thyroid imaging Flashcards
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
Imaging modalities for thyroid, which is best
US, MRI, CT. US is best. Radiograph is not useful.
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.
Use of PET/CT scan in thyroid imaging
Staging and restaging of differentiated thyroid cancer
Thyroid nodule on US
discrete lesion within the thyroid gland that is radiologically distinct from the surrounding thyroid parenchyma.
Incidentaloma
Nonpalpable nodules detected on US or other anatomic imaging studies are termed incidentally discovered nodules
compare cystic vs solid nodule on US
Solid nodule is hypodense/brighter. Cystic nodule is dark in the middle
Usefulness of CT in thyroid imaging
Useful to define extension to lymph nodes and distant metastasis
Normal thyroid on CT
Thyroid is hyperdense and hypervascular.
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
Normal thyroid on MRI and limmitations
Thyroid is slightly hyperintense on T2- cant differentiate sold vs cystic nodules. Cant visualize microca
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
Agents that affect thyroid iodide accumulation
thyroid meds, contrast agents, amiodarone. Must be discontinued before iodine scan
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
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.
compare risk of cancer in cystic vs solid nodules
Solid: 15-25% cancer risk. Cystic: benign
compare risk of cancer in functioning vs non-functioning nodules
Functioning: malignancy unlikely (<1%). Nonfunctioning: 5-10% risk of cancer
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
Thyroid nodule workup
- Hx, PE. 2. TSH, T3, T4. 3. I-123 scan or ultrasound. 4. CT or PET/CT. 5. MRI
First imaging test if TSH is normal or high (palpable thyroid mass)
ultrasound
First imaging test if TSH is low (palpable thyroid mass)
I-123 iodine scan
If cold nodule on I-123 scan, what is next imaging test
ultrasound
What is best imaging test to differentiate solid vs cystic nodule
ultrasound
If cystic nodule, what next
fine needle aspiration
