Evaluation of Lymph Nodes Using DW-MRI

Summary

Presence of lymph node metastases and thus prediction of nodal malignancy remains one of the most important challenges in treatment and prognosis of patients with cancer. Diffusion-weighted MR imaging (DW-MRI) can identify differences in molecular water mobility in the extracellular spaces, reflecting cellular organization and density, microstructure and microcirculation. Improvements in DW-MRI techniques have overcome most of the drawbacks and limitations of whole-body imaging and enables nodal characterization. The generally higher cellularity of malignant lymph nodes facilitates their detection on high b-value DW-MR images, even in lymph nodes which are normal in size. Using quantitative ADC evaluation, pre-surgi-cal assessment based on ADC threshold values may be valuable but must be interpreted with caution given the varying cut-off values for malignancy published in the literature. Moreover, necrotic areas, often encountered with squamous cell carcinomas, and inflammatory nodal hyperplasia accompanied by increased cellularity and nodal heterogeneity remain limitations when ADC values are applied to characterize nodal disease. ADC mapping relative to the primary tumour or standardized to reference structures such as the renal cortex, together with increased spatial resolution may further improve the diagnostic performance of DW-MRI. In the future, combining DW-MRI with lymphotrophic agents such as ultrasmall superparamagnetic iron oxide particles (USPIO) may enhance detection and characterization of lymph nodes. The pre-sur-gical planning for lymphadenectomy, radiotherapy and follow-up of oncological patients will profit from well-conducted DW-MRI studies even though histopathology remains the gold standard for nodal staging. The impact of DW-MRI on clinical practice for confident identification and risk strati-fication of patients for nodal metastases remains to be clarified.