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Objective:
To evaluate the utility of the postvascular phase of contrast-enhanced ultrasound (CEUS) to differentiate between benign and metastatic lymph nodes (LNs) in patients with breast cancer (BC).

Materials and Methods:
Eighty-seven suspicious LNs in the lymphatic drainage area of the breast in 85 patients with BC were retrospectively analyzed. All LNs were assessed by conventional ultrasound (US) and CEUS. Nodal malignancy was histologically confirmed through surgery or biopsy, while benignity was ultimately confirmed through surgery or follow-up. The correlations between US, CEUS indicators of LNs, and LN metastasis (LNM) were analyzed.

Results:
Among the 87 LNs, 56 were metastatic LNs. 83.87% (26/31) of benign LNs overall showed relatively high enhancement in the postvascular phase, whereas 96.43% (54/56) of metastatic LNs showed relatively low enhancement (<em>P</em> < 0.001). This CEUS finding was highly predictive of metastasis with a sensitivity of 96.43%; specificity of 83.87%; positive predictive value of 91.53%; negative predictive value of 92.86%; and accuracy of 91.95%. The mean enhancement intensity (MEI) of the postvascular stage was significantly lower in malignant (median MEI of 12 dB) LN than in benign (median MEI of 76 dB) LN. The postvascular stage was more sensitive, specific, and accurate than the vascular stage of conventional US or CEUS for the diagnosis of LNM, with an area under the curve of 0.96 (95% confidence interval: 0.89-0.99).

Conclusion:
Qualitative and quantitative indicators of the postvascular phase of CEUS provide a reliable diagnostic approach to differentiate benign and metastatic LNs in patients with BC.