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.