Background Ultrasonography (US) is an important tool to evaluate the status of internal mammary lymph node (IMN). US features of metastatic IMNs could help determine when biopsy should be performed. Purpose To compare US features of metastatic IMNs to those of benign entities. Material and Methods In women with suspected IMN metastasis on US, their intercostal space (ICS) abnormalities were classified into metastatic IMN, benign IMN, and lymph node (LN) mimickers. US features, distribution, and depth of abnormalities in one ICS and involved ICS level were analyzed. Results Among 66 ICS abnormalities in 53 women, 46 were metastatic IMNs, ten were benign IMNs, and ten were LN mimickers. For metastatic IMNs, the second ICS was the most commonly involved ICS (n = 22), followed by the first (n = 13), the third (n = 8), and the fourth (n = 3). ICS level distribution of metastatic IMNs was not significantly ( P = 0.5407) different from that of non-metastatic lesions. Metastatic IMNs were predominantly seen in the posterior layer of ICS, significantly ( P < 0.0001) different from LN mimickers. Both metastatic IMNs and non-metastatic lesions were evenly distributed over the upper, middle, and lower part (in craniocaudal direction) of one ICS. Conclusion Metastatic IMNs are more likely to be found in the posterior layer of ICS. This can help distinguish them from LN mimickers. Any part (upper, middle, or lower) of one ICS in craniocaudal direction could be involved. The second ICS was the most commonly involved level.
Keywords: Breast cancer; intercostal space; internal mammary lymph node; ultrasonography.