Abstract
We thank Dr. Rosario for his letter regarding our article (1). We carefully read the letter and the publication by Rosario et al. (2). They reported a low malignancy rate of 3.7% (33/881) for solid thyroid nodules without suspicious sonographic features. In our study, the malignancy rate of solid, round, isoechoic thyroid nodules without coexistent malignant sonographic features (a spherical shape is more appropriate than a round shape) was examined on the basis of real-time examination and cytopathological results (1). Unlike the rate reported by Rosario et al. (2), the malignancy rate of solid, round, isoechoic thyroid nodules without coexistent malignant sonographic features was 25.9% (7/27) in our study, and other solid thyroid nodules with hypoechogenicity, hyperechogenicity, or ovoid shape were not included. Furthermore, the prevalence rate of solid, round, isoechoic thyroid nodules without coexistent malignant sonographic features was only 3.7% (27/727). We believe that the prevalence rate of solid, round, isoechoic thyroid nodules without coexistent malignant sonographic features in the general population may be lower than this rate, because our study was performed in a single center (a specialized hospital for the diagnosis and treatment of thyroid cancer) and by a single radiologist. We reported that the frequency rate of overall malignant cytology in ultrasound-guided fine-needle aspiration of thyroid nodules was 23.3% (102/438), and this result represents a high selectivity for thyroid malignancy (3). In our retrospective study on solid, isoechoic thyroid nodules without coexistent malignant sonographic features, the malignancy rate of solid, isoechoic thyroid nodules was 8.8% (10/114) on the basis of histopathological results, but the malignancy rate of ovoid and round solid thyroid nodules was 7.3% (7/96) and 16.7% (3/18), respectively (4). The findings of our prospective and retrospective studies show that the malignancy rate of solid, round, isoechoic thyroid nodules is not negligible; therefore, it is necessary to pay closer attention to these nodules. Nevertheless, large-scale studies are necessary to expand on the findings reported in these studies.
For reference, we have used the following sonographic categories for the diagnosis of thyroid nodules: (i) malignant features, including marked hypoechogenicity, a spiculated margin, microcalcifications, a taller-than-wide shape, and associated cervical lymph nodes with an intranodal cystic component or microcalcifications; (ii) borderline features, including hypoechogenicity, macrocalcification, and centrally predominant vascularity; and (iii) benign features, including an ovoid shape, isoechogenicity, a smooth margin, and peripheral vascularity (5). On the basis of the findings in our studies, we believe that solid, round, isoechoic thyroid nodules without coexistent malignant sonographic features should be classified in the borderline category.