Ultrasound of the thyroid and parathyroid glands: controversies in the diagnosis of thyroid cancer.

Among the articles and features of this issue of Ultrasound Quarterly is an excellent review of thyroid and parathyroid ultrasound from Dr. Michael Hill’s group at George Washington University in Washington, DC. Their article contains a comprehensive review of the techniques for performing thyroid and parathyroid scans, for interpreting the results (particularly in attempting to distinguish benign from malignant conditions), as well as an excellent description of biopsy techniques. The authors provide excellent correlative information on the role of radionuclide imaging of the thyroid and parathyroid glands, because these 2 techniques offer complementary anatomic and physiologic information that can further our understanding of disease processes in these glands. With the increased resolution of state-of-the-art ultrasonography, the role of radionuclide imaging in the thyroid has diminished. In the past, palpable thyroid nodules were worked up with radionuclide imaging, searching for cold nodules, because malignancy occurs only rarely in warm or hot nodules. In a 10-year analysis from Denmark of 990 patients undergoing surgery for thyroid nodules, the overall incidence of malignancy was 6.3% and only 1 follicular carcinoma was identified in a warm nodule. Ultrasonography was initially performed to search for cystic lesions of the thyroid that might be included in a group of patients with cold nodules, but it soon became apparent that ultrasound scans were showing numerous additional lesions that were neither palpated nor detected on radionuclide scans. Most of these lesions were less than 2 cm in size and hence could not be readily assessed for activity by radionuclide imaging. The question was then raised regarding the clinical significance of nonpalpable thyroid nodules. In a small study from Israel of 61 nonpalpable thyroid nodules, only 1 (1.6%) was carcinoma. A surprising feature in this study is the fairly large size of these nonpalpable lesions, with a mean diameter of 2.4 cm and a size range of 1.1 to 5.5 cm. The authors conclude there was a low prevalence of carcinoma in nonpalpable lesions, although the study was quite small. Another study was published regarding the natural history of benign thyroid nodules, in which a group of patients who had benign fine-needle aspiration biopsy were then followed for 5 years. Most of these nodules showed significant growth in volume of 15% or greater over the follow-up period, and the authors concluded that enlargement of nodule size on follow-up ultrasound is not a reliable predictor of malignancy. Several studies were undertaken to attempt to define sonographic criteria for malignancy. Features suggesting malignancy included a solid hypoechoic appearance to the nodule, ill-defined or lobulated margins, a shape that was more tall than wide, and, most specifically, microcalcifications. Using these features in a series of 155 nonpalpable thyroid nodules that were sampled, a sensitivity of nearly 94% for detection of cancer was achieved, but the specificity was only 66% and the positive predictive value was 56%. Another study assessed the added value of color Doppler sonography in the prediction of malignancy in thyroid nodules, and the authors concluded that extensive internal vascularity within a solid