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Flashcards in Fiser Chapter 22 THYROID Deck (34):
1

Thyroid embryology

1st and 2nd pharyngeal ARCHES

2

Thyrotropin releasing factor (TRF)

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

3

Thyroid blood supply

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

4

Thyroid veins

1. Superior thyroid vein -> IJ vein

2. Middle thyroid vein -> IJ vein

3. Inferior thyroid vein -> innominate vein

5

Nerves around thyroid

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

6

Ligament of Berry

Posterior medial suspensory ligament close to RLNs; need careful dissection

7

Thyroglobulin

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

8

Most sensitive indicator of thyroid function

TSH

9

Thyroxine-binding globulin

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

10

Tubercles of Zuckerkandl

Most lateral, posterior extension of thyroid tissue

-Left behind with subtotal thyroidectomy because of proximity to RLNs

-Rotate medially to find RLNs

11

Calcitonin comes from what cells

Parafollicular C cells of thyroid

12

Thyroxine treatment

TSH levels should fall 50%

Osteoporosis is a long-term side effect

13

Post-thyroidectomy stridor

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

14

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

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

15

Tx of thyroid storm

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

16

Wolff-Chaikoff effect

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

17

Asymptomatic thyroid nodule: risk of malignancy

90% are benign

18

Asymptomatic thyroid nodule: management

1. FNA (best initial test) and TFTs

19

Indeterminant thyroid FNA for asymptomatic thyroid nodule: next step?

-Radionuclide study

20

Hot versus cold nodule management

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

Cold nodule -> Lobectomy (more likely malignant)

21

Follicular cells on thyroid FNA, tx

Lobectomy (10% cancer risk)

22

Cyst fluid on thyroid FNA

Drain fluid

Lobectomy if bloody or recurs

23

Colloid tissue on thyroid FNA, tx

Thyroxine (colloid goiter, low chance of malignancy)

Lobectomy if enlarges

24

Normal thyroid tissue on FNA but TFTs elevated

Monitor if asymptomatic; PTU and 131-I if symptomatic

Likely solitary toxic nodule

25

Abnormal thyroid enlargement, dx and tx

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)

26

Abnormal thyroid enlargement, dx and tx

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)

27

Substernal goiter

Usually secondary (vessels originate from superior and inferior thyroid artery)

Primary substernal goiter rare (vessels originate from innominate artery)

?

28

Mediastinal thyroid tissue

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

29

Abnormalities of thyroid descent

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

30

Lingual thyroid presentation and tx

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

31

Thyroglossal duct cyst presentation and tx

-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)

32

Hyperthyroidism treatment

PTU (propylthiouracil)

Methimazole

Radioactive iodine (131-I)

Thyroidectomy

33

PTU (propylthiouracil)

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

34

Methimazole

Inhibits peroxidases and prevents iodine-tyrosine coupling

Good for youn