Role of diffusion-weighted MRI: Predicting axillary lymph node metastases in breast cancer

Background: Ultrasound (US) is probably the standard imaging procedure in most centers, and US-guided fine needle aspiration can be added if suspicious lymph nodes are found. However, US-guided fine needle aspiration is an invasive method to diagnose a metastasis and has showed relatively low sensitivity. In general, diffusion-weighted (DW) magnetic resonance imaging (MRI) has become an emerging technique for discriminating benign from malignant breast lesions in a short imaging acquisition time. Purpose: To evaluate the potential for using DW MRI with an apparent diffusion coefficient (ADC) value to predict axillary lymph node metastases in patients with invasive breast cancer. Material and Methods: This study enrolled 110 axillary lymph nodes from 110 consecutive women who were diagnosed with invasive breast cancer for preoperative breast MRI and US. The largest enhancing ipsilateral axillary lymph nodes were included in this study, and benign and metastatic axillary lymph nodes were compared according to the pathologic reports. The cut-off ADC value to differentiate between benign and metastatic axillary lymph nodes was evaluated with receiver-operating characteristic curve analysis. Diagnostic performance of ultrasound and DW MRI was calculated for enhancing lymph node in dynamic contrast-enhanced MRI. Results: Nodal metastases were documented in 68 (62%) axillary lymph nodes. The mean size of metastatic axillarylymph nodes was larger than that of benign axillary lymph nodes (15.5 mm vs. 10.9 mm, P<0.001). The mean ADC value (0.69×10^-3mm²/s) of the metastases was significantly lower than that of the benign axillary lymph nodes (1.04×10^-3mm²/s) (P<0.001). The ADC value cut-off between metastatic and benign axillary lymph nodes was 0.90×10^-3mm²/s. Using ADC cut-off, sensitivity, specificity, and accuracy of DW MRI were 100%, 83.3%, and 93.6%, respectively. The sensitivity, specificity, and accuracy of US showed 94.1%, 54.8%, and 79.1%, respectively. Conclusion: DW MRI of axillary lymph nodes can provide reliable information for the differentiation of benign from metastatic axillary lymph nodes in invasive breast cancer patients.