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Head and Neck > Thyroid and Parathyroid Glands > Flashcards

Thyroid and Parathyroid Glands Flashcards

1
Q

First embryological stage of thyroid development

A

Epithelial proliferation at the site of the foramen caecum at the base of the tongue in week 4

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2
Q

When does the thyroid gland reach its final position during development

A

24 weeks

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3
Q

How is the thyroid connected to the tongue during development

A

Thyroglossal duct

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4
Q

What is the fate of the thyroglossal duct

A

Initially solidifies before finally disappearing

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5
Q

Describe the origin and location of thyroglossal cysts

A
  • Cystic remnants of the thyroglossal duct

- Can be found along its path of descent

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6
Q

List the potential sites of accessory thyroid tissue

A
  • Tongue
  • Near hyoid bone
  • Deep to SCM
  • Superior mediastinum
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7
Q

Describe the principles of thyroglossal cyst removal

A

Removal of the cyst, track, and origin is mandatory (as the track can loop behind the hyoid, the central portion of the hyoid is usually excised with the tract)

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8
Q

When do thyroglossal fistulae arise

A

When a thyroglossal cyst is incised and drained in the mistaken belief that it is a simple abscess

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9
Q

What hormones are produced by the thyroid gland

A
  • Thyroxine (T4)
  • Triiodothyronine (T3)
  • Calcitonin
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10
Q

Where is calcitonin secreted from

A

Parafollicular C cells of the thyroid

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11
Q

Which thyroid cancer produces calcitonin

A

Medullary thyroid cancer (cancer of the parafollicular C cells)

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12
Q

Which of T3 and T4 is faster acting and why

A

T3 - as T4 has greater affinity for binding proteins

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13
Q

T3 half life

A

1 day

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14
Q

TSH half life

A

5 minutes

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15
Q

List the 8 stages of thyroid hormone synthesis

A
  1. Trapping
  2. Oxidation
  3. Secretion into Colloid
  4. Binding
  5. Pinocytosis
  6. Proteolysis
  7. Secretion into plasma
  8. Transport
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16
Q

What catalyses the conversion of iodide to iodine

A

Thyroid peroxidase

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17
Q

When is TBG raised

A
  • Pregnancy

- Oestrogen therapy

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18
Q

When is TBG reduced

A
  • Liver disease
  • Nephritis syndrome
  • SLE
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19
Q

What is the clinical use of thyroglobulin

A

Monitoring of follicular and papillary thyroid cancers

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20
Q

Describe the 3 components of the thyroid gland

A
  1. Isthmus (overlying 2nd and 3rd tracheal rings)
  2. Lateral lobes (extend to 6th tracheal ring)
  3. Inconstant pyramidal lobe extending up from the isthmus
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21
Q

What connects the thyroid to the cricoid cartilage and trachea

A

Berry’s ligament

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22
Q

Anterior relations of the thyroid

A
  • Strap muscles
  • SCM
  • Enclosed in pretracheal fascia
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23
Q

Posterior relations of the thyroid

A
  • Larynx
  • Trachea
  • Pharynx
  • Oesophagus
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24
Q

Lateral relations of the thyroid

A

Carotid sheath

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25
Q

Outline the arterial supply of the thyroid gland

A
  • Superior thyroid artery from ECA passes to upper pole (closely related to external branch of superior laryngeal nerve)
  • Inferior thyroid artery from thyrocervical trunk is related to the recurrent laryngeal nerve close to the gland
  • Thyroidea ima (inconstant)
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26
Q

Outline the venous drainage of the thyroid gland

A
  • Superior thyroid vein drains upper pole to IJV
  • Middle thyroid vein drains to IJV
  • Inferior thyroid vein drains lower pole to brachiocephalic vein
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27
Q

Thyroidectomy incision

A

Transverse incision two finger’s width above the sternal notch

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28
Q

Structures encountered when approaching the thyroid gland via transverse incision

A
  1. Platysma
  2. Investing fascia
  3. Strap muscles (divided in upper half)
  4. Pretracheal fascia
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29
Q

Where should the superior thyroid artery be divided when performing thyroidectomy and why

A

Close to the gland to avoid damage to the superior laryngeal nerve

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30
Q

Where should the inferior thyroid artery be divided when performing thyroidectomy and why

A

Far from the gland to avoid damage to the recurrent laryngeal nerve

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31
Q

Describe a diffuse non-toxic goitre

A

Diffuse enlargement involving the whole gland without producing nodularity and is not associated with hypo- or hyperthyroidism

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32
Q

Causes of non-toxic simple goitre

A
  1. Physiological due to increased demand for thyroid hormones e.g. pregnancy
  2. Dietary iodine deficiency
  3. Treated Grave’s
  4. Lymphoma
  5. Anaplastic carcinoma
  6. Autoimmune thyroiditis
  7. De Quervain’s thyroiditis
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33
Q

Treatment of non-toxic simple goitre

A
  • Small = conservative

- Large = hemi- or total thyroidectomy

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34
Q

Pathophysiology of non-toxic simple goitre

A

Hypertrophy AND hyperplasia secondary to a relative reduction in output of T3 and T4. Causes rise in TSH which causes gland enlargement.

