Extrathyroid extension of well-differentiated papillary thyroid microcarcinoma on US

Background: Extrathyroidal extension is an important factor to determine the extent of thyroid surgery. The aim of the present study was to evaluate the usefulness of high-resolution ultrasound (US) for predicting the extrathyroidal extension of papillary thyroid microcarcinoma (PTMC). Methods: This study included a total of 221 PTMCs in 181 patients. PTMC was defined as thyroid papillary carcinoma equal or less than 1 cm in size. The US findings, such as contact and disruption of thyroid capsule, were evaluated to predict the extrathyroidal extension of thyroid carcinoma. We calculated the diagnostic accuracy and odds ratio for each US finding. Results: Of the 221 PTMCs, extrathyroidal extension was present in 89 (40.3%) based on pathologic results. The mean size was not significantly different between PTMCs with and without extrathyroidal extension (p = 0.527). When the degree of contact was high, extrathyroidal extension of the thyroid cancer was high (p < 0.0001). Considering the odds ratio, Az value, and positive predictive value of each US finding, more than 25% contact with the adjacent capsule is the most accurate measurement for predicting extrathyroidal extension. Conclusions: This study suggests that the presence and degree of contact between a PTMC and the adjacent capsule as found on preoperative US can provide an useful predictive information about an extrathyroidal extension.