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Appendix > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Original attachment of thyroid in oral cavity is where?

A

foramen cecum

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2
Q

Foramen cecum becomes what?

A

thyroglossal duct

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3
Q

C-cells of thyroid make what hormone?

A

calcitonin

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4
Q

Thyroid gland is endodermal in origin, what part of thyroid gland not endodermal?

A

C-cells

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5
Q

Thyroid tissue found in neck lateral to jugular vein is considered what?

A

thyroid Ca– typically papillary

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6
Q

Two pyramidal lobes are joined together at the ?

A

isthmus

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7
Q

What % of pts have a pyramidal lobe?

A

30% -50%

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8
Q

This suspensory ligament is main point of fixation of thyroid posteriorly and laterally;

A

ligament of Berry

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9
Q

Surgical importance of ligament of Berry?

A

close association with recurrent laryngeal nerve

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10
Q

Course of recurrent laryngeal nerves?

A

ascend on either side of the trachea

lie lateral to ligament of Berry as they ascend the larynx

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11
Q

On the right side, the recurrent laryngeal nerve crosses under what artery?

A

right subclavian

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12
Q

During neck dissection, how can we find the right recurrent laryngeal nerve>

A

1cm lateral to or within the tracheo-esophageal groove

usually at level of lower thyroid border

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13
Q

Most commonly encountered congenital cervical anaomaly?

A

thyroglossal duct cysts

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14
Q

What causes thyrglossal duct cysts?

A

by 5th week of gestation thyroglossal duct starts to obliterate, completed by 8th week

rarely it can persist in whole or in part

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15
Q

80% of thyroglossal duct cysts are found where?

A

next to hyoid bone

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16
Q

How do we diagnose thyroglossal duct cysts?

A

smooth midline neck mass that moves with swallowing

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17
Q

Tx for thyroglossal duct cyst?

A

Sistrunk procedure; en bloc cystectomy and excision of the central hyoid bone to minimize recurrence

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18
Q

What % of thyroglossal duct cysts are found to contain cancern?

A

1%

usually papillary

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19
Q

What cancer do we never find in thyroglossal duct cysts?

A

medullary

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20
Q

What’s a lingual thyroid?

A

failure of thyroid tissue to descend during development

can be the only thyroid tissue present in the body

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21
Q

When do we perform interventions for lingual thyroid?

A

when there is concern for choking, dysphagia, airway compromise, hemorrhage

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22
Q

Before treating someone for lingual thyroid, what needs to be done first?

A

need evaluate for normal thyroid tissue in the neck or else the pt can become hypothyroid once lingual thyroid removed

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23
Q

Medical tx for lingual thyroid?

A

exogenous thyroid hormone administration to suppress TSH

administration of radio-active iodine followed by hormone replacement

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24
Q

What is ectopic thyroid?

A

normal thyroid tissue can be found anywhere along the central neck region

includes esophagus, trachea, anterior mediastinum

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25
Q

If we see thyroid tissue lateral to the carotid sheath and jugular vein, previously termed lateral aberrant thyroid tissue, we should be concerned about what?

A

usually its metastatic thyroid cancer (papillary mostly)

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26
Q

Normal thyroid gland weighs how much?

A

20g

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27
Q

What % of pt’s have a pyramidal lobe?

A

30-50%

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28
Q

The thyroid capsule is condensed into the posterior suspensory ligament called:

A

Berry’s

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29
Q

Superior thyroid arteries arise from?

A

ipsilateral external carotid A

superior thyroid A divides into anterior and posterior branches at thyroid apex

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30
Q

Inferior thyroid arteries arise from what?

A

thyrocervical trunks from ipsilateral subclavian arteries

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31
Q

Superior and inferior thyroid arteries originate from where?

A

STA–> external carotid A

ITA–> thyrocervical trunk from subclavian A

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32
Q

Whats the thyroid IMA artery?

A

seen in 1-4 % of pts

arises directly from aorta or innominate and enters isthmus (sometimes replacing an inferior thyroid artery)

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33
Q

When dissecting the inferior thyroid artery and before ligating the inferior thyroid artery, what needs to happen?

