What is the role of imaging studies in the diagnosis of thyroid cancer?

Updated: May 14, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
  • Print


Ultrasonography is the imaging modality most commonly used to evaluate thyroid disease. This noninvasive study enables accurate evaluation of the thyroid gland. However, the usefulness of ultrasonography for distinguish between malignant and benign nodules is limited. Simple cysts found on sonograms are benign, but simple cysts are rarely found. Cysts are most commonly complex, with at least some solid component that could potentially harbor malignancy. Microcalcifications noted on sonograms are associated with thyroid malignancy. Ultrasonography is highly sensitive for thyroid nodules and can depict nodules only a few millimeters in size.

A sonogram ordered to evaluate a solitary nodule often reveals additional nodules of questionable clinical significance. The accuracy of FNAB results increases when sonographic guidance is used. Use of ultrasonography-guided FNAB can be useful for biopsy of small or difficult-to-palpate thyroid nodules as well as for FNAB of nodules in children. Ultrasonography can also be useful for accurate measurement of thyroid nodules that are being monitored serially.

In 2013, researchers at the Mayo Clinic reported that recent dramatic increases in the diagnosis of low-risk thyroid cancer in the United States are fuelled by the overuse of ultrasonography. [11, 12] The incidence of thyroid cancer in the United States has tripled in the past 3 decades, from 3.6 per 100,000 in 1973 to 11.6 per 100,000 in 2009, making it one of the fastest growing diagnoses. The vast majority of the thyroid tumors being detected are small low-risk papillary thyroid cancers that are unlikely to ever progress enough to cause symptoms or death. That this represents overdiagnosis is supported by the observation that the death rate for these cancers has remained stable (0.5 per 100,000 in 1979 and in 2009), even with the increasing incidence. [11, 12]

Radioiodine imaging can help in determining the functional status of a nodule. Nonfunctional nodules do not take up radiolabeled iodine-123 and appear as cold spots in the thyroid (cold nodules). [13] Hyperfunctioning nodules take up radioiodine and appear as hot spots (hot nodules). Warm nodules appear similar to the surrounding normal thyroid tissue. Hot or warm nodules were historically thought to be benign; therefore, they did not require further evaluation for malignancy. However, in a review of 5000 patients undergoing thyroidectomy regardless of radioimaging findings, Ashcraft and Van Herle (1981) found that 4% of hot nodules harbored malignancy.

Carcinoma cannot be excluded on the basis of radioiodine scans. Therefore, radioiodine scans are usually not helpful for the routine evaluation of thyroid nodules. In select situations, radioiodine studies can be diagnostic adjuncts. When results of repeated FNAB of a nodule are nondiagnostic, a radioiodine imaging can help in directing management if a hot nodule is to be monitored clinically.

CT scanning and MRI can be used to evaluate soft-tissue extension of large or suspicious thyroid masses into the neck, trachea, or esophagus and to assess metastases to the cervical lymph nodes. These studies do not have a role in the routine management of solitary thyroid nodules. The use of iodinated contrast agents should be avoided in patients with possible thyroid carcinoma because they interfere with the postoperative use of radioactive iodine.

Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!