Fiser Chapter 22 THYROID

Question 1

Thyroid embryology

Answer 1

1st and 2nd pharyngeal ARCHES

Question 2

Thyrotropin releasing factor (TRF)

Answer 2

Hypothalamus releases TRF -> acts on anterior pituitary -> TSH release -> acts on thyroid to release T3 and T4 (via increased cAMP)

T3 and T4 control TRF and TSH release by negative feedback loop

Question 3

Thyroid blood supply

Answer 3

1. Superior thyroid artery (1st branch off external carotid)
2. Inferior thyroid artery (off thyrocervical trunk): supplies all parathyroids; so ligate close to thyroid to avoid injury to parathyroids
3. Ima artery: occurs in 1%, arises from innominate or aorta and goes to isthmus

Question 4

Thyroid veins

Answer 4

1. Superior thyroid vein -> IJ vein
2. Middle thyroid vein -> IJ vein
3. Inferior thyroid vein -> innominate vein

Question 5

Nerves around thyroid

Answer 5

1. Superior laryngeal nerve: motor to cricothyroid, runs lateral to thyroid lobes, tracks close to superior thyroid artery (but variable); injury causes loss of projection and voice fatiguability
2. Recurrent laryngeal nerve: motor to all larynx (except cricothyroid m), runs posterior to thyroid lobes in T-E groove, can track with inferior thyroid artery (but variable), L RLN loops around aorta, R RLN loops are innominate artery; injury causes hoarseness; bilateral injury can obstruct airway (need emergency tracheostomy); 2% has a Non-recurrent laryngeal nerve (more common on R); risk of injury is higher for non-recurrent laryngeal nerve during thyroid surgery

Question 6

Ligament of Berry

Answer 6

Posterior medial suspensory ligament close to RLNs; need careful dissection

Question 7

Thyroglobulin

Answer 7

Stores T3 and T4 in colloid

Plasma T4:T3 ratio is 15:1

T3 is more active form (tyrosine + iodine linked together by peroxidases; separated by deiodinases?)

Most T3 is produced in periphery from conversion of T4 to T3 via deiodinases

Question 8

Most sensitive indicator of thyroid function

Answer 8

TSH

Question 9

Thyroxine-binding globulin

Answer 9

Thyroid hormone transport: binds majority of T3 and T4 in circulation

Question 10

Tubercles of Zuckerkandl

Answer 10

Most lateral, posterior extension of thyroid tissue

• Left behind with subtotal thyroidectomy because of proximity to RLNs
• Rotate medially to find RLNs

Question 11

Calcitonin comes from what cells

Answer 11

Parafollicular C cells of thyroid

Question 12

Thyroxine treatment

Answer 12

TSH levels should fall 50%

Osteoporosis is a long-term side effect

Question 13

Post-thyroidectomy stridor

Answer 13

Open neck and remove hematoma emergently -> can result in airway compromise; can also be due to bilateral RLN injury -> would need emergent tracheostomy

Question 14

Tachycardia, fever, numbness, irritability, vomiting, diarrhea, high-output cardiac failure

Answer 14

Thyroid storm (MCC of death is high-output cardiac failure)

• Most common after surgery in patient with undiagnosed Grave’s disease
• Can be precipitated by anxiety, excessive gland palpation, adrenergic stimulants

Question 15

Tx of thyroid storm

Answer 15

Tx: Beta-blockers (first line), PTU, Lugol’s solution (potassium iodide -> Wolff-Chaikoff effect), cooling blankets, oxygen, glucose. Emergent thyroidectomy rarely indicated.

Question 16

Wolff-Chaikoff effect

Answer 16

Give patient high dose of iodine (Lugol’s solution, potassium iodide), which inhibits TSH action on thyroid and inhibits organic coupling of iodide, resulting in less T3 and T4 release

Question 17

Asymptomatic thyroid nodule: risk of malignancy

Answer 17

90% are benign

Question 18

Asymptomatic thyroid nodule: management

Answer 18

1. FNA (best initial test) and TFTs

Question 19

Indeterminant thyroid FNA for asymptomatic thyroid nodule: next step?

Answer 19

-Radionuclide study

Question 20

Hot versus cold nodule management

Answer 20

Hot nodule -> monitor if asymptomatic (if symptomatic, PTU and 131-I)

Cold nodule -> Lobectomy (more likely malignant)

Question 21

Follicular cells on thyroid FNA, tx

Answer 21

Lobectomy (10% cancer risk)

Question 22

Cyst fluid on thyroid FNA

Answer 22

Drain fluid

Lobectomy if bloody or recurs

Question 23

Colloid tissue on thyroid FNA, tx

Answer 23

Thyroxine (colloid goiter, low chance of malignancy)

Lobectomy if enlarges

Question 24

Normal thyroid tissue on FNA but TFTs elevated

Answer 24

Monitor if asymptomatic; PTU and 131-I if symptomatic

Likely solitary toxic nodule

Question 25

Abnormal thyroid enlargement, dx and tx

Answer 25

Goiter: most identifiable cause iodine deficiency Tx: Iodine replacement If diffuse enlargement but no functional abnormality = nontoxic colloid goiter -Unusual to require surgery unless causing airway compression or suspicious nodule -> subtotal or total thyroidectomy (subtotal has reduced risk of RLN injury)

Question 26

Abnormal thyroid enlargement, dx and tx

Answer 26

Goiter: most identifiable cause iodine deficiency Tx: Iodine replacement If diffuse enlargement but no functional abnormality = nontoxic colloid goiter -Unusual to require surgery unless causing airway compression or suspicious nodule -> subtotal or total thyroidectomy (subtotal has reduced risk of RLN injury)

Question 27

Substernal goiter

Answer 27

Usually secondary (vessels originate from superior and inferior thyroid artery) Primary substernal goiter rare (vessels originate from innominate artery) ?

Question 28

Mediastinal thyroid tissue

Answer 28

Most likely from acquired disease with inferior extensions of normally placed gland (eg substernal goiter)

Question 29

Abnormalities of thyroid descent

Answer 29

1. Pyramidal lobe: extends from isthmus toward thymus 2. Lingual thyroid: thyroid tissue persisting in foramen cecum at base of tongue 3. Thyroglossal duct cyst

Question 30

Lingual thyroid presentation and tx

Answer 30

Dysphagia, dyspnea, dysphonia 2% malignancy risk Tx: - Thyroxine suppression - Abolish with 131-I - Resect if worried about CA or does not shrink after medical therapy - is the only thyroid tissue in 70% who have it

Question 31

Thyroglossal duct cyst presentation and tx

Answer 31

- Moves upward with swallowing - Susceptible to infection and may be premalignant Tx: Sistrunk procedure (resect cyst and take midportion or all of hyoid bone along with it)

Question 32

Hyperthyroidism treatment

Answer 32

PTU (propylthiouracil) Methimazole Radioactive iodine (131-I) Thyroidectomy

Question 33

PTU (propylthiouracil)

Answer 33

Inhibits peroxidases and prevents iodine-tyrosine coupling Safe for PREGNANCY, good for young patients, small goiters, mild T3 and T4 elevation Side effects: aplastic anemia, agranulocytosis

Question 34

Methimazole

Answer 34

Inhibits peroxidases and prevents iodine-tyrosine coupling Good for youn