidis to prevent aspiration or produce a good cough
What separates the carotid sheaths?
The alar fascia
