Purpose: To evaluate the diagnostic performance of unenhanced axillary T2-weighted and diffusion-weighted (DW) magnetic resonance (MR) imaging for axillary nodal staging in patients with newly diagnosed breast cancer, with node-by-node and patient-by-patient validation.
Materials and methods: Institutional review board approval and informed consent were obtained. Fifty women (mean age, 60 years; range, 22-80 years) underwent high-spatial-resolution axillary 3.0-T T2-weighted imaging without fat suppression and DW imaging (b = 0, 500, and 800 sec/mm(2)), followed by either sentinel lymph node biopsy (SLNB) or axillary lymph node dissection. Two radiologists independently scored each lymph node on a confidence level scale from 0 (benign) to 4 (malignant), first on T2-weighted MR images, then on DW MR images. Two researchers independently measured the mean apparent diffusion coefficient (ADC) of each lymph node. Diagnostic performance parameters were calculated on the basis of node-by-node and patient-by-patient validation.
Results: With respective node-by-node and patient-by-patient validation, T2-weighted MR imaging had a specificity of 93%-97% and 87%-95%, sensitivity of 32%-55% and 50%-67%, negative predictive value (NPV) of 88%-91% and 86%-89%, positive predictive value (PPV) of 60%-70% and 62%-75%, and area under the receiver operating characteristic curve (AUC) of 0.78 and 0.80-0.88, with good interobserver agreement (κ = 0.70). The addition of DW MR imaging resulted in lower specificity (59%-88% and 50%-84%), higher sensitivity (45%-64% and 75%-83%), comparable NPV (89% and 90%-91%), lower PPV (23%-42% and 34%-60%), and lower AUC (0.68-0.73 and 0.70-0.86). ADC measurement resulted in a specificity of 63%-64% and 61%-63%, sensitivity of 41% and 67%, NPV of 85% and 85%-86%, PPV of 18% and 35%-36%, and AUC of 0.54-0.58 and 0.69-0.74, respectively, with excellent interobserver agreement (intraclass correlation coefficient, 0.83).
Conclusion: Dedicated high-spatial-resolution axillary T2-weighted MR imaging showed good specificity on the basis of node-by-node and patient-by-patient validation, with good interobserver agreement. However, its NPV is still insufficient to substitute it for SLNB for exclusion of axillary lymph node metastasis. DW MR imaging and ADC measurement were of no added value.