ObjectiveThe objective of this retrospective study was to develop and validate a simple diagnostic prediction model by using ultrasound (US) features of thyroid nodules obtained from multicenter retrospective data.Materials and MethodsPatient data were collected from 20 different institutions and the data included 2000 thyroid nodules from 1796 patients. For developing a diagnostic prediction model to estimate the malignant risk of thyroid nodules using suspicious malignant US features, we developed a training model in a subset of 1402 nodules from 1260 patients. Several suspicious malignant US features were evaluated to create the prediction model using a scoring tool. The scores for such US features were estimated by calculating odds ratios, and the risk score of malignancy for each thyroid nodule was defined as the sum of these individual scores. Later, we verified the usefulness of developed scoring system by applying into the remaining 598 nodules from 536 patients.ResultsAmong 2000 tumors, 1268 were benign and 732 were malignant. In our multiple regression analysis models, the following US features were statistically significant for malignant nodules when using the training data set: hypoechogenicity, marked hypoechogenicity, non-parallel orientation, microlobulated or spiculated margin, ill-defined margins, and microcalcifications. The malignancy rate was 7.3% in thyroid nodules that did not have suspicious-malignant features on US. Area under the receiver operating characteristic (ROC) curve was 0.867, which shows that the US risk score help predict thyroid malignancy well. In the test data set, the malignancy rates were 6.2% in thyroid nodules without malignant features on US. Area under the ROC curve of the test set was 0.872 when using the prediction model.ConclusionThe predictor model using suspicious malignant US features may be helpful in risk stratification of thyroid nodules.

ObjectiveTo validate a new risk stratification system for thyroid nodules, the Korean Thyroid Imaging Reporting and Data System (K-TIRADS), using a prospective design.Materials and MethodsFrom June 2013 to May 2015, 902 thyroid nodules were enrolled from four institutions. The type and predictive value of ultrasonography (US) predictors were analyzed according to the combination of the solidity and echogenicity of nodules; in addition, we determined malignancy risk and diagnostic performance for each category of K-TIRADS, and compared the efficacy of fine-needle aspiration (FNA) with a three-tier risk categorization system published in 2011.ResultsThe malignancy risk was significantly higher in solid hypoechoic nodules, as compared to partially cystic or isohyperechoic nodules (each p < 0.001). The presence of any suspicious US features had a significantly higher malignancy risk (73.4%) in solid hypoechoic nodules than in partially cystic or isohyperechoic nodules (4.3–38.5%; p < 0.001). The calculated malignancy risk in K-TIRADS categories 5, 4, 3, and 2 nodules were 73.4, 19.0, 3.5, and 0.0%, respectively; and the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for malignancy were 95.5, 58.6, 44.5, 96.9, and 69.5%, respectively, in K-TIRADS categories 4 and 5. The efficacy of FNA for detecting malignancy based on K-TIRADS was increased from 18.6% (101/544) to 22.5% (101/449), as compared with the three-tier risk categorization system (p < 0.001).ConclusionThe proposed new risk stratification system based on solidity and echogenicity was useful for risk stratification of thyroid nodules and the decision for FNA. The malignancy risk of K-TIRADS was in agreement with the findings of a previous retrospective study.

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Based on US, the majority of MTCs can be classified as suspiciously malignant due to the presence of micro- or macro-calcifications. Small MTC size (≤ 10 mm) and a smooth margin may be factors predicting false-negative FNA results.

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