Endocrine thyroid overview

Question 1

From what branchial structures does the thyroid develop?

Answer 1

The thyroid develops from an endodermal diverticulum of
the floor of the primitive pharynx. The medial primordia is
derived from the first and second pharyngeal pouches. The lateral primordia is derived from the fourth and fifth
pharyngeal pouches.

Question 2

The ultimobranchial bodies develop into what structures?

Answer 2

Ultimobranchial bodies derive from the fourth pharyngeal
pouch neural crest cells and give rise to parafollicular cells
(C cells) of the thyroid, which release calcitonin.

Question 3

What is the relationship of the ultimobranchial

bodies to the thyroid gland?

Answer 3

The ultimobranchial bodies fuse with the thyroid gland
during its descent, consistently in the middle to upper
thirds of thyroid gland.

Question 4

What is the most common pattern of descent of

the thyroid gland in relation to the hyoid bone?

Answer 4

The thyroid gland descends anterior to the hyoid bone

during gestational weeks 4 through 7.

Question 5

What is the most common location of ectopic thyroid tissue?

Answer 5

As the thyroid forms from an endodermal diverticulum of
the pharynx, the most common location of ectopic thyroid
tissue is found in the base of tongue (lingual thyroid).

Question 6

What does the proximal portion of the thyroglossal duct form?

Answer 6

Foramen cecum of the tongue

Question 7

What does the caudal remnant of the thyroglossal

duct form?

Answer 7

Pyramidal lobe of the thyroid, which is present in 40 to 55%

of patients

Question 8

What is the recommended surgical treatment for a thyroglossal duct cyst?

Answer 8

The Sistrunk procedure, which includes complete removal of the thyroglossal duct along with a portion of the central
hyoid bone

Question 9

What is the most common path of the right and left recurrent laryngeal nerves?

Answer 9

The right recurrent laryngeal nerve wraps around and passes deep to the right subclavian artery. It then travels in
a more oblique path to enter the larynx just posterior to the
cricothyroid joint. The left recurrent laryngeal nerve wraps around and passes deep to the arch of the aorta. The nerve then travels in a more medial path within the tracheoeso-
phageal groove.

Question 10

What does the recurrent laryngeal nerve innervate?

Answer 10

The intrinsic muscles of the larynx and sensory innervation
of the glottis (shared innervation with internal branch of
superior laryngeal nerve) and subglottis

Question 11

What is the relationship of the recurrent laryngeal nerve and the cricothyroid joint?

Answer 11

The recurrent laryngeal nerve enters the larynx posterior to the cricothyroid joint.

Question 12

What does the external branch of the superior laryngeal nerve innervate?

Answer 12

The cricothyroid muscle

Question 13

What is the function of the cricothyroid muscle?

Answer 13

The cricothyroid increases tension on vocal cords, inducing
a higher pitch when vocalizing, and is innervated by the
superior laryngeal nerve.

Question 14

What does the internal branch of the superior

laryngeal nerve innervate?

Answer 14

The internal branch of the superior laryngeal nerve pierces the thyrohyoid membrane to enter the larynx. The superior laryngeal nerve provides sensation to the supraglottic
structures and shares sensation of the glottis with the
recurrent laryngeal nerve.

Question 15

Where does the superior laryngeal nerve branch

off from the vagus?

Answer 15

Immediately below the nodose ganglion (inferior ganglion)
of the vagus nerve, which is located just inferior to the
jugular foramen

Question 16

Where does the thyroid gland obtain its blood

supply?

Answer 16

Typically from the superior and inferior thyroid arteries but
occasionally from a thyroid ima artery

Question 17

What is the name of the prelaryngeal lymph node?

Answer 17

Delphian node

Question 18

What are the boundaries of the level VI cervical

lymph nodes?

Answer 18

Level VI represents the central neck compartment and is
bordered by the hyoid bone superiorly, the brachiocephalic
(innominate) vein inferiorly, and the carotid arteries
laterally.

Question 19

What is the name of the naturally occurring

thyroidal enlargement on the lateral portion of the gland?

Answer 19

The tubercle of Zuckerkandl

Question 20

The tubercle of Zuckerkandl

Answer 20

Berry ligament

Question 21

Define the borders of the Simon triangle.

Answer 21

The Simon triangle is defined as the space between the esophagus medially, the carotid artery laterally, and the
inferior thyroid artery superiorly.

Question 22

Define the borders of the Joll triangle.

Answer 22

The Joll triangle is defined as the space between the inferior
pharyngeal constrictor and cricothyroid muscle medially,
the sternothyroid muscle laterally, and the superior thyroid
pole inferiorly.

Question 23

Which is the active form of thyroid hormone?

Answer 23

Triiodothyronine (T3). Thyroxine (T4)must be deiodinated to T3 to act on peripheral tissue.

Question 24

Describe the internal regulatory pathway of

thyroid hormonogenesis.