A

need to identify the recurrent laryngeal nerve

ITA crosses the recurrent laryngeal nerve

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34
Q

Venous drainage of the thyroid?

A

superior V–> internal jugular
middle V–> internal jugular

inferior V–> form a plexus–> drain into brachiocephalic veins

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35
Q

Describe the course of the left recurrent laryngeal nerve:

A

arises from vagus

crosses aortic arch

loops around ligamentum arteriosum

ascends medially in neck along tracheo-esophageal groove

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36
Q

Describe the course of the right recurrent laryngeal nerve;

A

arises from right vagus

crosses under right subclavian artery

enter larynx posterior to cricothyroid m.

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37
Q

What m. do the recurrent laryngeal nerves innervate?

A

all intrinsic m. of larynx

except cricothyroid m

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38
Q

What nerve innervates the circothyroid m.?

A

external laryngeal nerve

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39
Q

What happens when we have injury to one recurrent laryngeal nerve?

A

ipsilateral vocal cord paralysis

cord stuck in paramedia/abducted position

**pts have hoarse voice, ineffective cough

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40
Q

B/l recurrent laryngeal nerve injury causes what?

A

airway obstruction necessitating trach

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41
Q

The superior laryngeal nerve branches off into what?

A

internal

external

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42
Q

What does internal branch of superior laryngeal nerve innervate?

A

sensation to supraglottic larynx

injury to this nerve is rare, but injury can lead to aspiration

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43
Q

What does the external branch of superior laryngeal nerve innervate?

A

circothyroid m.

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44
Q

Injury to the external branch of superior laryngeal nerve causes what?

A

difficulty with pitch, can’t hit high notes

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45
Q

Most common anatomic variant of external branch of superior laryngeal nerve as it enters circothyroid m?

A

type 2A variant

nerve crosses over below tip of superior pole of thyroid

seen in 20% of pts

puts nerve at greatest risk of injury

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46
Q

Damage to a recurrent laryngeal nerve leads to?

A

ipsilateral vocal cord paralysis

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47
Q

When dissecting the superior thyroid artery, care must be taken not to damage what nerve?

A

external branch of superior laryngeal nerve

48
Q

Describe path of inferior thyroid artery?

A

comes off of thyrocervical trunk from subclavian A

enters thyroid posteriorly near ligament of Berry

49
Q

Thyroid IMA artery comes off brachiocephalic or aorta, and seen in what % of pts?

A

5-10 %

50
Q

When dissecting the inferior thyroid artery, care must be taken not to damage what nerve?

A

recurrent laryngeal

51
Q

Inferior thyroid A supplies which parathyroids?

A

inferior + superior

52
Q

Most thyroid cancers drain into what lymph node region?

A

central lymph nodes (VI)

53
Q

How do we locate the parathyroids?

A

follow branches of inferior thyroid A into the parathyroids

54
Q

Blood supply of the parathyroids?

A

inferior thyroid artery

if inferior thyroid artery is sacrificed on that side of the gland, parathyroids have no collaterals

55
Q

What hormones does thyroid make?

A

T4; thyroxine

T3; tri-iodo-thyronine

Calcitonin

56
Q

Describe iodine metabolism:

A

we get iodine from fish, eggs, salt,

converted to iodide in stomach/jejunum

absorbed in bloodstream

iodide then actively transported into thyroid follicles

57
Q

Which is more potent, T3 vs T4?

A

T3 is more potent

T3 plasma circulating levels less than T4

T3 is less bound to plasma proteins, enters tissues more rapidly

58
Q

Half lives of T3 and t4?

A

T3 is 1 day

T4 is 7 days

59
Q

What controls thyroid secretion?

A

hypothalamic-pituitary-thyroid axis

hypothalamus release TRH–> stimulates pituitary to make TSH

TSH then mediates iodide trapping, release of thyroid hormones

TRH and TSH can be negatively fed back by T3 and T4

60
Q

What enzyme is important in thyroid hormone synthesis ?

A

thyroid peroxidase

helps form MIT, DIT

61
Q

Most thyroid hormone released from thyroid gland is in the form of?

A

T4

T4 gets de-iodinated in peripheral tissues to T3

62
Q

What hormone facilitates conversion of MIT and DIT into T3 and T3?

