In vitro B-mode ultrasonographic criteria for diagnosing axillary lymph node metastasis of breast cancer

Axillary lymph node status is an important factor for staging and treatment planning in breast cancer. Our study was performed in vitro on a node-by-node basis to evaluate the ability of B-mode ultrasonographic images to distinguish metastatic from nonmetastatic nodes. Immediately prior to histologic examination, individual dissected axillary nodes were scanned in a water bath using a 10 MHz B-mode ultrasonographic transducer. Four B-mode features (size, circularity, border demarcation, and internal echo) were evaluated for their ability to distinguish metastatic from nonmetastatic lymph nodes. Lymph node metastasis was indicated by (1) a large size (i.e., a length of the longest axis of 10 mm or greater); (2) a circular shape (i.e., the ratio of the shortest axis to the longest axis between 0.5 and 1.0); (3) a sharply demarcated border compared with surrounding fatty tissue; and (4) a hypoechoic internal echo, with obliteration of the fatty hilum. The sensitivity and specificity were compared for all combinations of features. We examined 84 histologically characterized axillary nodes from 27 breast cancer patients, including 64 nonmetastatic and 20 metastatic nodes. Of the criteria cited, circular shape was the best single feature for distinguishing metastatic from nonmetastatic nodes (sensitivity, 65%; specificity, 73%). The best combination of sensitivity (85%) and specificity (73%) was obtained using the criterion that a lymph node contained cancer when at least three positive features were present. The present in vitro study demonstrated that the sensitivity and specificity of B-mode ultrasonography for diagnosing lymph node metastasis were lower than 90%. Therefore, B-mode ultrasonography may not be an optimal noninvasive screening method for diagnosing axillary lymph node metastasis in breast cancer patients, particularly under in vivo clinical conditions.