Risk for Malignancy of Thyroid Nodules As Assessed by Sonographic Criteria: the Need for Biopsy

Objective: To correlate sonographic and color Doppler characteristics of thyroid nodules with the results of sonographically guided fine-needle aspiration biopsy to establish the relative importance of these features in predicting risk for malignancy.

Methods: We retrospectively analyzed the sonographic features of 34 malignant and 36 benign thyroid nodules with respect to size, echogenicity, echo structure, shape, border, calcification, and internal vascularity. Individual features and combinations of features were analyzed for their correlation with benign or malignant disease. A comparative analysis of several authors' previously proposed methods for distinguishing between benign and malignant nodules using sonographic criteria was also performed to determine their sensitivity and specificity in predicting nodule disease within our study data.

Results: Nodule size ranged from 0.8 to 4.6 cm in greatest dimension (mean, 1.96 cm; SD, 0.877 cm). The prevalence of malignancy in our study population was estimated to be nearly 5.33%. Intragroup comparison of sonographic features among benign and malignant nodules resulted in identification of intrinsic calcification as the only statistically significant predictor of malignancy (35.3% sensitive and 94.4% specific; P < .005). Presence of a "snowstorm" pattern of calcification was 100% specific for malignancy. Echogenicity, echo structure, shape, border classification, and grade of internal vascularity did not show any significant difference between benign and malignant nodules in this study. Various combinations of features previously suggested to be significant predictors of malignancy were also analyzed and shown to have very little sensitivity or specificity in predicting benign or malignant disease among nodules in our study population.

Conclusions: This study indicates that the presence of intrinsic microcalcification is the only statistically reliable criterion on which to base increased suspicion for malignancy in thyroid nodules. Our results indicate the need for biopsy in determining further workup. All nodules that show the presence of intrinsic microcalcification should undergo biopsy, particularly if calcifications have a snowstorm appearance on sonography.