Diffusion-weighted magnetic resonance imaging in the characterization of axillary lymph nodes in patients with breast cancer.

PURPOSE To assess prospectively the accuracy of diffusion-weighted magnetic resonance imaging (DWI) in differentiating between metastatic and benign axillary lymph nodes in patients with breast cancer. MATERIALS AND METHODS In all, 215 patients with histologically proven breast cancer, prior to axillary dissection, underwent breast and axillary 1.5 T MRI. In 102 patients in whom at least one axillary lymph node with a short axis of 6 mm or more was found the apparent diffusion coefficient (ADC) was measured in one lymph node per patient by means of an echo planar, parallel imaging DWI sequence. Forty-three lymph nodes were finally included which, on histological examination, either contained a metastasis larger than 5 mm or were metastasis-free; nodes with metastases smaller than 5 mm were excluded. RESULTS From histological examination, 19/43 lymph nodes had a metastasis at least 5 mm, while in 24/43 no malignant cells were found. The ADC values of the lymph nodes with metastases (mean: 0.878 × 10(-3) mm(2) /s; range: 0.30 -1.20) were significantly lower (P < 0.001) than those of the benign lymph nodes (mean: 1.494; range: 0.60 -2.50). Adopting a threshold value of 1.09 × 10(-3) mm(2) /s DWI resulted in 94.7% sensitivity, 91.7% specificity, and 93.0% accuracy in the identification of metastasis in this series of lymph nodes. CONCLUSION From these preliminary data DWI seems a promising method in the differential diagnosis between metastatic and benign axillary lymph nodes in patients with breast cancer.