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Ultrasonographically detected small thyroid bed nodules identified after total thyroidectomy for differentiated thyroid cancer seldom show clinically significant structural progression.

BACKGROUND
High-resolution ultrasound (US) is the primary tool used to identify locoregional recurrences in differentiated thyroid cancer. Although small thyroid bed (TB) nodules are a commonly reported sonographic finding, their natural history, regardless of whether they are benign or malignant, has not been well characterized. This study was designed to determine the likelihood, magnitude, and rate of growth of small TB nodules identified on routine surveillance neck US after thyroidectomy for differentiated thyroid cancer as well as to identify ultrasonographic and clinical predictors of growth.


METHODS
This retrospective review identified 191 patients with at least one TB nodule (≤ 11 mm) on the first postoperative US performed at a comprehensive cancer center. Change in size of each TB nodule was determined using serial US studies over time. Clinicopathologic and sonographic characteristics were analyzed as possible predictors for growth of the TB nodules.


RESULTS
Over a median clinical follow-up of 5 years, 9% (17/191) of patients had increase in size of at least one TB nodule. Median size of the TB nodules was 5 mm (range: 2-11 mm). Suspicious US features were seen in 63% (121/191) of patients with TB nodules identified on initial US and in 31% (21/67) of those with TB nodules detected on subsequent follow-up US. The rate of growth was 1.3 mm/year in those nodules showing an increase in size and thus demonstrated a significant increase in size only after several years of follow-up. The negative predictive values associated with the absence of any suspicious US features (0.97), the absence of abnormal cervical lymph nodes (0.94), and the lack of a rising serum thyroglobulin (0.93) provided clinically useful information regarding the likelihood that nodules would not increase in size.


CONCLUSION
Most TB nodules do not show clinically significant growth over several years of follow-up. Thus, TB nodules can be followed up with cautious observation and serial ultrasonography using an approach similar to that recommended by the American Thyroid Association thyroid cancer guidelines for the management of small abnormal cervical lymph nodes.