[Predictive value of sonographic features in preoperative evaluation of malignant thyroid nodules]

To retrospectively evaluate the diagnostic accuracy of ultrasonographic (US) features for the pre-operative differentiation of benign and malignant thyroid nodules by using pathological diagnosis as the reference standard.

A total of 1501 patients with 2123 thyroid nodules (1864 malignant, 259 benign) diagnosed intra-operatively and undergoing pre-operative ultrasonography at our hospital were recruited. The following characteristics of US images were evaluated: nodule size, shape, margin, echotexture, echogenicity, presence and type of calcification, blood flow inside or around nodules and the presence of ipsilateral cervical lymphadenectasis.

(1) The risk of malignancy was higher in a solitary nodule than in a non-solitary nodule [16.7% (109/653) vs 10.2% (150/1470), P=0.000]. The mean diameter of benign nodules was larger than that of malignant nodules [(2.4±1.4) vs (2.1±1.9) cm, P=0.009]. (2) Microcalcification, irregular shape, ill-defined border, solid and hypoechogenicity were more common in malignant nodules. Irregular shape had the highest sensitivity and positive predictive value while microcalcification had the highest diagnostic accuracy. (3) Nodules with a rich blood flow inside tended to have a higher risk of malignancy. The distribution pattern of blood flow around the nodules was not associated with the differentiation of benign and malignant thyroid nodules. Nodules with the presence of ipsilateral cervical lymphadenectasis had a higher risk of malignancy than those without lymphadenectasis [28.3% (80/283) vs 9.6% (92/963), P<0.01]. (4) If microcalcification, irregular shape, ill-defined border, solid, hypoechogenicity and the presence of ipsilateral cervical lymphadenectasis were treated as the characteristics of malignancy, a higher frequency of these characteristics was correlated with a higher risk of malignancy.

Despite a lack of specific US imaging characteristics in malignant thyroid nodules, microcalcification and irregular shape appear closely correlated with malignancy. A combined use of conventional US characteristics may improve the accuracy of differential diagnosis.