Answer 24

Hypothalamus releases thyroid-releasing hormone (TRH). TRH binds a receptor in the anterior pituitary that increases production and release of thyroid-stimulating hormone (TSH). TSH stimulates the release of stored T3 and T4, increases production of T3 in relation to T4, and increases the production of thyroglobulin and thyroperoxidase (TPO). The entire system is controlled by negative feedback by downstream hormones.

Question 25

What is the Wolff-Chaikoff effect?

Answer 25

The Wolff-Chaikoff effect describes decreased thyroid
hormone production as a result of excess iodine ingestion
such as with Lugol iodine administration in patients with
Graves disease.

Question 26

What hormones are produced by the thyroid gland?

Answer 26

The thyroid produces T3 and T4. These are made by iodinating the amino acid tyrosine.

Question 27

Thyroid storm is a medical emergency. What medications are the mainstay of treatment in the
acute setting?

Answer 27

Propranolol to control tachyarrhythmias, and methimazole to reduce thyroid hormone production. An hour after methimazole has been given, potassium iodide can be given
to decrease hormone release and vascularity of the thyroid gland if surgery is considered.

Question 28

What are the key components of thyroid hormone?

Answer 28

Thyroglobulin and iodine represent the key components to

make and store thyroid hormone.

Question 29

What is the name of the key enzyme required for

thyroid hormonogenesis?

Answer 29

TPO, an enzyme that performs the iodination of thyro-

globulin and coupling of monoiodotyrosine and diiodotyrosine to form T3 and T4

Question 30

What is the most common cause of unilateral proptosis?

Answer 30

Graves’ ophthalmopathy, which results in deposition of glycosaminoglycans and lipogenesis in the orbit.

Question 31

What are the two ways in which amiodarone can cause hyperthyroidism?

Answer 31

● Type 1 amiodarone-induced thyrotoxicosis: Excess iodine
(amiodarone is 37% iodine) causes excessive thyroid hormone production and is best treated with thionamides and discontinuation of amiodarone.
● Type 2 amiodarone-induced thyrotoxicosis: Amiodarone-
induced thyroiditis causes a destructive thyrotoxicosis
and is best treated with prednisone. Amiodarone use can
continue.

Question 32

Describe the preferred treatment for subacute (de Quervain) thyroiditis in the hyperthyroid stage.

Answer 32

Symptomatic treatment with β-blockers and NSAIDs is the standard treatment. Severe cases are treated with high-dose prednisone.

Question 33

A rare cause of thyrotoxicosis is a hydatidiform

mole. What is the mechanism?

Answer 33

Hydatidiform moles, a form of gestational trophoblastic disease, produce chorionic gonadotropin, which has TSH-like activity

Question 34

Where is a hormone-producing focus of metastatic follicular carcinoma typically found on radioactive body scan?

Answer 34

Usually in the lungs or bone

Question 35

In a nongravid woman with thyrotoxicosis, radioactive iodine uptake is found in the pelvis. What is the diagnosis?

Answer 35

Struma ovarii, a teratoma of the ovary that contains

functional thyroid tissue

Question 36

What findings indicate a diagnosis of thyrotoxicosis factitia?

Answer 36

Thyrotoxicosis factitia is a disorder in which a patient takes
exogenous thyroid hormone surreptitiously, typically for weight loss. Typical findings are a suppressed TSH, low thyroglobulin, high T4 and T3, a negative radioactive iodine
uptake level, and absence of a goiter.

Question 37

Name the four main classifications of hypothyroidism.

Answer 37

● Primary hypothyroidism is the result of a dysfunctional
thyroid gland.
● Secondary hypothyroidism is caused by a dysfunctional
pituitary gland.
● Tertiary hypothyroidism results from hypothalamic dys-
function.
● Finally, peripheral hypothyroidism is caused by hormone
receptor resistance.

Question 38

What is the most common cause of hypothyroidism in the world?

Answer 38

Iodine deficiency

Question 39

What is the most common cause of hypothyroidism in the United States?

Answer 39

Hashimoto thyroiditis

Question 40

What is the cause of myxedema coma?

Answer 40

Myxedema coma is an extreme hypothyroid state that is

typically brought on by some systemic stress, often infection, in a hypothyroid patient.

Question 41

Why should head and neck cancer patients have thyroid function closely monitored?

Answer 41

Hypothyroidism is common in patients with head and neck
cancer after surgery and particularly after radiation therapy.
Patients should have thyroid function tests drawn after 6 weeks
of intervention and then every 6 to 12 months thereafter.

Question 42

What is the recommended starting dose of levothyroxine for young healthy adults with hypothyroidism, and how is this different for older adults with underlying ischemic heart disease?

Answer 42

● For young adults, the typical starting dose is 1.6 μg/kg
and adjusted depending on the TSH level after 6 to 12 weeks on a stable levothyroxine dose.
● For those with known ischemic heart disease or
arrhythmias or for elderly adults, the typical starting dose
is 25 μg daily with 25 μg increases every few weeks.

Question 43

Approximately how long does the hypothyroid

phase of thyroiditis last?