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35
Q

What is Plummer’s disease

A

Autonomous hyperfunctioning (hyperthyroid) nodule in a multinodular goitre

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36
Q

Treatment of multinodular goitre

A
  1. Medical - aim to suppress TSH to zero with thyroxine

2. Surgical - hemi- or total thyroidectomy

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37
Q

Indications for multinodular goitre surgery

A
  • Local symptoms e.g. dysphagia
  • Enlarging dominant nodule
  • RLN palsy
  • Cosmesis
  • Hyperthyroidism
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38
Q

Cause of true solitary nodules

A
  • 80% are adenomas
  • 10% are cancer (papillary)
  • 10% are cysts, fibrosis or thyroiditis
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39
Q

GOLD standard investigation of thyroid nodules

A

FNAC

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40
Q

Action to be taken for FNAC Thy 3

A
  • Follicular lesion (35% risk of malignancy)
  • Diagnostic lobectomy should be performed
  • If cancerous then thyroidectomy with level 6 dissection
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41
Q

Action to be taken for FNAC Thy 4

A
  • Suspicious for papillary malignancy

- Thyroidectomy with level 6 dissection

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42
Q

What does a total lobectomy involve

A

Removal of a single lobe and the isthmus

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43
Q

Most common type of thyroid cancer

A

Papillary - 70%

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44
Q

Most common site of spread in papillary thyroid cancer

A

Lymphatic spread to cervical nodes

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45
Q

Histological features of papillary thyroid cancer

A
  • No capsule
  • May be multifocal
  • ‘Orphan Annie’ nuclei
  • Psammoma calcification is diagnostic
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46
Q

What are Psammoma bodies

A

Clusters of calcification, diagnostic of papillary thyroid cancer

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47
Q

Treatment of papillary thyroid cancers >1cm (controversial as most treated as if >1cm)

A
  1. Total thyroidectomy with neck dissection
  2. Radioiodine ablation
  3. Lifelong TSH suppression with T4
  4. Annual thyroglobulin
  5. Lifelong follow-up
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48
Q

How are papillary thyroid metastases detected

A

Whole body scintography with iodine-131

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49
Q

Most common site of spread of Follicular thyroid cancer

A
  • Bone

- Lungs

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50
Q

Histological features of Follicular thyroid cancer

A
  • Capsulated (but if breached = carcinoma)

- Cannot be distinguished as malignant on FNAC alone

51
Q

How is a diagnosis of follicular thyroid cancer made

A
  1. Cannot be diagnosed solely on FNAC
  2. Thyroid lobectomy
  3. If capsular transgression or vascular invasion then the other lobe is removed also
52
Q

Sole histological difference between follicular carcinoma and adenoma

A

Capsule is breached in carcinoma

53
Q

Describe medullary thyroid carcinomas

A

Tumour of calcitonin-secreting parafollicular C-cells

54
Q

Biochemical marker for medullary thyroid cancer

A

Calcitonin

55
Q

Treatment of medullary thyroid cancer

A
  • Total thyroidectomy and neck dissection
  • T4 given but doesnt need to suppress TSH
  • Monitor calcitonin (rising indicates mets)
56
Q

Genetic associations of medullary thyroid cancer

A
  • 20% genetic

- MEN 2A

57
Q

Most likely cause of advanced thyroid cancer

A

Anaplastic carcinoma

58
Q

Age distribution of anaplastic thyroid cancer

A
  • Older patients

- 60-70

59
Q

Treatment of anaplastic thyroid cancer

A
  • Debulking surgery
  • Palliative external-beam radiotherapy
  • 90% die within 1 year
60
Q

What must be excluded when suspecting anaplastic thyroid cancer

A

Lymphoma - can be treated!

