Objective  To investigate the value of conventional ultrasound versus contrast-enhanced ultrasound (CEUS) in the differential diagnosis of benign and malignant cystic solid thyroid nodules.

  Methods  From 2011 to 2016, clinical data about patients with unifocal thyroid cystic solid nodules who underwent conventional ultrasound and CEUS before surgery in the First Medical Center of Chinese PLA General Hospital were evaluated in this retrospective study. The diagnosis performances of conventional ultrasound and CEUS were compared with the pathological results from surgery as the gold standard.

  Results  Totally 157 nodules from 157 patients were included; 57 were malignant and 100 were benign. There was no significant difference in the echogenicity, macro-calcification and vascularity between the benign and malignant nodules (P ＞ 0.05). The benign nodules were more likely to be regular, smooth and horizontal-shape, and the solid part in the cystic nodule was mostly isoechoic, hyperechoic and less sand-like calcification (micro-calcification) (10.00%). The malignant nodules were more likely to be ill-defined, lobulated and irregular, and the solid part was isoechoic, containing hypoechoic area and micro-calcification (64.91%). CEUS showed that in the benign nodules, diffuse enhancement was dominant in the solid part of the cystic solid nodules (92.00%), mostly with homogeneous enhancement, and circular  rim enhancement was observed at 36.00% of the edge. The malignant group was dominated by heterogeneous enhancement (61.40%), and the margin between the malignant group and the peripheral thyroid gland was unclear. The sensitivity (80.7% vs 64.9%), specificity (93.0% vs 81.0%) and accuracy (88.5% vs 75.1%) of CEUS were all significantly higher than those of conventional ultrasound (all P＜0.05).

  Conclusion  Compared with conventional ultrasound, CEUS has an appreciated value for the differential diagnosis for benign and malignant cystic thyroid nodules.