thyroid imaging

Question 1

Macro anatomy of thyroid

Answer 1

two lobes connected by midline isthmus. Some pts have a small pyramidal lobe which arises superiorly from the isthmus and lies in front of thyroid cartilage

Question 2

Imaging modalities for thyroid, which is best

Answer 2

US, MRI, CT. US is best. Radiograph is not useful.

Question 3

Functional imaging of thyroid

Answer 3

•Iodine ( I123 or I131) scan. To evaluate for function of the thyroid gland or nodule in patient with abnormal thyroid function. Evaluate for distant metastatic disease.

Question 4

Use of PET/CT scan in thyroid imaging

Answer 4

Staging and restaging of differentiated thyroid cancer

Question 5

Thyroid nodule on US

Answer 5

discrete lesion within the thyroid gland that is radiologically distinct from the surrounding thyroid parenchyma.

Question 6

Incidentaloma

Answer 6

Nonpalpable nodules detected on US or other anatomic imaging studies are termed incidentally discovered nodules

Question 7

compare cystic vs solid nodule on US

Answer 7

Solid nodule is hypodense/brighter. Cystic nodule is dark in the middle

Question 8

Usefulness of CT in thyroid imaging

Answer 8

Useful to define extension to lymph nodes and distant metastasis

Question 9

Normal thyroid on CT

Answer 9

Thyroid is hyperdense and hypervascular.

Question 10

Usefulness of MRI in thyroid imaging

Answer 10

–Useful in identifying infiltrative disease particularly in post-therapy neck where anatomy is distorted. Detection of deep nodal disease

Question 11

Normal thyroid on MRI and limmitations

Answer 11

Thyroid is slightly hyperintense on T2- cant differentiate sold vs cystic nodules. Cant visualize microca

Question 12

How does iodine scan work

Answer 12

Thyroid imaging with radioiodine demonstrates the distribution of functioning thyroid tissue, including ectopic tissue, since thyroid tissue is the only tissue that concentrates large amounts of iodine

Question 13

Agents that affect thyroid iodide accumulation

Answer 13

thyroid meds, contrast agents, amiodarone. Must be discontinued before iodine scan

Question 14

Describe different types of iodine scans

Answer 14

I 123 scan- To evaluate function of the thyroid gland and thyroid nodule in patient with abnormal thyroid function. In graves dz, overactivity will be seen. I131 scan- Diagnostic and therapeutic role

Question 15

compare cancer risk in hot vs cold nodules

Answer 15

Hot nodules are almost always benign. Cold nodules have 15-25% risk of cancer. Normal scan has 20% risk of cancer.

Question 16

compare risk of cancer in cystic vs solid nodules

Answer 16

Solid: 15-25% cancer risk. Cystic: benign

Question 17

compare risk of cancer in functioning vs non-functioning nodules

Answer 17

Functioning: malignancy unlikely (<1%). Nonfunctioning: 5-10% risk of cancer

Question 18

Size of thyroid nodule and cancer risk

Answer 18

•Nonpalpable nodules have the same risk of malignancy as palpable nodules with the same size. Generally, only nodules >1 cm should be evaluated, since they have a greater potential to be clinically significant cancers. Nodules <1cm should be evaluated if associated lymphadenopathy, hx of head/neck irradiation, hx of thyroid cancer in first degree relative

Question 19

Thyroid nodule workup

Answer 19

1. Hx, PE. 2. TSH, T3, T4. 3. I-123 scan or ultrasound. 4. CT or PET/CT. 5. MRI

Question 20

First imaging test if TSH is normal or high (palpable thyroid mass)

Answer 20

ultrasound

Question 21

First imaging test if TSH is low (palpable thyroid mass)

Answer 21

I-123 iodine scan

Question 22

If cold nodule on I-123 scan, what is next imaging test

Answer 22

ultrasound

Question 23

What is best imaging test to differentiate solid vs cystic nodule

Answer 23

ultrasound

Question 24

If cystic nodule, what next

Answer 24

fine needle aspiration