Chapter 17 Flashcards
How is the thyroid encapsulated?
By a fibrous capsule, which is in turn invested by a false capsular layer arising from the deep cervical fascia (pretracheal fascia)
-The fascial attachment between the gland and the upper two or three tracheal rings is also known as the ligament of Berry
Where do the strep muscles reside?
The strep muscles are the sternothyroid and sternohyoid
They reside anterior to the lobes of the gland are innervated by the ansa cervicalis
What define the posteromedial borders of the thyroid gland?
The trachea and the esophagus
What lies lateral to each lobe of the thyroid?
Common carotid artery
Internal jugular vein
What lies medial to each thyroid lobe?
Vagus, in the cleft between the trachea and esophagus, and beneath or embedded in the ligament of Berry
Blood supply of the thyroid- general
Predominantly from the paired superior and inferior thyroid arteries
Superior thyroid artery
The first branch off the external carotid artery and descends toward the superior pole of the thyroid lobe, where it divides into anterior and posterior branches
Inferior thyroid artery
A branch of the thyrocervical trunk and travels posterior to the carotid sheath before it reaches the posterior surface of the mid-portion of the gland
-Also provides the principal blood supply to all 4 parathyroid glands in ~80%
Thyroid ima arteries
Present in 5-10% of the population
Arise from the brachiocephalic trunk or directly from the aortic arch and can provide additional blood supply to the thyroid
What veins drain the superior poles and lateral aspects of the thyroid, respectively?
Superior and middle veins
Drain into the internal jugular veins
What arise from the inferior poles of the thyroid and course anterior to the trachea?
Inferior thyroid veins
Drain into the brachiocephalic veins
Lymphatics of the thyroid
Interlobular lymphatics communicate with intrascapular lymphatics
Pretracheal lymph nodes, paratracheal lymph nodes, and the tracheoesophageal lymph nodes along the recurrent laryngeal chain
The supraisthmic pretracheal lymph nodes that run alongside the pyramidal lobe are also known as the delphian nodes
The regional nodal basins are a frequent site of metastatic thyroid cancer?
How is the thyroid innervated?
By postganglionic fibers that originate from the cervical sympathetic ganglia
RLN
Comprised of all intrinsic laryngeal muscles except for the cricothyroid muscle
Injury leads to hoarseness and difficulty in phonation secondary to paralysis of the ipsilateral vocal cord
What does bilateral RLN injury result in?
Abduction of both vocal cords with complete airway obstruction necessitating emergent intubation or tracheostomy
Branching of the RLN
Branches from the vagus nerve and loops around the origin of the right subclavian artery to ascend in the tracheoesophageal groove
Branching of the left RLN
Branches from the vagus nerve and loops around the aortic arch near the ligamentum arteriosum
Nonrecurrent laryngeal nerve on the right side
Present in ~1% of the population and is often associated with an aberrant subclavian artery
A left is much less common and may be associated with a right-sided aortic arch
What innervates the cricothyroid muscle?
What can an injury to this nerve result in?
External branch of the superior laryngeal nerve
Loss of vocal projection and volume, particularly at higher pitches
Hormones involved in the thyroid
Thyroid hormones
Calcitonin
Thyroid function tests
Unlike T4 or T3 levels, which vary depending on the plasma level of TBG, albumin, and prealbumin, serum TSH levels are independent of the concentrations of carrier proteins in the circulation
What should be done following adjustment of an oral T4 dosage?
Serum TSH measurement should be delayed for at least 4-8 wks
When are TSH levels not reliable indicators of thyroid dysfunction?
In pts who have neuropsychiatric disorders or diseases of the pituitary gland (pituitary adenoma)
TRH stimulation test
Check baseline TSH level, administer synthetic TRH, measure TSH level again after 30-60 mins
- Normally, a rise in TSH from baseline is observed after TRH administration
- Pts with hypothyroidism have a blunted response or no rise in TSH
Thyroid imaging
US is noninvasive and inexpensive (solid vs cystic)
FNA
Radionuclide imaging- functional assessment of the thyroid gland
-Allows for localization of thyroid tissue, detection of functional metastatic lesions from thyroid cancer, and an estimation of the size of the thyroid gland