61
Q

Associations of thyroid lymphoma

A

Hashimoto’s thyroiditis

62
Q

Treatment of thyroid lymphoma

A
  • Chemotherapy
  • Occasionally radiotherapy
  • Surgery if localised or persistent disease
63
Q

Investigations for thyroid lymphoma

A
  1. Core or open biopsy

2. Staging CT

64
Q

Describe routine neck dissection in thyroid malignancy

A
  • Thyroid glands drain to lymph nodes in level 6 in the middle of the neck
  • Region extends from hyoid to suprasternal notch and laterally to IJV and RLN
  • SCM and IJV preserved
65
Q

Which thyroid cancer patients may receive radioactive iodine

A
  • Papillary cancers >1cm and/or node positive

- Follicular cancers

66
Q

What is performed to make radioactive iodine treatment more effective

A

Patients are rendered hypothyroid prior to treatment to increase iodine uptake

67
Q

Describe thyroid adenomas

A
  • Benign lesion (mostly follicular adenomas)
  • Discrete lesion with glandular or acinar pattern
  • Encapsulated
  • Can cause hyperthyroidism
68
Q

How are thyroid adenomas diagnosed

A

Thyroid lobectomy (cannot be differentiated from follicular carcinoma on FNAC)

69
Q

Cause of acute thyroiditis

A

Bacterial - usually streptococci

70
Q

Features of acute thyroiditis

A
  • Pain, tenderness and erythema over the thyroid
  • Fever
  • Raised ESR and WBC count
  • TFT normal
  • FNA for MC&S
71
Q

Treatment of acute thyroiditis

A

Antibiotics and analgesia (occasionally steroids)

72
Q

Describe subacute (De Quervain) thyroiditis

A
  • Granulomatous thyroiditis

- Caused by viral infection

73
Q

Cause of De Quervain thyroiditis

A

Viral:

  • Mumps
  • EBV
  • Measles
74
Q

Clinical features of De Quervain thyroiditis

A
  • Painful goitre
  • Period of hyperthyroid followed by hypothyroid then euthyroid
  • ESR and WBC count raised
75
Q

Treatment of De Quervain Thyroiditis

A
  • Aspirin
  • Prednisolone
  • 6-8 weeks
76
Q

Antibodies detected in Hashimoto’s thyroiditis

A
  • TPO antibodies

- Thyroglobulin antibodies

77
Q

Cause of Hashimoto’s thyroiditis

A
  • Defect in T-cell function
  • Allows T-helper cells to be sensitised to thyroid antigens
  • B-cells are stimulated to produce anti-thyroid antibodies
78
Q

Describe Riedel’s thyroiditis

A
  • Idiopathic fibrosing condition
  • 30-40% end up hypothyroid
  • Palliative treatment
79
Q

MOA and type of Radio-iodine used in the treatment of Grave’s disease

A
  • Iodine-131
  • Single oral dose
  • Causes direct damage to the replicative mechanism of the thyroid follicular cells
80
Q

Pre-operative requirements in thyroidectomy

A

All hyperthyroid patients should be rendered euthyroid:

  • Carbimazole and propylthiouracil
  • Beta-blockers
  • Iodine
81
Q

Symptoms of unilateral RLN palsy

A
  • Weak breathy voice

- Bovine cough

82
Q

Treatment of laryngeal oedema following thyroidectomy

A

48 hours of ventilation

83
Q

Describe tracheomalacia

A
  • Rare complication following removal of large goitre
  • Trachea collapses after loss of its support
  • Require tracheostomy
84
Q

Why is hypocalcaemic tetany a complication of thyroid surgery

A

Accidental removal of the parathyroid glands causes drastic reduction in PTH

85
Q

Symptoms of external laryngeal nerve injury

A

Weak voice when trying to sing or shout

86
Q

Consequence of external laryngeal nerve injury

A

Cricothyroid muscle paralysis

87
Q

Origin of the superior parathyroid glands

A

Dorsal endoderm of the 4th branchial pouch

88
Q

Origin of the inferior parathyroid glands

A

3rd branchial pouch (along with the thymus)

89
Q

Which parathyroid glands are more likely to migrate

A
  • Inferior

- Descend with thymus

90
Q

Ectopic positions of the parathyroid glands

A

Superior glands:

  • 90% constant
  • Behind oesophagus
  • Carotid sheath

Inferior glands:

  • Along inferior thyroid veins
  • In front of trachea
  • Superior mediastinum with thymus
91
Q

Parathyroid arterial supply

A

Inferior thyroid artery

92
Q

Venous drainage of parathyroids

A

Thyroid venous plexus which drains into brachiocephalic vein

93
Q

Histology of parathyroid cells

A
  • Mainly chief cells
  • Some oxyphil cells
  • Some water-clear cells
94
Q

Where is PTH released from

A

Chief cells of the parathyroid glands

95
Q

PTH half-life

A

2-5 minutes

96
Q

Where does PTH elicit its effect and how

A
  • Bone
  • Gut
  • Kidney

Via cell surface receptors, and increases cAMP production

97
Q

% of total body calcium that is free in the extracellular fluid

A

1%

98
Q

Most common presentation of parathyroid pathology

A

Hypercalcaemia

99
Q

Most common causes of primary hyperparathyroidism

A
  1. Single adenoma (85%)

