Flashcards in Chapter 17 Deck (64):
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
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 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
US is noninvasive and inexpensive (solid vs cystic)
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
What can detect areas of calcification in the thyroid?
Identify regions of increased vascularity?
Ultrasonography with Doppler
What are three hyperthyroid causes that more commonly require surgical intervention
Graves dz (toxic diffuse goiter)
Toxic nodular goiter
Solitary toxic nodule
Possible accompanying sx of hyperthyroid diseases?
An autoimmune disorder characterized by the presence of antibodies against the TSH receptor on the follicular cell
Graves dz is _____ more common in ____ than ____
Clinical manifestations of Graves dz
Exam of Graves dz
Thyroid gland is typically diffusely enlarged, symmetric, and smooth
Tx options for Graves
Radioactive iodine thyroid ablation
Surgical thyroid ablation
Medical therapy for Graves
Aimed at reducing thyroid hormone levels and is the first-line therapy for most pts
Thionamide therapy must be continued for a prolonged period to control thyroid levels and allow for spontaneous remission
Beta blocking agents such as propranolol may be used as adjuvants
Radioactive iodine therapy for Graves
Induces long-standing remission in most pts, with relatively few side effects, and is the definitive tx used for most adult pts with Graves dz in the US
Advantages and disadvantages for radioactive iodine therapy for Graves
Primary advantage- Does not require an invasive procedure
Disadvantage- high incidence of hypothyroidism
Who are not considered candidates for radioactive iodine therapy in Graves disease?
Pts with concomitant thyroid nodules
Those with very large glands
Generally avoided in children
When is operative intervention indicated for Graves?
Pts who are noncompliant with, or intolerant to, antithyroid drug therapy
Those who are refractory to medical therapy
Those with contraindications to radioactive therapy
Those with large glands (greater than or equal 80 g)
Those with concern for malignancy
Pts who are younger than 20 yrs with large goiters
What should be done preoperatively for Graves?
Achieve a euthyroid state with administration of pTU in combo with propranolol typically initiated 4-8 wks before operation and continued during and after the operation
Lugol solution can be given to pts to decrease the vascularity of the gland and make it firmer and easier to resect
Autonomously functioning thyroid nodules
Function and grow independent of TSH
Appear hot on radionuclide studies
Majority of these nodules enlarge, develop central necrosis, and become nonfunctional
Solitary toxic nodules
Have a peak incidence during the fifth decade of life and are much more common in women
Toxic multinodular goiter
Accounts for approximately 20% of pts with hyperthyroidism and is most common in women older than 50 yrs
Tx of solitary functional nodules
Influenced by size and degree of function, as well as by the pt's age and overall health
When to treat toxic nodules surgically
Ones that exceed 3 cm in diameter
What is the standard tx for toxic multinodular goiter?
Antithyroid drug therapy, followed by thyroidectomy
Presentation of hypothyroid
Neurocognitive disturbances, such as depression, irritability or impaired memory
What is the MC inflammatory condition of the thyroid and the most frequent cause of spontaneous hypothyroidism?
What can occur during the acute phase of Hashimoto thyroiditis?
Findings on palpation in Hashimoto thyroiditis
Gland is usually firm and rubbery with a lobulated surface
What is usually sufficient to make the dx of Hashimoto thyroiditis?
Elevated antimicrosomal antibody titer, along with a suggestive clinial exam
When is thyroidectomy indicated in Hashimoto thyroiditis?
When the gland continues to grow despite thyroid suppression therapy
When should a Hashimoto thyroiditis pt be evaluated for lymphoma?
A rapid enlargement of the thyroid gland
An infectious disorder, which is more common in women
Organisms of acute thyroiditis
Usually spread via the lymphatics from local infectious sources
Presentation of acute thyroiditis
Acute onset of neck pain and fever
Pts typically euthyroid
Tx of acute thyroiditis
Appropriate IV abx
Surgical drainage if abscess present
A dz that typically occurs in middle-aged women within wks of an upper respiratory or other viral infection
Sx of subacute thyroiditis
Anterior neck pain
Referred pain to the ear or angle of the jaw
Exam of subacute thyroidits
Pt usually afebrile
Thyroid firm and extremely TTP
Thyroid may be swollen unilaterally, and the overlying skin is occasionally erythematous
Tx of subacute thyroiditis
Typically self-limited and usually resolves within a few mos
A very rare chronic inflammatory proliferative d/o in which the thyroid tissue and frequently the adjacent strap muscles and carotid sheaths are replaced by dense fibrous tissue
Presentation of Riedel struma
Pts are most often euthyroid, although hypothyroidism may be seen in up to 30% of pts
Workup for Riedel struma
Open bx to r/o thyroid carcinoma or lymphoma