Imaging

Thyroid Masses

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

  • Can detect nonpalpable nodules and sub-centimeter nodules, and differentiate between cystic and solid masses.

  • Inexpensive and non-invasive.

  • Can adequately assess the rest of the thyroid gland for hemiagenesis or hypertrophy, which may be mistaken as a nodule.

  • Can be used to assess for regional staging.

  • Improved assessment of malignancy and staging if combined with Doppler.

  • Used to guide fine-needle aspiration biopsy (FNAB), which is of utmost importance in the workup of thyroid masses.

Disadvantages

  • Limited in assessing any sub-sternal extent or extent into adjacent structures.

  • Operator-dependent.

  • Limited in patients with obese neck tissue.

III. What are the contraindications for the first-line imaging technique?

  • There are no major contraindications to the use of ultrasonography.

IV. What alternative imaging techniques are available?

  • CT scan of the neck with IV contrast

  • MRI of the neck with IV contrast

  • 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

  • Better capability of determining the relationship of the thyroid mass to adjacent structures such as trachea and esophagus.

  • Ability to determine sub-sternal extension, any associated lymphadenopathy, or locoregional/metastatic spread.

  • Better capability of visualizing the anatomy behind the sternum, trachea, and esophagus.

Disadvantages

  • Requires the use of iodinated contrast, which should be used with caution in patients with multinodular goiter or well-differentiated thyroid cancer.

  • Use of iodinated contrast agents prevents the use of radioiodine ablation for 2-3 months after.

  • More expensive than ultrasound.

  • Requires the use of ionizing radiation.

MRI of the neck with IV contrast

Advantages

  • Better capability of determining the relationship of the thyroid mass to adjacent structures such as trachea and esophagus.

  • Ability to determine sub-sternal extension, any associated lymphadenopathy, or locoregional/metastatic spread.

  • Better capability of visualizing the anatomy behind the sternum, trachea, and esophagus.

  • Better than CT at distinguishing persistent thyroid tissue/tumor from post-operative fibrosis.

Disadvantages

  • Expensive and not as easily accessible as ultrasound.

  • Requires the use of IV contrast, which has inherent risks.

  • Less tolerated in obese patients and those with claustrophobia.

  • More time-consuming than ultrasound and CT.

Radionuclide thyroid scan

Advantages

  • Can determine the functional status of a thyroid mass.

  • Not used in isolation, but often used as adjunct with ultrasound for patients who are found to be hyperthyroid on thyroid function tests.

Disadvantages

  • Expensive and requires two days to complete.

  • Unable to accurately assess the size of the thyroid mass.

  • Unable to assess the surrounding structures, including nodal basins, adjacent spread, or substernal extension.

  • 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

  • Contraindicated in pregnant women, patients allergic to iodine, and those with acute renal insufficiency.

MRI of the neck with IV contrast

  • Contraindicated in patients with pacemakers, those with implantable, MRI-incompatible devices, and those with chronic renal failure.

Radionuclide thyroid scan

  • There are no contraindications to the use of this imaging modality.

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