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Flashcards in thyroid imaging Deck (24):
1

Macro anatomy of thyroid

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

2

Imaging modalities for thyroid, which is best

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

3

Functional imaging of thyroid

•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.

4

Use of PET/CT scan in thyroid imaging

Staging and restaging of differentiated thyroid cancer

5

Thyroid nodule on US

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

6

Incidentaloma

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

7

compare cystic vs solid nodule on US

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

8

Usefulness of CT in thyroid imaging

Useful to define extension to lymph nodes and distant metastasis

9

Normal thyroid on CT

Thyroid is hyperdense and hypervascular.

10

Usefulness of MRI in thyroid imaging

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

11

Normal thyroid on MRI and limmitations

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

12

How does iodine scan work

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

13

Agents that affect thyroid iodide accumulation

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

14

Describe different types of iodine scans

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

15

compare cancer risk in hot vs cold nodules

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

16

compare risk of cancer in cystic vs solid nodules

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

17

compare risk of cancer in functioning vs non-functioning nodules

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

18

Size of thyroid nodule and cancer risk

•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

19

Thyroid nodule workup

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

20

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

ultrasound

21

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

I-123 iodine scan

22

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

ultrasound

23

What is best imaging test to differentiate solid vs cystic nodule

ultrasound

24

If cystic nodule, what next

fine needle aspiration