Thyroid

Question 1

What is the lymphatic drainage of the thyroid?

Answer 1

Primary echelon- level VI (central neck)

secondary echelon- internal jugular chain (II-IV), posterior neck (V), superior mediastinum (VII)

inconsistent, and skip mets directly to lateral neck compartment in 20%

Question 2

Epidemiology of thyroid cancer

Answer 2

• 1% of all malignancies; 95% of endocrinology malignancies
• F>M (2.5: 1)
• PTC and FTC 40-50 y/o; MTC and ATC 60 y/o
• Increasing incidence due to increasing recognition of thyroid nodules on surveillance

Question 3

Risk factors for thyroid cancer

Answer 3

• Sporadic
• Ionising radiation (H&N RT, atomic bomb survivors)
• Low iodine (FTC and A TC)
• Family history of thyroid cancer
• Genetic syndrome
  o PTC/ FTC: Cowden (PTEN gene), Gardnes (APC gene)
  o MTC a/w MEN 2A and MEN 2B (RET proto-oncogene mutation)

Question 4

What types of thyroid cancer fall into the differentiated or undifferentiated categories?

Answer 4

Differentiated: papillary, follicular, medullary

Undifferentiated: anaplastic

Question 5

What thyroid cancers arise from follicular cells?

Answer 5

Papillary and follicular

Question 6

What thyroid cancer arises from para-follicular C cell?

Answer 6

Medullary

Question 7

What is the epidemiology of Papillary thyroid carcinoma?

Answer 7

• approx 80% of thyroid cancer
• M:F ratio 1:3
• > 90% of thyroid malignancies in children

Question 8

Presentation of papillary thyroid cancer?

Answer 8

• painless thyroid nodule/mass in neck or cervical nodes
• at presentation 2/3 thyroid only disease, 1/3 have nodal disease
• COLD on RAI scan

Question 9

What are poor prognostic factors in papillary thyroid cancer

Answer 9

tall cell/ hobnail/ columnar variants,
vascular invasion,
node+,
extra-thyroid extension, increase age

Question 10

What is the biological behaviour of papillary thyroid cancer?

Answer 10

o Generally indolent, good prognosis (except diffuse sclerosing, tall cell, and columnar cells)
o 5-20% local recurrence
o 30% nodal involvement (cervical nodes involvement does not affect prognosis)
o 5% distant mets (lung and bone)

Question 11

Workup for thyroid cancer: labs

Answer 11

• Thyroid function (TSH, T3/T4), thyroglobulin
• PTH and calcium (to rule out hyperparathyroidism)
• In MTC: Calcitonin (calcitonin level correlates with tumour burden), CEA, RET proto-oncogene
  germline mutation

To exclude other DDx:

• LDH/ ESR (elevated in lymphoma)
• B-HCG and AFP (elevated in germ cell tumour)
• Urine and serum catecholamine (to rule out pheochromocytoma)

Question 12

Work up for thyroid cancer: imaging

Answer 12

• Thyroid USS
• Radioactive iodine I(123) RAI scan
• CT neck (NON CONTRAST) iodine contrast will preclude RAI treatment for next 1-2 months)
• Systemic staging if high risk of distant mets
  —- CT Chest/abdo
  —- Bone scan
  —- FDG PET- useful in undifferentiated

Question 13

Thyroid USS findings suggestive of benign nodule

Answer 13

Purely cystic

Question 14

Thyroid USS findings suspicious of malignancy

Answer 14

1. solid hypoechoic nodule,
2. irregular margin (infiltrative, micro-lobulated), 3. microcalcification,
3. taller (than wide) shape,
4. rim calcification with extrusive soft tissue component,
5. evidence of ETE

Question 15

What can RAI be used for?

Answer 15

Imaging and therapy

Question 16

What types of thyroid cancers can RAI be used for?

Answer 16

Papillary and Follicular, not medullary or anaplastic

Question 17

What are the radionuclides used in RAI and their respective uses

Answer 17

I-131 (imaging and therapy)
I-123 (just imaging)

Question 18

What is the half life of I-131 and I-123

Answer 18

I-131 8 days
I-123- 13 hours

Question 19

How is iodine uptake optimised prior to RAI treatment?

Answer 19

• Low iodine diet for 10 days before treatment
• T4 deprivation
• Administration of recombinant TSH (Thyrogen) as this drives iodine internalisation by thyroid cells

Question 20

What other tissues express sodium-iodine symporters?

(Which may also be damaged by RAI therapy)

Answer 20

Parotid glands
Gastric mucosa
Nasolacrimal ducts
Breast tissue