Assessing internal mammary lymph node metastasis by breast magnetic resonance imaging in breast cancer.

The internal mammary lymph nodes (IMLNs) are a main pathway of metastasis in breast cancer, and breast magnetic resonance imaging (MRI) plays an important role in staging that disease. We investigated the MRI parameters that can predict metastatic IMLNs and evaluated their diagnostic performance by comparing the breast MRI findings for metastatic and benign IMLNs. From January 2016 to December 2020, 474 cases of enlarged IMLNs on breast MRI were identified. By cytopathology or integrated positron emission tomography/computed tomography (PET/CT), 168 IMLNs were confirmed as metastatic, and 81 were confirmed as benign. Breast MRIs were reviewed by 2 radiologists, and various parameters (node axes, fatty hilum, necrosis, margin characteristics, restricted diffusion, and involved levels; primary tumor location and skin involvement) were assessed. Independent t-tests, receiver operating characteristic (ROC) curve analyses, chi-square tests, and Fisher exact tests were performed to compare and evaluate the diagnostic accuracy of the imaging findings. Significant differences in the breast MRI findings for the short and long axes, fatty hilum, necrosis, margin characteristics, diffusion restriction, and tumor location were observed between benign and metastatic IMLNs. Compared with the long axis and the ratio of the axes, the short axis had the best diagnostic value (higher area under the ROC curve) for predicting metastatic IMLNs. In conclusion, breast MRI parameters such as short axis, presence of fatty hilum, necrosis, margin characteristics, and diffusion restriction can be used to evaluate and differentiate benign from metastatic IMLNs, offering valuable insights to improve diagnosis and treatment planning in breast cancer.