L16 - Radiology and Radioactive iodine therapy

Question 1

List the imaging techniques to confirm enlargement of thyroid gland?

Answer 1

Ultrasound

CT

Question 2

List the imaging technique for thyroid function?

Answer 2

Radionucleotide scan

Question 3

List the imaging techniques to characterize nodules and masses?

Answer 3

Ultrasound

Radionucleotide

Question 4

List imaging techniques for evaluating thyroid carcinoma?

Answer 4

Evaluate local disease: US, CT, MRI

Detect recurrence after thyroidectomy / treatment: US, CT, MRI, radionuclide scan

Question 5

Limitation of CXR for imaging thyroid?

Answer 5

Cannot evaluate soft tissue structure, evaluate extent of local invasion/ compression, characterize thyroid lesion

Question 6

Advantages of using ultrasound for thyroid imaging?

Answer 6

No radiation

High frequency probe good for superficial structure evaluation: characterize nodule, vascularity

Excellent spatial resolution, sensitive to tiny nodules

Question 7

List 5 physical features pf thyroid nodules that may be identified by ultrasound imaging?

Answer 7

1. Solid vs. cystic (internal necrosis)
2. Vascularity (colour doppler)
3. Calcification
4. size and number of nodules
5. Margin of nodules

Question 8

Solid vs cystic thyroid nodule: which is more likely malignant?

Answer 8

Purely cystic: very rarely malignant

Purely solid: 23% malignant

Mixed solid & cystic: 14% malignant

Question 9

Thyroid Ultrasound shows Rung-down artifacts: bright dots with comet tails. What is indicated?

Answer 9

inspissated colloid calcifications (colloid aggregates)

= benign cyst

Unlike microcalcification which indicated malignancy

Question 10

How does vascularity of thyroid lesion indicate malignancy?

Answer 10

Complete avascular= unlikely malignant

Intrinsic/intranodular vascularity: 69-74% malignant (e.g. papillary carcinoma)

Perinodular vascularity: 22% malignant

Question 11

Is thyroid nodule calcification a sign of malignancy?

Answer 11

Nonspecific – both in benign and malignant conditions

Question 12

Define 3 types of thyroid nodule calcification and their asso. neoplasm?

Answer 12

Microcalcifications (punctate calcification, psammoma bodies)
 Common in papillary carcinoma (also in follicular, anaplastic carcinomas)
 Benign: follicular adenoma, Hashimoto thyroiditis

Coarse calcifications: common in medullary carcinoma

Dystrophic calcifications: multinodular goiter

Question 13

How does the margin of thyroid nodules indicate malignancy?

Answer 13

Irregular margin = likely malignant

e.g. anaplastic carcinoma&raquo_space; local invasion beyond capsuleinto surrounding tissues (e.g. to vertebral muscle, vertebral body, displace carotid artery)

Well-defined = follicular adenoma

Question 14

How does the size of thyroid nodule indicate malignancy?

Answer 14

> 4cm = likely malignant

Question 15

How does the number of thyroid nodules indicate malignancy?

Answer 15

Non-specific, cant use to indicate malignancy

Question 16

Define the echogenic nature and vascularity of thyroid nodules in Grave’s?

Answer 16

 Diffuse enlargement of thyroid=homogenously hypoechoic (very dark)

 Increase vascularity (thyroid inferno)

Question 17

List 3 clinical uses for ultrasound related to thyroid pathologies?

Answer 17

1. Characterize nodule
2. Assess neck for lymph node metastasis in thyroid cancer
3. Guides fine needle aspiration (FNA)/biopsy for cytology

Question 18

Major limitation of Fine needle aspiration cytology in thyroid cancer ddx?

Answer 18

Cannot distinguish between:
Follicular adenoma and Follicular carcinoma

Requires histology: Rely on capsular or venous invasion

Question 19

What is the most sensitive and specific imaging for ddx benign vs malignant thyroid nodules?

Answer 19

Ultrasound + FNAC (fine needle aspiration cytology)

Question 20

Indication for CT and MRI in thyroid diseases?

Answer 20

CANCER
Cross-sectional anatomy: intrathoracic extension of goiter

• Post-surgery or radiology: surverillance*** for recurrence of cancer
• Evaluate local, regional and distant metastasis***

Question 21

Compare the function of 99m-Tc pertechetate vs Iodide scan for thyroid?

Answer 21

99m-Tc pertechnetate: Trapped by thyroid tissue but not incorporated into thyroglobulin for organification = NO FUNCTION CHECK

Iodide = Trapped and organified = FUNCTION CHECK

Question 22

Which iodide isotopes are used for thyroid scans?

Answer 22

I-123, I-124

I-131 = more for treatment, notoriously high false-negative rate

Question 23

What is indicated by “hot” and “cold” nodules seen on radionucleotide scans of thyroid??

Answer 23

Hot = increase uptake, Cold = no uptake
Shows ectopic thyroid gland + evaluate function

Hot: Hyperthyroidism, Iodine deficiency, functional adenoma: EXCLUDE CANCER

Cold: Hypothyroid/ adenomas/thyroiditis: COLD= CANCER, mostly benign, 20% malignant

Question 24

Radionucleotide scans are sufficient for dx of thyroid cancer. T or F?

