Preliminary Diagnosis: Thyroid Masses
I. What imaging technique is first-line for this diagnosis?
Ultrasonography of the thyroid
II. Describe the advantages and disadvantages of this technique for diagnosis of thyroid masses.
Advantages
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Can detect nonpalpable nodules and sub-centimeter nodules, and differentiate between cystic and solid masses.
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Inexpensive and non-invasive.
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Can adequately assess the rest of the thyroid gland for hemiagenesis or hypertrophy, which may be mistaken as a nodule.
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Can be used to assess for regional staging.
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Improved assessment of malignancy and staging if combined with Doppler.
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Used to guide fine-needle aspiration biopsy (FNAB), which is of utmost importance in the workup of thyroid masses.
Disadvantages
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Limited in assessing any sub-sternal extent or extent into adjacent structures.
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Operator-dependent.
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Limited in patients with obese neck tissue.
III. What are the contraindications for the first-line imaging technique?
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There are no major contraindications to the use of ultrasonography.
IV. What alternative imaging techniques are available?
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CT scan of the neck with IV contrast
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MRI of the neck with IV contrast
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Radionuclide thyroid scan
V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of thyroid masses.
CT scan of the neck with IV contrast
Advantages
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Better capability of determining the relationship of the thyroid mass to adjacent structures such as trachea and esophagus.
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Ability to determine sub-sternal extension, any associated lymphadenopathy, or locoregional/metastatic spread.
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Better capability of visualizing the anatomy behind the sternum, trachea, and esophagus.
Disadvantages
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Requires the use of iodinated contrast, which should be used with caution in patients with multinodular goiter or well-differentiated thyroid cancer.
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Use of iodinated contrast agents prevents the use of radioiodine ablation for 2-3 months after.
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More expensive than ultrasound.
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Requires the use of ionizing radiation.
MRI of the neck with IV contrast
Advantages
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Better capability of determining the relationship of the thyroid mass to adjacent structures such as trachea and esophagus.
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Ability to determine sub-sternal extension, any associated lymphadenopathy, or locoregional/metastatic spread.
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Better capability of visualizing the anatomy behind the sternum, trachea, and esophagus.
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Better than CT at distinguishing persistent thyroid tissue/tumor from post-operative fibrosis.
Disadvantages
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Expensive and not as easily accessible as ultrasound.
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Requires the use of IV contrast, which has inherent risks.
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Less tolerated in obese patients and those with claustrophobia.
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More time-consuming than ultrasound and CT.
Radionuclide thyroid scan
Advantages
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Can determine the functional status of a thyroid mass.
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Not used in isolation, but often used as adjunct with ultrasound for patients who are found to be hyperthyroid on thyroid function tests.
Disadvantages
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Expensive and requires two days to complete.
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Unable to accurately assess the size of the thyroid mass.
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Unable to assess the surrounding structures, including nodal basins, adjacent spread, or substernal extension.
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Limitations in visualizing non-functioning masses because of the overlying thyroid gland.
VI. What are the contraindications for the alternative imaging techniques?
CT of the neck with IV contrast
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Contraindicated in pregnant women, patients allergic to iodine, and those with acute renal insufficiency.
MRI of the neck with IV contrast
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Contraindicated in patients with pacemakers, those with implantable, MRI-incompatible devices, and those with chronic renal failure.
Radionuclide thyroid scan
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There are no contraindications to the use of this imaging modality.
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