What is the role of imaging studies in the workup of follicular thyroid carcinoma (FTC)?

Updated: Jun 18, 2020
  • Author: Luigi Santacroce, MD; Chief Editor: Neetu Radhakrishnan, MD  more...
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Answer

Ultrasonography is the first imaging study that must be performed in any patient with suspected thyroid malignancy.

Ultrasonography is noninvasive and inexpensive, and it represents the most sensitive procedure for identifying thyroid lesions and determining the diameter of a nodule (2-3 mm). Ultrasonography is also useful to localize lesions when a nodule is difficult to palpate or is located deeply.

A study by Xing et al demonstrates that the strain ratio measurement of thyroid lesions, which is a fast standardized method for analyzing stiffness inside examined areas, can be used as an additional tool with B-mode ultrasonography and helps increase the diagnostic performance of the examination. [19]

Ultrasonography can determine whether a lesion is solid or cystic and can detect the presence of calcifications. The rate of accuracy of ultrasonography in categorizing nodules as solid, cystic, or mixed is near 90%.

Ultrasonography may direct a fine-needle aspiration biopsy (FNAB).

Disadvantages of thyroid ultrasonography are that the test cannot distinguish benign nodules from malignant nodules, and it cannot be used to identify true cystic lesions.

Pulsed and power Doppler ultrasonography may provide important information about the vascular pattern and the velocimetric parameters. [20] Such information can be useful preoperatively to differentiate malignant from benign thyroid lesions.

Prior to the introduction of FNAB, thyroid scintigraphy (or thyroid scanning) performed with technetium Tc 99m pertechnetate (99mTc) or radioactive iodine (I-131 or I-123) was the initial diagnostic procedure of choice in thyroid evaluation.

Thyroid scanning is not as sensitive or specific as FNAB in distinguishing benign nodules from malignant nodules.

The scintigraphy procedure performed with 99mTc has a high error rate because although 99mTc is trapped in the thyroid, as iodide is, it is not organified there. 99mTc has a short half-life and cannot be used to determine functionality of a thyroid nodule.

Radioactive iodine is trapped and organified in the thyroid and can be used to determine functionality of a thyroid nodule. Iodine-containing compounds and seafood interfere with any tests that use radioactive iodine. Scintigraphic images of the thyroid are acquired 20-40 minutes after IV administration of radionuclide. In more than 90% of cases, clearly benign nodules appear as hot because they are hyperfunctioning and have a high uptake of radionuclide and, physiologically, of iodine. Malignant nodules usually appear as cold nodules because they are not functioning.

Thyroid scanning is helpful and specific in localizing the tumor preoperatively and identifying residual thyroid tissue immediately postoperatively. It also is used to follow-up for tumor recurrence or metastasis. Thyroid scanning could be useful in diagnosing thyroid tumors in patients with benign lesions (by FNAB) or solid lesions (by ultrasonography).

Integrated imaging, using 18F-FDG and coregistered total body PET and CT scan, seems to be effective in improving diagnostic accuracy in patients with iodine-negative differentiated thyroid carcinoma, allowing precise localization of the tumor tissue. [21] In addition, image fusion by integrated PET/CT offers more information than side-by-side interpretation of single images obtained separately with CT and PET.

Chest radiography, CT scanning, and MRI usually are not used in the initial workup of a thyroid nodule, except in patients with clear metastatic disease at presentation. These tests are second-level diagnostic tools and are useful in preoperative patient assessment.


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