Answer 43

Thyroiditis typically produces a transient hyperthyroid state
and then either recovery or a transient hypothyroid state.
When it occurs, the hypothyroid state typically lasts 2 to 8
weeks.

Question 44

What is the likely cause of subacute granulomatous thyroiditis (de Quervain thyroiditis)?

Answer 44

Most likely a viral illness is the cause. Common associations
include mumps, influenza, coxsackievirus, and adenovirus.
Some believe it is more likely a result of a postviral
inflammatory response than of viral infection itself.

Question 45

What laboratory values are elevated in patients with Hashimoto thyroiditis?

Answer 45

TSH (evidence of primary thyroid disorder), antimicrosomal antibodies (anti-thyroperoxidase antibodies), and anti-thyroglobulin antibodies are usually elevated. However, 10% of patients with clinical Hashimoto thyroiditis may be antibody negative.

Question 46

What causes the initial hyperthyroid state in some patients with Hashimoto thyroiditis?

Answer 46

Transient release of stored thyroid hormone from damaged thyroid cells (hashitoxicosis) causes a temporary surge in
serum thyroid hormone.

Question 47

What is the relationship between Hashimoto thyroiditis and thyroid cancer?

Answer 47

Patients with Hashimoto thyroiditis have a slightly increased
incidence of papillary thyroid carcinoma compared with the
general population.

Question 48

What are the indications for surgery in a patient

with Hashimoto thyroiditis?

Answer 48

Large goiter with obstructive symptoms, cosmetic concerns, or worrisome nodularity

Question 49

Is subacute thyroiditis always painful?

Answer 49

No. Painless thyroiditis is sometimes seen. The inflammatory component may be mild and not require therapy.

Question 50

What are the characteristic physical examination findings of Riedel thyroiditis?

Answer 50

Rock-hard, fixed, painless goiter. Compressive symptoms including dysphagia, dysphonia, cough, and dyspnea may
also occur.

Question 51

What organisms most commonly cause acute

suppurative thyroiditis?

Answer 51

Staphylococcus aureus, Streptococcus pneumoniae, β-hemo-
lytic streptococci are the most common offenders. Occasionally, it can be caused by Fusobacterium and Haemophilus species as well.

Question 52

What criteria for a thyroid FNA must be met in order to be considered diagnostic?

Answer 52

The presence of at least six follicular cell groups, each with
at least 10 cells, that are derived from at least two aspirates
of the cyst or nodule.

Question 53

Why is FNA of cystic thyroid nodules of low

diagnostic yield?

Answer 53

FNA of cystic nodules often yield nondiagnostic findings
because of the scant cellularity of fluid and the difficulty in
obtaining a biopsy of the very thin cyst wall.

Question 54

What are the false-negative and false-positive rates of thyroid nodule FNA?

Answer 54

For thyroid nodules, FNA is a sensitive and specific test. The false-negative rate is approximately 1 to 6%, and the false-positive rate is less than 5%.

Question 55

When should a benign (based on results of

previous FNA) thyroid nodule undergo rebiopsy?

Answer 55

When it changes significantly in size, a cyst recurs, or the

nodule changes texture

Question 56

What is the Pemberton sign?

Answer 56

Distension of the jugular veins, facial edema or erythema
when a patient extends both arms above the head,
indicating cervicothoracic inlet obstruction seen in patients with a substernal goiter

Question 57

What is the Chvostek sign?

Answer 57

The Chyostek sign is seen in cases of hypocalcemia and is
positive when tapping a finger on a patient’s cheek over the
course of the facial nerve results in contraction of the
ipsilateral facial muscles.

Question 58

What is the Trousseau sign?

Answer 58

The Trousseau sign is seen in cases of hypocalcemia, where
inflation of a blood pressure cuff above systolic blood
pressure for 3 minutes results in ipsilateral spasm of the
wrist and hand muscles.

Question 59

What are the main complications of thyroid surgery?

Answer 59

Major complications include hematoma, infection, superior

laryngeal nerve injury (most common nerve injured), recurrent laryngeal nerve injury, and hypocalcemia.

Question 60

Name the four main types of thyroid surgeries, and define each one.

Answer 60

● Thyroid lobectomy: Removal of a single lobe with or
without the isthmus
● Subtotal thyroidectomy: Incomplete removal of thyroid
tissue, leaving more than 1 g of thyroid remaining
● Near-total thyroidectomy: Incomplete removal of thyroid
tissue, leaving behind a small amount of tissue adjacent
to the recurrent laryngeal nerve
● Total thyroidectomy: Removal of all grossly visible thyroid
tissue

Question 61

Name some disease-specific risk factors for permanent recurrent laryngeal nerve injury during thyroidectomy.

Answer 61

Recurrent thyroid carcinoma, substernal goiter, and thyroiditis

Question 62

At what point in the thyroid dissection must one be aware of the superior laryngeal nerve?

Answer 62

The external branch of the superior laryngeal nerve, which
supplies the cricothyroid muscle, lies near the superior pole vessels. Special care should be undertaken during division of the superior pole to protect the superior laryngeal nerve.