Anatomy of the thyroid and parathyroid Flashcards
Where does the thyroid sit in relation to the spine?
Anteriorly to C7
What is the name of the narrow band that connects between the two lobes of the thyroid?
Isthmus
Where do the two lobes of the thyroid attach to?
Lateral aspects of the thyroid and cricoid cartilages as well as to the trachea
Where does the isthmus lie?
Between anterior 2nd and 3rd cartilages of the trachea
How will a lump in the thyroid gland or an enlarged gland move when a patient swallows?
Superiorly then inferiorly with the larynx This is due to the relationship between larynx, trachea and thyroid
How many parathyroid glands are there?
4
Where are the parathyroid glands situated?
On the posterior surfaces of the thyroid gland’s LATERAL lobes, external to fibrous capsule
What is the thyroid covered by?
Thin fibrous capsule which sends septa deeply into the gland
What do septa contain?
Larger blood vessels, lymphatics and nerves that enter the thyroid gland
What attaches the fibrous capsule to the cricoid cartilage and superior tracheal rings?
Dense connective tissue
What does dense connective tissue attach the fibrous capsule surrounding the thyroid to?
Cricoid cartilage and superior tracheal rings
What is external to the fibrous capsule?
Loose fascial sheath
How is the loose fascial sheath formed?
By the visceral portion of the pretracheal layer of deep cervical fascia
Where does the thyroid gland begin its development?
At the junction between the anterior 2/3rd and posterior 1/3 of the tongue, as a midline epithelial proliferation
What is the junction between the anterior 2/3 and posterior 1/3 of the tongue called in adults?
Foramen caecum
Where does the thyroid gland migrate to during developement?
It migrates inferiorly, whilst remaining attached to tongue via the thyroglossal duct
In its development, how does the tongue remain attached to the tongue as it migrates inferiorly?
Via the thyroglossal duct
When does the thyroid gland reach its final position?
7 weeks of development
Where can thyroid duct cysts or ectopic thyroid tissue be located?
At any point in the migratory path
Where does a pyramidal lobe most commonly originate from?
Left lateral lobe
What is the prevalence of pyramidal lobe?
About 45%
9% of pyramidal lobes arent connected with main thyroid gland. True or false?
True
- Where do most pyramidal lobes attach superiorly? 2. Where may the pyramidal lobe extend as far superiorly as?
- Thyroid cartilage 2. Hyoid bone
Define platysma
Skeletal muscle in the superficial fascia, runs near thyroid gland laterally
Where are the platysma muscles located?
Located immediately deep to the skin, within the superfiscial fascia of the neck, from lower border of mandible down the neck
What group of muscles do the platysma muscles belong to?
Fascial expression
What nerve supplies the platysma muscles?
Facial nerve
What is the name of the fascial compartment shown in green?
Investing (deep) fascia
What is the name of the fascial compartment shown in orange?
Prevertebral (deep) fascia
What is shown in red?
Carotid sheath
What fascial compartment of neck is shown in purple?
Pretrachial (deep) fascia
What muscle sits posterior to the neck?
trapezius
What are the muscles seen at the anterior edge of the neck?
Sternocleidomastoid
Where does the retropharyngeal space run from and to?
Base of skull to superior mediastinum
How fast will infection spread in the retropharyngeal space?
Extremely quickly
Where is the prevertebral (deep) fascia located?
Deep to investing fascia
Located posteriorly
What does the prevertebral fascia enclose?
The cervical vertibrae and postural neck muscles
What does the investing (deep) fascial compartment enclose?
All neck fascial compartments
2 pairs of muscles - R and L trapezius and anteriorly sternocleidomastoid
Where is the investing fascia located?
Deep to superficial fascia
How many carotid sheaths are there?
2
Where are the carotid sheaths located?
Anterolaterally deep to the investing fascia, either side of the thyroid gland
What do the carotid sheaths enclose?
- Internal jugular veins
- Carotid arteries
- Vagus nerves
- Deep cervical lymph nodes
Where does the pretracheal (deep) fascia lie?
Anteriorly, deep to the investing fascia
What does the pretracheal fascia enclose?
- Strap muscles
- Thyroid gland
- Trachea
- Oesophagus
- Recurrent laryngeal nerves
Where dot he carotid sheaths attach superoirly?
The base of the skull (around the jugular foramen and entrance to carotid canal)
How do carotid sheaths attach inferiorly?
Blend inferiorly with mediastinal fascia
What nerve supplies the sternocleidomastoid?
CN XI - spinal accessory nerve
What nerve supplies the trapezius?
CN XI - spinal accessory nerve
Where does the anterior jugular vein drain into?
External jugular vein
Where does the external jugular vein drain into?
Subclavian vein
Where does the sternal head of the sternocleidomastoid?
Manubrium of sternum
Where does the clavicular head attach to of the sternocleidomastoid?