A

thyroglobulin

63
Q

Which cells make calcitonin?

A

parafollicular C-cells

64
Q

Where do we find parafollicular C-cells which make calcitonin?

A

supero-laterally in each thyroid

65
Q

What does calcitonin do?

A

inhibits calcium absorption by osteoclasts

66
Q

What hormones stimulate thyroid hormone production?

A

epinephrine

HcG

67
Q

What hormones inhibit thyroid hormone production?

A

steroids

68
Q

What do thyroid hormones do?

A

vital in brain development and skeletal maturity

increase O2 consumption, basal metabolic rate, heat production

+ inotropic/chronotropic effects

affect GI motility

increase bone and protein turnover

69
Q

Which thyroid hormone responsible for negative feedback loop on TSH in pituitary and TRH in hypothalamus?

A

T3

70
Q

Specific actions of calcitonin take effect on surface of what cells?

A

osteoclasts

71
Q

Two anti-thyroid drugs?

A

PTU (propylthiouracil)

methimazole

72
Q

MOA of PTU and methimazole?

A

inhibit organification and oxidation of inorganic iodine

inhibit linking of MIT and DIT

**PTU inhibits peripheral conversion of T4 to T3

73
Q

WHich anti-thyroid drug can we use in pregnant pts?

A

PTU

74
Q

Which anti-thyroid drug preferred in non-pregnant pts?

A

methimazole

75
Q

Major, but rare, side effect of PTU and methimazole?

A

agranulocytosis

76
Q

Side effects of PTU and methimazole?

A

agranulocytosis ( less than 1 %)

rash
arthralgias
liver dysfunction

77
Q

How do steroids affect thyroid hormones?

A

exogenous steroids suppress the pituitary-thyroid axis

prevent conversion of T4 –>T3 in periphery

**this allows steroids be used as inhibitory agent in hyperthyroid conditions

78
Q

What happens when we have iodine excess?

A

iodine transport and synthesis and secretion of thyroid hormones are inhibited

excessive large doses initially lead to increased organification followed by suppression ; Wolff-Chaikoff effect

79
Q

Wolf-Chaikoff effect?

A

high doses of iodine initially lead to increased organification followed by suppression of thyroid hormones

80
Q

Iodine when given in large doses, can inhibit thyroid hormone release by altering the organic binding process, what is this called?

A

Wolf-Chaikoff effect

81
Q

In terms of thyroid testing, what test is most sensitive and specific for diagnosis of hyper-hypo thyroid states?

A

TSH assay

82
Q

Why are T4 levels not reliable screening tests for thyroid dx?

A

T4 levels not only increased in pts with hyperthyroid states but also in pts w/;

elevated thyroglobulin levels such as; pregnancy, estrogen/progesterone use

decreased in anabolic steroid use; nephrotic syndrome

83
Q

Accurate evaluation of thyroid function involves measuring free T4 and T3, why?

A

total T4 and T3 assays measure free and protein bound hormone, which can be affected by changes in hormone production and hormone binding

84
Q

About 80% of pts with Hashimoto’s thyroiditis have elevated thyroid antibody levels, what antibodies?

A

anti-thyroglobulin
anti-microsomal
anti-TPO

85
Q

What use does thyroglobulin have in measuring levels?

A

helpful in monitoring pts with differentiated thyroid cancer for recurrence particularly after thyroidectomy and RAI

86
Q

What radio-active iodine isotopes do we use to image thyroid?

A

I- 123 (low dose radiation, used to evaluate lingual thyroids and goiters)

I-131 (higher dose radiation; used to evaluate pts with differentiated thyroid cancers for mets)

87
Q

What’s a cold vs hot thyroid nodule?

A

cold nodule–> trap less radioactivity than the surrounding gland

hot nodule–> areas that demonstrate increased activity compared to surrounding gland tissue

88
Q

The risk of thyroid malignancy is highest with cold vs hot nodules?

A

cold nodules have a higher risk; 20%

hot nodules have less risk; <5%

89
Q

Deficiency of circulating levels of thyroid hormones lead to hypothyroidism, which is termed what in neonates?

A

cretinism

90
Q

Causes of hypothyroidism in developing vs developed countries?

