Differentiation of benign and malignant thyroid nodules based on the proportion of sponge-like areas on ultrasonography: imaging-pathologic correlation

Purpose: The purpose of this study was to determine whether it is possible to differentiate benign from malignant thyroid nodules according to the proportion of sponge-like appearance within the nodules. Methods: A total of 201 thyroid nodules containing sponge-like appearance from 195 patients (157 women and 38 men) were included this study. Each thyroid nodule was classified into one of three grades by real-time ultrasonography (US) based on the areas with a sponge-like appearance within nodule: grade I had sponge-like areas occupying <50%; grade II, between 50% and 75%; and grade III, >75%. We evaluated whether a correlation existed between these grades and cytopathologic diagnoses. Results: Of the 201 nodules, 196 were benign and five were malignant, and according to the US classification, 101 nodules were grade I, 45 were grade II, and 55 were grade III. Of the five malignant nodules, four were grade I, and one was grade II. No statistically significant difference was found in the rate of malignancy between grade III and grades I and II, due to insufficient statistical power. A sponge-like appearance was correlated with follicles filled with colloid and cholesterol granules in benign nodules and with papillary fronds around the dilated cystic spaces in malignant nodules. Conclusion: No malignancies were found in thyroid nodules with >75% sponge-like appearance. Due to the overall low incidence of malignancy and the limited number of patients, a statistically significant difference could not be found in the prevalence of malignancy depending on the proportion of sponge-like areas within the nodule.