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ABSITE > Fiser Chapter 22 THYROID > Flashcards

Fiser Chapter 22 THYROID Flashcards

1
Q

Thyroid embryology

A

1st and 2nd pharyngeal ARCHES

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2
Q

Thyrotropin releasing factor (TRF)

A

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

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3
Q

Thyroid blood supply

A
  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
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4
Q

Thyroid veins

A
  1. Superior thyroid vein -> IJ vein
  2. Middle thyroid vein -> IJ vein
  3. Inferior thyroid vein -> innominate vein
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5
Q

Nerves around thyroid

A
  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
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6
Q

Ligament of Berry

A

Posterior medial suspensory ligament close to RLNs; need careful dissection

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7
Q

Thyroglobulin

A

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

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8
Q

Most sensitive indicator of thyroid function

A

TSH

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9
Q

Thyroxine-binding globulin

A

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

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10
Q

Tubercles of Zuckerkandl

A

Most lateral, posterior extension of thyroid tissue

  • Left behind with subtotal thyroidectomy because of proximity to RLNs
  • Rotate medially to find RLNs
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11
Q

Calcitonin comes from what cells

A

Parafollicular C cells of thyroid

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12
Q

Thyroxine treatment

A

TSH levels should fall 50%

Osteoporosis is a long-term side effect

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13
Q

Post-thyroidectomy stridor

A

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

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14
Q

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

A

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
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15
Q

Tx of thyroid storm

A

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

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16
Q

Wolff-Chaikoff effect

A

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
Q

Asymptomatic thyroid nodule: risk of malignancy

A

90% are benign

18
Q

Asymptomatic thyroid nodule: management

A
  1. FNA (best initial test) and TFTs
19
Q

Indeterminant thyroid FNA for asymptomatic thyroid nodule: next step?

A

-Radionuclide study

20
Q

Hot versus cold nodule management

A

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

Cold nodule -> Lobectomy (more likely malignant)

21
Q

Follicular cells on thyroid FNA, tx

A

Lobectomy (10% cancer risk)

22
Q

Cyst fluid on thyroid FNA

A

Drain fluid

Lobectomy if bloody or recurs

23
Q

Colloid tissue on thyroid FNA, tx

A

Thyroxine (colloid goiter, low chance of malignancy)

Lobectomy if enlarges

24
Q

Normal thyroid tissue on FNA but TFTs elevated

A

Monitor if asymptomatic; PTU and 131-I if symptomatic

Likely solitary toxic nodule

25
Q

Abnormal thyroid enlargement, dx and tx

A

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
Q

Abnormal thyroid enlargement, dx and tx

A

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
Q

Substernal goiter

A

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

Primary substernal goiter rare (vessels originate from innominate artery)

?

28
Q

Mediastinal thyroid tissue

A

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

29
Q

Abnormalities of thyroid descent

A
  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
Q

Lingual thyroid presentation and tx

A

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
Q

Thyroglossal duct cyst presentation and tx

A
  • 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
Q

Hyperthyroidism treatment

A

PTU (propylthiouracil)

Methimazole

Radioactive iodine (131-I)

Thyroidectomy

33
Q

PTU (propylthiouracil)

A

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
Q

Methimazole

A

Inhibits peroxidases and prevents iodine-tyrosine coupling

Good for youn

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