To investigate the diagnostic value for differentiating benign nodules from malignant by the peripheral rings in contrast-enhanced ultrasound (CEUS).

Conventional ultrasound and CEUS were performed in patients who suffered with thyroid nodules before the biopsy. During CEUS, both the enhancement patterns in nodule and the rings around nodules were observed and classified into different types. The diagnostic value of CEUS was obtained by comparing to pathology results. The relationship between peripheral rings of nodule with nodule′s size was analyzed.

Peripheral rings were found in 113 thyroid nodules, including 85 benign and 28 malignant nodules. In four types of peripheral rings, all 76 nodules with regular high-enhancement rings were benign, and all 9 nodules with irregular high-enhancement or no enhancement rings were malignant. Regular no enhancement rings were found in 9 benign nodules and 3 malignant nodules. The diagnostic sensitivity, specificity and accuracy of CEUS were 96.43%, 96.47% and 96.46%, respectively. Significant difference of nodule′s size was found in four types of peripheral rings (H=18.73, P<0.01). The maximum diameters of nodules with peripheral regular rings were larger than those of nodules with other three types of rings (all P<0.05).

Peripheral rings are very important for the differential diagnosis of thyroid nodules in CEUS. Regular high-enhancement rings indicate benign nodule, and irregular high-enhancement or no enhancement rings indicate malignant nodule.