Medial end of the clavicle
Where do both heads of the sternocleidomastoid attach to superiorly?
mastoid process of the temporal bone
What two arteries supply the thyroid?
Inferior and superior thyroid arteries
What artery supplies the parathyroid glands?
Inferior arteries supply both inferior and superior parathyroid glands
What are internal jugular veins a branch of?
Brachiocephallic veins
What veins drain the thyroid gland?
Superior, middle and inferior thyroid veins
Where do the superior and middle thyroid veins drain into?
Internal jugular vein
Where do the inferior thyroid veins normally drain into?
Left brachiocephallic vein
What are the yellow structures that look like dots on this diagram?
Superior deep cervical lymph nodes
What is the name of the purple dots on this diagram?
Inferior deep cervical lymph nodes
What is the name of the red dot on this diagram?
Pretracheal node
What is the name of the green dots on this diagram?
Paratracheal nodes
On the right hand side, how is the lymph drained?
Via the right lymphatic duct to the right venous angle
How does lymph drain on the left hand side of thyroid?
Returned via the thoracic duct to the left venous angle
Describe the lymphatic drainage of the thyroid and parathyroid glands
Initially pass to the prelaryngeal, pretracheal and paratracheal lymph nodes
Drain into superior and inferior deep cervical lymph nodes
Right - lymphatic duct then right venous angle
Left - thoracic duct then left venous angle
In the neck, is the vagus nerve medial or lateral to the recurrent laryngeal nerve
Lateral
Where does the left recurrent laryngeal nerve recur?
Under the arch of the aorta
Where does the right recurrent laryngeal nerve recur?
Under the subclavian artery
Where does the vagus nerve exit the base of the skull?
Jugular foramen
What somatic branches does the vagus nerve give to the larynx in the neck?
- Superior laryngeal nerve
- Right recurrent laryngeal nerve
Where does the vagus nerve exit the brain?
An extension of the spinal cord into the brain called the medulla oblongata
Describe the route of the right vagus nerve
- Right lateral aspect of trachea
- Posterior to right lung route
- Forms plexus onto the oesophagus
Describe the route of the left vagus nerve
- Left side of the arch of the aorta
- Posterior to the lung route
- Forms plexus onto the oesophagus
Where do both vagus nerves pass through?
The diaphragm along with the oesophagus
Where do the vagus nerves divide into terminal branches?
Surface of the stomach
What nerve supplies the abdominal organs with parasympathetic axons to the distal midgut?
The vagus nerves
How many strap muscles are there?
8 in total, 4 on the left and 4 on the right
What is another name for the strap muscles?
Infrahyoid muscles
What is the most lateral strap muscle and what are its attachments?
Omohyoid
Attaches to the hyoid bone and the scapula
What are the names of the 4 strap muscles
- Superior belly of omohyoid
- Inferior belly of omohyoid
- Sternohyoid
- Thyrohyoid
What does the fascial sling attach?
The intermediate tendon of the omohyoid to the clavicle
What are the four surgical approaches to the thyroid gland?
- Classical thyroidectomy (similar approach to tracheostomy)
- Endoscopically assisted thyroidectomy
- Endoscopic trans-axillary approach
- Endoscopic trans-breast approach
Describe the process of thyroidectomy
A collar incision is made within a natural skin creaseor Langer’s lines
Incision should be just superior to the clavicles and jugular notch
Why should a thyroidectomy incision be just superior to the clavicles and jugular notch?
Optimal aesthetics as the scar is hidden behind clothing
Reduces risk of keloid formation
Define a keloid
A scar that grows lumpy or larger than the wound that is healing
In a thyroidectomy, what layers is the incision made in?
Through the skin and platysma
What is A on this diagram?
Anterior jugular veins (in superficial fascia)
What is B on this diagram?
Right sternohyoid
What is C on this diagram?
Sternal head of the right sternocleidomastoid
What is D on this diagram?
Laryngeal prominence of the thyroid cartilage
What is E on this diagram?
Left sternohyoid
What is F on this diagram?
Pretrachial fascia
Where does the right recurrent laryngeal nerve ascend in the neck?
In the groove between the trachea anteriorly and oesophagus posteriorly
Describe how you would remove the thyroid gland
Mobilise the thyroid gland anteriorly
Dissect parathyroid glands
Dissect their blood supply free from the posterior surface of the gland
Where does the right recurrent laryngeal nerve provide somatic motor supply to?
Most of the skeletal muscles that move the right vocal cord (intrisic muscles of the larynx)
What does injury to the recurrent laryngeal nerve cause?
Paralysis of the vocal cord
What is the rima glottidis?
Opening between the vocal cords
What does unilateral damage of 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 make sound)
- Inability to close the rima glottidis
- Can no longer prevent aspiration or produce a good cough