2. Parathyroid hyperplasia (12%)

100
Q

Primary hyperparathyroidism biochemical presentation

A
  • Hypercalcaemia
  • Normal or high PTH
  • Hypophosphataemia
  • Hypochloraemia
  • Mild acidosis
  • Normal vitamin D level
101
Q

Describe the structure of parathyroid adenomas

A
  • Consist of chief cells
  • Monoclonal
  • Rim of compressed normal parathyroid tissue at the periphery
  • Capsule with loss of fat and stroma within the adenoma
102
Q

Pathophysiology of secondary hyperparathyroidism

A

Excessive PTH production by the parathyroid glands in response to low calcium (e.g. renal failure of malabsorption)

103
Q

Biochemical presentation of secondary hyperparathyroidism

A
  • Normal calcium
  • High phosphate
  • Very high PTH
104
Q

How is the incidence of secondary hyperparathyroidism prevented against in renal failure

A
  • Low phosphate diet

- Activated vitamin D

105
Q

Inheritance pattern of familial hypocalciuric hypercalcaemia

A

Autosomal dominant

106
Q

Symptoms of hypercalcaemic crisis

A
  • Drowsiness/confusion
  • LOC/coma
  • Dehydration
  • Weakness
  • Vomiting
  • Renal failure
107
Q

Treatment of primary hyperparathyroidism

A

Surgical intervention is the only cure (to prevent end-organ damage)

108
Q

When is bilateral exploration of the neck in hyperparathyroidism indicated to look for multiple adenomas

A
  • MEN1 or 2A
  • Known bilateral disease
  • If hyperplasia is seen in two glands on the same side of the neck
  • If no abnormality is found on unilateral exploration
109
Q

How is excised tissue confirmed to be parathyroid tissue

A

Immediate frozen section

110
Q

Post-op medication to be given in parathyroid surgery

A

1 alpha-calcidol supplements

111
Q

List the complications of parathyroidectomy

A
  • As for thyroid surgery
  • Damage to RLN less so than in thyroid surgery
  • Hypoparathyroidism and hypocalcaemia
  • Bleeding/haematoma
  • Inability to identify all four glands
112
Q

Indications for surgery in primary hyperparathyroidism

A
  • Elevated serum calcium >1mg/dl above normal
  • Hypercalciuria >400mg/day
  • Creatinine clearance <30% of normal
  • Episode of life-threatening hypercalcaemia
  • Nephrolithiasis
  • Age <50
  • Neuromuscular symptoms
  • Reduction in BMD >2.5 SD below peak bone mass
113
Q

Procedure for single parathyroid adenoma

A

Remove the affected gland and leave the 3 remaining glands

114
Q

Procedure for multiple parathyroid adenomas

A

Remove all affected glands

115
Q

Procedure for parathyroid hyperplasia

A
  • Excise 3.5 glands

- Mark the remaining gland or autotransplant into brachioradialis

116
Q

Procedure for parathyroid carcinoma

A

En-bloc dissection with thyroid lobectomy and lymph nodes

117
Q

Procedure for hyperparathyroidism in MEN

A
  • Total parathyroidectomy
  • Autotransplantation
  • Thymectomy and exploration of the carotid sheath
118
Q

List the causes of hypoparathyroidism

A
  • Iatrogenic
  • Autoimmune
  • Pseudohypoparathyroidism (decreased sensitivity to PTH)
  • Congenital e.g. DiGeorge syndrome
119
Q

Non-parathyroid-related causes of hypocalcaemia

A
  • Acute pancreatitis
  • Small bowel disease e.g. CD or large resection
  • Post-vagotomy
  • Massive blood transfusion
  • Renal failure
120
Q

List the features of MEN 1

A
  • Parathyroid hyperplasia
  • Pancreatic and duodenal endocrine tumours
  • Pituitary adenoma
  • Thyroid adenoma
  • Adrenal adenoma or carcinoma
  • Carcinoid
  • Lipoma
121
Q

List the features of MEN 2A

A
  • Parathyroid hyperplasia
  • Phaeochromocytoma
  • Medullary carcinoma of the thyroid
122
Q

List the features of MEN 2B

A
  • Phaeochromocytoma
  • Medullary carcinoma of the thyroid
  • Mucosal and ganglioneuromas
  • Marfanoid appearance
123
Q

Result and management of the RET mutation

A
  • Causes MEN 2 and can be screened for

- All should have thyroidectomy

124
Q

What can be used to stain the parathyroid glands intraoperatively

A

Methylene blue

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