Answer 24

Always require needle biopsy/aspiration

Question 25

Multinodular goiter produces "hot nodules" T or F?

Answer 25

False Mixture of hot and cold

Question 26

3 clinical uses for radionucleotide scans for thyroid diseases?

Answer 26

- Assess metabolic function: Hot or Cold - Shows position of ectopic thyroid glands - Surveillance after treatment with whole-body I-131 scan

Question 27

Increased thyroglobulin always shows up on 131-I scans. T or F?

Answer 27

False High rate of false negative on 131-I Need to use 99mTc-MIBI or 18F-FDG PET/CT scans for higher specificity and sensitivity

Question 28

List the iodine isotopes for thyroid treatment

Answer 28

I-131

Question 29

List the iodine isotopes for prostate cancer imaging and treatment

Answer 29

I-125

Question 30

List the iodine isotopes for thyroid imaging

Answer 30

I-123 I-124

Question 31

Describe the radiation emitted by I-131 and how it's used for thyroid diseases?

Answer 31

I-131 trapped inside follicles destructive beta- particles = destroy parenchymal cells w/o damage to surrounding tissue Gamma-radiation detected externally for thyroid function monitoring

Question 32

Which thyroid diseases are treated by I-131?

Answer 32

- benign thyroid disease/ hyperthyroidism: GRAVE'S ******* - Toxic multinodular goiter *******and thyroiditis - well-differentiated thyroid cancer (e.g. papillary and follicular) - Iodine-induced hyperthyroidism (amiodarone) - Ectopic/ metastatic thyroid cancer

Question 33

Admin of I-131?

Answer 33

orally, sodium iodide, capsule

Question 34

Limitation of I-131 in identifying metastasis? *think about which tissue take up*

Answer 34

Uptake by Salivary gland, esophagus, thymus, breast, Liver, stomach, colon, bladder >> easily misinterpret as metastasis

Question 35

C/O of I-131 therapy for hyperthyroidism?

Answer 35

* Absolute contraindication: pregnancy and lactation * Relative contraindication: children and adolescents Worsening Grave's ophthalmopathy

Question 36

Indications for using I-131 to treat hyperthyroidism?

Answer 36

Poor compliance, ADR and recurrence after anti-thyroid drugs Patients with CVS diseases : Cardiac arrhythmias, heart failure thyrotoxic periodic paralysis

Question 37

ADR and long-term safety of I-131/ Radioactive iodine?

Answer 37

1) Mild, well-tolerated: Neck swelling, painful swallowing 2) Nausea, GI discomfort 3) High risk of HYPOthyroidism after one year 4) Rare: radiation cystitis, gastritis, fibrosis 5) Very rare: Bone marrow suppression, anaplastic anaemia, leukemia No long-term effect on fertility, cancer, congential malformations

Question 38

Treatment for hypothyroidism caused by I-131?

Answer 38

regular serum thyroid function test and thyroxine replacement

Question 39

List advantages of I-131 therapy for thyroid diseases?

Answer 39

- Cost effective - Few adverse effects - Out-patient therapy - Reduction in goiter size

Question 40

List disadvantages of I-131 therapy for thyroid diseases?

Answer 40

- Radiation exposure - Risk of exacerbation of ophthalmopathy - Need to delay pregnancy and avoid breastfeeding - Radiation thyroiditis: 10%

Question 41

Treatment of Differentiated Thyroid Cancer ?

Answer 41

Total thyrodectomy/ lobectomy +/- radioactive iodine I-131: - for eradication of residual cells - reduce risk of metastasis - increase sensitivity of serum thyroglobulin and I-131 WBS for surveillance

Question 42

Anti-thyroid medication can be taken concurrently with I-131 therapy. T or F?

Answer 42

False Stop anti-thyroid medications 4-14 days before RAI (hyperthyroidism)

Question 43

Precautions and preparations before starting I-131 therapy?

Answer 43

- No breastfeeding and practice contraception for 4 weeks before (female) - Low iodine diet for 2 weeks: cut seafood, dairy, soy - Stop all T4/T3 therapy or switch to recombinant human TSH: increase radioactive iodine uptake by tumour cells

Question 44

Which patients need recombinant human TSH before I-131 therapy?

Answer 44

* Hypopituitarism * Severe ischemic heart disease * psychiatric disturbance * Functional metastasis causing TSH suppression

Question 45

Precautions after I-131 therapy?

Answer 45

- Distant/ social isolation (radioactive) - No pregnancy, breastfeeding, fathering for a year - No iodine food, meds

Question 46

Indication for I-131 whole body scan?

Answer 46

- Screen for residual thyroid uptake or distant metastasis

Question 47

Summarize all the long-term follow-ups after I-131 therapy?

Answer 47

Regular monitoring with serum thyroglobulin 131I-whole body scan 6-12 months after:detect any relapse/metastasis thyroxine (TSH suppression therapy) to keep TSH below the lower limit