A

developing; iodine deficiency

developed; Hashimoto’s thyroiditis, radioactive iodine therapy, or surgical removal

91
Q

What are some clinical features of hypothyroidism?

A

neonates; severe mental retardation, failure to thrive

adults; tiredness, weight gain, cold intolerance, constipation, menorrhagia, dry skin, brittle hair, loss of outer 2/3 of eyebrows, low libido, bradycardia

92
Q

Pts w/severe hypothyroidism tend to develop myxedema, facial puffyness, periorbital puffyness due to?

A

deposition of glycosaminoglycans

93
Q

What drugs can cause hypothyroidism sometimes?

A

too much PTU, methimazole

amiodarone

lithium

94
Q

In primary hypothyroidism, what lab values can we see?

A

low circulating levels of T3 and T4

elevated TSH levels

95
Q

Causes of secondary hypothyroidism?

A

pituitary tumor
pituitary resection or ablation

** we see decreased TSH levels

96
Q

Tx for hypothyroidism?

A

levothyroxine; T4

available PO, IM, IV

97
Q

Major cause of hypothyroidism is?

A

Hashimoto’s thyroiditis; auto-immune mediated destruction of thyrocytes

98
Q

What antibodies do we see in Hashimoto’s thyroiditis which causes primary hypothyroidism?

A

anti-thyroglobulin
anti-thyroperoxidase
anti-TSH-R

99
Q

This is an autoimmune process which is initiated by activation of CD4 cells with specificity for thyroid antigens;

A

Hashimoto’s thyroiditis

CD4 T cells recruit cytotoxic CD8 cells which destroy thyrocytes, in combination with auto-antibodies

100
Q

What do we see on microscopy of Hashimoto’s thyroiditis?

A

thyroid tissue infiltrated by small lymphocytes and plasma cells

101
Q

Hashimot’s is more common men or women?

A

women

102
Q

How does Hashimoto’s present clinically?

A

minimally enlarged firm granular gland discovered on routine PE

painless anterior neck mass

103
Q

How do we confirm diagnosis of Hashimoto’s?

A

elevated TSH levels + presence of thyroid Ab

104
Q

Serious complication of Hashimoto’s thyroiditis?

A

lymphoma

**has 80 x higher prevalence than in general population

105
Q

Tx for Hashimoto’s?

A

thyroid hormone replacement therapy

surgery if suspicious for malignancy or goiters that cause compressive sxs

106
Q

What is Riedel’s thyroiditis?

A

rare entity

replacement of all part of thyroid by fibrous tissue

tissue also invades nearby structures, trachea, esophagu

107
Q

How does Riedel’s thyroidits present?

A

seen in women 30-60
painless, hard, anterior neck mass

see symptoms of compression; dysphagia, choking, hoarseness

pts have sx of hypothyroidism as gland is replaced by fibrous tissue

you feel a hard and ‘woody’ thyroid

108
Q

Hard ‘woody’ thyroid on exam, makes you think of?

A

Riedel’s thyroiditis

109
Q

How do we diagnose Riedel’s thyroiditis?

A

open biopsy

the firm and fibrous nature of the gland makes FNAB difficult

110
Q

Mainstay of tx for Riedel’s thyroiditis?

A

surgery; decompress the trachea by wedge resection of thyroid isthmus

hypothyroid pts; tx w/thyroid replacement

some pts benefit from steroids and tamoxifen

111
Q

Microscopically what does RIedel’s thyroiditis look like?

A

dense fibrous tissue

almost total obliteration of normal follicular structure

112
Q

What is acute suppurative thyroiditis?

A

thyroid gland is usually resistant to infection due to rich blood supply, lymphatics, fibrous capsule

infectious agents can still seed it via hematogenous/lymphatic spread

113
Q

MOst common bacteria causing acute suppurative thyroiditis?

A

streptococcus species + anaerobes make up 70%

**more common kids, preceded by URI/OM

114
Q

Tx for acute suppurative thyroiditis?

A

antibiotics

drainage of any abscesses

115
Q

Causes of subacute thyroiditis?

A

autoimmune vs post-viral in origin

affects women 2;1

116
Q

Tx for subacute thyroiditis?

A

usually NSAIDs + steroids effective

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